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Techical Discussions => Tech- - Engine => Topic started by: Stan Paralikis on October 02, 2009, 05:05:41 AM

Title: What's my compression ratio
Post by: Stan Paralikis on October 02, 2009, 05:05:41 AM
Trying to figure out what compression ratio I'm going to end up with.
Original piston/head combo would have been 8.2:1.
4.  .039 head gaskets.
I'm guessing aprox. 10.5:1  but I'm no rocket scientist on head stuff.  Anybody have a good idea?  :-/
Title: What's my compression ratio
Post by: firedome on October 02, 2009, 05:34:42 AM
You'd need to get exact dimensions with the new pistons and gasket used
to calculate the precise cubic volume of the combustion chamber
incorporating the revised bore & stroke at TDC and the total
cylinder volume at BDC and then derive the ratio mathematically to get
a truly accurate figure, otherwise it's pure guesswork, but it will be
higher, that's for certain.  I'd go with 8:1 and stick on a
Garrett T-4! 

Title: What's my compression ratio
Post by: Steve on October 02, 2009, 05:45:28 AM
Yep
 
Better get the rocket fuel Stan
 
That's a good guesstimate though
Title: What's my compression ratio
Post by: Butch Houghton on October 02, 2009, 06:12:28 AM
The only way to really know is to mockup 1 piston & rod with the crank & actually see how far in the hole the piston is.    Hit TDC & with a straightedge & feeler gauge you can get real close.

Did you actually measure those heads or just use the advertised CC'a.   Should be checked,   88 cc's is closer to nominal.   

The reason I say all this is we had a 440 that someone else built here in a 70 Cuda convert that we just had to finish a couple of things on & fire the engine.    Even with the timing backed to TDC it pinged under light loads.   Supposed to be Ross 9.5's in it & after teardown sure enough they were.   Chamber cc'd right at 88 where they should be.  Compression calculated at 11.1:1?   Taled to Ross & for one thing the pistons were'nt far enough in the hole for one thing so I had to conclude the deck was heavily decked.   took it to the machine shop & he checked it for me,  sure enough it was decked .040!  

You never really know unless you check it.

Butch


Title: What's my compression ratio
Post by: firedome on October 02, 2009, 06:42:17 AM

Nothing beats direct empirical observation and measurement.
firedome2009-10-02 11:42:56
Title: What's my compression ratio
Post by: Stan Paralikis on October 02, 2009, 08:55:45 AM
Sheesh.  All you anal guys.  All I wanted was an aproximation. (http://www.moparfins.com/forum/smileys/smiley2.gif)
I'm not going bracket racing, ya know....
 
I'll find out with my first tank of regular.
Title: What's my compression ratio
Post by: Steve on October 02, 2009, 09:49:54 AM
It's actually
 
What was the compression ratio of the original engine and what was the compression ratio of the head donor engine.  If the head donor was higher, then you could be in between the two.  I can't recall any 440 over 10:1 stock though.  Your original engine was around 8.2 to 1. 
 
Just looked it up.  The 73 440 was also 8.2:1.  What year is the block?  Sometimes they lowered the compression ratio with the pistons and the heads.  The piston did not reach the top of the deck.  So without knowing th year of the block, it's hard to tell.  Or even guess. 
 
POLARACO2009-10-02 14:54:03
Title: What's my compression ratio
Post by: Stan Paralikis on October 02, 2009, 10:06:52 AM
It's my 1976 block with these pistons:
 
Piston head volume +5 cc so that's why I said my head volume was 82-83 cc.
 
Commando12009-10-02 15:08:46
Title: What's my compression ratio
Post by: Stan Paralikis on October 02, 2009, 10:51:33 AM
Never mind.  i figured it out myself. (http://www.moparfins.com/forum/smileys/smiley36.gif)
 
(http://i35.tinypic.com/fm2vx0.jpg)
 
And I was right about 10.5:1....(http://www.moparfins.com/forum/smileys/smiley17.gif)
 
 
Title: What's my compression ratio
Post by: Steve on October 02, 2009, 12:26:35 PM
well hell!  We didn't have that info.  So if that is the case, you were right
 
My crystall Ball was in getting an oil change
 
(http://www.moparfins.com/forum/attachments/5/Choke1.gif)
Title: What's my compression ratio
Post by: Butch Houghton on October 03, 2009, 04:39:47 AM
Since you have the Compression height listed take your old piston & measure with a caliper it's compression height to compare as a double check.

Just measure from the center of the wrist pin to the top,  that's your compression height.

Plug the old height number into the calculator & see what it comes out with too.  The old piston should have a lesser compression height.

Just a real eyeball verification.  Irregardless they look like nice pistons!  I dubious about a real 10.5:1 compression & if it is you're gonna have issues with detonation with Iron heads.

Butch


Title: What's my compression ratio
Post by: firedome on October 03, 2009, 05:03:23 AM
Those do look like some nice pistons!

Title: What's my compression ratio
Post by: Stan Paralikis on October 03, 2009, 07:10:55 AM
Quote from: HemiFury
... & if it is you're gonna have issues with detonation with Iron heads.
Nonsense!  With 92 octane and the hardened seats, there will be no problem.  You know yourself there were nothing but iron heads in the sixties and even the car makers were giving us engines with 11.5:1. 
AND (!!!!!) my heads are the motorhome heads with the extra cooling passages. (http://www.moparfins.com/forum/smileys/smiley4.gif)
Title: What's my compression ratio
Post by: firedome on October 03, 2009, 02:30:14 PM
True - as I recall one of the Olds W series had 11.75 CR, and iron is far more forgiving of heat and  pressure than aluminum anyway.
Title: What's my compression ratio
Post by: Butch Houghton on October 04, 2009, 05:51:27 AM
Yeah,  but the octane rating were much better back then too.  Everything was RON rated & now  it's it's an average between RON & MON ratings ....much lower octane.

But whatever,  go right ahead...




Title: What's my compression ratio
Post by: Stitcherbob on October 04, 2009, 07:15:38 AM

Cast iron heads hold the heat in, aluminum wick it away faster.....so you are better off with aluminum heads if you are planning to run anything over 9 to 1 compression on todays fuel (can't call it gas anymore with all that alky-haul and other crap in it). Iron heads and 10 to 1 compression is going to make you run 93+ octane and play with the timing to curb detonation (or install water injection like Steve mentioned).....or maybe you have an airport nearby with someone willing to fill yer jerry cans with AV-gas 
(http://www.moparfins.com/forum/smileys/smiley4.gif)
Title: What's my compression ratio
Post by: Stitcherbob on October 04, 2009, 07:18:14 AM
Or build the motor to run on E-85.....Hey Butch, how many gallons of that "clear liquid" you showed Steve and I can you send up to NJ to blend our own race fuel? (http://www.moparfins.com/forum/smileys/smiley2.gif)

Title: What's my compression ratio
Post by: Stan Paralikis on October 04, 2009, 12:15:08 PM
Bullpuckey.  Iron heads and 10.5:1 on 92 octane is not a problem.  (http://www.moparfins.com/forum/smileys/smiley19.gif)
Title: What's my compression ratio
Post by: firedome on October 05, 2009, 03:44:16 AM

AL will radiate heat away faster, but will warp and crack much more
easily when heated,  iron can take far more heat abuse before
being damaged.   In 1972 we once (unintentionally) went 40 miles
on the Wilbur Cross Pkwy in CT with NO coolant in a Volvo 122 with iron
block & head B-18 (Willys designed) engine - when we stopped the
manifolds were glowing BRIGHT red, much to my horror... my wife's first
car and her baby! Let it cool 2 hrs, poured in coolant, and drove the
car for 7 more years... but had to stop every 50 mi that trip to Boston
due to the radiator leak. Iron can take it! The pistons might be another story.


firedome2009-10-05 08:44:52
Title: What's my compression ratio
Post by: Stan Paralikis on October 05, 2009, 04:44:27 AM
The last word...  (http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/index.html)
Title: What's my compression ratio
Post by: firedome on October 05, 2009, 05:01:25 AM

Whazzit say?  The link  caused Firefox to crash on my creaky pooter when I tried to open it...

I need a new one desperately, but ... car parts or pooter... hmmm..  that's an easy one!


firedome2009-10-05 10:02:00
Title: What's my compression ratio
Post by: Stitcherbob on October 05, 2009, 06:16:22 AM
 ".....has pretty well demonstrated that a dyno seems to have far more detonation tolerance than do actual driving conditions in a car (http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/dyno_results.html#). So, ultimately, we don't think we pushed that limit enough to make a positive finding."

That plus water jacket differences between Chevy and Mopar and I say

Bullpuckey!


Title: What's my compression ratio
Post by: firedome on October 05, 2009, 06:37:24 AM
What's "the rest of the story"? - I can't read it -  supports
Stan? - is a BB Mopar more poorly cooled, water-jacket head-wise, than
a Chebby? The block? How about an LA? (I believe the LA is the superior
engine compared to BBs larger than 383), but in any case, wouldn't the
pistons likely hole or melt from detonation before any significant iron
head or block damage? I don't see how a dyno would differ if air flow
thru the radiator is equalized.

Title: What's my compression ratio
Post by: Stan Paralikis on October 05, 2009, 11:15:54 AM
Quote from: firedome
What's "the rest of the story"? - I can't read it -  supports Stan? 

In summary: NO perceptable differences....
Now, if anybody disagrees with me any further I'm going to lock up this thread.
(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)(http://www.moparfins.com/forum/smileys/smiley2.gif)
Title: What's my compression ratio
Post by: Steve on October 05, 2009, 03:45:39 PM
Those two Ying Yangs are Chebby Freaks
 
Let me ask E Booger.
 
FYI. . .Butch knows his shtuff.
Title: What's my compression ratio
Post by: Steve on October 06, 2009, 07:10:22 AM
The E Man has replied with the following
 

If spark curve is right, and coolant temp reasonable, you can run as much as 11:0:1 on pump 93 with some aluminum heads. HOWEVER, Rick's rule of thumb: If you have to retard spark from the "known max HP point" on any chamber shape to prevent detonation, you're better off with less CR.
 
Any detonation you can hear - even a slight rattle -- is VERY bad.

Title: What's my compression ratio
Post by: Stan Paralikis on October 06, 2009, 09:03:29 AM
(http://www.moparfins.com/forum/smileys/smiley24.gif)  His reply told us absolutely NOTHING to answer our debate....
Title: What's my compression ratio
Post by: Steve on October 06, 2009, 11:42:55 AM
OK  I'll ask him to clarify
Title: What's my compression ratio
Post by: Stan Paralikis on October 06, 2009, 12:51:16 PM
Ask him simply this:
 
Motorhome Iron heads, 180 degree thermostat, 92 octane, 10.5:1 CR
Yes or no.
K.I.S.S.
Title: What's my compression ratio
Post by: Steve on October 06, 2009, 01:31:03 PM
Aluminum heads wick away more heat of combustion. So, all else being equal, iron heads will always make more HP. However, this same phenomena allows more CR in alum-head engines, with the same fuel, typically making up for the HP shortfall. But the effect diminishes at higher RPM - there's less time per combustion even for the heat to be transferred, so alum-headed, high-CR engines are more prone to detonation at higher RPMs,  sometimes requiring a rather strange spark curve.
Rick
Title: What's my compression ratio
Post by: firedome on October 06, 2009, 03:35:32 PM
Interesting. The  ability to run as hot as possible without damage
is a plus, for example, in theory air cooled diesel tractors like the
German Deutz are much more efficient because the heat of combustion is
converted to HP and not taken away in the coolant or out the exhaust.
But making it durable and reliable is the real challenge... ask a John
Deere owner, he'll tell you!  ... the old farm boy



Title: What's my compression ratio
Post by: Steve on October 06, 2009, 03:39:47 PM
Sure. . .the Cummins loves hot weather, but is more efficient when you keep the Exhaust temp down and the intake temps down.  The colder the inbound and outbound in hot weather, the better.  But don't let it get over 205 degrees, then it goes down hill
Title: What's my compression ratio
Post by: Stan Paralikis on October 06, 2009, 03:53:42 PM
So I was right.........
Title: What's my compression ratio
Post by: Steve on October 06, 2009, 04:59:04 PM
It depends on how you look at it I guess. . .   Butch is thinking track like Rick is.  You're thinking street like I do.  I could give a rats ass how fast it does the 1/4 myself.
Title: What's my compression ratio
Post by: Stan Paralikis on October 07, 2009, 02:55:49 AM
So it goes back to
what I've been saying from the beginning
I'll be fine running 10.5:1........
Title: What's my compression ratio
Post by: firedome on October 07, 2009, 03:52:13 AM
And I'm thinkin 12 bottom plows!!  I'd think you'd be safe Stan, just take out a 2nd mortgage when you go to buy gas!

Title: What's my compression ratio
Post by: Stan Paralikis on October 09, 2009, 04:36:33 AM
http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=5531036&an=0&page=1&gonew=1#UNREAD (http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=5531036&an=0&page=1&gonew=1#UNREAD)
Title: What's my compression ratio
Post by: Butch Houghton on October 09, 2009, 06:01:27 AM
You think that confirms your assumptions?   Better read again.   If anything it backs up what I said more so.

You've got to have the quench just right,  timing spot on with the curve or it's gonna detonate at 10.5:1

You've said nothing about trying to set the quench & those pistons aren't a quench pad design.   You've done nothing but plug a bunch of Advertised specs into a chart & think it's okay with no measuring.

Most of us agree that 10:1 is about it for a reliable street motor on pump gas with a good quench..   The Ross forgings in my SB are a true 9.5:1 with the stock 340 heads ( slightly worked ),  the Hemi is a true 10.6:1 with Aluminum heads & I've got the timing about as far as I dare with that setup with 16 initial & 34 total,  any more & it detonates.

I dare say you're not gonna have 10.5:1 anyway with those pistons no matter what the chart says.   Most blocks aren't at Blueprint deck height so that'll be lower compression anway.   Many peole have pulled apart original 440 magnums & found the true compression ( after careful measuring) at more like 9.5 - 9.7:1 so the advertised rating mean nothing.

Go read a bunch more.




Title: What's my compression ratio
Post by: Stitcherbob on October 09, 2009, 08:15:05 AM
Not that it adds anything to this, but why push the limits on an engine buildup when your last one had a rod sticking out of it? I would want to play it safe after a disaster like that.......

Title: What's my compression ratio
Post by: Stan Paralikis on October 09, 2009, 11:44:18 AM
Quote from: stitcherbob
Not that it adds anything to this, but why push the limits on an engine buildup when your last one had a rod sticking out of it? I would want to play it safe after a disaster like that.......



 
Because...
 
[/QUOTE]
 
Hemifury nailed it on the head (bad pun).   I know damn right well if the CR Calculator says 10.5,  I'm really going to be down around 9.5.  This ain't no blueprinted engine by a race shop.
 
Title: What's my compression ratio
Post by: Butch Houghton on October 09, 2009, 02:15:22 PM
Well now your talking!   As long as you understand that you're good!  It sounded like you really believed it was gonna be 10.5.

I think we all know the last motor was a Fluke,  probably a weak rod bolt that just failed.   You are gonna use good bolts this time right!   LOL!


All this motor talk has me thinking.....the Hemi is old news, I do have a couple of 440 Blocks & a 4.15 crank & an Aluminum 6-pack intake & C-bod magnum manifolds already in stock.

Butch


Title: What's my compression ratio
Post by: Stitcherbob on October 09, 2009, 05:38:25 PM
ok send the Hemi & those motor mounts up here......it'll fit in my Imperial! (http://www.moparfins.com/forum/smileys/smiley31.gif)
Title: What's my compression ratio
Post by: Stan Paralikis on December 15, 2009, 03:58:25 AM
Update for WIW: After several tankfulls:
 
Premium fuel and recommended timing............No knock.
Downgrade the fuel a/o advance the timing.....Knock.
 
So, in my opionion, the motor (and the CR) are dead on right on the money.
Title: What's my compression ratio
Post by: Guests on February 10, 2010, 07:22:08 AM
Since you already have the engine together, you can run the 87 octane without the ping but you have to start thinking about the advance curve slowed down to reduce the ping process. This is slight high, not high compression, so simply cut back to 10degrees at the crank, then slow down the advance springs inside the distributor so the curve itself is slower. Start with a firm and medium firm spring, might be able to go firm and medium, but start firm and then go lighter, takes a bit to change the springs. Disconnect the vacuum advance, also, big blocks and high compression like slow advance (all in around 2800rpm), small blocks and high compression are more like all in by 2200rpm. This usually applies to 10:1 and above and 87 octane. Higher octane is just that much more power and performance and can handle more advance, but doing this with a 440 will save money on gas and still be better than a 9:1 440 for power.
 
To put it into context, I have several small block Chevy (I know, I was stupid when I was young(http://www.moparfins.com/forum/smileys/smiley7.gif)), but I had them set a 12.5:1 and 13.3:1 and was able to run them with 87 octane no problem, they only pinged on the hills with 75octane in Mexico, 79 octane unleaded didn't ping, a lot of it is in the porting of the heads and combustion chambers. B/RB and early LA are open chamber, but there are still a few places to improve the flow and reduce the sharp edges to prevent the pinging. Any engine can run this, just takes some head work to make it simple.
Ed
Title: What's my compression ratio
Post by: Stan Paralikis on February 10, 2010, 10:28:05 AM
Quote from: dana44
... you have to start thinking about the advance curve slowed down to reduce the ping process. ...

 
(http://www.moparfins.com/forum/smileys/smiley8.gif) Wow. you know your stuff.
Can't I simply send you my distributer.  I have no idea what you're talking about. (http://www.moparfins.com/forum/smileys/smiley2.gif)
Title: What's my compression ratio
Post by: Steve on February 10, 2010, 11:09:10 AM
Stan
 
Ed has me beat on all this fine tuning stuff. . . . .  I've been a stocker all these years.  But I can curve a distributor.
 
Don't let the old geezer get off cheap Ed. (http://www.moparfins.com/forum/smileys/smiley2.gif) (http://www.moparfins.com/forum/smileys/smiley2.gif) (http://www.moparfins.com/forum/smileys/smiley2.gif)
 
He'll ship it to you and forget he sent it. (http://www.moparfins.com/forum/smileys/smiley36.gif)
 
Really Ed, Stan is a cool guy.  Good man and friend.  Even if he can't figure out how to answer his cell phone. (http://www.moparfins.com/forum/smileys/smiley12.gif)
Title: What's my compression ratio
Post by: Guests on February 10, 2010, 11:41:47 AM
Yeah, yeah, yeah, I'm just a bucket of information.  If Stan knows what a distributor is, how to remove it from the block, (and mark it so the rotor points the same way as it is running right now) pull the cap off and wire connection, he can then pull the rotor off, and undo the two screws on the side of the case where the clamp attaches (two phillips screws), and gently lift the plate off the inside (might need to remove the vacuum advance (again, two phillips screws) and once the two are loose, it will unhook from the vacuum advance plate.
 
Underneath you will see two small springs. If you hold the top of the distributor shaft and twist the bottom of the shaft, you will see these two springs allow a certain amount of twist for mechanical advance. This is what we need to slow down from occuring. We still want it to advance, just not as fast as it is doing it. The auto parts stores have these springs as an advance kit (Mopar, SBC, SBF, doesn't matter they are all the same springs), and you want the heavy one that is on it now (a stock one, looks like it is stiff enough to lift your garage door), and in the kit you want one that looks to be the next step below this stiff one, and this will slow down the advance curve, allow cheaper gas octane without harming anything.
 
Put her back together and then play with the timing to see how much you can put into the harmonic initial advance, thinking if you can run 12degrees advance and 91-93octane keeps her from pinging, 85octane should be starting with 6degrees advance and then advance her two degrees at a time after driving her around a bit to make sure different circumstances don't kick in and make her ping.
 
You can do it, it isn't that difficult.
Title: What's my compression ratio
Post by: Steve on February 10, 2010, 01:35:38 PM
We have to first change his Depends.  Then a gallon of Geritol, then a 6 of that Iron Gut he drinks. . . .
 
As you can see Ed, we can relax over here.  But don't get too relaxed. (http://www.moparfins.com/forum/smileys/smiley2.gif) (http://www.moparfins.com/forum/smileys/smiley2.gif)
 
Stan is a moderator. . . .(http://www.moparfins.com/forum/smileys/smiley5.gif)
Title: What's my compression ratio
Post by: Guests on February 10, 2010, 02:39:13 PM
Aaaaaa crap, gimme a few days, see if I can raise some hell or piss someone off(http://www.moparfins.com/forum/smileys/smiley17.gif).
Title: What's my compression ratio
Post by: Leaburn Patey on February 10, 2010, 03:15:05 PM
I agree with Ed that a recurve and fine tuning is key.
I did that with my 440 in the  68 C Barge.
Just a reminder that whenever anything is changed (i.e. cam,pistons,etc) you can toss  the factory timing specs out the window.
Test and tune,trial and error.
Originally,my 440 called for 8 degrees initial with factory cam,points,single exhaust,etc.
After a rebuild,cam swap,452 heads that were massaged,dual exhaust,electronic ignition and a recurve,10.5 initial.She comes in at full advance around 2300 with a total of 41 degrees.My dizzy had a parts jobber vacuum advance pod with 9.5 on it (18 degrees).
Swapped it out to 11.5 (23 degrees)
I get almost 21 inches vacuum and she idles smooth.
I re-used the factory flat top pistons so it does ping only when I run cheap low grade gas.
I never get ping when running Ultra94.
My best MPG is 16.28 MPG on my trip to Joisey in 2008. 
Just ask Steve,my 4600 pounder moves quite well!! LOL!
 
Title: What's my compression ratio
Post by: Leaburn Patey on February 10, 2010, 03:44:20 PM
(http://www.moparfins.com/forum/smileys/smiley3.gif)
Ed,I am in the middle of rebuilding a 68 383 2bbl engine (9.2 CR factory)
I am converting it to a 4bbl HP set up.
Despite having 62,000 miles on it,the block had to be bored 40 over.
Piston selection is very limited and my builder located a set of Sealed Power cast pistons.
They shaved ten thou off the block's deck.
Original 906 heads got hardened valve seats and planed (do not know by how much).
But were cc'd to 87.8 cc's.
 
(Some extra specs that you may want to know,but not directly related;
I will be running the 268H Comp Cams,911-16 springs,Cloyes timing set,factory points dizzy-recurved,with Pertronix conversion.750 Eddy carb stock intake,HP logs with TTi 2.5" duals.Stock convertor, 2.94 gears and 26.69 OD tire.)
As Steve mentioned,I will be doing further massaging on the heads once they come back home,port match the HP logs and intake.
 
1: Any idea what the CR ratio would be?
2; do I need special length pushrods after all the machining??
If so,how can I calculate what lenght I need?
 
 
Title: What's my compression ratio
Post by: Steve on February 10, 2010, 04:45:16 PM
Ed
 
Lea tells me they took an extraudinary amount off the heads and deck. I'm inclined to think he's going to need pistons with valve reliefs.  The 383 does not have, what do they call that. . . .  Valve relief.
 
I told Lea to have the intake shaved to match.  Lea said they took something like .25 off the heads and another 10 off the block.  That's nuts!
 
I'm alittle pissed off at that.  I have a feeling those pistons are not going to work.  He'll be bending valves
Title: What's my compression ratio
Post by: Steve on February 10, 2010, 04:48:48 PM
Leaburn
 
I think you're going to need something like these
 
http://www.summitracing.com/parts/UEM-KB400-040/ (http://www.summitracing.com/parts/UEM-KB400-040/)
Title: What's my compression ratio
Post by: Guests on February 10, 2010, 06:15:53 PM
And you could run that cheap 87octane if you slowed it down just a little bit more, full in at 2800-3000rpm would probably do it.
 
Here's another way to look at this. Take an engine that runs stock compression at around 9:1. It has a smaller duration cam in it and those valves close sooner and build more compression and yet it doesn't ping does it? The shorter the duration the more pressure built inside the cylinder and in all reason it should ping like all getout at low speeds but they don't do they? Raise the compression and increase the duration, the duration bleeds off the cylinder pressure so it can build at higher rpm, and yet it pings (remember those rules, where it says in the cam directions, a cam this large needs this or that compression minimum? That's the reason for it). Lower compression due to bleed-off, yet there is pinging, something is wrong with this, it is backwards, so it isn't so much the level of compression it is the speed of which the spark happens, so reduce its speed and cheap gas works.  When you get above the 10.5:1 range then you have to work on the combustion chamber itself (kind of like why a Hemi head can have higher compression and not ping on cheap gas, yet a wedge head can't run that high). Also, additionally, the speed of the explosion increases with the higher compression, thus a spark that makes the gas explode and cross the cylinder at (example only) 500fps at 9:1 may travel 600fps at 10:1 compression, so slow it down and it works.
Ed
Title: What's my compression ratio
Post by: Leaburn Patey on February 11, 2010, 01:46:35 AM
Hoping to see the pistons today if they showed up.
I will check for valve reliefs
 
Title: What's my compression ratio
Post by: firedome on February 11, 2010, 03:35:49 AM
That's a HUGE amount to shave off - were the surfaces really bad or were they warped?

Title: What's my compression ratio
Post by: Steve on February 11, 2010, 06:00:42 AM
Hell Yeah. . .If those numbers are accurate. . .  Lea was quoting, but not sure
 
I never heard of anyone taking that much off.  That's way out there
 
Ed
You didn't comment on my thought about the pistons
Title: What's my compression ratio
Post by: Leaburn Patey on February 11, 2010, 07:01:39 AM
I could be wrong,guys.
Not really fluent in engine mathematics and geometry.
Still trying to contact Rob at Bullet
CBarge2010-02-11 12:02:27
Title: What's my compression ratio
Post by: Guests on February 11, 2010, 08:39:01 AM
Quote from: CBarge
(http://www.moparfins.com/forum/smileys/smiley3.gif)
Ed,I am in the middle of rebuilding a 68 383 2bbl engine (9.2 CR factory)
I am converting it to a 4bbl HP set up.
Despite having 62,000 miles on it,the block had to be bored 40 over.
Piston selection is very limited and my builder located a set of Sealed Power cast pistons.
They shaved ten thou off the block's deck.
Original 906 heads got hardened valve seats and planed (do not know by how much).
But were cc'd to 87.8 cc's.
 
(Some extra specs that you may want to know,but not directly related;
I will be running the 268H Comp Cams,911-16 springs,Cloyes timing set,factory points dizzy-recurved,with Pertronix conversion.750 Eddy carb stock intake,HP logs with TTi 2.5" duals.Stock convertor, 2.94 gears and 26.69 OD tire.)
As Steve mentioned,I will be doing further massaging on the heads once they come back home,port match the HP logs and intake.
 
1: Any idea what the CR ratio would be?
2; do I need special length pushrods after all the machining??
If so,how can I calculate what lenght I need?
 





http://www.rbracing-rsr.com/compstaticcalc.html (http://www.rbracing-rsr.com/compstaticcalc.html)
 
Here is an easy and explainable compression calculator, just plug six items in, the missing two are the distance of the piston at TDC to the top of the deck, and the head gasket thickness.  The heads didn't get shaved very much because of the combustion chamber size, pretty close to stock still, 906 is an open chamber design and about 88-89cc stock, so they were cleaned maybe .010 at best (big block heads rarely need more than .005-.010 to get them straight). Blocks on the other hand can be as much as .015 out of square from one corner to the other, that's why blueprinting Mopars is such an improvement over flat stock.
 
So, using 4.290 bore, 3.375 stroke, .038 gasket thickness, zero on the deck height to piston clearance, zero on the piston top (valve reliefs are good for 4cc which you don't have), and the combustion chamber of 87.8cc. This information gives you 9.25:1 compression. This is decent compresssion for the street and will run strong.
 
Now, the pushrods, myself, I prefer to have adjustable rockers, especially with heads and block machined. Since you are going four barrel and all that, decent cam, you want to be able to adjust the rockers and use a set of anti-pump-up lifters to take advantage of what you have, otherwise 5300rpm valve float will be a given (built into the engine design). Anti-pump-up lifters prevent the lifters from pumping up too much at high rpm and floats the valves due to the fixed preload with non-adjustable rockers. It is also easier on the cam itself and can save a valve or two when floating. The only thing I don't like about adjustable rockers is the cost, which is right around $250 and above cost. Aluminum are OK, steel is best, they last longer. And of course you need pushrods with cups in the end to go with them, stock length would be fine, but then you know exactly how much preload is on the lifter (I like setting zero lash, none of that take it to zero and then 3/4 turn crap, don't need it, adds a little extra no valve float possibility and some give if a valve touches a piston). Port match the stock intake (no aluminum dual plane to port match?), TTi is great sounding, (I have 3inch on my Charger and HP manifolds, it has been referred to my young daughter by passerbys as "Your dad's Charger sounds like a %ucking monster.") 2.5 is a bit quieter, but still nicer sounding than the  "other" brands, Dynomax is a sweet sounding muffler. I can help with the head porting when you get to it, port match, short side turn, gasket rim, intake manifold ports, couple lumps and bumps, some edges at the carb flange to fix.
 
Distributor sounds good for now, might need some fine tuning, carb is OK for now,fine tuning later, and run a 180 degree thermostat...there.
 
 
Title: What's my compression ratio
Post by: Steve on February 11, 2010, 09:05:53 AM
I sure hope Leaburn is wrong about the amount they took off those heads.  383's aren't that forgiving in that department.
CBarge2010-02-11 17:58:21
Title: What's my compression ratio
Post by: Guests on February 11, 2010, 09:12:47 AM
Quote from: POLARACO
I sure hope Leaburn is wrong about the amount they took off those heads.  383's aren't that forgiving in that department.
Yeah, pretty sure they didn't take off a quarter of an inch...(http://www.moparfins.com/forum/smileys/smiley2.gif) CBarge2010-02-11 17:58:59
Title: What's my compression ratio
Post by: Steve on February 11, 2010, 09:39:44 AM
Sheeesh
 (http://www.moparfins.com/forum/smileys/smiley36.gif)
I never even looked at that.  You're right
Title: What's my compression ratio
Post by: Leaburn Patey on February 11, 2010, 01:09:15 PM
Steve,you really did not think I said 1/4 inch??
Hope not.Sheesh.
Like I said,I am not 100% sure and have no numbers in front of me.
 
Ed,thanks for your reply.
It reassures me that Bullet is doing it right.They are professionals with a high profile and good reputation around here.
Rob did telling me the cc's  gave a clue to how much they planed the heads.Thanks.
 
Title: What's my compression ratio
Post by: Guests on February 11, 2010, 02:18:17 PM
Yeah, I would say they just cleaned them up, which is proper. You got the formula to calculate, just need to figure the depth of the piston at top dead center, put a flat edge across the top of the cylinder and feel gage the depth for the most accurate compression, and the thickness of the head gasket itself, but I would say real close to just above 9-9.5:1 which is good enough.
Title: What's my compression ratio
Post by: Leaburn Patey on February 12, 2010, 11:50:17 AM
Spoke to Rob today.
Compression will be at 9.0:1
The pistons are here-flat tops that have no valve reliefs.
However,they sit lower in the hole.
So,good news that is reassuring.
I decided also to get them to do up the shortblock.
That way all the critical tolerances will be checked,and less work for me.
I can put the heads on after i work them up.
 
Title: What's my compression ratio
Post by: Guests on February 12, 2010, 02:00:33 PM
Sounds good!
Title: What's my compression ratio
Post by: Steve on February 12, 2010, 04:22:41 PM
Good! 

Now I don't have to do it. (http://www.moparfins.com/forum/smileys/smiley36.gif) (http://www.moparfins.com/forum/smileys/smiley2.gif)
Title: What's my compression ratio
Post by: Leaburn Patey on February 14, 2010, 11:02:26 AM
Ed,I found this from Comp Cams
(http://www.compperformancegroupstores.com/store/graphics/00000001/1322-16_600.jpg)
http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=1321-16&Category_Code=WedgeRockers (http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=1321-16&Category_Code=WedgeRockers)
I can use their pushrods:
http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=7422-16&Category_Code=WedgePushrods (http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=7422-16&Category_Code=WedgePushrods)
Is this the way to go with the machining done and avoidd expensive custom length pushrods?
Thanks
CBarge2010-02-14 16:05:07
Title: What's my compression ratio
Post by: Guests on February 14, 2010, 02:55:55 PM
I prefer adjustable rockers, removes the chance the lifters are going to pump up and allow the valves from sitting with enough pressure on the seats to prevent valves from burning. it also allows you to get a set of anti-pump-up lifters, which help prevent valve float, and you can set the valves to zero lash (another anti-valve burning technique), where you simply rotate the engine until one valve is open on a cylinder and that automatically puts the other valve closed, adjust it to the point of zero pressure or movement without any preset pressure and tighten it down. When you get the first one done, rotate the engine so that valve is now open and do the next valve until all 16 are done. If the valve does something like float and touch a piston, which is rare, but if it does, the lifter has an extra .150 it is able to bleed down to prevent the valve from bending, and the anti-pump-up itself is a performance bleed to prevent them from floating above the notorious 5300-5500rpm of stock Mopar lifters and non-adjustable rocker engines. Just don't let anyone talk you into Rhoades lifters, they sound like they are loose all the time, and you don't need them, they are really for high rpm racing (street use allows them to bleed extra at lower rpm to give better vacuum by reducing your cam duration. Good idea, just noisy, been around since mid 1970s).
 
Pushrods are cupped end with ball tip for the lifter, and other than the hassle of determining the special length for fixed rockers, I don't think the cost is that much more than simple stock pushrods (maybe a buck or so more per).
Title: What's my compression ratio
Post by: Leaburn Patey on February 14, 2010, 03:35:52 PM
So,are the Comp's good choice???
They describe that conventional ball end-type pushrods can be used.And are adjustable.
 Or do you recommend a different name??
So,are the hydraulic lifters that came with my Comp 268H (CL-21 215-4) cam no longer any good for my application?
Remember it is not a race motor with highway gears.
My open valve spring pressure will only be 305 or so.
Just need reassurance I get the right parts.
I would rather use the stock set up,but I was told I need custom length pushrods.
Plus some aftermarket set ups require machining of the bosses,and factory valve covers cannot be used.
I want to use factory valve covers.
Much rather spend the money on the right parts now rather fix it twice later.
CBarge2010-02-14 20:44:03
Title: What's my compression ratio
Post by: Guests on February 14, 2010, 04:00:51 PM
These rockers are really nice and I would use them myself, so good choice.

You can still use the stock rockers if you like (save a bunch of bucks there, reimburse me 25percent, (http://www.moparfins.com/forum/smileys/smiley2.gif)), and the lifters are fine with the cam, but here is what you need to do. Find out how much was removed from the block deck and how much was removed from the heads. If this amount is between .015-.020, everything stock will work without an issue, the lifters themselves should be the same height from the base to the plunger, it's the way they make aftermarket cams to fit stock engines. If this amount shaved off the head/block is greater, there are shims that can be added under the rocker shafts themselves to return to factory height (let's say .030 was shaved off the heads/block, the shim is .030 to return geometry back to factory), I think Mopar Performance carries them, they are just curved thicknesses of metal to add as a shim and there is nothing wrong with using them to regain geometry, otherwise make some yourself, it is a recognized correction in the Mopar manuals. The only real thing you have to worry about is the one rocker pedistal that has the oiling hole coming through it, make sure the hole in the shim allows the oiling of the rocker shaft and all is good to go stock. dana442010-02-14 21:03:38
Title: What's my compression ratio
Post by: Steve on February 14, 2010, 04:35:16 PM
Lemme ask you a dumb question.
 
Hypethically. . . .
 
There's at least .020 of slop in a relaxed rocker on a 383.  Wouldn't it lift the valve sooner and hold it open a bit longer?  Not to mention more lift.  Assuming ot was all stock hardware. . .
Title: What's my compression ratio
Post by: Leaburn Patey on February 14, 2010, 06:30:19 PM
So,shimming the stock set up is a good economical suggestion that will work if everything measures up OK..
The heads were 88cc.
They cc'd to 87.8
So,is there a way to calculate how much they shaved to get to the 87.8 cc??
I know for a fact the block deck was shaved ten thou.
 
My understanding is I should be OK without having to buy special pushrods or rocker kits.
The rocker arm kit will cost almost if not more than the pistons.
I did find some cheap alloy kits but they would be overkill for my application.
Another question..
How about 1.6 ratio??
Any improvement or gains in it for my application??
CBarge2010-02-14 23:37:44
Title: What's my compression ratio
Post by: Leaburn Patey on February 14, 2010, 07:48:58 PM
Found this PRW stainless steel set in a 1.6 for less money than the Comp kit..
http://www.prwonlinestore.com/stainlesssteelrockerarmkit1.aspx (http://www.prwonlinestore.com/stainlesssteelrockerarmkit1.aspx)
CBarge2010-02-15 00:49:30
Title: What's my compression ratio
Post by: Guests on February 14, 2010, 08:20:18 PM
That .020 slop is from the lifters bleeding down over time, all hydraulic lifters do this with our engines (it's why they rattle for a second or two after startup sometimes, not to worry).
 
Like I said, I like adjustable rockers, aluminum, stainless, some are cheaper than others, they are all good compared to non-adjustable ones. As far as the 1.6s go, now you are talking about clearance issues depending on the cam you have, but in looking at the lift, you calculate to under .500 easy, so no problem at all. If you want to save the money given the small cut off the head and block, save the money, like you said, it isn't a race engine, flot away.
 
dana442010-02-15 01:25:23
Title: What's my compression ratio
Post by: Leaburn Patey on February 14, 2010, 08:41:11 PM
I am very familiar with the lifter bleed off..
My Diplomat's 318  takes a lickin and keeps on tickin'..LOL!
Thanks for the consultation Ed.
I can upgrade the rockers later on.
I can get away using my old pushrods and rockers for now.
The work I am getting done is costing me as it is so far.
 

Title: What's my compression ratio
Post by: Guests on February 14, 2010, 08:52:48 PM
I hear you there on the cost, and sometimes the good toys, if you can't see them and don't really need them, well, I live without them, too, when I have to.
 
Why do you think I think I know so much? Too cheap to allow anyone else to do things, and in the past, when I did, turned out it cost more than it should have, ended up redoing half of it later, turned out they knew less than me to begin with over the years, and I had a good mentor/teacher/machinist/inventor that taught this little padawan well.
Title: What's my compression ratio
Post by: glen cyr on February 15, 2010, 05:50:52 AM
Here are the shims that were mentioned. http://store.440source.com/Rocker-Shaft-Shims-pkg-of-30/productinfo/127-1020/ (http://store.440source.com/Rocker-Shaft-Shims-pkg-of-30/productinfo/127-1020/) I have made some out of brass stock i got from princess auto. It might be an idea to get some of the adjustable pushrods if those shims don't cut it. http://www.hughesengines.com/Index/products.php?browse=category&level0=QmlnIEJsb2NrICA0MTMtNDI2LTQ0MCAoUmFpc2VkIERlY2sp&level1=UHVzaHJvZHM=&partid=11091 (http://www.hughesengines.com/Index/products.php?browse=category&level0=QmlnIEJsb2NrICA0MTMtNDI2LTQ0MCAoUmFpc2VkIERlY2sp&level1=UHVzaHJvZHM=&partid=11091)





Glen
Title: What's my compression ratio
Post by: Leaburn Patey on February 15, 2010, 06:29:55 AM
Thanks,Glen!!
Certainly an excellent option to consider.(http://www.moparfins.com/forum/smileys/smiley4.gif)
$169.00 versus $600.00 to do the same job.
CBarge2010-02-15 11:43:39
Title: What's my compression ratio
Post by: Rich on February 15, 2010, 06:45:51 AM

 You can buy an adjustable checking pushrod from Comp to figure out the length that you need, and they will make you a set for not much more than the stock length ones they sell. However,  the amount of metal they removed from your block and heads will be made up by using the thicker blue Felpro head gaskets (.039" thick as opposed to the factory steel ones that are .020 thick) so you can reuse your old ones. I would  try a set of these heavy duty factory type rockers to replace your worn old ones - they will be more than adequate for any street engine. I have used these in several builds including my own, and they're only a hundred bucks:
http://www.jegs.com/i/Mopar+Performance/312/P4529743/10002/-1 (http://www.jegs.com/i/Mopar+Performance/312/P4529743/10002/-1)

 
(http://www.moparfins.com/forum/attachments/171/312-P4529743.jpg)

krautmaster2010-02-15 11:48:30
Title: What's my compression ratio
Post by: Guests on February 15, 2010, 09:20:40 AM
All good options guys.
Title: What's my compression ratio
Post by: Stewart Van Petten on March 07, 2010, 09:45:31 AM
[/QUOTE]

Kind of coming in late on this one but I may have a few things useful to add.
 
If you are not racing the engine these rockers will be more than enough. Even if you are running an after market cam and having a little bit of fun with it they will work well unless you are using a fairly high lift cam.
 
I built a few 440s over the years. Looking at the OP's parts list I noticed that he is using almost the exact same parts for his bottom end as a few of our projects (pistons, rings, bearings) . My brother and I tried a few different cam combinations for one of our 440s. The first cam was not much better than stock. It was classed as an "RV" cam. This was not what we were after for a street/strip machine. The cam that we really liked was a Crane Fireball. It idled with a bit of a lope but still made good torque for streetability. It started to turn on  around 2200 rpm and ran strong to around 5500 rpm. I am sure that there are many more cam choices now for the big block Dodge engine. If I had the budget I would look into roller cams for this engine. I have found that street roller cams give a guy great bottom end and also an element of fuel economy. I usually don't care as much about fuel economy in a toy but sometimes that is also a focus for a person's hobby machine.
 
Good luck with your project!