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Author Topic: What's my compression ratio  (Read 2956 times)

firedome

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What's my compression ratio
« Reply #30 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



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Steve

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« Reply #31 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
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Stan Paralikis

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What's my compression ratio
« Reply #32 on: October 06, 2009, 03:53:42 PM »

So I was right.........

Steve

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« Reply #33 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.
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Stan Paralikis

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What's my compression ratio
« Reply #34 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........

firedome

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« Reply #35 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!

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Butch Houghton

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What's my compression ratio
« Reply #37 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.




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Stitcherbob

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What's my compression ratio
« Reply #38 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.......

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Stan Paralikis

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« Reply #39 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.
 

Butch Houghton

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« Reply #40 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


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Stitcherbob

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« Reply #41 on: October 09, 2009, 05:38:25 PM »

ok send the Hemi & those motor mounts up here......it'll fit in my Imperial!
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Stan Paralikis

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« Reply #42 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.

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What's my compression ratio
« Reply #43 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), 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
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Stan Paralikis

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« Reply #44 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. ...

 
 Wow. you know your stuff.
Can't I simply send you my distributer.  I have no idea what you're talking about.
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