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Author Topic: What's my compression ratio  (Read 3206 times)

Stitcherbob

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What's my compression ratio
« Reply #15 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 

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Stitcherbob

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« Reply #16 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? 

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Stan Paralikis

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« Reply #17 on: October 04, 2009, 12:15:08 PM »

Bullpuckey.  Iron heads and 10.5:1 on 92 octane is not a problem. 

firedome

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« Reply #18 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
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Stan Paralikis

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What's my compression ratio
« Reply #19 on: October 05, 2009, 04:44:27 AM »

firedome

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« Reply #20 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
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Stitcherbob

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« Reply #21 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. 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!


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firedome

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« Reply #22 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.

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Stan Paralikis

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« Reply #23 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.

Steve

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« Reply #24 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.
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Steve

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« Reply #25 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.

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Stan Paralikis

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« Reply #26 on: October 06, 2009, 09:03:29 AM »

  His reply told us absolutely NOTHING to answer our debate....

Steve

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« Reply #27 on: October 06, 2009, 11:42:55 AM »

OK  I'll ask him to clarify
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Stan Paralikis

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« Reply #28 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.

Steve

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« Reply #29 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
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