Yes, some Team Chevelle people are girls!

I have a 402 Chevy and need someone with the correct data to calculate my compression ratio. I have a 1970 402 Chevy bored .030, 1970 iron #3964290 heads, TRW L2383F 396 .060 pistons, and head gaskets from a Fel Pro KS2618 gasket set.

What will my comp ratio be with these parts?

Thanks, Fast Chick

Someone here will be able to give you a ballpark figure, but here's something to think about...if those heads were ever milled or the block has been decked, the numbers won't be on the money.

Who built the motor? If it was an outside machine shop, have them cc it and you'll get an exact number wich is I'm sure what you really want.

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"Too fast for love"
Dave Armstrong...New York!
'67 Chevelle 396/Th400/4.10
The Burnout (http://chevelles.com/showroom/BBD1burnout.jpg)
The Launch (http://chevelles.com/showroom/BBDavelaunch.jpg)
The Engine (http://chevelles.com/showroom/BBDave396.jpg)
The MAN!!! (http://chevelles.com/showroom/BBDave.jpg)(the guy in the black shirt)

Fast Chick,

How did you get the .060 pistons in the
.030 bore? http://www.chevelles.com/forum/eek.gif S l o w d o w n and give more info. http://www.chevelles.com/forum/biggrin.gif
What is cc of heads? ( Assuming they are not milled )
I don't know what the displacement of the dome on the pistons is, if any. This makes a difference.
Gaskett thickness?

Typically, if you bore an engine and do nothing to the pistons,heads,or stroke, compression will go down.


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Dave
"Fire all your guns at once and
Explode into space."
Steppenwolf "Born to be Wild"

Golly gee whiz,


"too fast for love" and a "fast
chick" http://www.chevelles.com/forum/eek.gif

Can't help wonder who is faster.
http://www.chevelles.com/forum/cool.gif http://www.chevelles.com/forum/cool.gif http://www.chevelles.com/forum/cool.gif

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Dave
"Fire all your guns at once and
Explode into space."
Steppenwolf "Born to be Wild"

The .060 over pistons are probably for a 396 which would be a .030 over 402.

<BLOCKQUOTE>quote:</font><HR>Originally posted by Fast Chick:
I have a 1970 402 Chevy bored .030, TRW L2383F 396 .060 pistons, and head gaskets from a Fel Pro KS2618 gasket set.

Thanks, Fast Chick<HR></BLOCKQUOTE>

She's right on the boring sizes and such. Think before you act there Dave http://www.chevelles.com/forum/wink.gif

ARe those the closed chambered heads? or are the 70s open? I bored my 402 over .060" and used TRW-L2328F. They where said to give me 10.81 : 1 I don't see the pt# you listed in my summit catalog though http://www.chevelles.com/forum/frown.gif . You tried calling up Speed Pro, or summit maybe? they should be able to tell you what the data sheet reads out.

as far as 3 digit accuracy. not really that important. I can run 93 octane with a total timing of 36BTDC and my 414cid motor is happy as can be. It's a bit above stock also.

Glad to have you aboard Fast Chic. I know of at least 4 ladies onthe board, so you aren't alone. special maybe, but not alone http://www.chevelles.com/forum/wink.gif


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Member of TC Superfreind's society for goodness and camaraderie.
BB414, TH400, 3.73 Eaton posi,
13.16sec @ 105.15 MPH (TH400 needs clutch pack, Radial T/As = zero traction)
" Don't worry about the world coming to an end today. It's already tomorrow in Australia"
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Video of me staging (smoke of course) (http://www.notabusinessracing.org/videos/mike_chevelle_burnout.avi)

BB_Mike,
Your are right. I was in the middle of a typing a retraction when my browser locked up. http://www.chevelles.com/forum/redface.gif

this site here might help out some.
http://tubby.tuskar.net/dart/math.html

Lets assume the block has not been decked and heads have not been surfaced. Im just looking for a ballpark number to help me pick a cam. The 290 heads are stock L34 heads that have not been reworked. The only numbers I can come up with on the heads are from the Chevrolet book of numbers. This book shows them at 100.9cc.


The .060 396 pistons fit the .030 402 bore as some of you already realized.

The only numbers I can come up with on the heads are from the Chevrolet book of numbers. This book shows them at 100.9cc.

I dont have the specs on the pistons (they are from the mid 1980's and I cant find any specs on them). I also dont have the specs on the head gasket.

I was hoping some other gearhead out there had access to these numbers. If I have the specs on the pistons, gasket, and head even this girl can do the math!

Once you know all your specifics go here:
Compression Ratio Calculator, etc. http://www.bgsoflex.com/auto.html

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"Laissez Le Bon Temp Rouler' Cha!"

"Jungle"Jim
A&P/ASE T/C#105
70SS396 & 70 Malibu
"I don't drive FAST, I just FLY low!"

I looked on this web site to see if your
TRW L2383F 396 .060 pistons were listed.
Not there, however, they have a toll free number and they should be able to tell you all about your pistons.
http://store.yahoo.com/gofast/forgedpiston.html

FAST CHICK:

I did some calculating using the NHRA blueprint numbers and the Chevrolet by the Numbers book, and here is what I came up with:

NHRA
Bore (inches): 4.156
Stroke (inches): 3.76
Deck Height (inches): 0.021
Gasket Thickness (inches): 0.008
Combustion Chamber (cc): 105
Valve Relief (cc): 12.1 cc
Compression Ratio = 9.41 to 1

Chevrolet By The Numbers
Bore (inches): 4.156
Stroke (inches): 3.76
Deck Height (inches): 0.008
Gasket Thickness (inches): 0.021
Combustion Chamber (cc): 100.967
Valve Relief (cc): 12.1 cc
Compression Ratio = 9.77 to 1

Now, on the pistons, the NHRA lists the L2383 as a legal replacement for the 71-72 CHEVY, 210-300hp, 402 cubic inches, so I used the specs for that piston in the above equation. I also used the NHRA specs of gasket thickness and deck height, which are thier MINIMUMS, so unless you block has been decked and you have the gasket they recommend, then your compression will be lower than what I posted. Also, the combustion chamber #s for the heads may be off depending on whether or not your heads have been shaved or not. But, this will be within a point of compression.

Also, 69454Malibu, the bigger the bore, the higher the compression is.


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Rob Clary
'69 Yenko Chevelle
Interested in COPOs, Yenkos or other dealer built muscle cars then go here: www.yenko.net (http://www.yenko.net)


[This message has been edited by Chevy454 (edited 11-02-2000).]

Thanks Chevy 454 for the numbers. I was hoping for around 9.5:1 so i am in the right ballpark. Im just curious where you got the specs, if they are posted somewhere where I can get them. If not could you list the specs on this post so that i can have them for my files, Thanks again.

Also, Rob, for the NHRA specs you list
Deck Height (inches): 0.021
Gasket Thickness (inches): 0.008
and for the "by the numbers" you list

Deck Height (inches): 0.008
Gasket Thickness (inches): 0.021

was this a misprint? should they be the same?

thanks

L2383 - 13.9cc dome. I suspect the gasket at .039 or .041, and the deck at .008. I get 9.57.
Looks like your'e there. BTW, welcome aboard!

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Tino #28 Gold
72 Malibu 350-300,700R4
83 Grand Prix LJ 305

I found most of the specs on the NHRA page, under "engine blueprints". Then, I used this page ( http://www.prestage.com/carmath/calc_Compression.asp ) to plug the numbers in the formula. The only difference between the numbers above was the combustion chamber CC. The rest is the same.

Tino: thanks for the info on the dome...the NHRA was close, but I didn't know for sure. I did some checking today, and found that the thinnest gasket Fel-Pro offered was .039, so I used that # and got 9.57:1, so you are right there Fast Chick!

I agree with all the above, but in the real world, factory tolerances tend toward combustion chamber CC's and deck heights larger than factory spec. Unless the heads have been milled and block decked, I would bet if actual CC's and deck height were measured and used in the calculation, the true compression ratio would be around 9.0 to 9.25-1.

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von '69 300 Dlx SS TC #15 ACES #1575

OK, thanks everyone for your help. This site is super!

Just three more questions:

1. Where did you get the figure of 12.1cc for valve relief?

2. I see the heads listed at 96.4cc on NHRA, and 100.697cc in the Book of Numbers. Does anyone know which is correct for a stock 290 head?

3. With the engine out and heads off how difficult is it to measure this ratio using kits (like from Powerhouse Products)?

Also, in checking with the previous owner, I discovered that the block was decked .010 and the heads were surfaced just enough to clean up the mating surface. How much will this affect my compresion ratio?