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Old 11-03-2008, 05:17 PM   #1
bytor
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Default Flat Top Pistons

Do any of you guys know what the valve relief volume is on the stock L-82 flat top pistons?
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Old 11-03-2008, 05:49 PM   #2
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I think they are 5cc's.

-Mark.
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Old 11-03-2008, 06:05 PM   #3
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Sorry to hi-jack the thread, but if you put on 70cc heads do you know what the compression ratio would be?
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Old 11-03-2008, 06:19 PM   #4
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You can get it yourself using that online calculator :

http://www.csgnetwork.com/compcalc.html

That way you can tinker with the best suited head volume/piston compression volume.
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Old 11-03-2008, 06:41 PM   #5
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Quote:
Originally Posted by HamadUP View Post
You can get it yourself using that online calculator :

http://www.csgnetwork.com/compcalc.html

That way you can tinker with the best suited head volume/piston compression volume.
I already have 70 cc heads so I just want to know what the CR is. do you have these values for an L-83, sorry to copy off of your homework.


Cylinder Bore Size
Piston Stroke Length
Head Gasket Bore Diameter
Compressed Head Gasket Thickness
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Old 11-03-2008, 07:53 PM   #6
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Quote:
Originally Posted by Clint's C3 View Post
I already have 70 cc heads so I just want to know what the CR is. do you have these values for an L-83, sorry to copy off of your homework.


Cylinder Bore Size
Piston Stroke Length
Head Gasket Bore Diameter
Compressed Head Gasket Thickness
Unless you have had the block worked at all you have the stock 350 specs: 4.000" bore, 3.48" stroke.

Now if you have 70 cc heads on it, you've obviously replaced them, which means you replaced the head gaskets. So there's no way we can tell you what your head gasket bore diameter or thickness is. You could take a conservative approach and say your gasket diameter is 4.060" and your thickness is 0.041". That should give you the lowest compression ratio you could expect from your motor. To see your max, use a 4.000" diameter and a 0.015" thickness.

You probably want stock deck height: 0.025".

Last edited by LeMans Pete; 11-03-2008 at 07:55 PM.
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Old 11-03-2008, 10:43 PM   #7
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Thanks, stingr69. I have seen other references of 5cc's for L-82 flat tops but no actual detailed specifications. All I could find was,

TRW L2417
Gm Part Number 474190
350
9:1
76cc
336747,
464664 or
464692
71-80 L-82. Piston OD 3.998 to 3.999".

But no valve relief info..
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Old 11-03-2008, 11:54 PM   #8
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L2417F is replacement for L82 piston.

My sealed power cat shows these specs for L2417F

flattop w/ single trough
dome volume: -3.4cc
compression distance: 1.560"

sealed power (Federal Mogul aka TRW) has a static compression ratio calculator that's quite accurate & handy:

http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx

btw ... thin steel shim gasket fp1094 volume = 3.2cc x 0.015" thick.
gm comp gasket 10105117 volume 5.8cc x 0.028".

Last edited by jackson; 11-04-2008 at 12:01 AM.
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Old 11-04-2008, 04:56 PM   #9
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Quote:
Originally Posted by foxymophandlpapa View Post
Unless you have had the block worked at all you have the stock 350 specs: 4.000" bore, 3.48" stroke.

Now if you have 70 cc heads on it, you've obviously replaced them, which means you replaced the head gaskets. So there's no way we can tell you what your head gasket bore diameter or thickness is. You could take a conservative approach and say your gasket diameter is 4.060" and your thickness is 0.041". That should give you the lowest compression ratio you could expect from your motor. To see your max, use a 4.000" diameter and a 0.015" thickness.

You probably want stock deck height: 0.025".
Wow, the head gasket can make difference of .5 in the CR! Thanks for the education.
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Old 11-05-2008, 09:11 PM   #10
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Quote:
Originally Posted by HamadUP View Post
You can get it yourself using that online calculator :

http://www.csgnetwork.com/compcalc.html

That way you can tinker with the best suited head volume/piston compression volume.
No meaning to hi jack but....
That is so cool. I'm working on building my 383 -12 cc dish pistons, 64 cc heads. It's cool to see how you can regulate your cr by either changing your head gasket thickness, shaving you block etc.
Thanks guys
Clyde
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