choosing cc size?
Melting Slicks
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From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
This all depends on the rest of your set up, such as piston type, flat top, dished, dome,, etc. Factory dished will have approx 9.5 with 64 cc, flat tops will be higher, approx 10.2. With 72 cc and dished about 8.5 and flat tops about 9.2. Again these are approx. Head gasket thickness and bore size will allo chage this numer. Do a search here on the forum and you will find the formula to be a little more exact.
For a street engine able to live on pump gas stay under 10.0 compression, with the aluminum heads. I have a 383, dished pistons, Trick Flow 195 / 64 cc heads and I have a calculated 9.7 compression ratio using a composite head gadket .039 compressed thickness. I can run 89 octane without any problems. Haven't tried 87 yet. The more total timing you run, will give you performance but can limit your gas choices Best of luck
For a street engine able to live on pump gas stay under 10.0 compression, with the aluminum heads. I have a 383, dished pistons, Trick Flow 195 / 64 cc heads and I have a calculated 9.7 compression ratio using a composite head gadket .039 compressed thickness. I can run 89 octane without any problems. Haven't tried 87 yet. The more total timing you run, will give you performance but can limit your gas choices Best of luck
Last edited by mbeeman350; Jul 1, 2007 at 11:21 AM.
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From: alberta
was going to go with mahle flat top pistons,( confused: flat top, domed, dished, is it all about the compression when choosing the piston type?looking for formula.)
want 10.1 compression and a driveable street car. ( still using afr 195 street heads)
want 10.1 compression and a driveable street car. ( still using afr 195 street heads)
Last edited by pointy1; Jul 1, 2007 at 11:40 AM.
Melting Slicks
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From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
SCR Calculator
Couldn't find the one I used. Did a Google and found this one. Looks like it should work
http://www.csgnetwork.com/compcalc.html
Mark
http://www.csgnetwork.com/compcalc.html
Mark
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From: alberta
looked at it, going to try and use it, looks complicated!, maybe i'm just an idiot?!.
no laughing out there!
(383 stroker afr 195 street heads)
bore/stroke?
cylinder bore size?
piston stoke legnth?
head gasket bore diameter?
compressed head gasket thickness?
comb chamber ( no problem there!)
piston dome vol in cc, neg for dished?
piston deck clearance?
no laughing out there!
(383 stroker afr 195 street heads)
bore/stroke?
cylinder bore size?
piston stoke legnth?
head gasket bore diameter?
compressed head gasket thickness?
comb chamber ( no problem there!)
piston dome vol in cc, neg for dished?
piston deck clearance?
Last edited by pointy1; Jul 1, 2007 at 12:05 PM.
Melting Slicks
Joined: Feb 2003
Posts: 2,529
Likes: 27
From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
looked at it, going to try and use it, looks complicated!, maybe i'm just an idiot?!.
no laughing out there!
(383 stroker afr 195 street heads)
bore/stroke? 1
cylinder bore size? 4.030 stock 350 bore 0.030 over
piston stoke legnth? 3.75
head gasket bore diameter? 4.050
compressed head gasket thickness? 0.29 - 0.39
comb chamber ( no problem there!) 64 or 72
piston dome vol in cc, neg for dished? flat tops = 0
piston deck clearance? .024
no laughing out there!
(383 stroker afr 195 street heads)
bore/stroke? 1
cylinder bore size? 4.030 stock 350 bore 0.030 over
piston stoke legnth? 3.75
head gasket bore diameter? 4.050
compressed head gasket thickness? 0.29 - 0.39
comb chamber ( no problem there!) 64 or 72
piston dome vol in cc, neg for dished? flat tops = 0
piston deck clearance? .024
if you can read the numbers on the pad, then the block has not been decked
I got 11.14 cr with the 64 cc heads and 10.19 cr with the 72 cc heads using a 0.039 head gasket and assuming the block has not been decked
Last edited by mbeeman350; Jul 1, 2007 at 12:53 PM.
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From: alberta
okay, compression is where i want it (10.1)
another dumb question: why do they deck the block?
it's probably a bad idea to do this if i have a mathching #'s block!
will have to find another block!?
another dumb question: why do they deck the block?
it's probably a bad idea to do this if i have a mathching #'s block!
will have to find another block!?
Last edited by pointy1; Jul 1, 2007 at 01:18 PM.
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Flat top pistons are never "0" They have either 2 or 4 valve relief cuts in the dome. so they might be anywhere from -5 cc - 9 cc dished.
Head gaskets dia. are listed by the manufacturer. Generally the one size fits all is the 4.060 Racing gaskets can be bought to the actual bore size
Head gaskets dia. are listed by the manufacturer. Generally the one size fits all is the 4.060 Racing gaskets can be bought to the actual bore size
Last edited by gkull; Jul 1, 2007 at 01:36 PM.
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St. Jude Donor '08-'09
Melting Slicks
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From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
Flat top pistons are never "0" They have either 2 or 4 valve relief cuts in the dome. so they might be anywhere from -5 cc - 9 cc dished.
Head gaskets dia. are listed by the manufacturer. Generally the one size fits all is the 4.060 Racing gaskets can be bought to the actual bore size
Head gaskets dia. are listed by the manufacturer. Generally the one size fits all is the 4.060 Racing gaskets can be bought to the actual bore size
Team Owner
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From: Reno Nevada
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Without a central spark plug domed pistons have flame travel issues. Bigger chambers and lower compression also leave more residual burnt gas in the chamber which dilutes the fresh incoming fuel charge.
Flat tops or even dished pistons and a smaller chamber are superior.
with enough cam duration you can run higher compression. My 383 is at 11.2 and my 434 is at 11.8
Flat tops or even dished pistons and a smaller chamber are superior.
with enough cam duration you can run higher compression. My 383 is at 11.2 and my 434 is at 11.8
Burning Brakes
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I had my block decked and the machinist did not deck the pad area so as to not disturb the #'s
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From: FL
Static compression ratio is meaningless without knowing cam timing. You can run 11:1 on pump gas if you use a big enough cam to bleed off cylinder pressure at low rpm.
Dynamic compression ratio which takes cam timimg into account is a much better tool.
Good discussion and a DCR calulator here: http://www.empirenet.com/pkelley2/DynamicCR.html
Excerpt from that site:
Also, some good info and engine combos here: http://purplesagetradingpost.com/sum...comb-sm-1.html
Dynamic compression ratio which takes cam timimg into account is a much better tool.
Good discussion and a DCR calulator here: http://www.empirenet.com/pkelley2/DynamicCR.html
Excerpt from that site:
Why it matters: A 355 engine with a 9:1 static CR using a 252 cam (110 LSA, 106 ICL) has an intake closing point of 52º ABDC and produces a running CR (DCR) of 7.93. The same 9:1 355 engine with a 292 cam (having an intake closing point of 72º ABDC) has a DCR of 6.87, over a full ratio lower. It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane. The larger cam's DCR falls outside this range. It would have markedly less torque at lower RPM primarily due to low cylinder pressures, and a substantial amount of reversion back into the intake track. Higher RPM power would be down also since the engine would not be able to fully utilize the extra A/F mixture provided by the ramming effect of the late intake closing. To bring the 292 cam's DCR up to the 7.5 to 8.5:1 desirable for a street engine, the static CR needs to be raised to around 10:1 to 11.25:1. Race engines, using high octane race gas, can tolerate higher DCR's with 8.8:1 to 9:1 a good DCR to shoot for. The static CR needed to reach 9:1 DCR, for the 292 cam mentioned above, is around 12:1.
This lowering of the compression ratio, due to the late closing of the intake valve, is the primary reason cam manufactures specify a higher static compression ratio for their larger cams: to get the running or dynamic CR into the proper range.
This lowering of the compression ratio, due to the late closing of the intake valve, is the primary reason cam manufactures specify a higher static compression ratio for their larger cams: to get the running or dynamic CR into the proper range.
Last edited by SteveG75; Jul 2, 2007 at 01:19 PM.