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499 Posts
Discussion Starter · #1 ·
Hi guys, some more questions re my 383 build.
I've been reading up on Dynamic CR.

I was looking at the 10.4CR Dished piston kit from Scat with XFI 280 cam but after reading more on DCR wondered if i'm too low on CR.
They also do a 11.8 CR kit with flat top pistons. Doing several calcs with Comp Cams XFI 280 & 292 cams would give me something like the following:

FLAT TOP 5CC 12.257 CR & 280 Cam (69) = 9.44 DCR 196.7 PSI Cranking Pressure
FLAT TOP 5CC 12.257 CR & 292 Cam (75) = 8.92 DCR 182.94 PSI Cranking Pressure

DISHED 16CC 10.86 CR & 280 Cam (69) = 8.39 DCR 169.07 PSI Cranking Pressure
DISHED 16CC 10.86 CR & 292 Cam (75) = 7.94 DCR 157.43 PSI Cranking Pressure

On the KB piston website 9.0-9.5 DCR is doable with this setup.

What do people think with this setup or just go with the Higher CR with the bigger cam anyway??

Thoughts please.


807 Posts
I dont claim to be an expert concerning everything there is to know about
static and dynamic compression. I do know that usually more compression
relates to more power up to a point and then we have to start talking about detination. Anyway it seems that some engines with high compression, where there is not good ring seal, perform about as good as
lower compression engines with very good ring seal. Just one example,NASCAR SPRINT CUP SERIES engines in and around 1998 were allowed to run up to 14.0:1 CR in their 350 ci engines. Because NASCAR was made to switch to unleaded fuel,these engines have had to cut back to about 10.0:1 CR WIH THE SAME 350 CI engines. Back in 98 the average
NASCAR motor was putting out about 750 HP, today these same motors with 10.0:1 CR are making about 900 HP,yes they have had more time to R & D and were allowed to switch to a factory like fuel injection system,but I think one of the advances that came out of this was better cylinder sealing and probably alot of other things that are considered trade secrets. If I were building a motor today,I think I would be investing alot of time regarding ring seal and how to keep the power from escaping
around the piston rings. ed
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