Edzred72

I have Keith Black hyperutectic flat top pistons rated at 10:2 W/76cc 11:4 W/64cc. I currently have Protopline 64cc aluminum heads I would like to run. Couple of questions please:
#1) Is it possable to run detonation free on the street at 11:4 and how is this accomplished.
#2) Can the compression be brought down somehow to a managable upper 10's. I.E. cam duration...thicker head gasket...etc???
#3) If answer to #1 is a definitive NO...can the 64cc combustion chamber on the heads be machined to 76cc cost effectivly...or is it cheaper just to buy new pistons?
Thank you... and my 406 thanks you...
Eddie

Oh CRAP...I posted this in General

Z-man

#1 - Well, no matter what other changes are made, you can always retard timing to allow you to run at 11.4:1 on the street. Performance may not be the best however. Octane booster would also be a short term fix...

I'm sure others have the long term solutions.

comp

gkull

#1) I would not use over 11:1 My 383 motor was 11.2 To make it work I used thermaly coated pistons, exhaust valves, and chambers. I also used a .021 copper head gasket to keep a tight quench along with a big solid roller cam to get my Dynamic compression ratio down to the 8.3-8.4 range.

It's not worth you time, money or effort to run a motor right on the edge and have to carry octane boost for the gas stations that didn't give you true super unleaded.

#2) thicker head gasket is worse for detonation than a thinner one with a tighter quench.

#3) No, chamber machining could upset the whole swirl design and who knows how close to the water you might end up.

IMO - you can't use KB pistons and performance in the same sentence. They are better than old cast pistons, but they have feet per minute limitations of 7000 rpm in a 3.48 stroke so that would be mid 6000 in a 3.75 stroker 406. I was very dissapointed when i smoked a set of KB's in my Vette.

MYBAD79

The comp ratios that the piston manufacturer advertizes are based on a stock deck height (9.025") - if your block was decked the CR will be even higher.... if you plan on getting the block bored and decked then I'd buy forged pistons with advertized CR 9.2:1, there are many to choose from. After decking you should get around 10:1 CR

The hypereutectic pistons are not bad, however for a 406 that's likely going to see 6500rpm I'd buy forged.

Edzred72

I kind-a thought 11:4 was too high, thanks for the replies. New pistons it is, which bring up another issue.
The entire rotating assembly has been ballanced, so new pistons would mean it must be re-ballanced RIGHT???
Eddie

MYBAD79

unfortunately yes.....

BigBlockk

You may be able to find pistons of the same weight. Look around.

BigBlockk

Later.....