GREGGPENN

Not necessarily. If running a 355 or 383, I'd estimate 8.7DCR with 11:1 SCR using that cam. Since factory 113's are NOT the best chamber design, maximum RECOMMENDED alum DCR was exceeded in a build where the head design didn't help prevent detonation.

AFRs (or other better-than-factory-designed heads) MIGHT have handled it. But that 93-octane gasoline quality, engine temps, timing, and other issues would still have been very important.

Call any large builder. They recommend 10:1 as the upper limit for static compression ratio's. Partly, that's a CYA policy. Partly, it's to cover other issues a builder might not be savvy enough to consider. Partly, it's in consideration of degrading gasoline quality. Partly, it's just to provide a safe margin -- beyond which you don't gain THAT much TQ/HP. It's only around 10tq/hp for every compression point IIRC.

GREGGPENN

BTW: Throw in the ZZ409 vs Comp268 cam and the dynamic compression drops from 8.7:1 to 8:1. So, there's a 3/4 point drop in dynamic compression between the two cams -- even though SCR would be the same for both.

That's what we're talking about when considering cylinder pressures with each setup...and why DCR is worth looking at. It's why the ZZ409 cam would work with alum heads...and why it's REALLY iffy for iron heads.

OTOH, you could pick a piston with a bigger dish and make it work.

rickbraley

Thanks to everyone for all the good info!

At this time the only thing I am committed to is the displacement and the heads. I have the block, crank, rods and heads from a previous build. All are in fantastic condition so naturally I would prefer to use them if possible. I have to buy the cam, pistons, intake, etc.

Goal is simply to have 400+ HP in a streetable, reliable engine. I want to be able to buy pump gas and not have to worry about problems due to the lower octane (89 - 91). Would be nice to be able to give a new Mustang or Camaro or even a Vette a run if I pull up beside one somewhere.

Looks like the concesous is I need to look for a different set of pistons. I am currently too high with my SCR even with the ZZ409 cam.

Have I intepreted the bulk of postings correctly? Any recommendations on pistons?

GREGGPENN

Add ~10cc to your relief/dish and you should be in a better range.

Also, pay attention to quench. Get it down near .040

C409

You're looking at 268XFI specs ... try XE268H ...........

rickbraley

Excellent advice.

Found another set with +16cc comb cham volume giving me a SCR of 9.84:1.

Do you think this config will get me the 400+HP streetable engine I am looking for?

Any recommendations on intake other than the TPIS mini-ram? Based on numerous other postings it appears I will not be able to get there with the TPI setup correct?

bjankuski

9.84 will be fine and I would look at the superram for your 400 HP goal. Alternative intakes would be the FIRST or the mini ram. Any one of those intakes with the ZZ409 cam will make 400 HP. A large tube runner TPI intake may also get your goal but I would choose one of the prevoiusly mentioned intakes before the large tube runner design.

856SPEED

go mini on the 383....don't even bother with a TPI set up....you will be disappointed.....unless you want 500ftlbs. and 380hp at the crank........very hard to get 400 out of a TPI set up....