SmokedTires

I will be needing to have custom pistons made for my new engine that's in the works. I also will be ordering new heads.

So here's the question. I realize that by going with a smaller chamber in the head, it'll raise the compression, but what if yoiu went with a larger chamber and a small dome piston? Is there advantages to dome vs flat top pistons/ large vs small chamber heads?

I think I want to end up with around 11.0:1 compression. I understand that with aluminum heads & MFI I should have no problem with detentantion(sp?) with pumpgas (91 oct).

TIA :cheers:

gkull

You have some real figuring to do. Your stroke isn't that uncommon. But if your specifying pistons you really need to have the block deck height. So they can make pistons near "Zero" You have to keep the quench right at .038 which would be a common Felpro compressed height. Your going to need to know your finished chamber cc because 64 cc heads Zero deck and blah ba blah.

Puts you right at 11.1. according to automath on smokemup! Right where you need to be with any kind of roller cam. You need to look at this site http://cochise.uia.net/pkelley2/

Don't even think about dome or big cc. 11.4 or less is good with a 3.75 stroke and anything over 284 advertised intake duration @ 232 degrees at .050 on 91 octane. Your 3.6ish stroke will even use less degree cam on 91

SmokedTires

Thanks George. I'm looking at te Dart Little M block so I'll have an idea after the machinist preps the block. :)

Twin_Turbo

The flat tops are a better choice because they won't obstruct the flame front like the (high) domed ones will.

Monty

I ran 11.3 CR in my NA SBC 427 on 93 octane and never had a problem with detonation.

I believe you're better off with a "flat top" or even partially dished piston, and a small cylinder head combustion chamber. The idea is to maximize quench area to aid combustion efficiency and aid against detonation. Piston domes often interfere with the flame travel, hampering combustion efficiency, and potentially promoting detonation.

SmokedTires

Thanks guys. Those are the exact kind of answers I was looking for. :cheers:

69 N.O.X. RATT

Smoked tires: Wether or not 11 to 1 will be too much for 91 octane depends on a lot of variables. Monty's 11.3 on 93 was with a very well planned out motor and a very large duration cam, 255 + at .050 if I remember correctly. If you run a cam of 230 ish at .050 and 11 to 1 on 91 octane it will probably ping like crazy.

I ran a high lift short duration solid roller with aluminum heads 242 and 248 at .050 and it had slight detonation problems on 91 with a little over 10.25 to 1.

For the miniscul amount of power between 10.25 and 11 to 1 (approx 3%) (unless you don't mind a little octane boost) it is best to error on the safe side.

SmokedTires

69NOX- Thanks fr the info. I ctually errored on the gas octane, I meant 93 octane since that is available at most stations :) . I currently run Sunoco 94 as much a possible.

I appriecate the info about the pinging though, thanks.