Max dynamic comp. for aluminum heads?

[swinger340]

What should be the max dynamic comp. w aluminum heads in order to run 93 octane w/o detonation? Im coming up w 8.9:1 DCR w the calculator im using and im thinking that may be a little to high. Anyone running close to that, before I decide to make a cam change or retard my existing cam a little?

 

[68 340]

I am running 55 cc closed chamber eddy heads. Static compression is 11.27 to 1. Dynamic compression is 8.8. Quench is 0.36. I run 93 octane fuel without pinging.

 

[swinger340]

I am running 55 cc closed chamber eddy heads. Static compression is 11.27 to 1. Dynamic compression is 8.8. Quench is 0.36. I run 93 octane fuel without pinging.

Good to know. Thats a little more settling. What is your cranking pressure? I have .035 quench 63 cc closed chamber. 10.6:1 static w 54 ABCD. I was a little nervous my DCR of 8.9:1 may be a little high for pump gas. On the verge of swapping cams to lower my DCR a little.

 

[Bad Sport]

I'm no pro engine builder, but it has been my understanding with aluminum heads you can run a tad higher compression ratio. The aluminum supposedly dissipates the heat better.

A friend of mine, wife's Duster is running about 9 or a little better with aluminum heads and she has no problems with detonation.

 

[1wild&crazyguy]

around/about 200 psi cranking is where i would stop.

 

[swinger340]

around/about 200 psi cranking is where i would stop.

Short stroke (3.31) 340 w 185 cranking pressure. Should be fine on pump gas (93 octane)?

 

[moper]

It's a little higher than I'd like. I use 8.75 as my max with tight quench and aluminum heads. But, with the shorter stroke and relatively low pressure, I'd think you're fine for pump premium. Might be able to run lower than premium with good tuning.

 

[1wild&crazyguy]

Short stroke (3.31) 340 w 185 cranking pressure. Should be fine on pump gas (93 octane)?

with aluminum heads? Yes.

i stop at 170'ish with closed chamber 'iron' or quench dome piston & open chamber 'iron'=both in the .030's quench distance...and thats with the 91 octane we have here.

im sure others may or may not have diff to say on the plus or minus, but thats just my experience.

 

[SRT_DSTRHOLC]

Gotta remember where your at elevation wise... Ive run 180 in CA on 91 with up to 34 deg. of timing. I plan on running 8.8 DCR in Ca on 91 in Northern Ca and 93 in So. Cal or 91 on less timing.

 

[swinger340]

Im hoping to get it together and get the girl dynoed next weekend. ill try my existing cam 1st and if there are any issues I will swap it out. Only problem is im not sure if ill get a 2nd shot at the dyno. Want to break it in and tune it before doping it in the swinger.