[crossbolted]

Ok guys, I'm working on a 350, 64 cc alum heads, forged piston etc...Putting values in "Patt Kelley" 's calculator, we got 9.27 for DCR , same number with KB's. KB's also gives 9.98:1 for SCR. Are these safe with pump gas (max 91) or we need to lower this?Any ideas appreciated..

[ap72]

with your combo and a really good tune and you'll be fine on 91 octane. I'd also only run a 180 tstat (or fill the block to the water pump holes and run a 160)

I know its money but a knock detector would be a BIG consideration, for when the weather changes or you get some bad gas. A combination this close is doable BUT you need a spot on tune.

[1Gary]

Those knock sensors are a hell of alot cheaper than the alternative repairs.A extra step to wire in??. Yes, but well worth it.

[janus]

IMHO, 9.27 is really really high for DCR, but then again i myself do not have practical proof for that



taken from this article: Engine Compression Ratio - Tech - Popular Hot Rodding Magazine

anybody done it just correct me, i'm willing to learn

[cobalt327]

Originally Posted by crossbolted

Ok guys, I'm working on a 350, 64 cc alum heads, forged piston etc...Putting values in "Patt Kelley" 's calculator, we got 9.27 for DCR , same number with KB's. KB's also gives 9.98:1 for SCR. Are these safe with pump gas (max 91) or we need to lower this?Any ideas appreciated..

Not knowing any more than this, I wouldn't run a 9.3-ish DCR on 91 octane. But hey- what do I know.

[Landshark928]

If that was your static, no problem. Your a good bit high for DCR. Need a bigger cam to bring SCR down, or you need to drop the SCR. Or run E85...

Post up your values here and someone can double check your work.

[crossbolted]

Thank you all for consideration.
Here I got : sbc 350 STD to be bored to 0.040 (never decked), cast crank , Probe FPS Flat top -4 cc, forged rods (5.7") , 64 cc aluminum heads (190 cc runners, 2.02/1.90), 1.5 ratio roller type rockers , Howard Hyd. 110041 cam (Duration :235 Ex, 225 In - Valve lift:.488 Ex ,.465 In. - 110 LC - 106 Intake C/L -Intake closes @38.5 deg. ABDC ), Head Gasket Fel pro 1003 (4.166 Dia, 0.041 compressed thickness)
Not sure or insufficient information about quench distance stuff or decking.
Any comment or help is really appreciated.

[GMC boogie]

No way you get a 9.27 DCR with that camshaft and CR. I think you entered some wrong numbers somewhere. You must enter the advertised duration.

[crossbolted]

You're right boogie... apparently I put " Duration @ .050" instead of "Advertised duration" which are different. With corrected input, I got 10.0:1 for SCR and 7.93 for DCR. Looks safe to me.

[janus]

that sounds about right, should be good to go! which calc are you using with the adv. duration? i've had quite some variations from the various calculators when it comes to determining DCR from IVC cam timing (0.050 vs. 0.006, 0.004 etc)