Is 10.8:1 compression ratio too much for 93 octane? This would be on a carbed 350 using 72 cc aluminum heads and speed pro hypereutectic domed pistons. Also what 72 cc alum. heads would you recomend for a 400 hp 350?

 

10.8:1 is too much for pump gas.

You really start to push into the limits of 93 octane at 9.75-10:1 with aluminum heads. People have gone higher, sometimes it's luck and usually it's a lot of math and experience.

 

realy? I think i would be ok because i am runing 10.2:1 now on iron heads with out a problem.

 

11.5:1 runs fines on pump gas. (sonoco 94) but im sure 93 would be fine too. but if you are planning on spraying i would toss some 110 in it or somthing so u dont detonate.

 

my ls1 has 10.1 to 1 factory so 10.8 should be no problem. definitly go with high octane (93 or 94) if available

 

I don't know if the alum. heads will make a difference but I'm running about 11:1 with Iron heads right now. Runs fine on 93.

 

Same here, I just add some racing fuel for my trips down the track. You will be able to get by with a little more compression using aluminum heads vs iron heads though.

 

How big of a cam are you guys running? You can run higher CRs with a pretty lumpy cam [more duration] because it bleeds off some cylinder pressure.

I guess I should stop reading magazines and the internet and start building motors!

 

I run 11:1 with Dart Iron Eagle heads, 36 deg. total timing, Comp cams 284 XE cam, and a 3500 stall converter. Car runs on 93 octane and was a daily driver for 3 years until I was able to get a beater(87 S10). Never had any detonation. I even ran a 150 shot without adding race gas or timing retard and never gave me any problems. Every car is differant but, I think with 10.8:1 and aluminum heads you will be fine.

I think a loose torque converter helps also. I remember an article in HotRod awhile back about a guy who ran a 14:1 sbc on 93 octane. Said he was able to do this because of the Nova's light weight, cam with ALOT of duration, timing was like 28 deg. I think and a very loose converter. Car ran consitant 10.80's on motor. I would never try this but, like I said every car is differant.