Running a high compression engine on pump gas

[VintageMusclecar]

The 496 in my Chevelle has 11.2-1 compression with square port closed chamber heads, and runs perfectly on 92 octane. The key(s) to making it work are 1) cam timing (needs to bleed off some cylinder pressure @ lower rpm), keeping the engine coolant temps ~160°-170°, and a nice, conservative timing curve--in this instance, 14° initial and 36° total, but it doesn't come in fully until ~4000 rpm. (no vacuum advance either)

FWIW, YMMV.

[Hemicolt]

Have the valve seats been changed to hardened versions?

[VintageMusclecar]

No, no need to.

[Hemicolt]

I was asking the author of the thread.

[67 Nova Boy]

There's that racing fuel smell that gets me going! [img]<<GRAEMLIN_URL>>/[/img]

I have Sunoco 260 running through my vains from birth...thanks to my Dad being a racer and my brother owning a Sunoco station. [img]<<GRAEMLIN_URL>>/headbang.gif[/img] I run VP 112 straight now in my 302...like the way it runs...will see if it likes the Cross ram. Was putting in octain booster at $8.65 for 32 oz. with Sunoco 93,it made more sence to just run 112 for the amount of time it gets driven.

Dave
67 Nova Boy

[miket1]

I agree with Eric, I have ran 11.1 engines for many years on 93 octane Shell gas setup same as his,
use mechanical advance , make sure the carb. is not running lean,

[ss427copo]

In 'ol Yeller, it's 12.7 to 1 and I've run AV gas since 1984. For every 5 gals., she gets 3 1/2 ounces of each lead additive and Lucas Octane Booster. Runs great and all looks good with a recent removal of the heads for a long overdue sets of valve springs....

[elonblock]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hemicolt</div><div class="ubbcode-body">Have the valve seats been changed to hardened versions? </div></div>

The seats have not been replaced yet.

[elonblock]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: VintageMusclecar</div><div class="ubbcode-body">The 496 in my Chevelle has 11.2-1 compression with square port closed chamber heads, and runs perfectly on 92 octane. The key(s) to making it work are 1) cam timing (needs to bleed off some cylinder pressure @ lower rpm), keeping the engine coolant temps ~160°-170°, and a nice, conservative timing curve--in this instance, 14° initial and 36° total, but it doesn't come in fully until ~4000 rpm. (no vacuum advance either)

FWIW, YMMV. </div></div>

Tell me more....

1) Can you elaborate on the cam timing?

2) Please provide more detail about your experience with the cam.

Thanks!

[JRSully]

I religously run a mix of AVGAS and 93, no other additives. The L78 actually runs better on a 100LL and 93 mix then all Avgas. I keep 5-10 gallons of it on hand and dump some in before heading to Sunoco. I have all the timing in at 3k rpm and never have any problems