E Class Race Cars W/9.8 Compression

[jamesjedi]

Very curious about these cars using 9.8 compression. Do they get detonation issues?

[Eagledriver]

If they run stock deck heights, they will have less than 9.8. If they shave the heads and run minimal deck height to get 9.8 they would be marginal on 91 or 92 octane. Running 28 degrees or less on ignition timing helps.

[Quinlan]

We use 93 gas at a minimum. Some guys run 100% 98 or 100 octane. I try to blend about 1/3 tank 100 with 2/3 tank 93. Especially in Canada where 100 octane is so expensive.
Most of the Eastern North America tracks have 100 available at the track

[jamesjedi]

Thanks guys. I have always wondered how they did not have detonation issues.

[Reiver]

I have a Euro SC w/9.8-1 stock set up with CIS SSI's.... 91 is the only available gas...I do use ACES4 as an additive but have had no issues at all after 38k miles.
I run it all year and summers are hot hot.... I keep the AFR on the fat side. No issues, great compression and leak down and bore scoped my jugs/piston tops this last week when I set the valves.

[Trackrash]

I am running 9.8 - 1 CR. 91 octane with 28* max advance. No detonation that I am aware of.

I am not running a stock cam, it is a GT-2 102 and have carbs.

The older 911Ss had 9.8 -1 and they are still running.

A friend of mine is running 10.5 -1 with single plugs. But that is another story....

[jamesjedi]

That’s interesting, as there may be issues with the rings in a seamingly well running engine. However your motor had a good leak down test.

I Am going through a 3 liter engine, I may just use the 8.5 compression pistons. If I find a decent set that is higher in compression I may use them.

[Reiver]

Originally Posted by jamesjedi

That’s interesting, as there may be issues with the rings in a seamingly well running engine. However your motor had a good leak down test.

I Am going through a 3 liter engine, I may just use the 8.5 compression pistons. If I find a decent set that is higher in compression I may use them.

My 930-10 had a top end a few years ago and I have 38k on the top end and 113k on the bottom.

When rebuilt I burned 8 to 10 oz. of oil every 3k mile oil change...iotw, I never topped off.
It still burns 8 to 10 oz. of oil in 3k miles.....can't be any ring issues with that going on.

[NICE 69 S]

Interesting that most of the late 60's and early 70's Detroit muscle cars had 10.5:1 compression, and one of the '65 to '67 Chevy 327's had 11:1.

[jamesjedi]

Different heads and different fuel. Perhaps I am wrong, but wasn’t the fuel from that era higher in octane?

[jamesjedi]

It seams as though many engine builders on this forum are recommending a conservative compression. Also, I am not certain that the SC 9.8 pistons actually CC to 9.8. They may be lower.

CP pistons may actually be 9.8 compression.

[Trackrash]

Originally Posted by jamesjedi

It seams as though many engine builders on this forum are recommending a conservative compression. Also, I am not certain that the SC 9.8 pistons actually CC to 9.8. They may be lower.

CP pistons may actually be 9.8 compression.

I can tell you this. The JE 9.5 pistons I am using ended up giving me 9.8 - 1. When you assemble your motor you, or your engine builder, should check what your CR actually is. You base gasket thickness, head work and actual pistons will make a difference in your CR.

[Walt Fricke]

The guys I know racing with the stock 3.0 Euro SC spec motor can't get by with 91 octane pump gas. Either rings or ring lands fail. Perhaps not immediately, and not necessarily disastrously, but they fail. They were made for a higher octane rating - which used to be available before the demise of lead.

Maybe street driving wouldn't put as much stress on everything.

['78 SC]

Originally Posted by Walt Fricke

The guys I know racing with the stock 3.0 Euro SC spec motor can't get by with 91 octane pump gas.

So Walt, what do the E-stock cars do? Don't PCA Club Racing rules require 93 octane pump gas? Is that adequate?

[Walt Fricke]

PCA CR doesn't have an octane limitation. Fortunately for most of us running in classes where stock parts are required, running more octane beyond what the motor needs hurts performance (less energy per unit of fuel) rather than helps, if not by much at the margins.

So race fuel, mixed or otherwise, or additives, if you have the problem. The extra cost has kept me in D, where I don't have to worry about this.

['78 SC]

Thanks for the correction, Walt. I had strayed down into the SPEC911 rules.

[Matt Monson]

Originally Posted by jamesjedi

Different heads and different fuel. Perhaps I am wrong, but wasn’t the fuel from that era higher in octane?

Yes, and leaded.