11 to 1 - too much on CA 91 pump gas?

[Dominik]

Sorry, if I repeat someone, haven't read the whole thread:

A thicker gaskets may actually have the opposite effect in offsetting the desired quench area resulting in a worse flame travel (assuming it's not a hemi head).

A long duration cam helps at part throttle, but it's unlikely to rectify knocking at WOT.
There you could retard total ignition (at WOT).

To reduce (avoid!) detonation at part throttle play with the timing curve (weights). I strongly suggest to get someone on a chassis dyno to assist with the timing curve.
You can hole your pistons in seconds.

Also, if your car is light and has a short (numerical high) rear end, it will accelerate through part throttle faster reducing duration of knocking.

Keep an eye on A/F ration (air/fuel) too.

I ran 12.5 to 1 on german 98 RON octane which is about your 93 MON with a 2000lb car and 3.54 to 1 diff. It was weather sensitive...

If all the above fails, mill the piston domes off. Ask the piston manufacturer for min head thickness, or get a new set of pistons!

If your cam is matched to the 11:1, change cam timing a bit (advance?) Speak to your engine builder.

[Excaliber]

Dominik, interesting point about using thicker head gaskets and loosing any potential "quench". The original FE's didn't have any to speak of, nor was it a concern with high octane being readily available at that time. The piston is as much a .030 below deck on a typical FE. I had custom pistons made to specifically address this concern by raising the piston height to just under the deck. I forget the exact amount, but it was very close to the deck height.

The OP may or may not have quench to speak of anyway, in such a case, nothing lost by running thicker head gaskets. But it sure is an interesting question!

[Dominik]

Hi Excaliber!
We made that experience a while back when the Chev LS7 was the toughest you can buy and tried the above resulting in "rattling like a bag of nuts". There are people here that can explain better the dynamics inside the head, but the proper quench initiates speedy flame travel.

The FE has a flat portion in the head, right?

Anyway, I guees you can make 11:1 work if you tweak all the minor options.
Is the car "above" build with ally heads? The Chevs benefit from bleed holes in the heads to reduce hot spots. So should the FE.

Fuel quality may also be different from gas station to station. It cold prove worth a while to shop around.

D

[Excaliber]

The FE's do have a flat spot in the combustion chamber, which works well for achieving quench. FE's also like a LOT of timing advance, quench allows for more of it with better control of pre-ignition which adds horse power. Or you could run "normal" timing with lower octane fuel. Either way, it's a win win. Anytime you increase the efficiency of a motor two things are going to happen: 1. Makes more power. 2. Get's better mpg.

[BAsque1]

I have a 427 FE SO and cannot figure out if it uses leaded or unleaded fuel. Any way to find out if I have to add lead additive or not?
Please any comments will help
Tks
Basque I

[Excaliber]

No matter what your engine is or how it is built, or when it was built, there is no need to worry about using unleaded gas. In spite of all the dire warnings you might have heard over the years, it just aint no big deal one way or the other. No worries.

[CobraEd]

I haven't read the whole thread, so this may have been stated earlier, but anyway, don't almost all gas stations sell 93 octaine. Why are we discussing 91 octaine ??


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[garry viohl]

Here in California its only 91

[bobcowan]

Same in CO, 91 is the best pump gas you can get.

[rodneym]

This may be old news to some of you guys but there are 76 stations in the southland (Fullerton, Pasadena, West LA - 2) where you can get Sunoco 100 octane at the pump. It ain't cheap, about $8/ gallon, but you can mix to get your octane up to 93, etc. Ask boat owners
Not to mention specialty shops where you can bring your own container. They have the good stuff.
I know a guy who says he gets aviation fuel from the Santa Monica airport at $30/gallon But he has an old Camaro so he's probably a liar

[RodKnock]

Originally Posted by rodneym

This may be old news to some of you guys but there are 76 stations in the southland (Fullerton, Pasadena, West LA - 2) where you can get Sunoco 100 octane at the pump. It ain't cheap, about $8/ gallon, but you can mix to get your octane up to 93, etc. Ask boat owners
Not to mention specialty shops where you can bring your own container. They have the good stuff.
I know a guy who says he gets aviation fuel from the Santa Monica airport at $30/gallon But he has an old Camaro so he's probably a liar

There's a 76 station nearby me that sells the 100 octane unleaded gas from the pump at $6.29/gallon. Cheap.

[patrickt]

Originally Posted by RodKnock

... $6.29/gallon. Cheap.

Alfred E. Neuman couldn't have said it any better.

[RodKnock]

Originally Posted by patrickt

Alfred E. Neuman couldn't have said it any better.

Batman's butler?

[CobraEd]

What ?? . . . . Me Worry ???


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[garry viohl]

Rod Knock
Where is that 76 gas station?

[razerwire]

Have to run 112 leaded in my sand car, not to big of deal because my trailer has 100 gal gas tank and nozzle in it. But its more of a pain in cobra, when motor was built 10.25 to 1 works with pump gas in cal, which is 91 octane. You can go to the distributor and get what ever you want. With electronic fuel injection and knock sensors the computer adjusts to what fuel you run.

[Dominik]

Originally Posted by razerwire

With electronic fuel injection and knock sensors the computer adjusts to what fuel you run.

That is correct, however the programmers for the mapping allow for the normal fuel(s).
The processor may not be fast enough to accommodate high octane via the knock sensor like running in a predefined mapping for the available gas.

It would constantly (cautiously=slow) advance and retard timing to make use of, say 112 octane, which cost processor speed and may even result in a trouble code being set (and may place you in the backup program, assuming 88 octane)

[razerwire]

Dominik I have Motec system which is tuned by Kroyer racing, not me thats for sure. Would like your input. I sometimes use Sunoco 260 Gold unleaded 97+ octane, which is whats available in cal. in the cobra, usually 1/2 and 1/2 with pump gas ,engine seems to run fine, do you see any problems?

[Dominik]

The mixing is straightforward.

In reference to my "octane maps" you would have to ask if the processor you use has a 94 (97+91)/2 map where the processor can feel "at home". Else your ECM is "thinking" too long (like a chess computer) if it can advance timing to make use of the higher octane.

The knock sensor does the critical work to protect your engine, but the ECU may not calculate fast enough to make use of better fuel by constantly advancing timing and computing A/F ratio accordingly. The processor speed may no be sufficient.

If your engine makes more power from the fuel can be verified on a dyno.
Run pump gas then add 97. Even run straight 97, too.

I left the department years ago and moved to another country. So I cannot quickly ask for new opinions.

IF you hit borderline of the trouble code setting conditions or even drop into backup mode (which I doubt!), using pump gas should reset your ECU.

An example of cautious programming:
The 1992 1.2 OPEL Corsa had two maps (plus one for backup mode). Uphill they sometimes switched into the 91 octane mapping compensating for pinging. Downhill, or on top it took forever to switch back into the 95 mapping.

(That's RON octane rating for Europe, where we even have 100 octane pump gas from SHELL)

[blykins]

Originally Posted by garry viohl

482 FE with aluminum heads and 35 total timing.

Do you think it will ping? What happens if the air temp goes to 100?

Thanks.

The simple answer is that it depends on a lot more than if the heads are aluminum and how much timing you have in the engine.

Some other things it depends on:

1. Camshaft
2. How close the pistons are to zero deck (quench distance)
3. If the pistons have been hand-worked to remove all sharp edges
4. Chamber design
5. Cam timing

There are LOTS of variables here.

I have ran a 428 FE with Edelbrock heads at a little over 11:1 with 93 octane. That was with 38 degrees total timing. No issues.

So yes, it can be done if all the parts are working well together. It's a little easier in a lightweight car like a Cobra, especially with lower (numerically higher) rearend ratios.