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

[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.

[ERA Chas]

Try it on 1/4 tank. If it does, either add octane, race gas or take out 2 degrees.

[Z-linkCobra]

On 91 octane with that much timing and that much compression...it will ping. Need to drop your compression down to about 10 to 1 ratio and set the timing at around 28 degrees...maybe 30. Pinging is not good....is hard on pistons...hard on everything.

Put a thicker head gasket on it, that will drop your compression some.

Just my thoughts...im sure someone will say im full of it...lol.

[RodKnock]

I think it's too much for 91 octane. You may have to shut it off in gear, but you may be able to get by, if you're lucky. If possible, I would stay at around 10.25:1 +/-.

You could also mix octane booster or find a gas station that sells street legal Sunoco 100/110 octane unleaded from the pump.

[patrickt]

If all else fails, a new cam that hangs the intake valve open longer to reduce the dynamic compression ratio could get you by. Barry, Keith, Brent, etc. could help you out on that.

[RodKnock]

Originally Posted by patrickt

If all else fails, a new cam that hangs the intake valve open longer to reduce the dynamic compression ratio could get you by. Barry, Keith, Brent, etc. could help you out on that.

Chas, I have to agree with you and say this suggestion was the dumbest. I mean, the whole package has to work together and getting a bigger cam might screw up the rest of the engine package.

[patrickt]

Originally Posted by RodKnock

Chas, I have to agree with you say this suggestion was the dumbest. I mean, the whole package has to work together and getting a bigger cam might screw up the rest of the engine package.

If he keeps pinging, and booster and timing changes won't work, I think it's his best option. Seriously, he could fix his problem for under $500.

[RodKnock]

Originally Posted by patrickt

If he keeps pinging, and booster and timing changes won't work, I think it's his best option. Seriously, he could fix his problem for under $500.

Doesn't higher duration and/or lower LSA = more lift = higher spring pressure = change springs.....yada, yada, yada? And then, MAYBE, your car can live with 91 octane gas?

I think we need Rick Lake on this one, even though I don't think I've ever read one his posts from beginning to end.

[Roush #1]

Garry,

I assume the 11:1 compression ratio you mention is the static ratio. If it is, you are on the cusp of detonation with aluminum heads.

However, if your dynamic ratio is down to about 8.5:1 with this set-up, I think you will be O.K., but it is really close.

Raising the octane a bit is probably the cheapest alternative to your delima.

J

[dcdoug]

I have 11:1 compression (iron block, iron heads, 427 with standard bore/stroke). I was told by my builder that 93 octane was the absolute min and to run octane booster if I was ever in states that only had 91 (or "bad gas" as he called it).

[Excaliber]

I gave up on "Octane Booster", in my opinion it's little more than snake oil.

For instance, if the can says it raises the octane by a full point, that would be 91.1 instead of 91.0 octane.

Point 1??? Come on, who ya kidding here?

[ERA Chas]

Cripes!

Don't change your compression-pistons are $600+ a set.

Don't get fat head gaskets-you want to drain your coolant, pull the intake, pushrods and heads and buy all new gaskets?

Don't change your cam to lower your DCR-$300+. And can you pull your cam in the car-even pulling half the nose off??

And ONE POINT of octane boost is 1.0- NOT .1

Just try running on 91-street drive it - not make 11 second passes. Then add booster or drop timing in a 2 degree increment if it protests-you WON'T melt the motor.

[RodKnock]

I'm no expert, but would going with a hotter, higher heat range, spark plug help matters?

Chas, I said, if possible, meaning if he were still in the pre-purchase stage, lower the compression (new pistons). I wouldn't do it if the engine was built already.

[Barry_R]

I think its on the high side, but a Cobra weighs next to nothin' so it'll never load the engine that hard. You may well get away with it.

A good hand on distributor curve work (or some electronics) will allow you to idle with a closed throttle and low enough low RPM timing to avoid dieseling.

A touch more cam would not hurt a thing in most combinations - especially one on the edge of detonation. The det will hurt a lot more...and dropping some low RPM cylinder pressure might just do the trick. At higher RPM the event speed works in your favor.

Cylinder head chamber design plays into this a lot. A traditional FE wedge needs a bunch of timing to make power. The BT or reworked Ed heads with a contoured shape will run with very little timing.

[Excaliber]

And ONE POINT of octane boost is 1.0- NOT .1

Who says so Chas? Is that some kind of Government regulated standard or something? Perhaps they mean MON octane instead of RON octane? Booster bottles can say whatever they want and do!

It could be 1 or .1, either way, it's fair game for the bottle to say it raises octane by a "full point", whatever that is. Not to mention there are a number of separate international standards when it comes to octane ratings.

Consider a couple of typically available boosters. Like "NOS", which claims a 7 point increase (and pigs fly). NOS is one of the best available! Tests show it actually does raise the RON by 1.8 points. Hardly a "7" point increase, but perhaps "NOS" really does raise it to a "7", depending on who and how the measurements were taken?

Wynn's, a common brand name, was good for 0.8 increase on the RON meter, while claiming a 2 to 5 point increase.

You all know "Super 104+", it was good for 0.9 boost, while claiming a 4 to 7 increase.
There are a number of boosters that barely make a .1 octane increase. Buyer beware. The bottom line is, "boosters" can make all kinds of claims without fear of running into truth in advertising laws.

I was running 12.5 to 1 compression with IRON heads on my side oiler. Knock was a constant problem. I learned a bunch about timing issues, lean or rich fuel settings, octane boosters, etc. etc. When the smoke cleared, literally after wiping the camshaft out, I went with new pistons. I was sick and tired of the constant "octane battle", the BS octane boosters and the $6 a gallon race gas. I would have tried thicker head gaskets, but my compression was already so high I needed to take drastic action.

Mostly I just backed off the timing, BUT, I could feel and measure (at the drag strip) the loss of power with reduced timing. Man that motor LOVED a lot of advance and dropping it would just kill the power. But, at least I could drive on the street...

[Bill D]

Can you add Toluene to raise the compression without any side effects?

[Excaliber]

Destroy the pistons may be dependant on what kind of pistons he's running. Hyper's? Yeah, they will be toast much quicker than forged.

[greg schroeder]

Originally Posted by Excaliber

Destroy the pistons may be dependant on what kind of pistons he's running. Hyper's? Yeah, they will be toast much quicker than forged.

Yep, and the pistons will get jacked either way in time before the guy sells the car. It sort of goes along with why is my motor blowing oil. I need warranty work. All I did was nail the gas a few times when the engine was new and cold after I picked it up on the way to the dyno.

[MFE III]

Quote:
And ONE POINT of octane boost is 1.0- NOT .1

Who says so Chas? Is that some kind of Government regulated standard or something? Perhaps they mean MON octane instead of RON octane? Booster bottles can say whatever they want and do!

One point does equal 1. Same as points on a mortgage. One point equals 1%. When you're speaking about values less that 1 point or percent, you're talking about basis points. 10 basis points equals .1%

So if the booster bottle says it increases the octane by one point, they mean 91 octane will go to 92. And since it's written on the bottle, it must be true, right?

Matt

[Excaliber]

Nor would I Patrick, what a PITA the whole octane booster scenario is no matter how you do it.

As far as the original OP goes, no problem, many threads have value that goes well beyond the original poster.