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.

[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).

[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.

[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.

[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

[patrickt]

He'd need a new cam, but the other stuff could stay the same. The idea is that the intake valve is still open for a while as the piston is headed back down on the compression stroke. It effectively lessens the compression by pushing back through the open intake passage.

[392cobra]

Originally Posted by patrickt

He'd need a new cam, but the other stuff could stay the same. The idea is that the intake valve is still open for a while as the piston is headed back down on the compression stroke.

Humm,maybe this is why small blocks are faster ?

[patrickt]

Originally Posted by 392cobra

Humm,maybe this is why small blocks are faster ?

Hmmm, could be. If it were me, changing the timing is nothing... but having to add stuff every time you fill up is a real PITA.

[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.

[rodneym]

This may seem odd but are you certain your CR is 11/1?
So far your problem is just hypothetical, right?
If the simple solutions don't end up working you should consider verifying the CR indepently. That way you'll know what you're dealing with.
Contrary to popular beliefs, the FE gods are human.
rodneym

[rodneym]

I guess what I was trying to say was that if you have problems after trying the easy stuff, your CR may be higher than believed.
I've heard a couple stories describing the above situation.
rodneym

[RICK LAKE]

garry V Yes you can run 11.0 on the street IF you buy a knock sensor kit, limit the timing to the mid 20's in degrees. This will kill the power this motor should make with a better gas. 2 schools of thought
#1 buying 5 gallons of race gas with 100 octane and adding to the tank with every fill about 2 gallons this should protect the pistons from knocking and get a rating of about 93 on a 20 gallon tank. The question is do you have a good place to store this gas???
#2 Snow water/alcohol injection. This is what was used during WW2 to help with poor gas in airplane motors. Snow make a mister setup that will work with any power adder car or high compression motor. Again this is like a custom carb and you will need to setup this system correctly. Distilled water and washer solvent in a 50/50 mix work the best. You get a kit with a 1 or 2 quart tank for the car. This will need to be filled each tank up of gas. You will be able to run more timing, reduce EGT'S, and even pick up about 10-15 HP in the upper end. The motor will also run cooler. Running the system and turning it off before shutting down the motor are the only thing that will take a little time to do, about 10-15 second more than turning off the ign switch. You will still need a knock sensor to get the right flow of fluid into the motor. Too much and you can wash down the cylinders or even hydrolock the motor, not enought and ping and knock city.
Swapping to thick head gasket may drop the compression only .2-.3 points. You could also enlarge the head cc's a little for more drop in compression. This would drop you another .2-.5. This will put you in a safer compression ratio. The rest is as others have said, pull apart the motor and have the pistons flycut to drop compression. The tops should be thick enough for this as long as they are not flat tops. You will need a machinist to do this. It will save you the cost of new pistons. The rotating assembly should not need a rebalance if the same weight is removed from each piston. If time and money are not a major thing, have the pistoned coated on the tops and on the sides to protect them from knocking in the bores and pinging. If too much is removed, would rebalance the whole assembly again.
If you run at night and have heavy cool air, you might not need any of this to be done with watching you timing. Problem is you will be down on power. Rick L.

Ps To Rod Knock, sorry for putting you to sleep with the long info threads. Just trying to give the best info, inside and outside the box. Does this mean I am not getting FRUIT CAKE for Christmas???