<div class="FTQUOTE"><begin quote>Originally posted by: Doctorturbo



No way IMHO will a true 10 to 1 aluminum headed engine detonate on pump gas. </end quote></div>

No matter what your compression ratio is, ANY engine WILL detonate if the timing is too far advanced. Doesn't matter what the heads are made of. He needs to find out where the timing is first. When I was at stock timing I could get away with 89 as long as the ambient air was below 80 degree. When I advanced the timing 6 degrees no matter what the air temp was it would detonate on anything lower than 93.

 

<div class="FTQUOTE"><begin quote>Doesn't matter what the heads are made of.</end quote></div>

You need to take your theories up with these people. They are the ones that make the fuel that goes in your GT, and they dissagree with you.

And for the record. I was being conservative with the half a point commment. As you can see; VP fuels give aluminum heads a full point.

 

I'm just saying that if you use 110 octane on an aluminum headed engine and have the timing advanced 30 degrees, it will detonate. If there was no worry about detonation, everyone would be running full advanced timing and 120 octane fuel. I have built and raced many MANY cars and bikes. I used VP C16 exclusively when I was using my Big Shot on my Mustang and on my Supra with 26lbs of boost. But you're comparing a water cooled car engine to an air cooled ATV motor. The basics are the same, but the needs are very different.

 

26lbs of boost?.....You must like changing head gaskets.

 

<div class="FTQUOTE"><begin quote>Originally posted by: 400exrcr

good question... i am e-mailing the guy i got it off of and seeing if it is a 10:1 or something different..</end quote></div>

I would grab a compression guage, before I trusted "this guy".

 

i will check the compression tommorow and see what it reads, what range of psi should i be looking for if i have a high comp piston?

 

<div class="FTQUOTE"><begin quote>I'm just saying that if you use 110 octane on an aluminum headed engine and have the timing advanced 30 degrees, it will detonate.</end quote></div>
No you didn't. You said this.
<div class="FTQUOTE"><begin quote>Doesn't matter what the heads are made of.</end quote></div>
I say bovine feces. I say it make at least a half a point difference. The pro's say a point. Since the OP quad has a aluminum head, this makes a BIG difference.
Sure timing influences detonation but lets be reasonable, nobody is going to put 55 degrees of lead into an engine running on gasoline. That's just silly.

And for your information, I do just what you say above and then some on a blown small block. 40 degrees lead total, 110 trick and I have no problems with detonation. Even with 15 pounds of boost on it let alone a N/A engine.

Anyway, the bottom line is there is no way in he!! the OP needs race gas in this engine if indeed it is a true 10 to 1 engine. Whether you use 87 or 91 it makes no difference to me.

<div class="FTQUOTE"><begin quote>i will check the compression tommorow and see what it reads, what range of psi should i be looking for if i have a high comp piston? </end quote></div>
This really hard to say. The problem is compression can be influenced by soooo many things. Maybe someone has a close base line to give you. My V is a 9.9 to 1 engine and I would be glad to give you a base line but I don't have thoses numbers on me and I'm a little busy tomorrow. Besides, like I said, there is tons of things that influence static compression figures so my figures won't do you much good.

If you are into such things, I suggest you do some reading on learing to read the signs of detonation on spark plugs. There is a lot of good info on the net if like to read about such things.

 

At about 200 pounds compression, 110 octane is needed. Stock is usually around 125 and 92 is recomended. So if you are in the 160's a 50/50 mix would be in the ball park. If its a little lower do a 30/70 or whatever.

 

ok i checked the compression today and it showed 175psi. so would that be about a 12:1 piston??

 

<div class="FTQUOTE"><begin quote>Originally posted by: sprayedgt]



No matter what your compression ratio is, ANY engine WILL detonate if the timing is too far advanced. Doesn't matter what the heads are made of.</end quote></div>

^^^^Is what I said. Don't take it out of context. If you have 2 identical engines, one with iron heads and one with aluminum, both with the same CR, and the timing too far advanced..BOTH engines will detonate. Yes you can run more timing with race fuel and cut back pre-ignition, but there is a point to where it will detonate no matter where the octane rating is. And this isn't my theory, it's me doing trial and error on MY personal drag and road racing cars. Anyone with any real world experience with ignition, CR's, and timing knows this.