I use a Gasoline/Toluene mix for my fuel. That allows me to come up with essentially any octane I want. In THEORY I could run straight toluene for a 114 octane rating, although it would probably be cheaper for me to run straight race gas at that point.


Here's the question; Assuming an otherwise stock bottomed, iron headed LT1 with 9-10lbs of boost on a centrifugal blower, what octane would be neccesary to avoid detonation? Also, detonation aside; is that going to be past the structural limits of the stock hypereutectic pistons and/or PM rods even WITHOUT detonation?

I don't mind running the chance of granading the engine, provided that it's just that; a RISK, as opposed to a certainty.



NOTE: Please avoid the temptation to read into the question and answer questions I didn't ask. Please try to stay on point.

 

First part of the question is vague... assuming stock timing etc?

 

Intercooler? If so, what kind. I wouldn't try to run that much boost on a stock bottom end with no form of intercooling.

 

Assuming stock everything and assuming intercooling.

The question is essentially about how far octane can go.

Conventional wisdom has the maximum safe centrifugal boost on an otherwise stock Iron Head LT-1 is around 5lbs, maybe 6 with good gas. The problem is of of course detonation. Can detonation be surppresed on a 10lb boost through the use of sufficiently high octane, how much octane is it likely to take and is the point moot because the cylinder pressures are too high even without detonation.

 

I"m not an LT1 guy, but I have friends with supercharged LT1's, and I think that 7-9psi on 93 pump gas with tuning is achievable, and an appropriate fuel system will work. Tuning includes scaling the timing as needed.

I think that 15psi with high octane is achievable, I have friends who have done it.

 

I think it would be cheaper in the long run to get a boost retard timing box off of ebay (vortech BTM) and then you wouldn't have to run so high of an octane, but with 10psi you never know.

I'd say start out with a mix of 105 or 110 and start working your way down. At the first sign of detonation jump it back up a few points. Each car is different and the only way to really know is to try it out.

 

Let's call it the Law of Diminishing Returns.

That's when you have to scale the timing back so much that there's no point in running that boost level.

I think 8-9psi intercooled is still worth it, but my friends have shown that 15psi on 93 is a waste. Not sure about 12, but I'm sure it's on the edge of being efficient.

 

From personal experience tuned a 15 psi ati di intercooled 355 lt1 made over 600 rwhp on sunoco 94 with 26 degrees total timing, I think cr is 9.2.
Not sure what hp level on my car is as we ran out of time on dyno (383 vortec sq aftercooler 10 psi 8.8 cr) we just got air fuel set with timing locked at 24 degrees, made 570 rwhp with 24 degrees total timing on 94 pump than added 5 degrees more timing with no knock. Not sure how much more power 5 degrees is worth but car ran a 11.01 @ 131.25 with a 1.79 60.

John

 

I have seen each 2 deg worth approx. 25hp on a lot of LT1 SC cars.

I'd rather run full timing instead of additional boost w/ retarded timing for best power under most situations with pump fuel.

 

Timing makes power for sure.