13-1/2 to 1 compression ...on the street?

Need more info, what kind of engine? Cast iron or aluminum heads? Any more details on the engine build will help us give you better answers. I may not be able to directly answer your question, but I know enough to know that you need to give more info :)

nate

#2 diesel?

Why not ask the owner ? With a compression ratio that high I think you wiil need race gas.

What engine and what type of heads? What cam & lifters?

If it has aluminum heads and the proper cam it probably would run just fine on 93 octane with water injection and playing with the timing some.

How old is it? If it's old enough to run without a catalytic converter,

100LL aircraft fuel should be okay on the street. May not be high enough octane.

The "octane booster" in a bottle stuff is usually just MTBE. You can also still get tetraethyl lead.

--scott

Cast iron or aluminum heads? Camshaft spec.'s Carb or EFI What might also help is what is the cranking compression of the engine (Do a Compression Test)

I know a bit about cars, but not why the ?? about Al heads is important- is it the fact it's Al and not cast iron, or just that Al heads are likely to be better engineered?

Dave

Aluminum heads shed heat to the cooling system better than do cast iron. You'd think that this would be a disadvantage, but in a high- compression engine, it helps to prevent detonation. I have heard as a rule of thumb that aluminum heads, all other factors being equal, allow you to safely run a half point more compression on the same octane fuel than do cast iron.

nate

As Nate said "Aluminum heads shed heat" "all other factors being equal, allow you to safely run a half point more compression on the same octane fuel than do cast iron."

But since most Aluminum heads are after market or late model factor design and most are some what better engineered / more efficient combustion chamber design, they can run more compression.

Alcohol

My thought, too. If the CR is actually that high I can't see it ever running on pump gas regardless of the heads, cam, etc.

Having driven a high powered high compression car on the street for a few years, I will say that it is not always as much fun as one thinks it might be.

Others have already posted that it depends upon the engine, timing, etc.

In my case, the car's cooling system was marginal for that type of engine, and that added to the distress.

I had to run 98 octane at all times, and was running less compression than this car.

It just wasnt a pleasure at all.

But the suggestion to ask the present owner what is involved is a good one.

Why not? NASCAR runs 12.5:1 on 98 octane using iron heads. They ran 13:1 on the old 105 octane leaded fuel. I have run 13:1 on pump gas with aluminum heads on a 427 with a set of Rhodes lifters to drop the cam down some. No problems at all.

I would think the Rhodes lifters would actually hurt, not help - they'll improve idle quality but at the cost of increased low RPM cylinder pressures. or am I thinkin' wrong?

I will say that at anything over 10.x:1 you probably need to have someone GOOD (not me!) tune the engine to avoid an inadvertent detonation incident.

nate

(currently running 10.25:1 with iron heads - stock 63-64 spec Studebaker R1 engine...)

No real pressure increase. You just need to play with the bleed rate some. Mine was set up to "hide" the real power of that engine. The only problem I ever had with it was that I kept putting my foot through the firewall....

Tuning of a true HP engine is an art. Not something you get from books or online.

OK, so you tuned down the rumpity idle some... but how do you tune out that "sharp" exhaust sound that you only get with high compression or a blower?

nate

(appreciates stealth performance)

Tuned the collectors, Installed an H pipe and used 4 mufflers. The first two were custom made and designed kind of like a straight through with concentric baffles(like a silencer). Behind the baffles were channels that allowed the exhaust to cancel out those hard notes. These fed into a normal pair of flowmasters. Until you really climbed on the loud pedal it sounded just a bit warmer than stock. Surprised more than a few folks.

Actually, NASCAR runs aluminum heads.

But why retard timing on a performance car. That handicaps it seriously, and can lead to overheating and other problems. Yet it takes a LOT of octane to run that kind of CR. I would think alcohol would be the fuel of choice. If it has a carb, conversion for alky is easy. Not so easy with FI.