more hp meanns higher octane fuel ?
 

thinking of having my 1998 502 efi hp increased to 575 hp @ crank does it always mean that i will have to run higher octane fuel or is it possible to still run 89 octane ,since this is the highest octane fuel that is available to me where i boat ?

i have a pair of 1000 that run on 93 you should be fine at 89 most places use a detergent that raises 89 to 91 any ways ( voodo science )

Are you going (small) blower, or higher compression.

If you go blower you need to watch how long you stay in boost with lower octane (89).

hi-perf-2000 i'm going na , no blower .

1st detergents don't raise octane rating.

2nd it will be a little difficult to get a na 502 to 575hp without premium pump gas. In my opinion you're gonna need around 10:1, the 741 Crane roller and good heads to get there.

my .02
DAVE

Your octane requirement is not dependent on horsepower. Lots of big inch 1000 hp engines run on 89 octane fuel. Higher compression will generally require more octane. Longer duration cams, aluminum heads, lower water and oil temps generally require less octane. Lots of people are getting 575 hp with low compression, good heads, Crane 741.

26Sonic,

First, I am sure there will be more in depth replies from Chemists and such but here is some info that will be helpful from a layman. Octane does NOT equate to HP. Octane is a rating attahed to a fuel to denote its anti knock characteristics. Essentially it is an anti knock rating. Higher Octane fuel burns cooler than does lower octane fuel. Hence it is needed in high compression applications. The HP of your engine should not determine the required Octane rather the compression ratio should have a bigger impact. Also, the other components used in your new engine such as cam lift and duration will all be determinants in which octane fuel you need to run. I would consult with your engine builder. Keep in mind that running higher Octane fuel will not hurt an engine only your pocket book, but running too low an Octane CAN cause pre-ignition or detination which can ultimately lead to engine failure.

There's only 3 ways to make hp
1 cubic inches. There's no doubt the more cubes you have the more hp it'll make. Simple math. Thats how the big motors get away with it.

2 RPM Match your cam and heads to the RPM you expect and the hp will be there.

3 Compression. the more compression you have the more hp you can make. The higher the compression the more cylinder heat you generate. The more need you'll have for higher octane fuel.

Now, lets take the factory motors for example. On a 502 (the motor in question) With 9.6:1, the best "out of the box" aluminum GM heads and a mid 220's/230's cam it makes a little more than 500hp at the flywheel.

To gain 75hp is easy but I cant see doing it around the stock 8.75:1 and staying on 87-89 octane.

PartiYacht, I guess my question for you should be, what do define as low compression?
I absolutly agree with you on the water temp and the aluminum heads. But even with both of those advantages I still think its a little tough to see 575 out of a 502 on 89 octane.

again, my .02
DAVE

Yo Dave whats up, We going to see that boat on the water this summer

8.8 to 1 is what I had in mind. Dart Pro 1 heads or AFR heads with cnc porting and a 741 cam should get you there. Good exaust is a requirement. With the longer duration reversion is a problem. Holley 800,830,850, any of the above. Teague is partial to the 830. Dart single plane manifold. I'm aiming for 700hp with my 540's next spring in a slightly wilder combination but on 89 octane fuel.