How much octane needed?

[quiet riot]

I'm trying to figure out what Pistons I should use. I'm building a 408 sbf with 60cc afr aluminum heads. I have the choice of 9.73 which should be fine for pump gas (22cc dish) or flat tops yielding 11.3 comp ratio. I've always been able to keep a consistant water temp of 165 with my jetboat.
With 11.3 comp, what kinda gas would I have to use? Could I get away with mixing 110 or av gas with 92 premium, and at what ratio? I don't want to use straight 110 for the expense and fact I can't fill up with it when I go on vac for a week with the boat. Could be willing to bring some 110 to mix with 92 if I can get away with a 4:1 / 92:110 ratio or something similar.
I currently run a 351w at 10:1 on 92 with iron heads no problem. I have a 250hp plate NOS kit which I switch to a different tank with 110 and use a timing retard, when I use it.
Thanks for any advice,
jd

[Infomaniac]

The 11.3 compression will run much stronger.
You can mix the 92 and 110 when you are not out of town. Keep the timing in it. 50/50 mix.
If you go out of town you can fill up with the 110. Run the tanks half way down and fill it back up with 92.

[quiet riot]

Thanks info, I guess I can always try and reduce the mix and read plugs like I did with the nos to see what I can get away with. I'm always leaning toward more power, as I always seem to build too conservative. (never done higher comp or blown, that'll prob be next winter though idea )
jd

[LakesOnly]

I agree with running the 11.3 c/r and that you can run a 50/50 blend of the 92/110 octane fuels.
Your jet boat will benefit largely with the additional 1.6 points of compression and you should be safe with the 100 octane fuel blend.
I, too, am careful about running adequate octane fuel; I have about 10.5:1 c/r and blend fuel in my 11 gallon tanks at 8 gallons/3 gallons (91/110).
LO

[quiet riot]

hey lakes, I feel like i'm in an institution when I have a cleanroom suit on at work also (assume thats what you got going on in the avitar)
jd

[Blown 472]

Cant you run higher comp ratio with alum heads as they get rid of heat alot faster??

[DogHouse]

Are you interested in using ceramic coatings? With coatings, I run 10.8:1 and 36 deg timing on 91 octane. Haven't had any problems yet with detonation.

[quiet riot]

do you just send the pistons/heads (combustion chambers) out to have them coated? Whats it run and what kinda warranty? I'm guessing I'd still have to run a little higher than 92 oct with 11.3 comp.
Thanx,
jd

[quiet riot]

blown, I've been told with alu heads I can get away with about 10.4 comp before I have to start limiting timing, getting funky camshafts that reduce effective comp ratio, and running the motor on the edge and robbing a little power. I've never run above 10:1 and only used iron heads before on my motors so I'm just taking peoples advice till I put the new motor together and then I'll test and see what I get away with.
jd

[Boozer]

Why do you want to run such a high compression ratio? Why not just run a 8.5:1 compression ratio with turbos? If you do it that way you can run pump gas and lower boost when AV gas isnt easily available or you can run AV gas and higher boost when AV gas is available.
I'd think that in the long run you'd save money over all because you wouldn't be spending $4 a gallon on gas all the time. You would probably also get better fuel efficiency with turbos.

[mickeyfinn]

Or just buy your AV gas here in Georgia. Only set you back 2.25/gallon.

[LVjetboy]

'Cause running compression and AV has a certain...macho image? Geez I donno.
There's options of course. And if on the edge of your engine choice then go exotic octane why not?
But then why run 75- mph and burn a semi-exotic or at least restrictive mix of 91/110? They sell that at the dock? What speed warrants restricting your fuel choices and lake experience?
jer

[DogHouse]

quiet riot:
do you just send the pistons/heads (combustion chambers) out to have them coated? Whats it run and what kinda warranty? I'm guessing I'd still have to run a little higher than 92 oct with 11.3 comp.
Thanx,
jd if you already have the parts, then yes there are many companies that can add the coatings. swain tech (http://www.swaintech.com) and polymer dynamics (http://www.polydyn.com/) are a couple places to try, or maybe you can find something local to you. i think swain's websights has some pricing info, but they are a bit higher than some others. if you don't have the heads yet, afr can arrange the coatings for you. dart did my heads before shipping, and polymer dynamics did the pistons. you might be able get away with that compression, just have to dyno with a knock sensor and see where the limit is.
-brian

[LakesOnly]

quiet riot:
hey lakes, I feel like i'm in an institution when I have a cleanroom suit on at work also (assume thats what you got going on in the avitar)
jd It was supposed to look like a straightjacket...thanks for blowing my cover! :rolleyes:
LO

[LakesOnly]

Blown 472:
Cant you run higher comp ratio with alum heads as they get rid of heat alot faster?? Oops, I skimmed the post so fast that I missed fact that you will be running aluminum heads.
I don't think you'll need 100 octane...
LO

[quiet riot]

Thanx for all the info from all. I think I'll check into the ceramic coating and see what they have to say. With all the time I put into the layout of the boat, I'm not gonna go with forced induction on this boat and change the engine compartment around.
Besides, seeing how I already run 12's at 80mph with the nos right now (400hp with 200 shot of nos) and that puts this little deep vee boat on the edge of squirrelly already, I don't want to get too crazy with a short deep vee. Just want to be able to do that without the nos and a few people in the boat. Then see how brave I am to try the nos with an empty boat.
Anyhows, I think I'll give this setup a try and read plugs for signs of detonation with different gas mixes. It holds 40 gallons in the main tank and 8 in the other fuel system set up for running with nos, so I can get a decent ways on that. I guess if I end up finding that I have to run over a 100 octane I'll know better next time or swap out pistons or cut em down some.
jd

[Blown 472]

LVjetboy:
'Cause running compression and AV has a certain...macho image? Geez I donno.
jer That and spending how much for a sticker???