What octane can I run with an all iron 10:25 350?

[MrSony]

It's an SP code 350 Buick that I'll be picking up soon. Factory rated at 10.25:1 compression, so the type of gas it needs is puzzling to me, as with my 8:1 350 I always threw whatever in it and it didn't care. I've never had a high compression engine. I was thinking 91, or maybe 93. If those aren't enough, how would I go about using octane booster? I don't know if it matters, but all buick heads are open chamber and pistons are all dished, factory or otherwise, and the pistons in stock form can sit anywhere from .050 to .060 in the hole, so there is very little quench area if any. Any input is appreciated as always.

 

[Injectedcutty]

You would be fine running 91 or 93 octane, anything less might cause it to ping. No need for an octane booster unless you just wanted to....once you hit 11:1 then higher octane becomes more of a need.

I always ran plus(89 here in KY) in the 307, but ran premium(93) in the gen1 sbc which was just above 10:1. I would occasionally get 10 gallons of 110 octane because it ran WAY better, but timing had to be adjusted or the engine would run hotter. Nothing like the candy smell of race gas, but once it went above $6 or $7/gallon i just went back to 93.

HTH

 

[Qdub24]

93 is the lowest octane recommended; that's the lowest octane that I will put in my Buick 455. v8buick.com is a wealth of knowledge for your Buick engine.

 

[MrSony]

I've plugged in the specs of the motor (piston dish cc, head gasket bore and thickness, stroke, bore size, cam specs, etc) and it put out a static compression ratio of 9.7:1. If that's correct, I think 93 will be good enough, maybe even 91. I guess I really won't know until I try. Once I put the motor in, get a gallon of 91 and a gallon of 93 and see what runs better I suppose.

 

[UNGN]

Open chamber Iron heads will likely ping and/or Diesel @ 10.25:1 with anything less than 93 octane. Buy 5 gallons of 118 leaded race gas and pour in a gallon with each tank. Don't buy commercial octane boosters, they are a waste of money.

 

[motorheadmike]

Verify your timing. Find TDC and mark on the balancer/timing cover, then you are going to be able to determine how much advance it can handle before it detonates/pre-ignites/auto-ignites/pings/etc. Making sure that your distributor is functioning properly and curved correctly will also help here. You will likely want to have max timing come in AFTER Maximum Brake Torque (MBT) where the engine is most efficient. So if this is stock engine you can probably find a dyno graph for it and start tuning accordingly.

93 octane should be plenty - even with the crappy combustion chamber and piston designs. Also, worry less about the static compression ratio, and start thinking about the dynamic compression ratio - calculate that out and you will have a better appreciation for your octane requirements.

Buy 5 gallons of 118 leaded race gas and pour in a gallon with each tank. Don't buy commercial octane boosters, they are a waste of money.

We had really good success with this on Drag Week last year: http://torcoracefuel.net/pro-accelerator.html Granted this was in our Procharged TBSS (at 12psi), with propane injection, 30% ethanol, and premium (93-94) in the tank. Thank God I know how to tune in Lambda - I'd hate to try and figure out the AFR for that cocktail.

I do agree that adding unleaded race fuel may be a cost effective alternative - if needed.

 

[pontiacgp]

has any tests been done to see what condition the engine is in?

 

[zdeckich]

Open chamber Iron heads will likely ping and/or Diesel @ 10.25:1 with anything less than 93 octane. Buy 5 gallons of 118 leaded race gas and pour in a gallon with each tank. Don't buy commercial octane boosters, they are a waste of money.

Why not do E85? it has an octane rating of 105ish and its less than $2 a gallon.

 

[Qdub24]

118 is about $15 a gallon lol. It would be close to $250 to fill a tank with Sunoco 118. Why not do E85? it has an octane rating of 105ish and its less than $2 a gallon.

Because other changes would need to be made to the fuel system, thus negating the cost savings of E85. Also, E85 isn't available everywhere and it's quality from the pumps is just as inconsistent, if not worse, than regular fuel.

 

[zdeckich]

Because other changes would need to be need to the fuel system, thus negating the cost savings of E85. Also, E85 isn't available everywhere and it's quality from the pumps is just as inconsistent, if not worse, then regular fuel.

Guess its pretty inconsistent where your at then, because its always been good here. 72-77 for me. But i get what you are saying. But for the cost of a new carb and maybe a new fuel pump, yes it might be more expensive start up cost, but it leaves you room to grow and will give a bump in power to be able to advance the timing. And most likely will always be cheaper than pump gas. Plus you dont have to worry about ordering fuel online just to drive your car.