hey guys
i just sent my motor in to curtis sparks and they are putting in a 12 to 1 piston in it.

does anyone know what kind of gas i need to run?

thanx

 

You need to run expensive race gas.

 

and where do i get this expensive race gas??

local places?
do u mean like vp race fuel?
cuz there is a place like 20 inutes from where i live that sells it

thanx

 

Ask Sparks directly what octane will be required...

Compression ratio can be an overall guide but not the end all final word in what octane is required. I've ran two stroke heads set-up to run 100 octane, but had 250 psi cranking compression, for an example of how the compression(and it's subsequent ratio) dont always set the octane required. I would talk to Sparks and ask what octane they reccomend for thier set-up.

 

To add to what back country said, did you get a cam too? If you get a radical cam and put it into a 12:1 motor since it opens the valves sonner and you actualy loose some of the compression but gain power in the amount of air and fuel that has entered the cylinder. So in reality if you have a 12:1 engine but you put a long durration cam in it the engine MIGHT only require the same amount of octane that a simiar engine with 11:1 compression needs, but keep in mind the engine with 11:1 compression isn't camed either. Also if you don't want to spend an arm and a leg on getting race fuel, diesel fuel makes a great octane booser [img]i/expressions/face-icon-small-happy.gif[/img] . The compression on a diesel runs anywhere from 32:1 to 64:1 compression. Don't use a lot of diesel if you do use it though, it will smoke quite a bit.

 

so you are telling me that i can use deasel fuel.
mix it with gas or staright deasel>?
my dad owns an f250 powerstroke deasel.


and yes i am gettin a longer rod and everything..im going through my whoe engine

but please get abck with me on the gas thing
thanx

 

Welll....where to start with this one....Ok. The compression ratio on a diesel engine is that high, typically from mid 20's up to the low 40's max, is that it does not have spark plugs. So...how do they get the fuel to ignite? Compression. The easier the diesel to get to ignite, hence lower "octane" rating, chiefly called "cetane" in diesel fuels, makes for better starting, reduced emissions, and crisper throttle response.

Hopefully common sense will prevail here and it becomes obvious that diesel is NOT a good choice of fuels or blending agents in a high output gasonline engine.

The refining differences in the two fuels show that gasoline, at the fraction that it is distilled at has a higher natural octane rating that diesel will. Diesel has a higher cetane rating. Gasoline is considered to be a high end fraction, whereas diesel is a middle fraction. The relationship of the two is inverse, meaning, the higher the octane rating, the lower the cetane, and then inversely the higher the cetane rating the lower the octane.

Due to thier inherent refining processes, the fuel's actual chemical composition varies, as supported from above paragraph. Some of the chief components of any fuel molecular composition are parafins and aromatics. Parafins are long thin, non branched molecules that by thier shape are readily igniteable and not very heat or pressure auto ignition resistant(aka DETONATION). Whereas aromatics are ring shaped molecules and in their shape are VERY heat and pressure auto ignition resistant. A very broad generalization would say that parafins can be called cetane and the aromatics called octane(they are not exact and not all inclusive, but for the sake of this argument we will)

Diesel fuels are primarily comprised of parafins, thats why you have to be careful at lower tempertatures to not have diesel "gel". The gelling process is simply that fuel has become cold enough that the parafins begin to come out of suspension and lump up. So that shows that diesel has a high parafin content, i.e. low octane rating. So if diesel is so readily ignitable what prevents detonation, or rather more accurately ignition of the fuel too soon. The injection system on a diesel. Unlike a carburated gasoline engine or even a fuel injected engine, diesel is injected into the combustion chamber just before top dead center under tremendous pressure as compared to a gasoline engine. Diesel is typically injected into the pocket in the magnitude of 15,000 to 20,000 psi, whereas gasoline is injected from 60 to 90 psi. This is partially why diesel engines are noisier, especially the old 12 valve Cummins, the injection pump accounts for alot of noise. So in showing some of the operation of a diesel we see that the fuel is injected at high pressure at the exact moment in the crank revolution so that it auto-ignites, burns complete, and does the "work" for you.

Back to gasoline. Inversley gasoline have a higher content of aromatics to prevent this autoignition. The spark plugs, valve or port timings, etc control when the fuel is ignited. We want the control of the ignition of the fuel to come from the "system" not from the fuel.

So in that if you blend diesel with gasoline you greatly compromise the octane rating and in doing so create the possibility for auto-ignition of the fuel--that's detonation. Detonation destroys engines.


PLEASE...you have spent the money to send your engine to a very reputable engine builder, do the right thing and call Sparks and ask specifically what thier reccomendation for your fuel is going to be with your engine. These are question that should have been asked or at least answered prior to determining a compression ratio for your needs. I've had my little rant for the day so I'll spare ya that one...CALL SPARKS!!!!!!!

 

I understand what your concerns are about denotation but I have personaly seen this done and seen a working engine run with diesel added to the gasoline as an octane booster. Now what you said about the relationship about the centain and octane seems to add up to me so I agree with you on that. But a local mechanic here always puts different engines in his tractors, pickups, cars you name it and he'll put a bigger engine in it. He doesn't run his tractors enough to see the long term affects of this on the engine but however his Suburban that has a modified 350 cam, valves, port job, high compression aluimnum pistons and intake and headers. He couldn't get away with running pump gass because of the thermastat so he began adding just a small amount of diesel to the tank. So far a little over 10,000 miles later that thing is pulling just as strong and fast as before. But keep in mind this is also on a small block liquid cooled engine, too much octane on an air cooled engine like the EX results in more heat less reliability and less power. So I'm saying just add a SMALL amount.