On a stock Raptor will higher octane make a difference? What octane should I be using?

 

The stock Raptor will run on even the lowest grade of gas. Running a high octane fuel in the stock Raptor will waste your money and actually slow you down.

 

Raptor720,

What about Raptors with airbox mods, pipe, and rejetted?

Thanks!

 

Ok, here is my 2.5 cents.

If you only have air box, pipe and jetting mods, cheap gas is still just fine. However, if you start changing cams, pistons and alter the porting, you may (or may not) need to reconsider your fuel needs.

On the compression ration issue, you must understand that the advertised compression ratio of a piston means little to an engine builder. It is very easy to run 12:1 compression ratio pistions on "pump" gas without pings. This is how it works:

Next, you must understand that the cam's valve timing events really controls your final compression ratio (cylinder pressures). For example, a late closing exhaust and early closing intake with substanitally limit the amount of fuel/air being compressed. (I could go into great detail on this issue but the example will do the job. Ford Motors SVO division actually ran 13.5:1 compression ratio pistons in a modified 4.6 (5.1)litre engine that ran on the cheap pump gas without problems. They did it using a special roller cam and careful adjustment of the ignition and fuel delivery systems.)

Following the compression and cam issues, we look at the shape of the piston dome and shape of the chamber. Unfortunately, this is where the Raptor is hurting. When you step up the compression with a large dome piston, because of the poor design of the 5 valve chamber, flame front (the travel of the lit fuel) is very rough. This is where a true hemi head or even the (yes I will say it, the DS -- yuck) has an advantage. However, with some work to the chamber and some fine tuning to the top of the piston dome coupled with the proper cam and ignition timing, you will be fine.

Here is the skinny on the octane -- the higher the octane (resistance to ping), the harder the fuel is to light and the slower it may burn. Also, if you are using one of the cheaper leaded race fuels, you might even experience lead fouling when the lead does not get hot enough to properly vaporize and melts to the spark plug. I prefer the unleaded MS103 from VP fuels at a 50/50 ratio with pump gas for the Raptor especially if you plan on a sustained hard run.

Understand that I have no problem running just pump gas even in a 105mm -- there is no problem. I can also verify that a 102mm with the 11:1 advertised c/r piston will run fine on pump gas with the stock cam or most other cams that do not require major piston and head mods. I have never seen a problem.

If you do experience pinging, I would seriously consider removing the 660 head and checking to see if oil is being sucked past the intake valve seals and guides. I have seen this problem on a few Raptors and the difference on the hill between a leaker and a clean burner is about 6 bikes period.

Finally, on the spark plug issue, I noted some recommendations to use colder plugs with the higher compression. That is generally good advice; however, start with the stock heat range properly gapped and see how it goes. Try a cold chop and check the plug. If everything is to your liking don't go colder. A colder plug can easily foul with carbon or lead especially if you went down on the range without a proper plug read. If you are running really high cylinder pressures, you may want to even close the plug gap down slightly if you use stock ignitions. The higher the cylinder pressure, the harder it is for the spark to jump the gap. I have seen a .003" change in gap make a 5 hp difference on a Banshee.

 

it will,you should probly be using 93 octan

 

well, in my 300ex, i HAD to run 93 octane gas, or else it just ran like crap. and in my tecate, i have to run 93 octane, and the 109 aviation full you can get at some airports makes it run like a completely different bike, it was awesome. higher octane also lets your motor run cooler, even if you dont get better performance. but like raptor720 said, you can get too high of an octaine, you have to realize that both of my quads were highly modified.

 

Using Avation fuel has its problems. It has a lower specific gravity than most other fuels, it is unleaded and it is designed not to freeze or vapor lock as easily as automotive fuels. I beleive the biggest problem with Av gas is the lower specific gravity. In simple terms, the lower the number, the less energy per unit of fuel

 

on a stocker regular unleaded is fine, maybe go to mid-range but high octane is a waste of money. remember that octane is an addive to prevent pre-ignition on the compression stroke, low octane fuel (like diesel) ignites without a spark plug which is fine in a diesel engine. the more octane in the fuel the farther you can compress the airfuel mix without pre-ignition (pinging), this is why you move up to high octane with a high compression piston

 

Vraptor is almost right BUT, like I have said, it is not the high compression piston that dictates the needed fuel. It is the cylinder pressure that is a result of air speeds, piston dome size and shape, chamber shape and size and the valve timing events.

 

raptor720,

What kind of modifications are available to the genesis-style head on the Raptor? Are folks completely reshaping it to allow for a better, more complete burn or ???

Thanks!