Racing fuels

[dadshillnut]

I have decided to give racing fuel because everyone seems to agree it makes jetting easier and doesn't crud up the power valve as bad. Problem is, the only kind I can find close is Unocal 76 compitition 110. Does anyone have any experience with this gas and would it be ok to run in a bone stock RMX250.

thanks for any help
Tom.

 

[SpectraSVT]

I run the 100 octane racing gas from 76 without any isuues in my YZ250. My proCircuit pipe is supposed to ping with regular 91 and the 100 hasn't pinged at all. My buddy runs 110 leaded from 76 and he loves it. I also ran 110 in my 93 RM250 but was to new to the sport to know any better. But the bike ran fine.

 

[Rich Rohrich]

It's overkill for a stock RMX but it should give you decent results. The biggest issue will probably be the freshness of the fuel because of the way 76 fuels are usually distributed.

It will more than likely run richer than pump gas so you may need to lean your jetting.

Let us know how it works for you.

 

[bclapham]

ive seen it sold around here in the 5 gal cans. although i havent tried it myself, i have a friend whos opinion i trust- he described it as a good fuel, but no as good as VP-C12 in terms of throttle response. However, i expect it will be infinately better than the dish water you get from the pumps. In socal, it seems every other rider on a 125 is seizing their bikes right now but they all tell me i dont need to run race gas.

get the 110, buy a bunch of jets and welcome to the club!:thumb:

 

[trialsmasta]

Originally posted by Rich Rohrich

It will more than likely run richer than pump gas so you may need to lean your jetting.

Don't most race fuel have a lower specific gravity than pump fuels? I thought this would make it run leaner. I'm assuming the 76 would have a lower SG.

 

[Rich Rohrich]

Specific gravity is just one very small part of how a fuel influences the final air fuel ratio. The distillation curve of the fuel has a far greater impact.

 

[nephron]

FWIW--I thought I'd throw in that I heard Mitch Payton on DMXS the other day say that the AMA is going to start making everyone use unleaded race fuel, possibly starting next year. He says it will require so much R&D to develop an acceptable fuel that it'll cost 20 to 30 bucks a gallon.

After being in a pinch, and trying some "Fuel for Racing" 100 octane unleaded (nothing else available)--I believe him. While I didn't have time to rejet for it, throttle response sucked and particularly zero to 1/4 throttle was weird.

 

[Rich Rohrich]

Mitch Payton doesn't know his :moon: from a hole in the ground about fuel blending and from the looks of it engine development. :silly:

If he was getting the kind of output per liter that GP roadracing was then unleaded fuel MIGHT prove to be more complicated iniitally, but the ground work is already been layed by engine developers far more talented than him.

Keep in mind these are the same guys (PC) that were melting engines when confronted by FIM spec fuel a few years back. Proper design and development is required when the crutch of 6 grams of TEL per gallon isn't present. I guess it's tough to do that with a Dynojet stuffed in the back corner of a warehouse full of t-shirts ;)


To quote Bugs Bunny "What a MAROON, what an IGNORAMOUS" :thumb:

 

[bclapham]

Micheal Pichons RM250 runs unleaded and i think the octane is pretty low also, maybe 96????? and his bike looks plenty fast to me!:) This sounds more like developing a fuel that we can justify selling for $20 a gallon and maybe have Troy Lee paint some nice flames on the can so we can bump that price upto $25 a gallon.

F1 racing cars have been using unleaded lower octane gas for years

 

[moto814]

PowerMist has been making unleaded race fuels for years. I've used them, and they have been on par with every other fuel I've tried.

-Steve

 

[2strok4fun]

Tom-

On the RMX, you can run a stock RM head gasket. That will bump your compression and increase the squish velocity to better take advantage of the added octane points. The stock RMX gasket is as thick as a oreo cookie.

I made the switch for the same reasons as you, the throttle response and jetting made easier, is worth it, but I ended up sending the head to Eric to fully take advantage. I love the bottom end grunt.

edit- I should add that it was my buddies newly aquired RMX that I did the top end on. My scoot is a 98dtm 250e
I originally ran 76 110 with no real complaints, but have been happier, and jetted leaner, with C-12.

 

[dthoms]

I agree with 2stroke4fun, I would go to the thinner head gasket, but I would also put in a RM piston and rings, wrist pin and bearing while I was at it. It should be around a 100 bucks and cheap insurance.
Also I don't know if it is technically correct or not but I used to mix the 110 half and half with 93. I did this on a 95 RMX and it stopped all the detination problems and it ran clean and stronger from top to bottom. With out the added 110 gas the bike would detinate.
If you do a lot of riding you might find it cheaper to have the cylinder ported and buy a better pipe and silencer. You will get better results and the race gas will not be needed.
What year RMX do you have?
DT

 

[nephron]

Keep in mind these are the same guys (PC) that were melting engines when confronted by FIM spec fuel a few years back.

What happened? I missed that.

 

[NO HAND]

Originally posted by nephron
...What happened? I missed that.

Wasn't it at the MX des Nations? The US team brought their bikes over with the engines modified to run on unleaded fuel (they have to for the event), and one of the bikes kept seizing in practice. I can't find what year or where I read about it. Was it a PC cylinder?

 

[Senior KX Rider]

I think it was when PC was getting a 125 ready for RC to race at MXDN

 

[dadshillnut]

DT, it is an '89 rmx 250 and I fibbed a little sorry. It does have an after market pipe and silencer called a dynoport ? never heard of them myself. It also has a wiesco piston but it is stock bore and stroke. nothing like some of these power mongers around in here. I only ride trails, I'm skeered of all that high flyin stuff lol

 

[Senior KX Rider]

Originally posted by dadshillnut
nothing like some of these power mongers around in here.

:aj: :aj:

 

[dadshillnut]

Hey DT, I understand about the head gasket but I was wondering what the advantage of the RM piston over the RMX. Is it just a reliability issue or will I gain power by going with the RM piston. Also , If it is a reliability issue would that be taken care of by the wiesco RMX piston.

p.s. thanks a lot for the info