Race gas

[Micahdawg]

I'm having a problem keeping a reliable race gas supplier close to my house. For over a year now I had access to C12 down the road, and now it has all but vanished. I really considered buying a $200 stock Zuk head to reduce compression and make my combo more pump gas friendly, but then stumbled on a good source of Sunoco 110. All I knew was 93 octane destroys crowns, 99 octane (or so it is called at the pump) keeps pistons alive, but my bike will jerk and ping at lower rpm.....C12 kept detonation at bay with 108, this Sunoco is 110 so all should be well.

Then I realized, I just went from an oxygenated fuel to non-oxygenated. Also, VP is rated in MON. I have no idea what the RON rating is, but Sunoco is 105 MON. At this point I don't even know if the octane rating is really higher. But I mixxed 3 gallons of Sunoco with 1 gallon of 87 (final octane of 104.25) because I felt that the C12 straight up was a little overkill.

Then I find this out:
---------------- C12 Sunoco

Specific Gravity - .717 .728
Reid Vapor Pressure - 7.3 5.6
10 - 131 179
50 - 194 222
90 - 228 248
EP - 233 ?
By mixing the one part 87, I'm guessing I pretty well bumped up each 10-50-90-EP #.

SO, the bike ran good. I just so happened to have jetted my midrange one clip leaner before running this new batch of Sunoco too (i had a little hesitation in the midrange which I want gone). Only thing I noticed was a little jerkiness down low, but otherwise the bike ran extremely well. I was considering mixing 3 parts Sunoco with 1 part 93 next time to raise octane a bit, but now I'm wondering if I should just run the stuff straight up to keep the evap rates as low as possible.

If anyone can offer advice on these two fuels and the effects I should be noticing by switching, please let me know. Cause I have no other race fuel to use, so if this Sunoco is a bad deal...I'll consider the factory head route again.

 

[whenfoxforks-ruled]

http://www.precisionautoresearch.com/page4.html

 

[UTDesertman]

I can get VP 110 pretty easy but at 10 bucks a gallon. I found that if I mix 50/50 race and supreme pump gas my CR250 runs great. When I'm using regular gas I use an octane booster and it runs OK. UT gas sucks because we are two octane lower than the rest the nation.

 

[Rich Rohrich]

VP C12 is not an oxygenated fuel so that's not an issue.

Going from C12 to Sunoco Standard purple 110 the bike will run leaner across the board in part because a lot smaller percentage of the fuel will be evaporated. Sunoco 110 also has a very high end point temperature so it is going the spooge a lot more than C12. Starting and warm-up in cooler weather will also be more difficult with 110. Throttle response will likely be fairly flat as well compared to C12.

There is no way to know for sure what the octane or distillation curve will look like when you mix 110 with 87 octane fuel. Those graphs people post are just to placate the chemistry impaired. All you can is test and tune till you find a point where your engine runs good and doesn't detonate. Cutting VP C12 with regular was a bad idea, and this holds true for 110 as well.

Basically Sunoco 110 is a really poor choice for your application, but it should do a very good job of suppressing detonation.

Sunoco GT or GT Plus (both oxygenated unleaded) run straight would be much better choices from a performance and tuning standpoint.

 

[CHR!S]

Hey (Rich??), can somebody shoot me a link to some basic info about fuel? So I can understand whats going on in these conversations?

 

[whenfoxforks-ruled]

Contact Dave at precision. He delivers or road trip to O'hare airport! Ask about firepower 537,2 stroke oil,2 stroke transmission oil,boost and racekool! You will be surprised! The boost brings the fuel to life,the racekool has a leak detector in it and dilutes with water,the oils are as good as I have ever used!

 

[Micahdawg]

thanks for the replies all. Since 110 is the only fuel I can buy as of now, this is what I'll use. So...no more cutting it. But Rich, do you know if it really is a higher octane than C12? The MON rating showed it being lower and I thought VP rates in MON.

As for performance, quite honestly, I couldn't tell a loss. In fact, the bike ran remarkably well. I'll definitely keep a focus on top end power and on starting issues as i won't be surprised if I discover problems on both ends now.

Thanks for the tips again...I'll keep my eye out for a better source of fuel.

Chris, just go to VP's website and read up. Their spec sheets on fuels offer some good explainations. Seems like the big stuff to worry about is if it's oxygenated (adds power), whether it's leaded or not (lead = detonation suppressant), octane rating (higher rate = better detonation suppressant), evaporation rate (on motors with virtually no intake length you want high evap rates...pump gas falls in the 400's for end point rates whereas c12 was 230's). And of course, color. I feel faster with a purple fuel. :) And this is just enough info to be dangerous...and it's probably not even that accurate, but I -think- it is. You are just trying to achieve a nice, full, complete, well timed burn. A fuel that is under or over spec is leaving something on the table.

 

[bclapham]

ive run a mixture of sunoco 110 and 93 premium pump in bikes that like to detonate, and it ran fine with few jetting tweaks needed....i only did that since i knew Rich would start pulling his hair out when i told him, :)

btw- Rich, i called you sat morning....call me back if you get a minute.

 

[CHR!S]

Thanks, Micah. Ill read through the VP site

 

[yamalast]

Well since this came up...

I'm riding an '07 YZ250, stock except for a 1/8" pipe spacer & jetted for crisp response on 93 octane Sunoco pump @ 32:1 Yamalube. It runs great but is on the edge of detonation at 1/4 throttle or so in fourth and fifth in deep sand, when kinda rolling the throttle on. With colder temps coming to central Florida I need to cost effectively raise my octane a bit without giving up any crispness in throttle response.

What's my best way to do this?

Thanks.

(BTW I sent you an email Rich, don't know if I did it right as I had a little PC issue :ugg: )