[Jlenning2314]

Me and my buddy both race. And we both have very similar builds. Stock bore and stroke. 13.5 to 1 piston. We both have port work in the heads. And we are both running a stage 3 hotcam. Now currently we run 93 with vp octanium. And we try to get the number around 101 octane. Give or take. We've been discussing mixing fuel and or swapping fuel. Most of the guys we run with run MR12. But it's extremely expensive. We did discuss possibly mixing MR12 and pump gas. Or possibly looking into mixing a different type of fuel with pump gas. Looking to see if anyone here has a similar setup. Or has any advice on what direction we should go. We race at a local track. And do some trail riding. We're hoping to find something we can mix with 93 preferably. But we're not opposed to switching fuels either. Any advice would be appreciated.

 

[JoeWV]

I run a very similar set up, except with stage 2 cam. I race gncc and ride similar trails here in WV. I use Sunoco race fuels, mostly the 260 GTX (98 oct). Their 260 GT is rated at 100 but it has ethanol in it, I try to stay away from the ethanol fuels and the GTX doesnt have it. Depending on where you live you can get 5 gallon pails at most Sunoco gas stations. You can search locations on their site. Another option, if leaded fuel isn’t a problem, is the 100LL AV gas, you can get it a most any local airports and I believe it’s rated around 114 octane. You would mix it 1 gallon with 4 gallons of 93. Sunoco and VP sell similar higher octane leaded fuels that you could mix with 93, but it’s more expensive than AV gas. I’ve never messed with leaded fuels so no personal experience with it, just read what others have used. I’ve also heard the common octane boosters don’t really give that much of a boost, it’s very minimal in 5 gallons of 93. Go over to the Vital MX forums and search for fuel options, there’s a ton of posts and arguments about it. Sunoco, VP and Renegade all have pretty useful websites that show octane levels and SDS forms for each of their fuels. Most all “race” fuels are made from Toluene (paint thinner) you can buy at any paint store. Some guys blend their own, but that’s too much work for me, haha. Good luck, it can be a real rabbit hole once you start reading more into it.

 

[CJM]

run the right fuel and be done with it. all this mixing and such isnt good in the long run. everyone i know who tried to do what you want to do just found buying the more expensive gas or dropping back to 12.5"1 compression easier.

 

[Jlenning2314]

run the right fuel and be done with it. all this mixing and such isnt good in the long run. everyone i know who tried to do what you want to do just found buying the more expensive gas or dropping back to 12.5"1 compression easier.

With that being said. What fuel would you recommend for my application?

 

[CJM]

anything 100 octane or better will do.

personally its easiest to just go down to the powersports store and buy whatever they keep in stock.

 

[hoser]

Why do you want to switch from what you are using now? Why do you feel you need such high octane? What are you trying to do by switching fuel?

 

[Jlenning2314]

Why do you want to switch from what you are using now? Why do you feel you need such high octane? What are you trying to do by switching fuel?

I run 100 octane now with the 13.5 to 1 pistons. I was told 93 wasn't enough for that. But I thought about switching or mixing fuels for added power when we go race at the track. A few friends of line run MR12 and claim it will make around a 6 horse difference swapping to it. Really just wanted to hear everyone's opinion before I did anything.

 

[hoser]

You won’t gain 6hp from that fuel. You will gain some power simply because it’s oxygenated, but you have to rejet and tune for oxygenated fuel. And that fuel is hard on components requiring draining and more maintenance. Maybe you are at a high elevation or something, but I don’t know why 93 wouldn’t work, or especially 100. I run 91 in my 13.5:1 builds.

There is a LOT of misinformation on fuels and what’s needed for certain motors and compressions. Lots of it is propagated by older guys that are used to old motors with iron heads and inefficient ports. You can have two motors, same CR but have totally different fuel requirements. The 450 motors are much more efficient and since they are water cooled, all aluminum, 4 valves, and a decent port layout (especially if your head was ported by a reputable shop), they can run a higher CR with lower octane than other motors. Throw in a big cam like your S3, and they are even more forgiving.

Buuuutttttt, I’m not going to tell you you will be absolutely safe with 91, 93, or even 115, that’s for you to decide and tune for. But remember, the lower the octane you can run, the more power you will make. And with trail riding, or even to a lesser extent on the track, you are generally not WOT for long periods of time where you will be getting super high temps that will cause issues. On the trail if you start lugging the engine, too low of an octane can be an issue, but since you chose to go with a S3 cam that tells me you only run at higher RPMs which is safer.

There are times that I will mix in or even run straight race gas, and that’s at the dunes. When it’s crazy hot ambient and you are working that motor extra hard in the sand and constantly at WOT you need some extra octane.

 

[CJM]

@hoser is correct the CR is bled down some by the cam, which means you can run less octane in some cases. i dont chance it cause where I am its all sand pits so you are working the engine A LOT in some cases. IE friend of mine had a 490 13.5 or 14:1? setup, web cam and porting and found 93 just wouldnt cut it in the hotter weather and ran Vp 100 octane. meanwhile i ran a similar setup and just added vp madditive with 13:1 and was fine. BUT i dont like to chance stuff. a slightly lower compression isnt going to make that much of a difference, i run CP 12.5:1 pistons for the last few years from AZ quad parts that he has custom made for 470, 490 type kits.

 

[Jlenning2314]

You won’t gain 6hp from that fuel. You will gain some power simply because it’s oxygenated, but you have to rejet and tune for oxygenated fuel. And that fuel is hard on components requiring draining and more maintenance. Maybe you are at a high elevation or something, but I don’t know why 93 wouldn’t work, or especially 100. I run 91 in my 13.5:1 builds.

There is a LOT of misinformation on fuels and what’s needed for certain motors and compressions. Lots of it is propagated by older guys that are used to old motors with iron heads and inefficient ports. You can have two motors, same CR but have totally different fuel requirements. The 450 motors are much more efficient and since they are water cooled, all aluminum, 4 valves, and a decent port layout (especially if your head was ported by a reputable shop), they can run a higher CR with lower octane than other motors. Throw in a big cam like your S3, and they are even more forgiving.

Buuuutttttt, I’m not going to tell you you will be absolutely safe with 91, 93, or even 115, that’s for you to decide and tune for. But remember, the lower the octane you can run, the more power you will make. And with trail riding, or even to a lesser extent on the track, you are generally not WOT for long periods of time where you will be getting super high temps that will cause issues. On the trail if you start lugging the engine, too low of an octane can be an issue, but since you chose to go with a S3 cam that tells me you only run at higher RPMs which is safer.

There are times that I will mix in or even run straight race gas, and that’s at the dunes. When it’s crazy hot ambient and you are working that motor extra hard in the sand and constantly at WOT you need some extra octane.

I'm from Mississippi. But I appreciate the information. That cleared some of this up. The shop that ported my head recommended 100 octane for my 13.5 piston. That's why I run that fuel. Which it's just pump gas with some vp octanium mixed in.