Premix And Race Gas for High Compression

[trevor.summerfield]

Hello everyone,

I just installed a 144 Athena kit on my 05 YZ125.

The Athena kit comes with a higher compression dome which I tested and pumps out a 190 psi compression test.

So I want to know what you all are putting into your gas tank? What octane fuel? What premix oil? what ratio to premix at? I can get 120 octane for $7.00 a gallon around here, and I have been using Maxima racing and Amsoil Dominator premix oil. So what are you using?

Thanks,
Trevor

 

[john stu]

really any brand name oil is good as long as you mix it right but dont switch back and forth between oils (like Maxima racing ,Amsoil Dominator) stick to one oil only all the time. for a high reving 125's i like the maxima 927 it doesn't burn quite as clean as other oils if you putt around and ride slow off the pipe but if you have the bike reved all the time (like in a 125) its great stuff for protection (and burns clean if you are on the pipe a lot)

 

[john stu]

what fuel are you getting at 120 octane? i would use vp c-12 stay away for avation gas great for planes not so much for bikes

 

[1BAD250]

i run 100 rocket brand race fuel i get it at the local gas city its all i run in my 2 strokes.. :cool:

 

[hot125mod]

what cc dome r u using

 

[hot125mod]

your safe with c12 up to 15:1 or about 220-230 lbs of cyl. pressure and 120 is totally unnecessary

 

[hot125mod]

i havent had a chance to try it yet but i think i am going to use u2 with the 927, but i can get amsoil at wholesale so i am torn between the 2. only stupid people mix there fuel at 50:1

 

[trevor.summerfield]

OK

So the compression dome is supposed to be 14.8:1, or at least thats what Athena says, but I'll take their word for it. So the 120 octane I can get is from these bike junkie men who own a little shop out here in Alaska, I'm in Alaska by the way. They use this stuff for ice racing in the winter and seem to know a lot about what they do. But I can get 108 octane leaded or 104 octane right out of the pump at a Shell gas station, but I dont know what brand it is or anything, the lady on the phone didnt know much. So which should I stick with. The leaded or the unleaded? If the leaded is higher octane. And should I be mixing my oil at 32:1 or 40:1, since half the people I know use either one.

Thanks

 

[Micahdawg]

VP Import is 120 octane. I think VP NO2 is close to 120, and maybe C23?

Is 190 high compression? What's the bike supposed to have. I think 93 octane is good to 190 psi, so even C12 would be overkill. I'd use straight VP Motorsport (101) or a 50/50 blend of C12/93 octane.

I've got 250 psi and run straight C12 at 32:1. I can run as little as 99 octane without breaking anything, but it pings badly at idle. At 93, the piston breaks.

 

[trevor.summerfield]

Alright, so Ill keep the octane over 100 by mixing 90 octane with 120, mix it was maxima at 32:1. Sounds good.

But can I maybe get a tech guy in here to say WHY does detonation occur unless I use a higher octane, and what actually IS detonation?

 

[ChopperDave]

If you will use the search function at the top of the page, I think you will find a wealth of information. Also on the main page, RichRorich has two articles on gas/race gas which are very informative!
:cool:

 

[Rich Rohrich]

WHY does detonation occur unless I use a higher octane, and what actually IS detonation?

These threads should help with your understanding. :cool:

http://www.dirtrider.net/forums3/showthread.php?p=774324#post774324

http://www.dirtrider.net/forums3/showthread.php?t=135137&highlight=detonation

http://www.dirtrider.net/forums3/showthread.php?t=116802&highlight=detonation

http://www.dirtrider.net/forums3/showthread.php?t=42496&page=1&pp=10&highlight=detonation

 

[trevor.summerfield]

Thanks for the LINKS!

And all the help!

Trevor

 

[trevor.summerfield]

But Still any other opinions are welcome, for those of you running high compression heads, what gas and premix are you running?

 

[HubertGarfunkleIII]

does anyone just use the regular high octane gas at the gas station? I think its what 92? I was thinking of doing that and adding some of that octane booster stuff they sell at walmart. Anyone use those octane boosters?

 

[Rich Rohrich]

Anyone use those octane boosters?

Here are some links to a number of threads that go into great detail on the subject :

http://www.dirtrider.net/forums3/showthread.php?t=56918&highlight=octane+boosters

http://dirtrider.net/forums3/showthread.php?t=60651&page=1&pp=20

http://www.dirtrider.net/forums3/showthread.php?threadid=15450&referrerid=16241

http://www.dirtrider.net/forums3/showthread.php?t=80491&highlight=octane+boosters



and some specifics I posted a few years back :

I've never liked octane boosters as a substitute for race gas, but given the number of people who send e-mails asking about them it's apparent that people want to know more. They will never replace the real thing, but octane boosters can be useful at preventing knock if you only need to raise the octane a few points, but they come with a host of caveats.

The pros:
- Conveniently located at your local dealer or auto parts store
- Easy to transport
- They are cost effective if your octane needs are minimal

The cons:
- Most boosters raise the RON octane more than the MON octane, which
makes them fairly useless for most race applications, or high load
high heat situations
- Most of the better additives at this point are either Toluene or MMT
based. Toluene has the advantage of being relatively cheap, and fairly
effective at raising the octane even in fairly high percentages. Plus
it has good resistance to pre ignition which is an important consideration
in a two stroke. The downside is as you raise the percentage of Toluene
(or most aromatic hydrocarbon based additives) , the throttle response
quickly becomes flat and mushy. The snap goes BYE BYE.
So the engine won't knock, but it probably won't run worth a damn either.
- MMT based boosters (the most common today) quickly reach a point of
diminishing returns (i.e. the more you add the less it helps)
- Organometallic boosters like MMT can cause a huge increase in engine
deposits, and increase the risk of plug fouling and pre ignition
- Most boosters tend to kill the throttle response and make it
difficult to jet. Mix in the constantly changing base fuel your mixing
it in and you have a constantly moving target.
- Most octane boosters (especially toluene based) have high solvent
properties which can raise hell with reeds and crank seals in two-strokes
- If you need to raise the octane a significant amount, octane boosters
are much more expensive and much less effective than race fuels


There's more to it than this but I'm sure you get the point. Basically
it boils down to this, if your engine only needs a small increase in
octane as a safety margin then using octane booster is still better than blowing it up, but you'll likely give up throttle response for the
convenience. If you need a large increase in MON octane you won't get it from octane booster without paying more than you would for real race gas in the first place, plus it will run BAD. No snap, and an impossible to read plug.

During some testing with VP "Octane Power Boost" (MMT based) on my YZ417 (13.25 :1 CR). I've also noticed a reluctance to start when the engine is cold, although this may be application specific. The throttle response isn't as good as running
VP-C18 or C-12 but it doesn't knock, and the power you give up on the top end would only be noticeable to guys running flat out all the time.

Even though I hate to recommend octane boosters, if you have to use them here's some things you can try in order of my preference based on my testing on a 92mm stock compression YZ400, and a 94 mm 13.25 compression YZ417. I used Amoco Premium MTBE based (non-alcohol) as my base fuel in all tests, which were done in fairly warm 80-95 degree weather. My results probably aren't really useful to anyone who isn't running a similar combination, but they hopefully will shed a little light on the subject.

VP - "Octane Power Boost" - MMT based mixed 1 OZ./gal.
Pretty good throttle response once you get the jetting sorted out which tended to lean out on this combination. This was probably the closest to good race gas that I've seen. Raising the percentage of VP quickly killed the throttle response and made it much more difficult to start cold. This would be a reasonable choice if you can't get race gas or just feel cheap. Street price $10 for a 16oz bottle.

Snap "The Outlaw Racing Formula" - MMT based mixed .75 OZ./gal. Reasonable throttle response not quite as sharp as the VP additive but close. Jetting tended to lean out on this combination. Raising the percentage killed the throttle response and made it much more difficult to start cold. This is easy to find at most auto parts stores and speed shops. Street price $10 for a 16oz bottle.


PJ1 - "Gas Energizer Octane Plus" Toluene based mixed 2 OZ./ gal.
Throttle response is fairly soft when mixed at 1 OZ./gal and gets worse as you increase the percentage, jetting tended to less sensitve to this additive. Top end pull was a better than the MMT based additives at 2 OZ./gal. I've heard that this product has been discontinued, but no confirmation at this point. Street price $6 for an 18oz bottle.

Maxima - "Hi-test Octane Booster" mixed 2 OZ./ gal.
This appears to be a Toluene based additive, but Maxima doesn't list the specifics in their literature. Like the PJ1 additive throttle response is fairly soft when mixed at 1 OZ./gal and gets worse as you increase the percentage, jetting tended to be less sensitve to this additive. Top end pull was a better than the MMT based additives at 2 OZ./gal. Street price $4.50 for a 16oz bottle.

 

[matego]

Rich, Have you ever tried "max lead 2000" before? It is tetraethyl lead and only requires a small amount to boost the octane.... so they say. I burn it in my old 327, which has original heads and valves. I have not tried it in my motorcycle yet, but would like to. What do you think? I would just like the "peace of mind" cushion when it gets over 100 deg. here, and not rejetting it to run on race gas. Thanks

 

[hot125mod]

the stuff at the pump is usually sunoco or phillips depending on the area 120 is av gas and if you read the real truth about av gas or aviation fuel it not the best to use in a bike. fuel and jetting can make a large difference so take your time and ask Qs

 

[Rich Rohrich]

Rich, Have you ever tried "max lead 2000" before? It is tetraethyl lead and only requires a small amount to boost the octane.... so they say. I burn it in my old 327, which has original heads and valves. I have not tried it in my motorcycle yet, but would like to. What do you think? I would just like the "peace of mind" cushion when it gets over 100 deg. here, and not rejetting it to run on race gas. Thanks

If all you are trying to do is eliminate knock with a fuel that is a bit low on octane then TEL is a reasonable way to do it.

What it won't do is cover for poor jetting, or situations where two-strokes are running a piston crown temperature that is too high and causing pre-ignition problems or post ignition detonation. In those cases you need a race fuel with a distillation curve that is modified at the 90% and end point temperatures to help cool the piston crown. Lead won't fix those problems, it just gives you a bit more leeway before you break something.

Fuels designed for high output two-strokes are very different from the fuels needed for the new generation of high rpm four-strokes.

 

[HubertGarfunkleIII]

thanks for the post, seems like octane boosters are not a good idea. Is just using the regular highest octane gas at the pump ok or should I only use race gas? Where do you get race gas anyways?

 

[Micahdawg]

FYI to Trevor...as I'm sure you are aware, if the gas you can get honestly is a 120 octane, then as you are probably aware, you only need one gallon of that to 3 gallons of 93 octane to get nearly 99+ octane fuel. Which in my experience would be plenty for 190 psi.