wiseco 12.1 race gas???

[nate650]

Ok, here's the deal. We just picked up a 1991 trx250x for my little brother and it needs a rebuild. I bought a rebuild kit from G&H Atv supply on ebay. The kit came with a new cylinder bored to 75mm, a Winderosa gasket kit, and a wiseco piston kit. My question is about the piston.
I looked it up and I think it's a 12.1 comp ratio.
High octane race fuel is out of the question and I live in cali so the highest at the pump is 91 octane. I searched this site and everyone recomends 11.1 to be the highest comp ratio and still use pump gas. I couldn't find a lower comp wiseco. should I buy a different brand piston and try to sell the wiseco or will 91 octane work with this motor/piston? Would I need stonger head studs?
The quad has a supertrapp exhuast and a K&N filter (which I'm going to trade out for a uni foam filter), other than that its stock.
Sorry for the long post.
Thanks,
Nate

[humblesquirel21]

i have 11 to one in my 300ex that i jsut put in im getin ready for its madon voyage and i choose that compresion because its the highest you can run on pump gas safely and it shouldnt hurt anytihng

in your situation i would try to sell the 12:1 and find an 11:1 wiseco i personaly think wiseco is the best piston brand

are you absolutly certain its a 12:1 most average wisecos are 11:1 i couldnt find a higher comp for my 300 on most sites

[biff440ex]

I agree 11 to 1 is the highest i would run on pump gas. You could always use avgas its about 100 octane and that would work just fine. youl find it at a local small airport it about half the price of most race gas. good luck.

[nate650]

I'm pretty sure it's 12.1
Every site I've checked only has 12.1 in the wiseco for the 250x

[humblesquirel21]

mm aight

from what i understand the 300ex and the 250x share the smae bore so you can get an 11:1 300ex and put that in
the only difference beteen the to quads (as it aplies here) is the stroke which dosnt affect the piston sizes so you should be good to pick up a300ex 11:1

[nate650]

hmmm, that might just work.
can anybody verify if a 300ex piston will work or not?

[GPracer2500]

Originally posted by nate650
hmmm, that might just work.
can anybody verify if a 300ex piston will work or not?

The bore is the same for both but the Wiseco piston part numbers are different for the two machines.

You can get an OEM piston from Honda in std., .25, .50, .75, and 1.00 oversizes that would be stock compression--about $50 plus rings, wristpin, etc.

[bradrenea]

If the stroke is different there is a possibility that the wristpin hole is not in the same locations on 250 pistons and 300 pistons.

[rooster300ex]

I would just buy some ocatane booster at rockymountainatv.com. Its made for atv's so it shouldn't hurt anything. I've been tryin to tell my buddy that has an 06 450r that he has 12:1 compression, and he still runs 87pump. When i tell him he should run higher octane he says "naw, it already goes fast" lol. Anyways he has had it awhile and it still runs, and thats all he runs is 87

[bwamos]

Originally posted by rooster300ex
I would just buy some ocatane booster at rockymountainatv.com. Its made for atv's so it shouldn't hurt anything. I've been tryin to tell my buddy that has an 06 450r that he has 12:1 compression, and he still runs 87pump. When i tell him he should run higher octane he says "naw, it already goes fast" lol. Anyways he has had it awhile and it still runs, and thats all he runs is 87

Using booster to treat fuel will cost more than buying aviation fuel or race fuel, honestly.

The standard Wiesco pistons are made to run on premium pump.

Try out the 250x with premium. You may not get detonation since it is a shorter stroke and a lower cc, less heat is produced.

If you do get detonation, then I'd worry about it.

The 250x does have the wristpin in a different location. Can't use a 300ex piston.

I think you're ok with the piston you have.

[underpowered]

the 250x is a shorter stroke than a 300ex. Wiseco only offer a 12:1 piston for the 250 and a 11:1 for the 300. the wristpin is higher in the piston on the 300ex than on the 250, so a 300 piston will not work in the 250. the 300 has lower compression mainly du to the e-start. Pro-X offers oversize piston for the 250x in lower copression ratio's, or you can get the factory honda piston. You could also try JE or Ross for a lower compression piston. OR have a machinist machine down the dome on your current piston to a lower ratio.

octane booster will NOT work. it marginally rasies your octane, but do not use it long term or just to run a cheaper fuel. run the right fuel, dont skimp.
why is race fuel out of the question? it is actually reasonable at the local small airport.

[bradrenea]

Originally posted by rooster300ex
I would just buy some ocatane booster at rockymountainatv.com. Its made for atv's so it shouldn't hurt anything. I've been tryin to tell my buddy that has an 06 450r that he has 12:1 compression, and he still runs 87pump. When i tell him he should run higher octane he says "naw, it already goes fast" lol. Anyways he has had it awhile and it still runs, and thats all he runs is 87

There are alot more variables that cause detonation and overheating than just compression ratio and fuel. Some of them are ignition timing, cam profile, shape of the combustion chamber, etc...
Your buddy might get by running 87 octane in his 450r, but I really doubt it would work on a 250x. They are completely different motors, not even close to the same technology used.

[humblesquirel21]

sry about my mistake on the 250x cylinder bwamos is correct i have never worked on the 250 and that was an assumption i really hope it didnt cause you any trouble

[nate650]

Ok, the reason race or AV fuel is out is because this quad is for my 10 year old brother. the agreement he has with my mother is he will be completely responsible for maintaining it and that includes buying his own fuel. There is a small airport in the next town over. they might sell me some. Could we get away with mixing the AV gas with 91 pump at say 3-1?
I thought I read somewhere that AV fuel wasn't good to run. Is that only because of the lead?

[bradrenea]

Some people will tell you that it is not good to run av gas because of lead deposits.
Some people will tell you that av gas is good for your motor because the lead acts as a lubricant for the top end.
I ran av gas in the motor in my pro street camaro for ten years before I pulled the motor to freshen it up. It was the cleanest engine I have EVER torn apart. There were no lead deposits, and VERY little carbon. I was amazed at how clean everything was.
Besides, if you pay attention a lot of race fuel is leaded too.
If I were you I would run the av gas and not worry about it. You should probably be able to mix 50/50 and not have any problems.

[deathman53]

av can read on plugs funny due to the high level of lead. AV is designed to run at high rpm's for a time, not like a atv's use low, high, low, high. I wouldn't use it. Race gas around here cost $6.50/gallon, also AV gas's octane is rated different, av gas is really at about 96 octane. I use leaded 114 on my atc295r and crf450r quad, it can burn weird and can effect plug color.

[bradrenea]

Oh yeah, I forgot to put the part in my post that aside from running it in my Camaro I have also been running leaded gas in my 400EX for the past three years and have not had any problems.

deathman53, why would you not buy cheaper gas just because it reads funny on plugs. I mean, if you know you are jetted correctly to start with, who cares what the affect on plug reading is? Not trying to be an *****, just curious.

[deathman53]

av gas isn't the easiest thing to get around here, race gas is fairly easy to get. besides a 250r with advanced timing, cr250r ignition and a 230 pounds needs better than av gas not to ping alot and it also has to run fairly cool since atc's don't have a aftermarket hi-compacity radiator support

[bradrenea]

OK, makes sense.:)

[rooster300ex]

Yea i c it would be costly,but 5 gallons of fuel lasts me a month, so its not very costly in that way.

[ww228king]

i run 114 leaded rocket brand race fuel in my 426ex ....i have 11:1 and i mix it 1 quart per 1 gallon of 93 , i have no problems and smells soo sweet....lead helps it run cooler and help seal in any week spots in the cyclinder....

[nate650]

Well I called the local bike shop and they said it's $40.00 for 5 gallons of high octane so I guess we're going to try mixing race gas half and half with 91 and see how that goes. thanks for all the info

[bradrenea]

If the octane rating of the race fuel is very high I would try mixing it 4:1 or 3:1 and see if it has any detonation or overheating problems before mixing it half and half.
Also, I have been told that lead does not raise octane proportionately, so if the fuel is leaded then you can get by mixing it weaker and still get the high octane numbers you need.
For example- If you mix five gallons of 90 octane pump gas with 5 gallons of 100 octane leaded gas, the end result will not be ten gallons of 95 octane. It will be closer to 97-98 octane, depending on the lead content.

you CANT use a 300ex piston for a 250x

i looked on 4 stroke techs website

go here for 11:1 pistons and stuff

http://www.powroll.com/P_HONDA_TRX250X-300EX.htm