Nitro fuel and motor ideas ?????

[Bigbore]

I need to build a motor for my kids to ice race with and has to ideas floating around in my head.
Class rules need to keep the cc's under 90cc's. They won't make any allowance for 4 strokes to run with the 2 strokes, i.e. like the CRF150 4 stroke can run in the 85cc 2 stroke class. BUT they also don't have any restrictions on what fuel can be run. So I need to get more from a 90cc Honda styled 4 stroke or build an 85 cc 2 stroke.

Has anyone here ever ran 10%, 15% or 20% nitro/alcohol mix like what’s used in a RC's?

The bottled fuel for RC's is 80%-90% alcohol with 10%-20% Nitro in it. I want to know if any has run an alcohol motor on a small percentage of Nitro and what the out come was.

If I build a 4 stroke, build a Honda styled CRF70 or clone motor, take it to 90cc's, run it 12 to 1, and run it as an alcohol/Nitro mix, running a manual 4 speed or auto clutch 4 speed.

OR

Machine a set of cases, like an Honda Odyssey cases, machine it to fit a CR 85 or YZ 85 crank and top it with a CR / YZ 85 cylinder and head. Have it run a CVT to a chain final drive, or even machine a LT80 case to fit the 85cc motor cross cylinder and head. I really want to stay away from the LT80 cases though. I think that the CVT would work better for the ice than a manual 6 speed already on the CR/YZ 85 motor. The problem with kids it that its harder for them to keep the rpm's up and not bog the motor.

I need ideas

[WIkid500]

I don't know a lot about the nitro but Alcohol doesn't like cold weather. Starting and running efficiently is a hard thing to do with alcohol in the winter time. What about a 116 race fuel/nitro mix? That might help you out?? That and along with some serious compression to ignite it all off.

[Vealmonkey]

If you really want to build an engine and you are stuck with 90cc's or less but other than that no real rules, ktm 80 engine!!! 2 stroke and rated at 23 horsepower. The parts are hard to find as well as the bikes, but you can't beat the engine and if you massage it a little, watch out.

[coldfuzion76]

I remember something about this when I was looking at pocket bike stuff. I can't seem to find it now, but they were mixing it with regular gas. They had some big gawd awful formula to figure out how much of each to use, but according to them it did work. Remember, though that most of the RC fuels have oils in them for 2-strokes, so it'd probably be pretty smokey in a 4 stroke motor.

[HondaHarry]

Too bad it has to be under 90cc... I was going to suggest a Yamaha KT100 Kart engine. I rode an RM85 that was built by Pro Circuit. WOW. little bike was a monster. maybe build him an 85 and have a steep learning curve? lol Maybe sleeve down a KT100 with a YZ piston, or mod it for the watercooled top end? HH

[cr480r]

a four stroke running only 10 or 20 percent nitro will need major fuel system upgrades and probably still get smoked by a 85cc 2-stroke... even if nitro wasnt expensive, hard on parts, and difficult to tune.. I still would not want my kid anywhere near it....

as for the cvt idea.. if your kid has enough skill to handle 25+ hp.. then he probably has enough skill to use a clutch.. with only a 90cc engine a manual gearbox is a must imo...

[Bigbore]

a four stroke running only 10 or 20 percent nitro will need major fuel system upgrades and probably still get smoked by a 85cc 2-stroke... even if nitro wasnt expensive, hard on parts, and difficult to tune.. I still would not want my kid anywhere near it....

as for the cvt idea.. if your kid has enough skill to handle 25+ hp.. then he probably has enough skill to use a clutch.. with only a 90cc engine a manual gearbox is a must imo...

The 4 stroke on alcohol with NITRO I'd run a 28-30 mm Lectron.... I think your right for getting smoked by the 2 stroke. I think the 4 stroke would be a pain.

The kids are good with a manual but Ice is nothing like dirt. Its too easy to get wheel spin. I'm thinking a set of cases just like the Yamaha 100 go-kart engine but with with a yz85 cylinder on top. Have the CVT engage right around 4000 rpm.

On my oldest son's machine, we're building now, has a CR80 in it ported and piped. We've lowered it 3 inches. But I need to build this one for the middle son.

[Billy Golightly]

Bigbore...if your serious about Nitro...go to www.planetsand.com, and sign up for one of their memberships. Its $20 a year, and its worth it. The guys in both the 2 and 4 stroke sections are SERIOUS mofo's when it comes to engine building and tuning. Theres atleast a dozen guys over there that run nitro in one motor or another as a common thing, and they will be able to offer help. Theres also a thread or two I remember running across. The biggest issue seems to be the volume required, since its even higher than methonal (like another 6x, or something ridiculous)