Snowmobile for the Asphalt

toocheaptosmoke · May 9, 2021

Maybe some of you will get kick out of this project. A couple years back it was decided that I needed to add snowmobilng to a 3rd season, regular riding in the winter and grass drags in the fall just wasn't enough... So, time to build an asphalt drag sled for summer use.

Was going to base the build off an older polaris chassis with a 500cc liquid triple engine, of which I have a bunch of parts already laying around. Scrounged up a second hand asphalt track and some skis off a friend, and bought a cracked suspension as a parts donor for the additional wheels needed. Plans changed however, when a sled on CL just wouldn't disappear and I had to go buy it. Turned out to be a really clean 1993 Arctic Cat Thundercat 900, $700 bought it.

These aren't the lightest machines, so the sellers service truck made loading easy. :grinpimp:

So the new plan was to basically just convert this complete and allegedly running sled over to asphalt quick and dirty and be racing, vs building the other sled from scratch.

This sled is way too nice for me, the shine make me uncomfortable... The drive chain was blown, which was known when I got it. However, I started finding some other issues here and there. Long story short, the engine ended up on the bench.

So much for a quick conversion... Ran out of time and motivation, so it ended up getting put to the side and forgot about for a while.

The box of wheels is for the suspension, below is a pic of an asphalt track if you're wonder how TF this all works. It's a smooth track with a soft compound molded into the surface.

Java230 · May 9, 2021

This should be fun :smokin:

toocheaptosmoke · May 11, 2021

Eventually got it back into the shop to try for a summer 2020 finish date.

When it comes to the rear suspension, a lot of guys buy an aftermarket setup that's custom made for this application. That gives you all the extra wheels needed, the right amount of travel, and easy adjustability. However, those cost money...

So plan B was to convert a stock suspension over. One major problem was the track I'm running, it's extra narrow for less rolling resistance, but also requires all the idler wheels to be close to the center, not how a stock suspension is setup. I modified the rear axle to move wheels inboard, and used a high precision yard stick to make sure all wheels had an even contact patch on the tar. Had picked up a $20 coil over shock at a swap meet, so mounted it in a way it was never intended to, and it worked perfect.

The engine got a complete once over, with a lightened counterbalance shaft, new pistons, and some strategic aluminum disposal.

Only the best $9.99 torque wrench touches my engines!!

Clutching is very important for performance, so we chose only the finest in second hand discarded parts I found next to a trash can. It all got "rebuilt", cleaned, and aligned. Another issue was the ignition, for some reason I decided to ohm out the exciter coils and found one was shot. Was able to send it out to a guy who rewinds them and it's as good as new.

Toreadorranger · May 12, 2021

Do you have a goal for times? Last time I was at the track there were a couple sleds running Mid 9s in the 1/4. They were impressive as hell.

toocheaptosmoke · May 12, 2021

I would love to get into the low 10's while keeping things mainly stock, it should be in the mid 10's when running decent. Most classes I'll run are bracket though.

woods · May 12, 2021

I saw one of these at the track about ten years ago during street night. Ran low 8s. I never saw anything like it. Fastest thing that went down the lane that night.

toocheaptosmoke · May 18, 2021

At the end of last season was finally able to get it out for a shakedown run. Made 3 passes, first one just burping the throttle to give the engine a little bit of a break in. Clutching was fairly close, but needed some more rpm, was running around 8000 and should be around 8300. The jetting was also a bit rich I feel, but had to start off somewhere. The sled handled pretty well, it was definitely a lot smoother than what I normally run on. Kind of wanted to run 10's on the first time ever running a 1/4 mile, but didn't quite get there. The tall windshield was also starting to fold over at higher speeds, so need to change that. :laughing:

Hope to get back out again soon for some more testing.

Another shot of the track. Suspension setup is important, most guys run everything very tight with very little weight transfer. In the grass drag side of things, you want enough transfer to just pull the skis off the ground a bit and hold them there. Asphalt guys usually tend to keep the skis planted the whole time. It needs some tweaking but was pretty close on the first shot, not very high tech or flashy but gets the job done.

If you're interested in seeing more, there's also a series of videos on this build.

toocheaptosmoke · Jun 27, 2021

Was able to get some more runs in last week, found out how much more work the suspension needs. Definitely getting an education on the whole asphalt side of things, was walking around on the line that had a good prep and was surprised at just how sticky it is! With the new found traction the front was lifting too much. Also need to work on reaction times, not used to the sportsman tree.

j20brett · Jul 1, 2021

Never wouldve guessed a snowmobile would see 117 mph, pretty badass

ThePanzerFuhrer · Jul 1, 2021

Lol 117 that’s nothing. The ice guys make wicked fast passes. Here is 189mph in 1/4mile. That was in 2010. I’m sure they are at 200 by now. Nuts

GLTHFJ60 · Jul 1, 2021

I've had a stock sled a **** hair above 110mph before on a frozen river up in canadia, a 1000cc twin. They are scary fast. Tough to put the power to the ground as the track just wants to spin from a stop. For drag, they probably have the sled equivalent of a slipper clutch to let the power down gradually from a stop.

EDIT: yeah in that video, they don't get on the throttle all the way till they're going probably 40 or 50mph.

SLOWPOKE693 · Jul 1, 2021

ThePanzerFuhrer said:
Lol 117 that’s nothing. The ice guys make wicked fast passes. Here is 189mph in 1/4mile. That was in 2010. I’m sure they are at 200 by now. Nuts

189 in the "1/4" isn't all that impressive either when it's from a roll.....

toocheaptosmoke · Jul 1, 2021

I still love the grass drags the best. Guys are now into the 140's in 500 feet!

Nothing better than a nice clay starting line and a track full of chisels. :smokin:

Java230 · Jul 2, 2021

This has always looked fun.

I've been 107 on a yami triple 700. That was cold....

SomeGuyFromOlympia · Jul 30, 2021

all I see is snot to your ears :laughing:

toocheaptosmoke · Oct 4, 2021

Finished the season up at the Super Sled Shootout in MI, it's the biggest asphalt sled race of the year. Got to see some of the big dogs run and some new records were set. I just ran bracket class, got to the 3rd round of eliminations before red lighting. :homer:

Sunday races got rained out.

Was able to run the best 1/4 mile times during the test and tune, bracket class was 1/8 mile, had a 10.59 at 121. Ran out of gear at 121 though with the clutches maxed out, so something to change for next season. Still got some more tweaking to do with engine and clutching, and I think there's at least a tenth or two in the 60' times to be had. New overly optimistic time goal: break into the 9's with the stock pipes and suspension :laughing: