1976 Nitro Grass Drag Set Ups

[midniterupper]

Hey, We are back for just a quick update regarding the Nitro. We raced it today at the Twisting Trails snowmobile club and we made quite an impact. We didn't place in all classes but we did WIN Vintage Stock 440, took 2nd in Vintage Open Mod and 3rd in Vintage Improved Stock!

The sled is not perfect by any means and the Improved stock winners were very fast, right out of the hole they were gone! One was a Yammie exciter and one was a Polaris 500. Both sleds have been around the circuit for years so I don't feel too bad, everyone has to pay their dues respectively right?

More to do, more to think about, more to learn....
Keep you all posted as progress continues,
Thanks again for your Team Red support!
-Paul

[Ruppsforever]

Congratulations !! Getting that first win under your belt is very good news. The first win is the toughest one to get !! Very cool !!

[mrrupp1]

Hi Paul, you have made the Rupp nation very proud. It’s great to see a Rupp liquid cool in the winner’s circle, especially in the stock classes. I have always said that a Rupp Xenoah is a very potent power plant. Can’t wait for the next race. Have a good one and take care. Clint

[midniterupper]

Okay, it's been a while since our last update. We did some experimenting with the profile on my primary clutch arms, blending in (actually blending off) about .015" in the transition area. It helped tremendously on the launch! Also tuck ground a little more and now we are engaging at 6200 rpm, very explosive out of the hole.
I also ground a slight chamfer on the back side of the arm tip to try and raise the final shift rpm which it did. Now we are tickling the elusive 8300 range. All these little tweaks have helped in the sled's performance.
However, now that we are reaching the 8300 mark, we are developing a high speed miss for some reason. I don't think it's a electrical issue but you never know. All connections are solid, changed spark plugs, swapped cdi unit. Changed carbs a couple of times and we have reduced the miss but it's still there somewhat.
Now, we did race again this weekend and we did very well again. We took 1st again in Vintage Stock, 2nd in Improved and 3rd in Open Mod! Not too shabby for a 45 year old basket case and an old man! This weekend had a great turnout for all classes but the Vintage is drawing a lot of attention and our Nitro was looking very nice. We had so many people looking at the sled we almost missed the finals! But it's all good for Team Red. We raced against Arctic Cat, Polaris Ski-Doo and of course the loyal Yamahas too. Sleds that beat us before are not beating us anymore! Even had grudge matches after the races were over between the Yammies and the Nitro, we won every time! People couldn't get over a stock Nitro beating the track favorites even in the Improved and Open classes. The Stock class has always been won by these boys as they are regulars there, been racing for generations and now we have beat them at 2 events. They went home rather quietly..... !!!!
So we did quite well, We have 5 trophies on the mantle now and 1 more race to attend next week then we are done for a while until ice racing. Still more things to try out, have some funky exhaust temps hanging low but we can work with what we have for now.
Thanks again to all on this forum, it has been a successful mission. Not done yet!!
-Paul

[midniterupper]

Well, it's hard to believe our grass drag racing season in Michigan is over already. It was a great season overall, especially considering the Covid impact on most events throughout the country. Hats off to the events and races that were allowed to go, it couldn't have been easy. Twisting Trails Grass Racing and their club members deserve a special tribute of thanks. They have faithfully held their grass drag races since 1970, haven't missed a year and now, like yesterday, had over 75 racers there. Some came as far as Pennsylvania and Wisconsin to race the iron here in Michigan. There were some seriously fast sleds competing, it was a very good turnout in spite of the weather. Thanks again to everyone who participated. Be sure to check out twisting trails grass racing on facebook to see some excellent pictures of old school grass drags. Be sure to look for #76

Now on our final results for the season, we entered the Vintage Stock, Improved and Open Mod classes. We took home 2nd in Stock, 3rd in Improved and Open. 9 classes for the season, 8 trophies on the mantle! Plus so many new friends (all with Rupp stories of course!) and now fellow racers that are true fans of our Nitro. Some people were calling it other names but we won't go there. Guys that I raced against over twenty years ago are now new found friends, no more competitive crap attitudes.

But, I think the best part of everything (besides running the sled down the track) was that so many people made positive comments about the sled. Now it certainly is not up the awesome work Bill does, but I have been cleaning her up and detailing it like she deserves. Inside and out she's looking pretty good. On top of that she actually runs and wins races against some very tricked out sleds. Some folks yesterday came by to say that our Nitro was the nicest looking, best running and fastest Rupp they have ever seen, quite a few actually. I know there are more out there that are way better, but still it's nice to hear. As hectic the hot pits can be, and as busy as you can be running in 3 classes, making it to semi's and then off to the finals, getting back to cool off and get back up to the line again. People hunt you down and stop you to say how much they appreciate seeing this old iron still kicking butt and wish you luck. How cool is that?

That is exactly why we spend hundreds of hours dialing in and restoring these old sleds to their original glory. isn't it?

There is still plenty of work to do to the sled, we certainly are getting out of the hole like a rabbit. We need to address our clutching to be more aggressive at mid track, get our exhaust temps up and raise our shifting rpm's. But overall, we have a great racing sled in our hands. Very impressive considering it's start.

So, thanks again to all who have contributed to the success of this sled, especially Clint, Josh, Mike, Kevin and so many others. Please forgive me if I overlooked some, give me a holler and let me know. We're not done yet, got a long ways to go. But to have a stocker chase down the Mods says a lot! We will continue with efficiency and perfection. If you may have any other ideas to try, please let me know.

So that's about it for now. Hope you all are doing well and are taking time to enjoy your passion too. Take care and stay safe.
-Paul

[Ruppsforever]

That is awesome news !!! I'm glad that our help helped you out !!! Well done !!!

[mrrupp1]

Hi Paul, you did an awesome job showing the snowmobile grass drag racing world what a Rupp liquid cool nitro can do. Now I can't wait to how she does on the ice. Talk to you soon. Clint

[midniterupper]

This is our Red Team photo for this season. Thanks again to everyone who has made this winning season possible through wisdom, expertise, great advice and parts support!

[midniterupper]

Hello to our Rupp Community! It's been quite a while since we had an update from our racing Nitro. We had a rough winter season health wise but we are back on track to improving our Red Sled.

First of all I want to mention how the popularity of Vintage sled racing is around here in Michigan. This past winter racing season had awesome sleds in both ovals and drag racing! Incredible attention to detail both in appearance and performance! The sleds were fast and flawless. People are realizing Vintage racing is fun and affordable, great to see people of all ages racing these fantastic machines. This coming grass drag season ought to be one of the best in years, we can't wait!

Now, getting back to the Nitro. Our plan all along was the assemble the sled and see first of all, to see what it was missing and then see what it was capable of. We were all pretty impressed with the sled. It went together well and was a strong runner right out of the gate. We certainly learned a lot with the clutching and with the assistance of many on the board, we got ourselves a competitive race sled!

So our objective grew a bit after winning a couple of races in the Vintage Stock class. Now we want to be even more competitive in the Vintage Improved and Open Mod classes but still remain "stock" enough to compete in the Vintage Stock class. Of course we cannot modify our engine by extensive porting and exhaust mods but we can always improve efficiency! I didn't think this would be even possible but after seeing these altered sleds race and realizing their speed of 70-72 mph is attainable with our Rupps.

The plan now is to improve our drive line efficiency beginning from the engine crankshaft to the jackshaft and driveshaft, and concluding at the rear axle.
To do this, I'm considering the following (actually I'm gonna do it, I just think about it first!) To begin, I'm going to drop off my crank assembly over to Kevin Haase at Pipestone. I would like him to go through the crank and replace bearings and get a good balance on it to ensure reliability and improve efficiency.
Hopefully I can tug on his ear to see if he may have any suggestions for us. He is a proven winner and a credit to all of us Rupp enthusiasts!

I also want to install ultra-low friction bearings in the jackshaft and driveshaft. There is a company named Microblue bearing that manufactures these bearings for many applications so I think we will give them a try. To go along with that concept, I'll replace the (4) wheel rear axle setup that we used last season. I think 4 wheels are not necessary for straight line racing so we will go down to 3. I will have to make a new rear axle to accommodate the 3 wheel set up. We will use low friction bearings in those rear idlers too.

Another thing I discovered this past winter season while working on a ZR600 was that their Primary clutch and secondary roller weigh almost 2 pounds lighter than my current Polaris primary and old Arctic secondary clutches. So, I am going to pick up a set to try on the Nitro. Should be somewhat similar to our current clutching, will be easier to swap out come testing time.

Finally, though it may not help it go any faster, I want to schedule an appointment with Bill Stull to have him do my hood and belly pan. I know it'll look way faster after he is done with it!

So we got a lot of work ahead to get done but that's all part of racing isn't it? Very exciting and so many cool friends!
We have more races to attend this year, going up against some really fine tuned and fast sleds. These boys have been at it for many years now and their sleds prove it. Looking forward to seeing what we can do to dis-Rupp-t their fun!

That's about it for now, I'll be sure to give a note as progress continues. Meanwhile, please feel free to contribute any ideas and thoughts you all may have. It's all greatly appreciated!

Until then, take care now!
-Paul

[Ruppsforever]

When you have Kevin do your crank have him stuff it. That is worth 3 HP. And nobody will ever be able to see this was done. I had two cranks done at the end of my racing and never even got to try them. But I might dust off the 440 next winter. And if I do one of these cranks are going in it for sure !!!

[midniterupper]

Hey thanks for your input, you always have great ideas and appreciate your help. It's a funny thing about that topic. Back when I was a kid I bought a Hodaka motorcycle, and of course I was always doing performance work to it too..
One of the first things I did back then was to stuff my crank following the directions in Dirt Bike magazine. It was a very informative article about crankcase pressures and increasing compression under the piston to help gain more fuel charge per stroke.

I used cork that I coated with epoxy and it worked wonderful! That little 100cc motorcycle could outrun 250s after I ported the cylinder, cut the head and made a pipe for it. Folks couldn't believe it, not bad for a 9th grade project! I wrote the company and they sent all the factory mods for racing motocross and flat tracks. They were a great company, too bad they went out of business back in 1976.
I happened to mention Hodaka's to Kevin and he started laughing. He said he used to be a Hodaka dealer back in the 70's so we got along great after that conversation. He is also a collector of the bikes and has quite a few.

So yes, I have my crank stuffed already but I will have him look at it to see if there is room for improvement. I truly believe it makes a big difference in the Xenoah powerplants. I have the crank ready to go down to Kevin's this week. I pulled the crank on Saturday and the cork stuffing held up flawlessly, no deteriation at all.
It appears a bearing may have begun to spin in the cases and the rubber o-rings are breaking up so it's a good thing we caught it in time. I measured the total run out of the crank and it measured between .008" - .012" so it needs a little tweaking. I'm also bringing the cases, cylinders and head along just in case he may have some ideas for them.

With our Vintage classes here in Michigan, the rules are rather relaxed for the Stock classes. The tech inspectors I have talked with say that with OEM parts being difficult to find, they have to consider that everyone has to do the best they can with what's available. Straight pipes are never allowed in the Stock class but other than that, it would be hard to be an expert at all the Vintage manufacturers.

I have to give Kevin a call to make my appointment with him for this week. I will let the forum know what he is gonna do, looking forward to seeing his shop.

All take care now, updates are coming. Thanks again for your continued interest and support. Team Red is going to shine strong in 2021!
Chat again soon,
-Paul

[Ruppsforever]

Another thing you could probably get away with is stuffing the top of the cases where the transfers are. High temp epoxy works great. Drill some small divots in the top of the case with a really small drill bit so the epoxy has a place to soak in so it stays in place. Xenoahs love that too !!!

[midniterupper]

Boy, that's a new one on me! I'm not familiar with that procedure but it sounds very interesting, anything for more power right? I will be sure to mention it to Kevin, I'm going to his shop (Pipestone Small Engine) on Thursday. So very excited! He mentioned to bring my cases along in case there is a problem from a bearing race spinning. I know he'll have it figured out. I sure appreciate Kevin taking some of his time to accommodate an old Team Red racer in the middle of his busy season.

I cleaned up all the engine components today, looks like one outer PTO crank bearing is a bit discolored from overheating. Also, the orange rubber 0-rings are disintegrating but for 45 years old, overall not too bad. The technology incorporated into these motors is amazing, not too far off from today's potent powerplants, minus the variable exhaust systems. They certainly produce the horsepower!

I'll have to clean up the engine compartment now, so much easier to detail it with the engine out. Also gives me chance to look at the jackshaft and brake assembly. Maybe while I'm in there I can sneak in a hydraulic brake caliper.

Well keep the suggestions and ideas coming, they are all helpful and greatly appreciated. Every added fraction of power and efficiency will prove helpful at the track. I will keep you updated on our continued progress, I can't wait to get her back together to begin testing again to try out some more ideas. The motor ought to be the best it's ever been.

Okay, until next time, keep thinking Red!
-Paul

[midniterupper]

Time for a quick update. I just returned from visiting Kevin at Pipestone headquarters and I must say "What a Shop!" That man (along with his right hand man Brad) are a wealth of knowledge!

Not just for our specific needs for our Xenoah motors but many other brands too. He has all kinds of experiments going on, it's mind blowing! He has a huge building that extends in every direction, filled with all kinds of goodies. Like Santa's workshop and he knows exactly where everything is at. So much equipment and nice machinery, not one inch of floor space is wasted. It's packed in there but everything is accessible and very well maintained. They even showed me their dynometer set up too. Man would that be fun to play with! Kevin has a very nice collection of rare sleds, stuff you just dream about.

He has many parts for Chapperal sleds also. I was amazed at the detail of some of the parts he has made for our sleds, very well thought out and the quality of machining is perfect. Needless to say, we could spend a lot of time and money in his place! But it's all so well worth it right? So, if you ever get a chance to get over to his shop, I know you'll learn something. If you ever need the right parts for your engine be sure to look them up, They'll certainly give their best to accommodate you!

So now back to my motor situation. Kevin and Brad evaluated the crank and it appears to still be salvageable but it definitely rattled pretty good. The bearings, cases and shims have some excessive wear on them. It's a good thing I didn't try to push it another season, she would've blown up sooner or later. I am very confident the crank will be better than new when I get it back.

I also left my cylinders and pistons with Pipestone. They can measure everything up to see if a hone is good enough to clean them up or if we need to bore up a size.

I also showed Kevin a problem I was having with the rubber intake manifolds. They tend to mushroom out around the flange area and cause a slight leak to occur. The manifolds I had were a cheaper aftermarket brand and they could not compare in quality of the steel version Kevin offers. I have a set on order with him. So if you too are experiencing a flange issue, he's got the cure!

Along with the intake topic, I asked about the V-Force reeds they offer for our Xenoahs. I brought along my Boyeson reed valves just in case he had a set of V's in stock. I originally used the metal petal reeds that came with the sled but I was hesitant to keep using them in case they fractured and the motor ingests them. I thought the Boyeson's improved the response and power but after comparing the V-Force, there is way more petal area. I'll be installing a set of those when I get the motor back too. Anxious to see the difference, maybe 70+ mph is attainable this year! That would be awesome!

Well, I'd better get back to work around here, just wanted to give an update regarding my visit to Pipestone. Sure has been a great day, looking forward to testing. I know we are on the right road for improvements!
Take care now, we'll chat again soon
-Paul

[Ruppsforever]

That sounds awesome man !! I want to pick up a set of those V forces too. I've always ran my stock rupp cages but I hogged them out for more opening. I used boyesen pedals all these years. Not sure if I can post pictures on here anymore but I could email you a picture of what I was taught to do to the top of the cases. It helps a lot !!!

[Ruppsforever]

I can't put pictures on here they are too big. I can email a picture to you if you want.

[midniterupper]

Hey Josh, That would be very helpful and greatly appreciated! My email is: [e-mail] and my cell phone number is [phone]. I'm not familiar with that procedure but I'm very interested in it.

Kevin showed me the aluminum plates he had machined to make the V-Force fit into the reed space on the cylinders. The reeds are huge compared to the Boyeson's and the plates look like stock with no special markings on them so they won't be drawing attention. I think the new reeds along with your case transfer work, the sled is gonna rock this year! Should be pretty smooth too with the crank rebuilt and balanced, looking forward to testing and getting her dialed in.

Thanks again for your help!
Have a great day!
-Paul

[midniterupper]

I just wanted to say a big "Thank You!" to Josh for sharing his transfer port technology with our Nitro, it sure looks effective and can't wait to implement it. I'm sure it'll wake up those hidden horses!
Keep you posted, until next time
-Paul

[Ruppsforever]

No problem Paul. I figured its time to start sharing some of this info to fellow Rupp racers.

[midniterupper]

Well Josh, we all sure appreciate your help on this board. You have much Hi-Performance knowledge and experience tucked away up there! It's still making those foreign invader sleds shake in their boots! Pretty cool, let's give 'em a run for their money at the track! The legend continues....

I have been busy with the Nitro. I have the jackshaft, rear suspension, driveshaft and track out of the sled right now for inspection. Tried to get some Ultra-low friction bearings for the driveline but didn't have much luck. Micro Blue Bearings.com was the only company offering these bearings for snowmobiles but they didn't carry all the ones needed for our Nitro. They have 1 for the jackshaft and 1 for the drive shaft which would leave us with having to use conventional type bearings on the opposite ends of each shaft. Didn't see much gain in using only half to I ordered low friction NTN's to replace the ones installed in the sled. The old ones were not terribly bad but our quest this year is to maintain the best efficiency possible so best to replace them all while we have it apart.

Just in case anyone is looking to replace their drive bearings, here are the numbers off the ones I just removed:

JackShaft: L.H. (clutch side) is: FG205-16, R.H. (chaincase side) is: SA205-14

DriveShaft: L.H. is: 6006 RS R.H. is: AL205-1



Everything else looks good, the idlers all held up well, hyfax and track look good too. The only item showing a lot of wear is the drive cogs, probably due to all the dirt we run in. Remember we have four drivers on the original shaft. That eliminated the ratcheting and exploding the original two driver set up. I wonder if Rick Weaver has made up any drivers for the Nitro's set up yet? I'll try to get a hold of him to see if they are available, I think I got the last 4 that Kevin had! Gonna need to replace them by the end of this year for sure.

So that's about it for now on this end, have a lot of cleaning and detailing to do. Still need to get ahold of Bill to schedule a bit of hood work too. We'll see how the budget goes after the mechanical work gets closer to being done. Also still need to buy a roller-type secondary clutch to play with, might help along the way.
Have a great Easter weekend everyone, Thanks again for your continued interest!
-Paul