1976 Nitro Grass Drag Set Ups

[midniterupper]

Yep, I agree. These sleds may be a lot of effort but all in all it's pretty cool to work on them and see them running again. The technology Rupp employed in it's day was rather advanced. It's fun to combine the newer technology along with the old. Frustration is just part of the game I suppose but it sure is nice to have the support and expertise of this Message Board, there's a lot of guys on here that truly know their stuff! I know that I for one of many have greatly benefited from everyone's friendship and input.
I finally finished up the fixtures I had to make in the shop so now I can get back to work on the Nitro, I have some ideas to try in order to gain clearance for the studs up front. I am curious though, Clint you mentioned maybe rolling the chaincase for additional clearance but I am not familiar with that procedure. Can you explain a little for me?

[mrrupp1]

Hi Paul, I have never rolled a chain case myself. So unfortunately I'm the wrong person to ask how to do it. I'm sure there is somebody on the board that can explain how it is done. It looks like a pretty complicate procedure, but I guess sometime that is your only option. I think putting smaller drivers in is what most do. I don't know if there is a smaller driver the would fit a Rupp shaft. I know you spent so much time making your shaft a 4 driver shaft the last thing you want to do is tear it apart and start over and put smaller driver on. Hopefully you can come up with a different solution. Sorry I couldn't help with your problem. I sure you will come up with something good. Clint

[midniterupper]

Hi Clint, thanks for your reply, as always your information is very helpful and encouraging. Hopefully everything is working out well for you too. Today I made a set of forward mounting brackets for the rear suspension as an attempt to lower the suspension in the chassis to gain more clearance for the studs. It was similar to the rear bracket we made a few weeks ago, it lowered the forward section by about an inch which is really helpful. I think we now have about 1 1/2" of clearance between the track and the forward portion of the suspension and also along the track drivers too. The rear portion of the track has around 2" now with the rear bracket in place. Tomorrow I am going to try to get in the 1" chisels I had in the track originally, I believe there is sufficient clearance now. I'll install a few and rotate the track by hand to ensure there is room for them, that would be so cool. I'll finally be hooking up the way we need to!
The sled height is a little bit higher with the brackets in use but I think it'll be alright. The track attack angle looks great and I think we may have reduced the ski pressure which will certainly help with the drags. I would love to see this sled finally lift the skis on launch.
Well, this project has certainly kept all of us busy and it has been a lot of effort but I think we may have something here. After I get the sled back together and fully studded I can get back to some serious testing again. We may have to wait for spring thaw now, good chance to send out the clutches for balancing at Cascade.
Keep you posted after the studs are in and we do some holeshots.
Until next time, keep seeing Red

[mrrupp1]

Hi Paul, I never thought of lowering the front part of the suspension to gain some clearance. I knew you would come up with a great idea. You should have tons of room now. I love how you always think outside of the box. Can't wait to here how she runs. The Yamaha boys are not going to like it when you show up with that little Red Rupp. Talk to you soon Clint

[midniterupper]

Well, time for another update: We have ourselves a very fast drag sled! I have been playing on it all day with no issues. With the new brackets in the forward mounting position, there is plenty of room for the studs so I installed (96) 1" chisels in the track with no interference. The tunnel protectors work great being full length too.
I set the rear suspension rather stiff but still movable when riding around. The track tension is 1" with 10 pounds downforce, no ratcheting from the drivers at that setting, no studs hitting either so I believe we are back in business. At wide open the motor spins at 7900 to maybe 8000 using the Cat arms weighing in at 44 grams leaving a little room for playing there.
With these studs hooking up relatively well, the sled caught me off guard when playing around. Cruising along nicely, punched the throttle, caught some good hardpacked snow, hooked up and about threw me off the sled! Never did that before, I love it! At midrange, a hidden turbo kicks in and you gotta hang on then too. I don't know where it comes from but it hits hard and is gone; no hesitation, no noises, no nonsense. Just gone. Like it is there to get a job done and it wants to get at it.
So I think we have hit a home run that will be a game changer here in Michigan. The sled is the best it's ever been and there is so much to test with now. With the sled finally hooking up and being so strong, I can't wait to start dialing it in. I know it will be a contender and am looking forward to seeing the results of our efforts against these Yammies especially.
I truly appreciate everyone's efforts and contributions with this sled, you all have been incredible and very helpful. I know I wouldn't have gotten this thing this far without you guys, I have learned so much though I know we aren't done yet. I still need to rebuild my clutches and send them out for balancing and I'd like to play with some anti-friction paint for my skis. I can clean up the sled and make it look respectable (she doesn't have to be pertty!) by then the weather will be cooperating for some serious testing. However, there is one last race here in Michigan next weekend if it doesn't get too warm. Sure would be tempting to load up the trailer just to see what she'll do.....
Okay, gotta run along here. Just wanted to give you the latest and also to say thanks again to all, come on over and take her for a ride!
Til next time, -Paul

[mrrupp1]

Hi Paul, I knew once you got all the little quirks fixed the sled would be an animal. Now when you get her dialed in I think you’ll be the sled to beat. The Yamaha boys will be building sleds to beat you. Great job can’t wait to here how she does. Talk to you soon. Clint

[midniterupper]

Thanks Clint for your support and confidence, I greatly appreciate it. The sled is strong and responsive, I can't wait to line it up with other sleds. Not sure about the races for this weekend, it's been warm and rainy. If nothing else, the waiting game will give me time and opportunity to go over the sled with a fine tooth comb and prep some weights and helixes for when testing time comes around. I still need to grade out our test lane too in order to get it as smooth as possible, it shouldn't take very long.
I can also use the time to do some body work to the old girl. Now that she's a true contender, we might as well make her look respectable! Take care now, chat soon!
-Paul

[midniterupper]

Well I figured I'd give an update on the latest from up here in Northern Michigan. The Nitro is running strong though I haven't had the opportunity to really run it hard since I updated the track. I added more studs to it, right now I have (120) 1" chisels in it and they seem to clear the tunnel without a problem, at least on the stand. I am concerned that the track may balloon out and the studs may hit but I guess I really won't know until I make some high speed runs with it.
I was planning on bringing the sled over to Houghton Lake at Fast Eddie's vintage races on Saturday. I added the extra studs, welded and ground up some ski runners for the ice but I just wasn't sure about bringing the sled there to race without any test runs under my belt with the new set up. I have never raced on ice before other than just playing around so I didn't know what to expect.
I went to the races and was SCHOOLED! First, I will need 192 picks/chisels in order to hook up. Second I know I need actual carbide ski runners with 8" minimum length in order to have any steering control. I also need ice grabbers for my boots too! The ice on the track was glare and smooth, many crew members fell behind the sleds. The track length was 660' two lanes with plenty of shut down area, they did a great job and the sleds were relatively fast. The big boys were running in the 120's. What I went there for was to record the Vintage sled speeds, primarily the 440's. I was disappointed that there were no stock sleds running only Improved stock and Pro stock 440 so my Nitro really didn't have a class to run in. This may become a dilemma, we'll have to see about that. I also need to make a skid to pull the sled around on to get through the parking lots.
Anyway, the 440 class had the same Yamaha's there that I'm focusing on to beat, none of them stockers. There is one guy in particular that I want to beat from a grudge over 30 years ago but I know he is at the top of his game, he does this stuff for a living and for a long time now. His sleds are always strong and flawless. Nice looking too. However, at this race, there was another sled there which didn't appear to be a threat at all. It was in the back of an old pickup, had a ton of studs and a nice VDO style tach on the side of the hood. An old gray haired man (just like me!) in dirty old carharts pulled it off the truck, put on his old beat up helmet that was missing the visor, fired up the sled and drove it onto the lake. No big deal right? It was an old 1978 Yamaha SRX 440 painted flat black (and natural rust) ripped up seat, no windshield and louder than heck. Let me tell you, that sled is the meanest, fastest 440 I have ever seen! That thing just cranked, unbelievable! He raced the guy I'm trying to beat on grass (yep, he's everywhere!) and these two sleds went at it big time. They both raced in the 440, 500 and 600 Improved and Prostock classes and dominated. Ultimately it came down to a shoot out and the old SRX ended up winning. I couldn't believe it, I clocked these guys topping out at 82 and 83 MPH at the finish line. Pass after pass they were consistent without any issues.
When I studied these sleds a little more I noticed the old SRX track had about 2" of slop and it didn't ratchet or have any stud slap. The other sled, (we'll just call him doc for short) when they brought it onto the ice, the crew member simply held onto the right handlebar and pulled the sled along like it was a wagon with wheels. No rolling resistance at all! So that is one of their tricks.
So now we have an actual top speed to achieve and beat, 83 mph if we're gonna race on ice. We all had a blast, though some of the crew needs to dress warmer but we're learning. If I'm going to race on ice next year, we need to have a different setup to ensure the sled handles nice and straight. A lot of guys lost their race because they had to over correct their sleds and let up. I do think however that we would have a chance to win on ice. We are achieving 67 mph on grass in 500' when we last tested and we should have gained with the new mods to the track so I think we could dial in the sled to be competent on ice too. September 12 is when I finally get to race the doc, we'll be ready!
Okay, I think that is the latest for now. I am still waiting for a couple of diamond plates to show up that I will install on the belly of the sled to protect the fiberglass when we have to cart the sled around. It'll make it stronger and easier to move around. Let you know how it turns out.
Thanks again, until next time -Paul

[mutt]

Nice update, when your write a novel though only do 4 to 5 lines then space it down with the enter key for the next set of lines. Makes its a ton easier to read. You picked up speed with that r track. Sometimes up to 10mph vs old vintage tracks. When those guys have lots of slack in the tracks most likely have anti rachet drivers. You have to watch out for those rat sleds. Back in the muscle car days with my nice street running new F class car. When I went to the strip first time got knocked into F2 because my tires were 1/4 inch too wide.

In that class better be all in or stay home. A 7 yr older rust bucket same thing couldnt here mine rev up over his. And same result he put it to me

[midniterupper]

Hey, Thanks for the tip on writing, sure helps. But yeah, those sleepers can be potent. I heard him start the sled and immediately knew his motor meant business, deep tone, responsive and about 9000 rpm.
I am kinda doing the rat nothing too but more due to budgeting. I'm trying to keep my expenses as low as possible in building up this sled as an attempt to prove Vintage racing can be within reach for the average guy. My Nitro looks like it's aged and has had some good times but it also looks like it just came off the trail too. It's still has the stock exhaust, headlight ect. to keep it looking classic and nothing too out of the ordinary. But make it kick butt without all the noise.
And there is the real challenge: Get this Xenoah power plant to produce as much horsepower as possible and get it to the ground as efficiently as possible. We'll call it "smart horsepower". If we can fine tune this thing to be it's very best without going crazy on motor mods, I think we will demonstrate and continue the legend Mickey Rupp started with the concept of these machines. It's pretty nice to see a variety of competent vintage sleds at the track and to represent Red.
We'll go get 'em!

[mrrupp1]

Paul, I have no doubt once you get your Nitro dial in she be a contender. Can’t wait to see her run. Please keep the updates coming. Clint

[mrrupp1]

Hi Paul, I just wanted to let you know if your running Stock skis on your Nitro. Older Polaris carbide work pretty good with a little modification. Not sure what the part number is. I use them on my 75 fan cool Nitro. I’ll see if I can find a part number for you. Clint

[midniterupper]

Yep, Got the stock skis on it. I welded up some stock runners that I bought from MFG supply, but I wasn't too confident that they would bite very well. I didn't get a chance to try them out yet so your idea of using old Polaris carbides would be great. If they're are close we can modify them to fit.
Several years ago I welded and ground some runners (without carbide) and ground the centers very sharp. Put them on my old skidoo, went to the lake, picked up a little speed and tried turning. I promptly flipped the sled from them grabbing too hard, sure surprised me!
I know I will have to install some regular ice picks for the ice next year too. Sure was impressive to see the sleds hook up on a surface too slick to walk on.
Still kicking around some thoughts and ideas for the old girl, been busy getting winter projects for the house done. Going through the motions but my mind is on the Rupp.....
Thanks again Clint, sure appreciate your efforts. Stay healthy during this virus crisis!
Take care all, -Paul

[mrrupp1]

Paul, I talk to the friend of mine that gave me the Polaris carbides, and he is pretty sure they were for one of his 75 TX leaf springer. So we think 71 to 85 leaf spring Polaris carbides will work. The stock Polaris ski uses one stud, but I think the carbide for the older Polaris use two. Here's a part number out of an old Central Snowmobile Salvage catalog. It's a Roetin carbide 102-202 it has 5" carbide, they say it fits 71 to 85 Polaris snowmobiles.
Hope this helps.
You and your family stay healthy.
Clint

[midniterupper]

Thanks Clint! I made note of them and will look around on line to see what we can find. Looks like we may have plenty of time on our hands, Michigan has pretty much shut down. I am glad we have our Rupps that need attention, I guess there may be a house project or two (lost my list, can't seem to find it with all the leaves on the ground!)
How are you contending with the situation? Hope you're doing well also.
By the way, this is a safe message: I cleaned my keyboard before I started typing =)
Take care now, -Paul

[nitrofa340]

Dont ever run wear bars/skegs when grass racing. Very dangerous at the finish line when you let off the throttle and the weight shifts foreward onto the skis. You can end up going for a tumble if the skegs bite too hard into the ground.

[midniterupper]

Well, it's been awhile since I shared some progress with the Old Rupp Vintage enthusiasts. I think we are all about ready for conversation other than this Coronavirus topic, hope everyone is happily hunkered down and enjoying good health.
When I attended the last ice race in Houghton Lake, I realized I needed to bring out the old sled dolly that we used when we raced our SkiDoo's twenty some years ago. The tires needed replacing along with a little lube but it's still quite functional. However, when I went to use it on the Nitro the rubber pads would be placed right on the fiberglass belly pan. I didn't want to actually lift the sled with the dolly because I thought it might crack the fiberglass when carting it around.
So I made a couple of cardboard templates that fit the location of the dolly's lifting pads and ordered (2) 8" x 10" polished tread plates and some aluminum rivets to secure them. I cut them, formed them to fit and riveted them in place. You really can't see them unless you look for them from the front of the sled but they work great. I can slide the dolly's pads forward until it touches the ski leaf springs then attach the rear strap to pick up the track. When I set the sled back down, the front end rests upward with the skis about 6" off the ground with no deflection in the belly pan. It should be much safer now to cart the sled around the parking areas when at the races. Still have to make another skid out of a old truck bed liner for at the ice races but that's not much to do.
The primary and secondary rebuild kits and bushings all came in so I went through both clutches with a fine tooth comb. The secondary was a piece of cake to replace the bushings, then I cleaned up all surfaces on the lathe. I also adjust the sheave clearance to allow the drive belt to ride about 1/8" above the edges, should help getting her out of the hole eh? We still have about 1" belt deflection too.
The P-85 primary took a little more time. Cleaned everything up, replaced everything that came with the kit. I ended up purchasing the EPI kit rather than the SPI rebuild kit. I researched both and found the difference in cost ($60.00 SPI vs. $130.00 EPI) is due to the material used in making the buttons. I'm hoping the rebuild will last so I figured I'd better get the good stuff. The trick to getting the old buttons out is to use a dull chisel to pop them out. I cleaned up the sheave surfaces on the lathe too. Both clutches look like new now.
Most of you know me as being semi-retired and on a limited income, I am trying to keep the cost down on building this sled and still be competitive in the Vintage classes. Next month (pension pay!) I will send both clutches to Cascade Clutch Balancing then we should be set to do some serious testing. The test track is shaping up, still need to do some final grading and then begin compacting. If we have the good weather, maybe I can get in some testing before I send out the clutches. Hate to miss a good opportunity!
Regarding the cost of this project, we're not doing too bad. After the balancing costs, we will have about $3000.00 total invested including the sled cost. We may have a little additional expense that is unforeseen at this point but all in all I think this sled is gonna be bang for the buck! It sure has been fun!
So that's about it for now, sure appreciate everyone's input and help. We'll be sure to document our testing and share the results on the board.
Hope everyone gets through this crisis safely and uses this time to do all the things you haven't had time for, Go have some fun!!
-Paul

[mrrupp1]

Hi Paul, I hope you and your family are staying healthy. Since I own an auto repair shop I'm still working, but in my spare time we're trying to get the drag car ready for the track. Last year the last two races we notice it was starting to smoke, we only had 20 runs on it so we thought it just wasn't broke end yet. Getting the car ready for the last race of the season it was smoking so bad you couldn't see behind when it was just Idling. So we park it for the season. Last month we tore into the race car, first we ran compression test which is great 165 straight across the board, then we ran a leak down on each cylinder which was very good.
The engine we run is an old school Ford big block FE, which part on the head runner is in the intake. It was sucking oil from the bottom of the intake out of the lifter galley, put a different intake on it and cured the problem. Now there's just a few things we need to do the car and she should be ready for the track.
Bandimere speedway was supposed to open this weekend, but because of the lock down there playing it week by week.
My next Rupp build is a 75 Nitro Free Air. I'm building a super stock sled out of it. I think I have most of the parts to get her together. I pick up a nice fresh K440-2RS Kohler Free Air, and pick up another K440-2RS in pieces, but it all there. So I will start putting together after the drag racing done in the fall. My 76 Liquid nitro oval sled is ready to go.
I can't wait to here how your Nitro runs on the grass, it's going to be an animal.
Well I guess I'm done rambling, stay safe and healthy.
Take care.
Clint

[mrmotors]

Hi Clint, could you check your PM's please? Thanks, Mike

[midniterupper]

Hi Clint, glad to hear you're healthy during this time out session. It's nice that you keep your repair business going to help out folks during this time too.
That was an excellent call to swap out intakes on your race car, not everyone would think about the location of the runners. Great compression too, that thing has to have powerful tone to it. Good that you're on top of it and will have it ready for the dragstrip, please keep us informed on how you do with it. Nothing like being around those cars on race day!
I'm still waiting to send out my clutches for balancing, should be able to in another week. Meanwhile, I'm always staring at the sled to see what else I can do to tweak things. It's amazing to see how far we have come along with this project, the sled is so strong. I ended up chaining the rear suspension down to allow only 2" of travel as required by ISRA rules. By lowering the sled, I noticed an increase in preload for the two forward springs thereby reducing the ski pressure significantly. I can lift the front end off the ground easier so I'm thinking it may even lift the skis off the ground now on take off. Now with the sled being low to the ground it really looks cool! I gotta figure out how to send in some pics of the old girl for everyone to see. And to think only a year ago it was sitting in the corner of the shop in boxes
Well, take care to everyone now. It won't be long and we'll all be back to being abnormal!
Til next time, -Paul