1976 Nitro Grass Drag Set Ups

[midniterupper]

Good evening to all our fellow Ruppers! It's a beautiful evening outside here tonight, nothing moving around here except a fox in the cow pasture. Rather entertaining for the cows and for me, this Corvo 19 virus has certainly quieted things down for everyone it seems. Oh well, good time to work on the Nitro in isolation.
This update won't take long. I sent out both clutches to get balanced at Cascade Clutch & Performance in Bend Oregon. I spoke with Dave the owner, he sounds like a very knowledgeable man who cares about each clutch that comes through his door. Looking forward to seeing the reports and testing the difference. I guess I never thought about the secondary clutch spinning 2000 rpm higher than the primary when in overdrive. That's over 10,000 rpm on my sled, incredible. Balancing the secondary should smooth things out a bit also. I will let you know when they come back. Check out their website sometime, pretty impressive.
While the sled is in limbo I thought I should look at the front skis and spindles. I put the sled on the lift and noticed the play in the skis was rather excessive so I pulled the left side assembly apart to take a look. The tube bushings are worn badly but now both sides are all being replaced thanks to Bill Stull. Incredible talent and skill that man has! He is a great resource for every Rupp head.
My skis turned out to be in bad shape also. They have been welded and re-welded and rebuilt once upon a time but they have several holes worn through so they will need a lot of attention to bring them back into shape. Not sure if there are any floating around out there for sale....
I did some research at the ISR website regarding skis on stock Vintage drag sleds and it looks like we can now race with plastic skis as replacements for our steel skis. For ovals we can't but for ice/grass drags they are allowed according to the 2019/2020 rules, which will be helpful I think. The coefficient of plastics is almost half compared to steel. Of course if they are in the air it shouldn't play a factor right?
With that in mind, I decided to modify a set of plastic skis left over from our 2001 Skidoo's. Had to mill out a little in the front of the ski to accommodate the forward spring mount and then make a bracket for the rear too. Not quite done yet but maybe tomorrow, looks promising.
I also want to see if I can remove one leaf from the ski springs as an attempt to lighten and lower the front of the sled a little bit. I weighed the stock ski and spring assembly; they weigh 18 pounds per side. Seems heavy to me, I will weigh the plastic set when I'm done with it just to see.
That's my latest, might jump into doing the bodywork on it now too. Can't just sit around doing nothing!
So, Take care all, Normality is getting closer!

[Ruppsforever]

Very interesting. I have always wanted to get my clutches balanced and sheaves machined but never did it. I should do this now. I plan on drag racing next winter at one event. It has been 4 years !! My 440 spins 9800 so with what your saying then my secondary is spinning almost 12,000 !! Any weight you can safely and legally remove off the Nitro will benefit. Even if your skis are off the ground that is still weight being carried. Them Rupp skis are heavy as hell. Get rid of them if you are allowed to. Every 20 pounds you remove from the sled will be 1/10th of a second quicker in 500 feet. Also for every pound of rotating weight that can be removed it equals removing 7 pounds of stationary weight.

[mrrupp1]

Hi Paul, that’s one thing I’ve never done is have the clutches balanced and trued up. I’m a firm believer that if you make everything as close to perfect as you can, you’ll have winning combination. Losing the stock skis is one the best weight reductions you can do, they weigh a ton. It’s to bad you have to run the stock muffler, they weigh a ton to. I can’t wait to here how she runs when you get all the little pain in the butt things fixed.
I hope you and your family are staying healthy. Everything is good here so far. The local drag track is starting to let a limited number of cars test and tune. So hopefully will get the Mustang on the track in the next few weeks.
Take care and stay healthy. Clint

[midniterupper]

Hey Clint, Great to hear from you! Glad to hear you and yours are doing well thru this crisis, appears things are loosening up a bit around the country. Sure has been tough on a lot of good folks, sounds like it may take a while but we'll all get thru this. I guess we are all living history right now, something to tell our grandkids about for sure!
I'm glad to hear you're getting ready for testing your race car, that'll be a good relief after all this mess eh? Can't wait to hear how she runs now that you have the gushing oil consumption figured out. Be sure to keep us informed on how it's going up there.
I'm still waiting to hear back from Dave at Cascade Clutch. We've spoke a couple of times now, I needed to make sure they arrived at his shop. It was good to hear that they made it safe and sound, can't wait to get them back home though. Got our testing lane just about done now so we can begin as soon as I finish things up on the sled.
I have "version 1.0" of my plastic ski conversion done but I think I need to make a better support for the length of the ski so I will have to make the 1.1 version. I have lots of ideas to explore so I will get some pictures of them as they get developed.
Last week I met a guy that is getting rid of his old sled collection due to health reasons. I went over to his house to see what he had as he knew we have the Nitro and said he had parts I may be interested in. He had a bunch of odd stuff for old sleds laying around and in the back of his shed was 2 Americans in disarray, not complete but he had a lot of parts for them. I have never fooled around with any Rupp model other than the Nitro but it looked like some parts are interchangeable like the idlers, springs and skis. For $50.00 I could have them both he said so I loaded them up and now have them home in the shop.
The engines have a tag on them that say TR440-3. One engine looks complete, the other is missing the coil and carb but they both roll over. Tracks look good, nice hoods with windshields, one has a complete seat that looks original. Like I said I don't know much about them, I just wanted some parts off them. If anyone out there could use the chassis, engines and body parts please let me know and we'll work out a great deal.
Well, that's about it for now. Can't wait for the clutches to come back and start testing again.
Take care now Clint, it won't be long and we'll all be breathing racing fuel fumes again soon!
Til next time, -Paul

[midniterupper]

I just realized I never addressed Ruppsforever's last reply, sorry about that. You do bring up an interesting fact about your secondary spinning at 12K, that baby is cooking! Figure for each second that's 200 complete spins, I can't comprehend that much mass and size being controlled. It would be scary to watch!
Also, thanks for the stats on losing weight, certainly helps! I haven't quite finished the plastic ski project yet but I did weigh the stock ski set up verses the plastic (minus 1 spring leaf on each side) and it looks like will be about 5-6 pounds lighter overall. I will have to weigh them out when completed and let you know. I also want to try an aluminum ski for a comparison weight too, maybe next month we'll do that.
Dave from Cascade called this afternoon, both clutches are done and being shipped home today - I can't wait! The charge for both came to $230.00 plus shipping, not too at all. I would certainly recommend their services to anyone. I'll be sure to let you know the difference once we begin testing next week.
Just for grins & giggles, I'm going to fabricate a couple of sleeves and the stingers Rupp recommended in their performance upgrades for the Nitros. I'll match the dimensions exactly and make the sleeves to slip over the stingers just for testing. I'd like to see the actual difference in performance. If it's significant, I'll pick up a couple of the ISR silencers now required at the races. This mod would move me into the Improved class but there really aren't too many stockers running around here anyway. I wanted to tweak this Nitro out for performance as a stocker that will beat most improvers if at all possible. Based on our radar readings, we will do just that! And we really haven't even tweaked her out yet! Oh boy, So much fun!!!
Okay, Gotta go now. Good luck to all!

[Ruppsforever]

So what exactly did they do to your clutches ?? Did he true up the sheaves too ?? Or just balance them ??

[midniterupper]

Well, before I sent the clutches out to Cascade I deburred all casting lines and edges blending them smooth. Not sure if it matters at all but I figured it wouldn't hurt, maybe create less wind drag or something.
I have a 30 mm taper plug for the lathe so I indicated that in to the best position then placed the primary on the lathe and trammed that in. I took a couple of light cuts on the O.D.'s to true them up. They really were not too far off actually, sure dressed up the finish. I made a fixture for the secondary too and pretty much repeated the same procedure on the O.D. as well.
The faces on both trammed in with a .004"-.009" TIR so I barely touched those surfaces. Of course, I replaced all bushings on the clutches before any lathe work to help eliminate excessive runout.
Cascade sends out a component balance report with each clutch they balance, sounds like they do the inners and outers individually then again as an assembly. I will let you know what the report says when I get them back this coming week. Can't wait to see if there is a noticeable difference. Remember I bought both those clutches used from Mickey's Snowmobile Salvage so I had no idea of their condition other than they looked pertty. If this set up works I wouldn't mind picking up another set for testing and do the same process. I guess it would save some time...
I did finish up the new version of the plastic ski set up, however I am a little disappointed in the weight savings. Actually, the stock steel ski without the spring is 1.2 pounds lighter than my Skidoo skis with the aluminum support brackets. The weight difference is made up in a way due to removing on leaf on each side but hopefully the coefficient of plastic verse steel will make up for it so we'll see. Easy enough to swap out if need be, sounds like it may justify another testing session.
Been thinking of reduced resistance bearings for the driveline and maybe slightly oversized rear idlers. Theory being the track would "float" over the sliderails and have more of a freewheeling effect increasing efficiency. If we can't make more horsepower we might as well help reduce their load!
Take care now,
-Paul

[midniterupper]

Well my clutches came in today from Cascade, they look really nice. He must vapor blast them to clean them up, look like new. He apparently drills different size holes at different depths to balance them in, all machining looks very precise.
I received 2 Dynamic Balancing Test Certificates, one for each clutch. The sheet defines what type of clutch is being balanced along with the total weight. It has balancing data ranging from 1500 rpm to 8000 rpm which is where I told him my target rpm is. It gives a report for each side of the clutch stating how much it is out of balance along with where it's out of balance in degrees. My P-85 primary was out of balance on the inner by 1.934 grams and the outer by 3.129 grams, both rejected by the machine's standards. The Arctic Reverse secondary was out by 2.023 gr. on the inner and 2.360 grams on the outer. Again the values were considered rejected.
Then you get a corrected report with the acceptable values complete with hole diameters, depth and angle values too. The primary is now balanced to within .071 grams max and the secondary is at .1409 grams max.
A very interesting chart was included with the reports that emphasizes just what kind of force 7 grams of unbalance condition can create. There is a formula but basically at 8000 rpm, 7 grams generates 112 pounds of force! That's a lot eh?

I mounted the clutches and fired up the sled as normal, letting it warm up of course. On the stand I revved up to my normal 7000-7500 rpm and she is just smooooooth! It definetly made a difference in the drive train, at least while on the stand. Hopefully I will get a chance to resume testing this week.
Until then, keep you posted!
-Paul

[Ruppsforever]

May 13, 2020 17:55:21 GMT -6 midniterupper said:

Well my clutches came in today from Cascade, they look really nice. He must vapor blast them to clean them up, look like new. He apparently drills different size holes at different depths to balance them in, all machining looks very precise.
I received 2 Dynamic Balancing Test Certificates, one for each clutch. The sheet defines what type of clutch is being balanced along with the total weight. It has balancing data ranging from 1500 rpm to 8000 rpm which is where I told him my target rpm is. It gives a report for each side of the clutch stating how much it is out of balance along with where it's out of balance in degrees. My P-85 primary was out of balance on the inner by 1.934 grams and the outer by 3.129 grams, both rejected by the machine's standards. The Arctic Reverse secondary was out by 2.023 gr. on the inner and 2.360 grams on the outer. Again the values were considered rejected.
Then you get a corrected report with the acceptable values complete with hole diameters, depth and angle values too. The primary is now balanced to within .071 grams max and the secondary is at .1409 grams max.
A very interesting chart was included with the reports that emphasizes just what kind of force 7 grams of unbalance condition can create. There is a formula but basically at 8000 rpm, 7 grams generates 112 pounds of force! That's a lot eh?

I mounted the clutches and fired up the sled as normal, letting it warm up of course. On the stand I revved up to my normal 7000-7500 rpm and she is just smooooooth! It definetly made a difference in the drive train, at least while on the stand. Hopefully I will get a chance to resume testing this week.
Until then, keep you posted!
-Paul

NICE !! Thanks for the update and info !!

[midniterupper]

I had a opportunity to do some testing the last couple of days. Wasn't sure how the sled would handle with the plastic skis and different track since last testing on grass.
The first pass was amazing! Smooth engagement and take off, no track ratcheting, no studs slamming, nice and straight, just perfect. Felt the speed increasing steadily, very nice and smooth pass. Could not believe the difference, like a brand new sled!
Okay, now for the stats. RPM stayed climbed to 7400 then stayed at 7900. Engaging at 5000, topped out at 66 mph. I kept everything the same that we had for last fall when we topped out at 66 mph, so it stayed consistent.

I had 14 pounds preload on the secondary, I dropped that down to 10 pounds but I wanted 12. Can't get that using the yellow arctic spring so I settled for 10 pounds for now. I have the Arctic white spring to try later to see where that preload goes.
I had A-2 (48.8gr.) arms in the primary which seemed to heavy (but effective!) so I swapped to the Polaris 10MW (44.7gr.)arms to see what they may do.

The clutch engaged at 4800 rpm so a slight drop there. The sled launched very nicely, for the first time it did a wheelie off the line! Ran smooth the entire pass, rpm's climbed to 7400 then 7900 and slammed down to 7600. Big notice there, achieved 65mph with that set up.
My exhaust temps were low, PTO @1197 degrees and the MAG @1049 degrees for some reason. I have 290 mains in her now, may have to try 280's but I will wait until I can do more testing on that. Too much fuel at this point is better than too little right?
So after the second test run I changed the primary weights to some J-1 non-bushed weights that I picked up from some guy on line. They weigh 44.4 grams, the profile looked identical to the 10MW. Wasn't sure about them since they didn't look much different. Put them in and fired up the sled on the stand.
Engages at 6200 rpm! Not sure how they will work out but it's worth a try. Max rpm's seem to be about the same as the MW's, about 7400 on the stand. Gonna be interesting.
I'm tied up for the next couple of days so I won't be able to test at all but the sled is ready to try. I'll leave it there for now.
I created a new testing form that is working out great. I'll see if I can get a copy of it here on the forum for you all to share, maybe you guys have one too that could be even better. Sure helps to document!
That's about it for now, hope you all are getting your stuff done too.
Take care now, until the next time......
-Paul

[mrrupp1]

Hi Paul, sorry it's been so long since I've been on. I have been reading all your posts. You shouldn't have any problem selling those TR motor's the sleds they came in are getting restored all over. I run modified Rupp pipes on my oval sled and they work great. Sounds like you are getting closer to speed you need to be king. I just picked up something red, but it's not a Rupp. A rancher friend of mine called me up and ask if I was still into old snowmobile's ( well we all know the answer to that ). I ask him what they were ? ( NO Rupps ) He said three old junky Yamaha's, so I thought what the hell, I know some guy's that love the darn things. When we got over there to pick them up behind his shop set a IH TD-6 track dozer with a V blade on it. I told him that out of everything I would love to own that. He said take it home. I thought he was kidding he said nope you want it's yours no charge. He's even going to deliver it. I love anything with tracks. My family has a IH TD14 dozer that my dad did all our dirt work with while building our house, he even dug our basement with it. Sorry I got sidetracked from Rupps. It does sound like your a little rich on your jetting, but like you said better rich then lean. Were at 80000 feet where most our races are and I run 200 mains in my mod piped nitro. I don't have a exhaust temp gauge so I don't know what my exhaust temp on the cylinders are. Plugs are nice and brown and she screams.
Good luck with your testing I'm sure you'll make her fast. Take care. Clint

[midniterupper]

Hey Clint, That is so Cool! IH Red around here is pretty nice too, glad you got a dozer out of the deal. Not many folks can say they got one for free too, congratulations. Great that it has a v-blade, not many of those around either.
Sure was meant to be yours for sure.
And yes, we have a great baseline to begin our testing now. Last year we started out at a top speed of 51 mph in 500'. 66 mph is way better, now we can wake up those ponies and put them to work! Keep you posted on our progress, Take care now, good luck in your tuning!

[mrrupp1]

We should have the Mustang on the track in the next week or two . I will let you know how she does. Our best time to date is 11.58 @ 118mph. Will see if we can match that or hopefully do better. Talk to you soon. Clint

[midniterupper]

Alright, finally time to get caught up with some of the testing we have been doing and the results. Intermittent testing but interesting nevertheless.
Since the last test using the Polaris 10MW's I installed the Polaris non-bushed J-1 weights (44.4 gr.)

With those weights the engagement went up to 6200 rpm, max rpm's @7700. Top speed only 60 mph so we lost there. Engine RPM did not increase even though the weights are 4.4 grams lighter, in fact, a drop of 100+ rpm's.
Installed the Pol P-1 non-bushed weights (44.3 gr.) next. Engagement also at 6200, max rpm's @7600. Top speed of only 58 mph. Again, lighter weight equated to 100 rpm less and 2 mph less.

Next test was to install the Arctic arms that I have 2 sets of, arm # 502-44.5 (44.5 gr.) with the idea of performing a comparison test. I left one set of weights at 44.5 grams and ground the other set down to 42.8 grams.
With the first set the engagement was at 5500 rpm, max rpm's @7500 climbing to 7800. Top speed back at 60 mph.

Testing using the lighter set of Arctic weights, same engagement at 5500 rpm, max rpm's @7300 climbing to 7600. Top speed down to 58 mph. With this set installed, the sled just felt slow and out of the power band. Not high enough R's to be into it actually, rather flat.

My jetting temps were also rather cold for these tests too so I'm gonna drop down to help bring them into a better heat range. I picked up some semi-synthetic oil today (dealers finally opened!!) and some C-12 also. We'll play with fuels later, I want to focus on improving the efficiency of the clutching first before we seek more power. Nice to have the stuff on hand though for when we are ready to play.

So what's weird about the testing results is that for some reason I'm still shy on rpm's for the power band. We have improved for sure, getting an accurate digital tach was a step in the right direction. At least I know we are really at 7800 which ain't bad but I would like to see what results we get at 8300 rpm.

The other thing that appears to be happening is that as we lighten our primary weights, we are losing rpm and effective overall speed. Our example is Arctic arms @42.8 grams = 7600rpm, 58 mph.

Comet A-2 arms @ 48.8 grams = 7800rpm, 66 mph.
Any ideas on what would cause this and remedies to try?

More testing with some heavier weights just to see what happens.
Chat soon, -Paul

[mrmotors]

Maybe a goofy idea, got a GoPro Camera? Leave the hood off and put the camera in a location to watch both clutches. See where the belts are going under load, if they are going all the way up and all the way down. Being rich may also be a factor in the RPM being down, not quite singin like a Singer sewing machine!!

[mrrupp1]

Hi Paul, I have heard of guys using weights as heavy as 58 grams in Rupp liquid drag sleds, and do very well. I have never used anything heavier then 48 gram, but I’ve never built a Rupp drag sled
just oval stuff. I think you could be a little rich, but it should still turn 8000 grand. One question what helix are you using, I found that my Rupp liquids did not like to steep of a ramp like 53 degrees it would not pull the Rs like it should. I ended up with a 44 which works pretty good and a white spring. I would like to try something in the 30s. They came stock with a 30 helix and worked pretty good. My sled stays around 8300 to 8400, the only mod is I’m using mod Rupp pipes and no cans. Xenoahs like RPM so I know there in there, and I’m sure you’ll find them. Keep us posted. Clint

[Ruppsforever]

If I were you I would put the fastest set you ever had back in it. Then do nothing but change the secondary springs and helixes and spring tension. I believe your problem is too steep of helix too.

[midniterupper]

Happy Memorial Day to all and Thank You to our Vets on this special day!
Thanks also to those who have continued to share their ideas and wisdom regarding this old Rupp, she is coming along nicely I must say. The go pro idea does sound fascinating doesn't it? It would be cool to watch the actual shift out under load but my test track isn't real smooth and it might bounce around. May have to try it though.

I think I will install a set of Comet A-25 arms in the primary next. They weigh 49.5 grams and are also notched. I have them on order at MFG supply but they won't arrive until the end of the week. Meanwhile I put the A-2 arms back in with a little tuck grind on them. I have only tried lighter weights so far to get my r's up but those all sacrificed speed and I didn't really get any higher rpm. I have also ordered Aaen's purple primary spring that has a little higher rate (136#/150#/320#) than the Polaris almond/gold (96#/150#/270#). 40 pounds more spring rate and 50 pounds more full shift load so that may help keep the motor singing a little higher. My theory being more arm weight may be compensated for by using a higher spring rate to make the motor work a little harder, keeping the rpm's higher. Not sure but worth a try!

Today I am fooling around with my secondary clutch. Trying all 6 hole positions using the yellow spring (92#)and documenting the preload tensions, then doing the same with the white spring (58#). I will get the positions closest to 12 pounds preload with each and then do a test pass to note any difference. I am also going to install a 51/49 degree progressive helix (verses 53 degree) that I picked up last fall at the salvage yard to see how that shifts out. We may be heading in the right direction using a prog cut with less angle, we will see!

Take care all!

That's it for now, until the next pass.......
-Paul

[Ruppsforever]

Have you ever thought about trying stock gearing ?? 19 / 35 ? Bad gearing can have adverse effects on clutching too. Just a thought. I think you are running 19 / 39 ??

[midniterupper]

You know, that's a good point. The sled came with a 19/39 (2.05 ratio) so I didn't know any better. When I changed over to the 13 wide chain and gears, I installed a 20 tooth top gear because that's all they had at the salvage yard at the time. That changes my ratio to 1.95. I really haven't noticed much difference between the two.

Going to the 19/35 will give me a 1.84 ratio which intrigues me. In the old days with our skidoo's, we always wanted to get as close to a 2.0 ratio according to the performance classes they held so a 1.84 is very interesting, especially coming from the factory. I will pick up a set of those gears along with a chain too. Would you happen to know how many links are in that set up? That would save me some time trying to figure that out.

I did drop down one size on my main jets. They were 280's which seemed to give a good temp for the winter runs, at least for starters. I installed 270's which seem kinda small but so far the temps have improved though I haven't made a pass with them in yet. The plugs look very nice and the response and idle tone have both improved. The thing sounds great!

We are stretching fences this week but in between I should be able to get in the tests for the secondary until the new weights come in. Looking forward to seeing the results! Springs and helix time, then we can move onto fuels and a head cut. Of course, the gearing experiments will have to sneak in there somewhere too.

The testing continues.....