1976 Nitro Grass Drag Set Ups

[Ruppsforever]

Also did you retime the motor after having Crank rebuilt ?? Or did you just replace outside bearings ?? I know from experience that when you replace with a different Crank it has to be retimed. No two cranks are pressed together the same.

[midniterupper]

Wow! Thanks guys! Great input and suggestions, good ideas to try and great things to remember too. What an awesome community we to belong to. I do have the old carbs set up with jetting that I used last season for testing, they are sitting on the bench ready to re-install for testing. I have the Boyesen reeds too, but like you say, let's try one change at a time. Finding the time is the hard part right now, but we'll make it happen.

Josh, thanks for your input too. I've been wondering about the actual timing as well since we rebuilt the crank. When I reassembled the motor back in spring, I coordinated my new timing marks at .100" BTDC vs. the old .087" location. But, I haven't performed the task of actually verifying the new timing with a light to be at the .100" mark so it would be worth checking it to make sure. I'll put that on the list, it's a great idea!

Now, for this weekend's race results. We did Good! There were a lot of really nice sleds at the track, a great turnout with a lot of racing enthusiasm. Weather was wet at first then dried out nicely. There was some new vintage iron there that had never been there before, some as far away as Pennsylvania and Indiana so it's great to see what folks are restoring and racing again. Nice to see some friends again from the old MSDRA gang that we haven't seen in 20+ years. Some are still racing, most are now just watching and helping but always great to spend time with them. Funny how we all have the grey haired effect now!

Anyway, we won 1st in Vintage Stock, 2nd in Vintage Improved and 2nd in Vintage Open. It was very close racing, pulling the best holeshot off the line is what made the wins for us. The sled launches so hard, fast and consistent. We have everyone beat for the first 60 feet as before, and then the other's power comes on and it's a scramble to the finish line. The other stocker's are not too much to handle right now, we finally are able to beat them - even with their new, younger and lighter drivers. So the Rupp power is shaking up their foundations, the Yammie boys are fit to be tied and the Polaris guys are switching to improved classes now by sending their motors out to Flannery for fixin. At $7K a pop, I think we'll do our own! But those motors do win races!!

There was one old 1977 polaris 440 f/a out there that was very respectable, he beat us in every race (except stock) as he was open mod. The sled was stripped as can be, nothing extra on it at all, barely even had a hood on it. The sled was Doug Flannery's own personal vintage racer so it had all the tricks done to it for sure and it was extremely fast! We clocked him in our grudge match at 74 mph, for a 440, that's pretty quick. The owner is an older racer too that also has a Magnum in his collection, we became friends quite quickly and had a blast beating up the Yammie dogs. I know we'll be working together soon to dial in this sled of ours, or at least have some fun playing with them.

In regards to our motor, the exhaust temps are at 1050/920 so we're not at it's worse. I think we'll straighten that out. The funny thing about it is, after researching my test records for the last 2 years, I decided to install my 280 mains (instead of the 190's) and close the adjuster screws. Instantly more power and an increase in exhaust temps. Strange that the temps went lower with the smaller main jets isn't it?

Clutching is another issue that needs to be solved. At the track, our peak rpm was reaching 8725 with the clutches slipping though we still won. After testing with the Arctic secondary, swapping springs and helixes, we found (this time) the 49 degree straight with a white spring at 16 pounds preload gave us 61 mph consistently. I installed a Polaris secondary with a 46/36 helix using a new polaris blue spring set at 17 pounds preload. That is giving us 63 mph consistently. We have 2 new springs coming in this week from Goodwin to try out for testing, I'll let you know how they work out.

The 96 studs seems to be the best combo for traction. Not to much digging at the finish line that sucks up horsepower, but a great holeshot! Real happy with the Chisels from Woody's.

So overall, it was a great weekend of racing. The Nitro is looking good, running consistent and strong. It's not it's best quite yet, I believe there is more power that can be put to the ground and we'll gain more top speed. We had so many people compliment the sled and say it is awesome to see it run against the mod sleds and still hold it's own. We have raced at that track for 2 1/2 years now, never a breakdown or no start at any of their races. What a great testament for the Rupp brand! Even the Race Director announced how great this sled is becoming, and nothing but shouts of praise when the trophies were handed to me.
Pretty cool!

Well, that's all for now. I gotta unload the trailer and get the shop ready for another week of testing. We have 2 weeks before our final race and we have lots to try out. Thanks for your help, thoughts and encouragement, it really means a lot to me. You guys are the greatest, wish you could come out and see this thing run. Hard to believe it's 46 years old, how awesome is that. Hope it makes Mickey proud!
Take care, chat soon
-Paul

[Ruppsforever]

Sounds to me the adjustable bowls aren't set right. Pop the plastic thing off the bowl screw and turn the screw all the way in with a screw driver. Then Put the plastic cap back on set to the lowest jet setting. Let me know how they were set.

[Ruppsforever]

Should of said turn the adjustable bowl so it is closed all the way. Take plastic cap off and see if screw turns in more. Put plastic cap back on with it turned all the way in. I bet this isn't set right.

[midniterupper]

Yep, great suggestion on the carb bowl screws. I pulled the carbs off last week and went through them thoroughly. Actually, one of the plastic covers for the adjuster screws must have fell off sometime so I popped the other one off and simply used the screw slot for calibrating.

I ended up closing both screws completely and installed larger main jets just to see how it affects the exhaust temperature. I was using 190 mains along with the adjuster screws set at 3/4 turn out. I installed 260 mains and I get about the same color on plugs and piston wash as the 190's and screw position but somehow we get 2 mph more. The exhaust temps have increased, not where we want them yet but it is an improvement. Pushing 1100+ degrees steady now on one, 1050's on the other side that has always been cold.

If I get a chance this week I will throw the original carbs back on with the same jetting to see if there is any difference in performance, power or temp.
Gotta get to work now, but Thanks again for your help!
Ridin' not Hidin'
-Paul

[Ruppsforever]

Those adjusters can be a real pain in the azz. If those O rings are shot you will have nothing but problems. I don't run bowls with those adjusters anymore. I use newer Mikuni carburetors. But yeah keep those adjusters all the way closed. Hopefully that solves your problem.

[midniterupper]

Funny how warped minds think alike! They are on the test list 2....

[midniterupper]

Well, time for another quick update from the Cow Pie 500. Lots of good things going on with the old Nitro.

After last week's races, we wanted to see if we could get back to the top speeds we were able to achieve last year and it has been quite a struggle. But, I think we may have finally made some gains there. In our testing session today we were able to reach 69 mph on our GPS tach. The thing has always proven accurate both here and at the track and our radar gun verifies the readings too. So we be on our way!

The lighter finishing rate on the new primary spring apparently agrees with the Xenoah's powerband. In all test runs today the primary clutch was nice and cool. We set up 3 Polaris secondaries with different rate springs and helix angles and they all performed differently but they all over-rev the motor. So, with that in mind, if we were to increase the arm weight we could possibly bring the rpm's down and really slam some forces into the shift. May have to try some heavier arms to see how that works out. So far the A2's at 48.6 grams are the magic combo.

Today's best run was using the Arctic secondary with an unknown red spring and an unknown helix angle but whatever it is, this sled likes it. I may have to see if there is a mold shop in our area that has a CMM to measure the ramp angle. It would be helpful to have some numbers for reference.

Exhaust temps are still improving, the PTO has been running at 1186 degrees average, MAG side still cold at the 800 range. At the races the Mag temps were in the low 920's so naturally I installed smaller mains to raise the temp right? Changed from a 280 main to a 250 and our temp dropped down to 790 degrees today, 130 degrees colder. We did good for such low temps on that side, not very much for cylinder contribution eh? I think I'll go back to the 280 main to bump up the temp and see what happens. We'll swap carbs after the races just to see what happens there too.

Yesterday I spent almost 8 hours dialing the timing in. I used the dial indicator and wire pointer method to establish TDC and also .100" BTDC for our reference marks, then used a timing light to verify the actual timing location at 6000 rpm. I had trouble getting the timing location to actually move even though I rotated the stator to each end of the slot. I ended up setting it at the most advanced reading I could get which was around the .070" indicator reading, I left it there for now.

Well that's about it for now, seems like we are on the right track. Thanks for all your thoughts and suggestions, what a great team effort!
-Paul

[Ruppsforever]

Anxious to hear how you did at the races today !!

[midniterupper]

Actually, the races are next weekend - October 23rd at Twisting Trails in Twin Lake Michigan. Come on out and support Team Red! Camp right at the track and have a great time. Racers come from near and far and bring sleds ranging from the youth 120's to 700 H.P. Outlaws. Of course there are some really awesome Vintage sleds (and racers!) participating too.

Two weeks ago there were 134 registered sleds for racing, it is always a good turnout. Check out their website at twisting trails grass racing on facebook for more information. I would love to see more Rupps at the track. At the last race there was a 10 year old girl racing her Rupp 340 American I think, I'm still learning all the Rupp models.

So, right now I'm enjoying the relief of our Nitro being it's best for the moment. Time to polish it up and make it look it's best also. Should be able to get my new hood from Bill, she'll really shine then. It'll be a new look for a new year, can't wait.

Gotta run along now, Take care now,
-Paul

[Ruppsforever]

Oops !! My bad !! Could of swore you said you have races 3 weeks in a row. Yeah don't touch anything on that sled !! LOL !! Another week of suspense here !!

[midniterupper]

No, you were right. we did have 3 races scheduled but this weekend's race in Lansing got cancelled.

Just polishing the hood and seat for this week. Everything is ready, Thanks again for your help!
-Paul

[midniterupper]

Well, another grass racing season is over here in Michigan. It was an interesting season overall for us and quite a long one too. It actually started for us back in July at our first sled show then followed by another show in August. One week later was our first race of the season at Snow Motion in 91 degree heat, not real fun in those conditions. Then we raced in Twisting Trails 3 race series near Muskegon, it's always fun there but expect rain and sloppy conditions. For some reason, it just always seems to rain at that track. But everyone else is racing in the same conditions so its all fair. If those $100K outlaws can run in mud so can we!

So, now for our race results. Not the best but not the worst either. First off, this race was packed! There were over 150+ total entries, more Vintage sleds than ever. That was the largest turnout they have ever had. Some from as far away as Indiana, Ohio and Pennsylvania. We had over 20 Vintage sleds racing including other Rupps, Merc Sno-Twisters and Sno-Jets so we were in great company. All the Vintage sleds ended up parking in our hot pit area too, it looked like a scene from the 70's! It was awesome to be there and see the old iron racing together. Of course, most of the pilots are vintage also but great guys (and gals!).

In Vintage Stock, there were 8 sleds total so at least 2 heats in that class. We won 1st in Stock as the sled wasn't it's best but it really accelerated hard and beat everyone.

However, things went south from there very quickly. The sled developed a terrible stumble (not really an engine bog) just after launch. I mean it would wheelie hard off the line then slam back down - stumble - then pick back up, wheelie again and just about gun the mod sleds down at the finish line. It just got worse and worse the more we ran the sled, stumbling on it's face. So unlike for this sled. Many people came by asking what was wrong and what could they do to help. Really disappointing and frustrating but that's racing isn't it? Not sure where we placed in the improved and open mod classes but it was bad for us.

The good news is, even with the stumbling, the sled clocked on radar at the track at 69 mph. I'm sure if we had a good run we would've clocked a 70 mph run. At the beginning or yesterday's race, the track was great. The clay starting line was packed and rolled hard but then it rained and it became a mud bog.

I haven't checked the sled out yet to see what the problem is but I'm thinking it may be a broken secondary spring. I should've brought more clutches and parts with me to the track to swap out in case of problems but that current set up by far left the other set ups in the dust, way slower so I didn't think we would use them at the track. Lesson learned!

We will continue our testing while we can around here but we do have to get ready for winter. I still need to power wash all the clay and slime off the sled and then see what is going on with it. It's staying warm in the shop and certainly won't be neglected. I made a Christmas list for it already, writing everything down while it's still fresh. I'll be getting ahold of Mr. Weaver very soon to get new drivers. This week we will be getting our new hood from Bill, icing on the cake for next year. I can't wait!

I did receive the official title as the oldest (active) racer at the track beating the 61 year old who previously owned the title. He is one of the Yammie boys that always gives us a good run, never knowing who would win. Lately we always beat him, even with a 16 year old driver now. He gave up!

Okay, better run along now. Just wanted to give an update. Out of 9 entries this year we brought home 2 paybacks and 7 trophies so not bad. Hit the 69 mph mark repeatedly. Made a lot of great friends who can't give up sled drag racing either. Overall it has been another successful season, Thanks again to our great community too!

Take care now,
-Paul

[midniterupper]

Okay, it's time for another quick update from Nitro Alley. We actually have an old road sign hanging in our shop now that says that! I had the Nitro sitting in our driveway a few weeks ago, drying on the dolly when a road commission truck drove by then stopped and backed up to our driveway. A guy got out and said he spotted our old Nitro and just had to stop and take a look. We quickly became friends, he has several vintage sleds that he has restored. They looked great! He also came out with his daughter to our races a week ago and fell in love with vintage sled racing. He and his daughter will be racing with us next year. But anyway, he makes road signs for the county and has already dropped 2 off that says Nitro Alley (like Gasoline Alley) and another one that says "Yield to Rupps". They're both really cool, even in Rupp red! I told him he should sell them on line, they would be hot sellers!

Now back to the sled. We verified the bog we experienced at the races was due to the helix. Tested the spring individually from the helix and that seems to be working fine when compared to using other springs, both new and used. However, when we installed the unknown helix, the bog returned. Strange thing about it though, we can always hit 69 mph using that helix even with the bog. The acceleration is awesome once it hits, the sled's powerband seems to love it! We ran 4 tests that day with different set ups and nothing could repeat the 69 mph. 51 to 63 mph were the test results of that day, using 2 cat set ups and 2 polaris set ups. After doing some research, I found that the "unknown" helix angle may actually be a radius cut, not a dual angle cut. Never seen one before, but we may have one on our hands. If so, they are truly effective. Just have to figure out how they measure them.

Anyways, two days later we made a couple more tests using some cat helixes I picked up from the salvage yard. First was a common 53 degree angle, only 59 mph with that. Then installed a 56/44 helix and the sled did great holeshots and good acceleration up to half track then the sled just kinda planes out. Just the opposite when using the unknown angled helix, so in a way, we are making progress there. The sled topped out at 65 mph repeatedly so with that helix, its a consistent set up. The fastest of this year's stock class sleds reached only 64 so with a good light and a good holeshot, it should be a winner in the Stock class. But as you all know, we won't be content with that now will we??

Sometime this week I would like to try testing with the cat 57/50 helix again, this time using the new red spring and also the Polaris blue spring just to compare the difference. The objective would be trying to load the motor a little more out of the hole and maybe the 50 degree finish angle would improve the mid-track acceleration over the 44 degree, increasing our top speed. Never know we until we try right?

So, I think my plan for attack regarding next year's races will be to install new track drivers, test with 19/39 gearing, play with a higher rate primary spring to see if we can lighten the engine load where that bog affects the launch. Those Thundershift arms we bought a while ago might come in handy for addressing that issue as well. That MAG cylinder temp mystery still needs to be solved also. The PTO is steadily 1150's now but the Mag is still only 800's. Maybe if we can get those equalized we will get the power to hit the 70's!

Until the next time, Stay Red My Friends!
-Paul

[mutt]

When you do a real big difference in helix angles 56/44 with the lower numbers. Spring required for the 56 not to slip and the low spring needed for a 44, its pushing very hard on the 44 if the 56 is working. Wont see much spring difference if its like 65/50 as a 50 spring (yellow) will work with a larger number. See if you can hunt up a helix shim kit. It will lower the start angle or shorten the time your on it and not effect the end angle for more tunning options

[midniterupper]

Well, my gosh it's already Christmas Eve here! Where did the time go? If we could race as fast as the time seems to be flying by we'd be in the Open Mod Winner's Circle! Wow, what a reminder that even the newer sleds are somehow turning into Vintage sleds. Another model year older, my '76 Nitro is now 46 years old and runs as good if not better than new. What a testament to the engineering and design of the Rupp Snowmobiles!

Mutt, I want to thank you for your suggestions to help solve the shifting out issue. It took me a while to comprehend your concept but I think I'm gaining on it now. I will get or make some shims for the secondary helix to help get past the area causing trouble. I noticed in Aaen's book on page 66 that cat offered a 57/50 helix in 2 versions: one with a .100" thicker at the base, one as standard with a flat. I also noticed cat offered some radical helixes such as 62/54, 70/35, 77/32 ect. Pretty wild!

Josh has also helped out too by arranging a ton of secondary springs to fall into the shop. Can't wait to test again! Lots of races this coming season, should be some fast action on the ice.

Well, it's Christmas eve so I better go play Santa. Take care to everyone, Merry Christmas and have a very Happy New Year too!
Keep you posted as we make progress, Thanks again for reading!
Take care,
-Paul

[midniterupper]

Let's all give Josh a standing ovation for an outstanding performance and Rupp representation at the ice races held in Wisconsin this past weekend! He kicked some hot sled's butts and taught them a lesson! Never underestimate a sleeping Bear

Thanks Josh for all your hard work and testing. Please tell us more about your weekend!

[mrrupp1]

Great job Josh, thank for keeping Rupps in the lime light. Clint

[Ruppsforever]

Thanks Paul and Clint !! Darth was running very well !! Might of been the best it ever ran !! 2nd place in Mod Vintage 341-440. My glasses fogged up and I couldn't see anything. I was last off the line and still managed a 2nd to the Ski Doo Blizzard. Mod Vintage 1st place. Improved 440 1st place. Managed to win while blowing motor up. Beat the Ski Doo. Motor went south probably 75 feet before the finish line. They were all catching me but I still won by 2 sled lengths. Blew the head gasket and destroyed right cylinder and piston. I had entered 5 more classes but Darth was done. Was a great day of racing and was nice to get the feel back after a 7 year break !! Darth will be back next year with a vengeance !!

[upmagnum]

Great job Josh. About time eh! Hope Darth is feeling better soon.