1976 Nitro Grass Drag Set Ups

[Ruppsforever]

So how wet were the edge of the pistons ?? You look at the piston where the transfer ports are. The outside edge you want a quarter inch of wash. The only accurate way to check it is after a full throttle run. Could you maybe have a leaky needle and seat ?? If you can't seem to figure the problem out maybe just swap those from carb to carb. Is the choke closing all the way ?? We lucked out with our timing system. It wasn't expensive and they only made it for a few years before they quit making them. Thunder shift weights will work with any sled. I've never played with them. If you need more wheels let me know. I doubt only 2 will do anything.

[midniterupper]

Thanks for your reply Josh, very good questions and suggestions. I was only able to see through the spark plug hole of course so I didn't have a real good view but the top of the pistons appeared to be a consistent wet brownish with the dome still being the original Wiseco color and kinda dry looking compared to around the transfers. The transfer area looks more dark and rather wet and follows the circumference of the piston. Would that indicate too rich?
Looks like a good even flow pattern and well lubricated. The piston skirts looked fresh and not worn in any way too. The 32:1 ratio keeps everything slippery! Seems to cut down on the mosquito's around here too.

Good idea about the needle and seat, so far I haven't had any flooding issues while it sits so I didn't consider that. If the problem continues I will try swapping them, good idea! I did verify and re verify the choke cables as I have had that issue in the past with other sleds. I like to maintain 1/8" freeplay in those cables. I also used my carburetor Uni-Sync and synchronized the carbs at idle and around 2,000 rpm just to ensure both are doing they're jobs equally. Sort of a cylinder contribution test.

We used to have a Port-A Tree 2 lane system that we bought back in 2002. We kept it until 2012 and sold it because we never used it anymore (then came Retirement!) sure could use it now! Good thing you held onto yours, we'll have to decide on one. The GPS system sounds interesting, maybe more affordable too.

The Thundershift kit could be fun to play with also, I like the concept of being able to shift the weight around on the arm itself. I have no experience with them, just heard they can be effective once you get them dialed in. Must be a secret....

Well, it's been really hot here for the last few days so the only time I can test is in the early morning and other chores are getting in the way. Can't spend as much time as I would like to on the sled (who does right??) but I may be able to stay cool in the shop and get these wheel kits mounted. I really haven't investigated the installation yet but I'm looking forward to using them. (Thanks again Clint!) I will see how many would optimize the set up and keep you posted for sure. The 2 idlers located near the very tip of the rails don't seem to have much pressure on them so I'm not sure if I need to replace those but we'll see. Anything to help reduce that power robbing friction. Thanks again for your offer!

Got my Grandson here to help out for the weekend so we ought to be able to make at least one test run in the morning. This will tell us if the float level on the mag side was off affecting the exhaust temp difference. Maybe we'll throw in some funny fuel to see what that does.

Have a great weekend!

Chat soon,
-Paul

[mrrupp1]

Hi Paul, I can't wait to here how the bogey wheels do. I put them by one of my spare suspension and it looked like 3 aside would work good that's why I sent 6. I have plenty more if you need them. Sound like you and Josh are getting things figure out, if it was a drag car I could offer some insight, but drag racing a snowmobile is out of my league. I will sit back and let the experts do there stuff. Clint

[midniterupper]

Thank Clint, great input as always! You are certainly no slouch when it comes to racing a sled or a car for that matter, you have a wealth of knowledge that you freely share. I know I value your help and opinion on these forums and I know others do too so please don't cut yourself short, you have helped many of us.
I wasn't sure how many wheels to add to the rear suspension. I want to locate them at the highest pressure points to reduce the friction so I think 6 is a good place to start at least to establish their placement. In the back of my mind I keep hearing "bearings cost horsepower to turn" but I don't know where the balance point is. I do know if the hyfax is rubbing on the track cleats while in dirt, that's sucking up horsepower also. I gotta believe that we can successfully reduce the rolling resistance in that area. We'll have to see what the magic combination consists of!

Okay, it's 6:30 am now, I think it's time to wake the Forest and get ready for testing. You all take care now and get out and play. Clint, good luck this weekend with your car, let us know your progress up there. Josh, Thanks again for your help too!

Until later,
-Paul

[Ruppsforever]

I wish Dale would chime in. When he got into grass racing he added a pile of wheels to his suspension. He would be a huge help to you too !! Are your throttle valves opening the same amount ?? I've never used a carburetor synchronizer I just made sure they were open the same at idle and open all the way at the same time. Good luck testing !!

[mutt]

Jun 20, 2020 4:42:42 GMT -6 midniterupper said:

Thank Clint, great input as always! You are certainly no slouch when it comes to racing a sled or a car for that matter, you have a wealth of knowledge that you freely share. I know I value your help and opinion on these forums and I know others do too so please don't cut yourself short, you have helped many of us.
I wasn't sure how many wheels to add to the rear suspension. I want to locate them at the highest pressure points to reduce the friction so I think 6 is a good place to start at least to establish their placement. In the back of my mind I keep hearing "bearings cost horsepower to turn" but I don't know where the balance point is. I do know if the hyfax is rubbing on the track cleats while in dirt, that's sucking up horsepower also. I gotta believe that we can successfully reduce the rolling resistance in that area. We'll have to see what the magic combination consists of!

Okay, it's 6:30 am now, I think it's time to wake the Forest and get ready for testing. You all take care now and get out and play. Clint, good luck this weekend with your car, let us know your progress up there. Josh, Thanks again for your help too!

Until later,
-Paul

They do cost in snow ,its offset with no lube on grass. Just a guess on the balance point, but a Wahl Bros.grass suspension has 20 wheels in it. Little is known on my sled history only has some interesting additions has 4 aftermarket or maybe the Rupp/mount? wheels added at some time. Still has heavy wear on the slides at the curve and just in front of the rear idler. Go old school on the lube dish soap/water mixture squirted on the clips just before running.  

[midniterupper]

Hey, Thanks guys for your input and help! Great ideas and suggestions, very helpful for sure.
We were able to do some testing this morning, it all turned out good. The exhaust temps improved, reading today mostly averaging 1188 degrees on the PTO side and 1006 for the MAG side. It's an improvement, actually very happy with the PTO readings but the MAG side will need some attention. I will try swapping the needle and seat assemblies just to see what happens there. A complete carb swap may be in order soon.....

I did try playing with fuel also, ran a 50/50 mix of rec 89 and C12. The sled loves it so far, running 1 mph faster than the same previous set up. The motor sounds stronger and certainly no bog of any sorts. We'll do more testing with the mix then move onto a straight C12 blend to see the difference in performance and maybe top speed. Oxygeninated fuel testing after that to compare.

I think the thing to do now is to install those wheels and brackets to see how they can help. I'm sure they will. That was a good comment regarding the Wahl Brothers suspensions using so any idlers, I guess I never really compared them before. Hopefully tomorrow I can begin the installation. I also want to switch back to the original Rupp steel skis (minus 1 leaf spring) as I feel the keel on the Skidoo plastic skis is digging into the grass track too much. They really dig in and leave a deep groove in the dirt, maybe too aggressive for grass dragging. Test and see right? The aluminum skis Mike sent over will be dedicated to ice racing at this point. Don't want to wreck them in the dirt!

This coming week I may be able to get over to Mickey's Salvage and pick up some more helixes for future testing. My rpm's with the 49 degree seem to be variable shifting from 7500 then climbing to 7900 and staying there. 64-65 mph steadily. She pulls strong even after the finish line so I'm thinking a 45 degree will push the 8,000 mark. The motor seems to have some good torque at that range.

That's the latest for now, Thanks again to all for your help and support. It's pretty nice to know you guys are out there.
Take care now,
-Paul

[Ruppsforever]

Sounds like a great day of testing !! One more thing to consider with your skis is to have minimal drag but still be able to steer. I've heard of people only running one wear rod. I wonder if you could even do less than that. Something to think about. Wish you were closer I'd like to help you more !! LOL !!

[midniterupper]

Thanks Josh! Great idea about the skis, I haven't mounted then back on yet and have a couple of spares. I think I may modify one pair so that one ski is smooth on the bottom and then weld a small bead along the length of the other. Nothing too obstructive but it may help guide the sled a little bit along with some body english. I think it's worth a try for sure. It would be a great improvement over the deep ruts I'm cutting now.

I remember back in the day like the late 70's and early 80's, MSDRA used to race near us at a place called Perch Point Conservation Club. Many sleds used Mikuni fuel pumps hooked up to a tank filled with either the soap mix or windshield washer solvent piped to outlets along the slide rails. They had a little valve to turn it on and off while the engine was running, a pretty simple but cool concept. I'll get those wheel kits on first to see how they affect our top speed. Can always add that set up once we get our testing more established.

Had to work on other stuff coming through the door, it's piling up and getting in my way in the shop floor so I started on that yesterday. Another couple of days and I'll be caught up with that. Should be able to install the skis and wheels right after and get back to testing. Calling for rain this week so we'll see.

Josh, I got a feeling that if we lived closer we wouldn't ever leave the shop except to test and race! I bet we would come up with some extreme concepts though. If we could get Clint and Dale on the team along with some input from Kevin Haase and Bill Stull, I believe we would build an unbeatable machine! Maybe someday, ya just never know!

Happy Father's Day to all fellow Ruppers!
Chat soon,
-Paul

[midniterupper]

Just a quick update, nothing too exciting quite yet. Got the original steel skis welded up with a keel/runner blended in along the center. Not much, but should help guide a little bit. We can always add more. Also welded up and blended all openings top and bottom sides so that dirt can't drag or build up in there. Primed, painted, installed. Ready to resume testing.

I have not installed the idlers yet, want to make one change at a time but they are next to be installed after the ski tests are completed.

Hope to fill you in soon, stay safe
-Paul

[Ruppsforever]

I can't wait to hear the gains from this. Should be very noticeable.

[midniterupper]

Hey, still no testing yet but I did get to play a bit. Ordered the Thundershift kit from Wahl Brothers so that will be included in the future testing sessions. Also spoke with Kevin Haase at Pipestone today and have another set of carbs coming too. Could be interesting to swap them out to see how the motor responds to them. They should look innocent enough.....

Now I did get a chance to install one set of the marginal snow brackets on the sled today also. Wanted to see the difference over the stock brackets and it's huge! There is a 1/4" gap now between the hyfax and the track guides, no pressure on the hyfax at all! I have not had the chance to seriously play around with the set up but it really looks promising. I want to add another pair of idlers located just in front of the large rear idlers as that's where the most wear is occurring. Will have to take one of my old original brackets and weld it in place on the rear suspension. Maybe I can get a picture once everything is finalized. Really excited about this set up, I believe it will make quite a difference.

I first must make some tests with the steel skis installed, hopefully tomorrow.

That's all for now, hope you all enjoy your weekend.
Chat soon,
-Paul

[nitrofa340]

OK. For what it is worth I will give my .02. Hope this helps.

YESSSS!!!!!!!!! on the wheels! WHEELS are the biggest "secret" in grass racing. Look at the Scorpion sleds with the Para-rail suspensions. Arguably the best stock class grass racers ever. Why? The wheels offer less rolling resistance on the grass than does a standard hyfax/slide suspension. What you want to do is mimick the Para-rail suspension design into the Rupp suspension. I gained .3 et on my 340 F/A in 500ft on grass by adding wheels. BUT....its not as simple as "bolt on and go". There are actually several different Rupp wheel brackets that came on several different models over a 3 year period. They are all different in height when actually installed on the liquid Rupp slide rail. Couple this with the fact that we are using USED Rupp suspension wheels that are 44 years old and have wear on the wheel rubber. The result is all the brackets are all going to hold the track at a slightly different height off the track. What I ended up doing was grinding the mounting bolt off each bracket and individually custom welding each mounting bolt to the bracket to give 1/8 inch clearance from the hyfax to the track clips. This was the single biggest performance gain I ever found grass racing. I never had any luck with lubing the slide rails with soapy water, slide lubrication systems ect. That trick works in the winter but on grass all it does is attract dirt. Also take a needle/syringe and inject a mixture of WD-40 and 5W motor oil directly into each idler and wheel bearing until it spins as free as possible.
Heres another suggestion to try. As a general rule, you will run higher mph but lower ET on the grass by loosening up the pretension on the secondary. Been there, done that. My little 340 F/A ran 64 mph consistently in 500 ft on grass with lots of wheels and a loose secondary clutch. Hope this helps.

[nitrofa340]

Suspension set up/weight transfer is critical when grass racing. The proper way to set any sled up for grass is to start by tuning the suspension, THEN work on the clutching. This may seem backwards at first but remember there is tremendous friction/resistance pushing the skis across the ground that will effect your clutch tuning. You want to just slightly float the skis off the ground during the entire run. I would suggest installing a set of F/A curved suspension leaf springs for greater weight transfer rather than the straight springs that come stock on the liquid sleds. Also turn your cross member so the canter/angle is foreward to provide the greatest lift.

[nitrofa340]

As for gearing I always ran a 14/28 combination in my 440 F/A and 19/39 on the 440 liquid. Seemed to work well. I would suggest staying close to a 2:1 ratio.

[midniterupper]

Excellent advice Josh, you have been through these sleds and your experience shows! I really value your input and assistance with this sled, I know every little detail we address will only make this thing faster, so very cool!

Let me get caught up with what I have got done in the last few days, didn't have much opportunity to do so. It's been rather hot around here lately, 95 degrees out right now. Tough to tune when it's so warm but a great chance to work on the race trailer. Not done quite yet but it's ready to go if needed. LED lights added, generator hook up, roof vent, steps all done.

Saturday we ran the sled with the original steel skis that I welded up. No difference in our top speed or handling which is not bad. Doesn't seem to be much difference between running the plastic over the steel as far as friction on the grass is concerned. I have a nice pair of aluminum pro-type skis but I think I'll hang onto those for the ice races. I don't know if they would bend banging around on the sod surfaces, they get pretty rough after a full day of racing.

The sled like the 50/50 mixture of Rec 89/C12. It's very responsive and has a really nice note to the exhaust. Just sounds like a happy motor, could purr all day. I love it! Nothing like the fragrance of race fuel in the morning. Now if I could just get my wife to put a little dab behind her ear....

I took my carbs apart again to see if there is an apparent cause of the difference in exhaust temps. I did as Josh suggested and swapped out the needle and seat assemblies to to see what happens there. An interesting observation is that the two carbs have different washers under the main jets. One is steel and the other is like a small brass cup. Don't know if that would make the difference or not but worth noting for sure. The next test ought to verify any difference regarding the needle and seat change. We should be getting the carbs from Pipestone any day now. They are bored out a tad, don't know if they'll help or not but it will be interesting to test with them.

I also had a chance to mount the additional idlers to the sled. I swapped out the original brackets with the marginal brackets and we have approximately a 1/4" clearance between the track and the hyfax. The gap appears very consistent along the slide rail. I also welded a pair of brackets to the suspension located at the end of the hyfax just in front of the large rear idler. Looks very effective and helpful, something you don't see everyday on an old Rupp! Looks badazz and serious, should scare those Yammies so bad they won't even come out of their trailers! We removed the drive belt to feel the resistance by rotating the secondary and we could not believe the difference. You can spin the track by hand so easily, unbelievable. Thanks again to Clint and Josh, I certainly listen to you guys!

The Thunder Shift arms came in also. I have the recommended placement of the bolts and washers that they suggest to try for the first pass. The total weight to start with is right at 50 grams, they said to throw as much weight as we can in there for an aggressive shift out so we'll see. The ramp profile is very simular to the Polaris M series weights which the sled liked (first wheelie off the line), should be an educational experience.

Today I made the find of my lifetime, at least in regards to the Nitro. There was an add on our forums last march about Rupp free air parts available. I called the gentleman and he has the rear suspension curved springs for me. Gotta send a cashier's check to him but they'll soon be on their way here. We'll install those as soon as they arrive. I may have to weld on tail fins! Would love to pull the skis the entire run!

Next testing session will be to verify exhaust temps and how the sled does with the added idlers. Should be very exciting (and hopefully very fast!) Also will make the first test with the Thunder Shift arms.

I don't know much about these forums and how they work but I can't seem to upload pictures of the sled and the work I have done to it. I get a message when I try to add the attachment that says "File too large, 1 meg max" and the pics are around 2 to 5 meg. Anyone have a trick? I was able to post pics earlier but not now for some reason. I'll keep trying

That's the latest, Thanks again Josh for contributing, we truly have a contender!
Stay safe,
-Paul

[midniterupper]

This may have worked for a picture.....
(The added idlers)

[Ruppsforever]

Nitrofa340 is Dale. I learned pretty much everything from Dale over many years of our friendship and many many phone conversations. I need to catch up with him one of these days. I am truly surprised that work you did to the skis didn't do more speed wise. Maybe it made a slight gain but not noticeable on your radar gun. But like what Dale said probably too much ski pressure yet. Hotter than hell here too. Testing in this weather it pretty tough. Keep up the good work !! Anxious to hear of next test session !!

[midniterupper]

I am so sorry Dale for not knowing who's who yet but it's no excuse on my behalf, so please accept my sincere apology. You guys are the best in these forums and have helped so many folks like me (well, maybe not quite as warped!) but thanks again to all.

Okay, now to the testing session from this morning. Not very hot at that time of day around here so it works out good for me. Must drive the neighbors in the forest nuts hearing the sled at that time of day. Gotta love it!

Anyway, with the new brackets and added idlers the sled ran consistently 3 mph faster!! No matter what changes we did she just ran phenominal. It takes me almost 25 feet longer to come to a stop at the end of the track now, incredible. Still at 66 mph at the tops, nothing lower than 64 mph and that was using the very first set up with the Thundershift kit. The A-2's are pulling very hard. I tuck ground them a while ago and they are very consistent. I am now moving on with massaging the profile at the beginning of the shift as an attempt to slightly raise the rpms just after launch. Kinda fun to see the results.

Now on the TS kit arms I removed two .8 gram shims off the very first bolt. Now I have to test more tomorrow.
Gotta run, the grandson is here!
-Paul

[midniterupper]

Today I had a chance to work with the TSK weights some more. We made a test pass early this morning, gained 1 mph over yesterday's set up using them so we are beginning to understand how they work. We gained about 100 rpm at the beginning of the shift point just after engagement by removing the 2 brass washers located in the first hole. We just tickled the 8,000 rpm mark at the big end using this set up. Tonight I removed the 2.8 gram steel bolt from hole #2 to raise the rpm's in the mid range shift, which was hanging around the 7700 mark. It is entertaining to see the results of moving weight around on these arms. Still have to do the idler bearing injections as Dale suggested, that will be a separate test session.

The skis have to be an overall improvement too. The only way to steer the sled now is by shifting my body weight, no more gouging in the test track. May have to build up a little better keel on the bottom of the skis.

Also, I removed my carbs just the way they were on the sled and packed them away for future use if needed. The sled is running great with them on so I want to have them handy. It took a while to install Kevin's carb set and get them dialed in enough to run as well as the originals. Installed 270 mains, reset the needle clips to the middle position, the bowl screw is all the way closed and she is running quite well now. Hopefully tomorrow we get get a chance to run it and see how the exhaust temps work out and dial the carbs in even better.

While I was adjusting the throttle cables to synchronize the carbs I noticed when at wide open the slides are not quite up all the way. I have a lot of free play in the cable that I cannot eliminate. I'm using a Kimpex universal dual carb cable so certainly nothing fancy. It did seem to work okay with the previous carbs, pulled the slides all the way flush with the bore. Has anyone used the Hy-Lex dual carb cable Wahl brothers offers? May have to give that one a try to help eliminate the extra play.

Our test track is taking a beating, getting worn down for sure. I'll have to plant some grass seed soon and give it a rest. Our first race is scheduled for next month at Nelson's Snow Motion in Greenville. We should be ready to beat the Yammie's by then!

Will write more as testing progresses.
Hope you all are staying safe again, take care now and thanks for reading.
Until the next time,
-Paul