1976 Nitro Grass Drag Set Ups

[Ruppsforever]

Racing on ice I always geared higher. The timing system always showed quicker times with my clutching with gearing higher. I ran a 1.75 ratio. 20 / 35 for my 440's.... On my 340 I ran a 19 / 35 Both mod motors and pipes of course. Even when I played with a stock 76 Magnum I ran a 20 / 35. Xenoahs like to be lugged down.

[mrrupp1]

I’m pretty sure 19-35 was 68 link chain and 19-39 is a 70 link chain. I will make sure tomorrow, and let if they are different. Clint

[Ruppsforever]

Yes 19/35 is a 68.

[midniterupper]

[midniterupper]

Sorry, I don't know how to send a pic with text apparently....
Anyway, that is a picture of our project sled

[mrrupp1]

Hi Paul, the sled looks awesome. It's to bad the only part of your sled the competition is going to see is your tail light. Your hood has 78 graphics which look great. Do your know what the serial number is on the tunnel ? The reason I ask is you might have a 77 Nitro instead of a 76. The 76 serial number will start with either 500 or a 510 and a 77 starts with a 76. If it is a 77 they were a little different then the 76. The porting is different, and the 77 had an extra main bearing little beefier rod. They ran good, but it seemed that my 76s would always out run my 77s. The easy way to tell what year you have is the plate on the crank case 76 starts with a 5 and the 77 starts with a 6. No matter what you have an awesome sled. Talk to you soon. Clint

[midniterupper]

Thanks Clint! I'm so glad you know this stuff! I don't know how you know it but I'm grateful that you do, thanks for sharing. I will look today for the serial numbers on the motor and the chassis. When I bought the sled at the A-1 show the guy said it was a 1976 but I think he just flipped sleds and maybe didn't really know.
I want to eventually strip the hood, do a little fill & sand and repaint the hood and belly pan then apply the correct graphics. I need to get a hold hof Bill Stull and find out how he gets his sled's finish. All his sleds look amazing. Once I get this sled dialed in and most of the work finished, I should be able to get her looking her best.
Thanks for your help and encouragement Clint, sure appreciate your help! We'll chat soon and let you know what's the latest. Take care now,
-Paul

[midniterupper]

Here is my form for testing the sleds that I mentioned earlier. Maybe someone could use it....Snowmobile Testing Form II.docx (13.56 KB)
Hopefully I did this right!
-Paul

[Ruppsforever]

Paul can you take a picture of the engine ?? Your handle bar clamp is 76 and skis and one other thing I notice is 76. If you have a 77-78 motor my clutching advise you can throw right out the window. Some might work but those motors are completely different.

[midniterupper]

All right now, got some information on my serial #'s and from 1 test pass.
My chassis # is 5100744 and my engine # is 502916. I think from your data it sounds like it is a 1976 so at least the gentleman was honest.

I definitely want to try a lower ratio gear combo after testing today. I think I will try a 21/39 combo (1.857 ratio) just to see then maybe swap to a 20/35 (1.75 ratio). I would like to see if there is a difference in loading the motor between the two. Maybe gain a little top end speed? Should be a great combo for the ice races.

I made only 1 pass this afternoon today. The only changes I made was to drop down 1 size on my main jets and changing the helix spring to white along with installing a 51/49 degree helix.

The jetting change helped, my exhaust temps topped out at 1065/1087 degrees. I went down 1 more size for the next test pass.
The helix and spring change did seem to help a little. My top speed returned to 65 mph with this set up compared to only 58 mph with the last set up. We have been up to 66 mph with a simular set up from last year so we are close to that now and we have a lot more to tweak yet. Both clutches appear to be fully shifting out, however with the White secondary spring, the clutch stayed very cool to the touch. Not sure if that is an improvement in efficiency or not. It has less side pressure as far as rating. Using the Yellow spring I always had a little heat in it.
I will test more tomorrow to compare the two for top speed.

I am also going to reduce the number of studs I am using too. Theory states too many studs suck up horsepower so once I get the next test done I will pull some out. Going from 120 down to 76 just to see......
(Never stops right??)

That's about it for now, sure appreciate everyone's input and assistance with this sled.
Take care now and we'll chat more tomorrow.
Stay Red!
-Paul

[Ruppsforever]

I would guess you are at maxed out with clutching and gearing right now too. You are geared super low. Looking forward to hearing what the 21/39 does. 20/35 might be too much for grass. I would still pick up a 19/35. I'm anxious to see how the gearing helps. It will keep the clutches at a different ratio too. I never had much luck having quick fast sleds shifting all the way out. Shifting out all the way isn't as efficient of a ratio.

[midniterupper]

Yep, I agree with your gearing suggestions. Gotta do something there for sure. I will see if I can get a 13 wide 19/35 gear set with a 68 link chain too next week. We seem to be flattening out between 63 and 66 mph, but I'm sure we can still do better.
This morning we made 2 more test passes.

The first test was to see if there may be a difference between the Arctic white (58#)and yellow (92#) secondary springs. We also dropped the main jets down 1 size to see if there is a improvement in the exhaust temps.

Exhaust temps improved and went up to PTO:1137 MAG:1085 degrees. I will try a few more test passes with those (260) mains to verify consistency in temperatures.

With the Yellow spring installed we dropped 1 mph off the previous top speed (64mph) compared to the white spring (65mph). Also the secondary does get warmer with the yellow verses the white spring, not by much though. Just something noticed. Could warmth mean inefficiency? Too much belt side pressure?

As you recall a couple of nights ago I installed a multi cut helix (51/49) to see if that affects my shift pattern at all for testing. We did test with it a little last week before these passes and made some notes. With the multi cut helix, my rpm's always climb near mid track around the 250 foot mark. It would typically go from 7500 climbing to 7700 so that got me thinking.

The 10MW weights were always strong but 1 mph slower and would drop my rpm's by 300 at the end of the test pass. So, I installed the 10MW's today and made another pass using the 51/49 helix and sure enough, my rpm's went up at the end of the pass. It went from 7600 to 8000 rpm! So that combo definetly raised the r's but once again, my top speed dropped down to only 63 mph. Sure sounded fast on the video, felt fast too but was a total of 3 mph off our best so far this season.

Tomorrow I am going to remove 48 studs and make a test pass to see if too many studs in the grass can cost horsepower. I will also try a small tuck grind on the 10MW's to raise the engagement rpm from 5200 to see if that helps.

The A-25 arms and Aaen's purple spring came in today too. We'll play with those next week to see what they do to establish a baseline then we can begin our gearing tests.

So until the next time,
-Paul

[midniterupper]

I'm still waiting to test. We have had rain then temps pushing 91 degrees so not the best conditions yet. I'm going to Mickey's sled salvage tomorrow to pick up the 19/35 gears and chain set, and probably a 48 degree helix too.

There is three more tests to do using the current (20/39) gears for comparisons then we'll drop in the 19/35 set and begin all over again. We've got a great baseline so far though and good archives for future reference too. Never a waste of time in my book!

Hoping to test soon,
-Paul

[Ruppsforever]

I just thought of one more thing. Are you running the track on the slides or do you have wheels installed to reduce friction ?? Wheels on grass is good from what I've heard. Or adding a slide lube system if allowed at races should work good too.

[mutt]

Dont think a 48 helix is OEM they go by 2 49,47,45 then a 42. In aftermarket a straight angle 48 would be a tuff find. On a salvage search look for helix spacers. Can change how long you want to be on the start angle on a multi cut helix good tuning tool

[midniterupper]

Hey, Thanks to you both for your help and suggestions, very much appreciated! I haven't tried eliminating the hyfax yet but it's worth a try for sure. We did that on our skidoo's back in the day also and it did seem to help. I'm using a set of hyfax that I bought last year from Kevin so they are pretty well worn at this point which may actually help reduce the friction for now, but it's in the works.

I quickly found out about the Cat helixes while at Mickey's Salvage yesterday. He had about every angle of helix there including a ton of Black Magic helixes. There is a code chart that describes them all but I ended up just bringing a 49 degree home to try. Great idea regarding the shims, I'll have to play with those.
I also brought home gears and chains that I want to install, beginning with the 19/35 combo.

Today was a great day of testing, found out a lot of stuff. We gained 1 mph over the last set up by just dropping our stud count from 120 to 72, that proved very consistent. Also today, we definetly proved the Arctic White spring (15# preload) is more effective with this particular sled. It always ran 1 mph faster than the Yellow spring (14# preload). So by the end of the day we gained 2 more mph with this new set up, topping out at 67 mph consistently. That was last year's fastest speed we recorded at the races and that was a 485 Mod Phazer they let run in the Stock Vintage class so we are in a very good place.

With that being said, now I can start all over by installing the new gear set. We should gain something there too, then off to play with fuels and slip on exhaust stingers for the Improved Class.

So Much Fun!.....

-Paul

[Ruppsforever]

I'm sure you already know this but I just wanted to be sure you do. You don't remove the hyfax, the wheels just keep the track from touching it in the places where the most friction occurs. Do you have any of the rupp brackets to add wheels ??

[mrrupp1]

Hi Paul, I didn't think there was a Phazer on the planet that could stay with a liquid Nitro. It must have been built to the hilt. Well it sounds like you are headed in the right direction. Go Rupp!!!!! Clint

[midniterupper]

Hey Ruppsforever, I don't have any extra idler wheel brackets at the moment. I thought I might be able to make something or modify some Cat brackets or something like that. I haven't seen any additional idlers installed to check placement either, I guess I haven't thought that far ahead. If you have any info or leads, I would really be grateful.

Sounds like we may be onto something here!
Take care now,
-Paul

[mrrupp1]

Paul, I have the brackets that fit the Rupp slides. I will donate as many as you need, just let me know how many. Clint