Aw geez. tell me it aint so!

After MUCH investigation and learning, I purchased a clutch kit for my '00 400 scrambler 4x4 w/ HPD midrange and RCR cut head (165 lbs compr.) Its also K&N w/no snorkle and one step leaner on the mains then HPD suggests.

IF the sun-pro tach's are right my stock clutch appears to be perfect. After buying an HPD kit and several spare springs so I could tweak as needed, I installed the tach, bought a GPS, and gained permission to use a service road at my local airport. Results are as follows:

FWIW note I'd increased pre-load to 2 / 1 and be aware I'd cleaned the belt drive up as I was getting a bit of slipping some weeks ago.

CONFIGURATION
Primary Spring Stock Polaris White
Weights Stock Polaris S-55
Secondary Sprin g Stock Polaris Red
Secondary Preload 2 / 1
Helix Stock Polaris 40 Dgr

RPM @ initital engagement 2200
RPM required to get over a 2x4 2600
RPM obtained @ full throttle 6300
RPM @ top speed 6800
Top speed 63.4

So I'm amazed. Unless the tach is wrong (and I don't yet trust it), I've nothing to gain. I think.
I engage low enough (as I wanted).
I've got enough bottom end torque to pull the wheels and jump up onto the pipes power band (within 2hp pf peak). Oh, maybe it takes 10 feet, but thats flywheel affect.
It carries that rpm all the way through shift-out and then pulls 500 more rpm to within 200 prm of the indicated peak hp and steep fall-off.
I'd not be surprised to see that I was actually carrying to the fall-off, as 200 rpm is statistically insignificant a delta at that point, and otherwise I'd have expected to keep climbing. (it was, slowly, but I ran out of room)

Now this was a coldish, dense air day, so I probably was making great power, but most of clutching is PRM based yes?
This leaves more questions then it answers.
1) Could the tach be wrong?
2) Am I not shifted out all the way? The over-rev after shift-out suggests its done shifting, and it sure looks shifted all the way out. Maybe 1/3" from the very top of sheeves.
3) Could I be slipping and not know it?
4) I don't think I can easily alter gearing (and it'd just kill the bottom), but 63 seems a bit low. Of course, thats a GPS 63, not the BS that gets kicked around all the time.
5) If the tach is right, my rpm points are perfect for me. What could a clutch kit do for me?

Oh man, after so much time learning this stuff, I'm kinda bummed to think it's fine stock. I likely will add the split helix just to be sure, and will back off the pre-tension a bit to see what happens, but it its wound out and shifted out. I think I'm done et?

Thoughts please?

 

Well, by no means should you be at 6300 then make your way to 6800. The rpms should be at the exact amount (peak HP) during the entire run. Only after a long distance should you maybe notice a slight rpm increase after the transmission has fully shifted out. The stock setup wont work well with the HPD trail pipe. Neither the regular or agressive kits from HPD uses any of the stock components. I personally like the snowmobile curve on the weights. They are a little softer on engagement and shift out harder in the mid range. The trail weights (S series) are real agressive on the engagement and low end. 63 mph on a non ported stock geared machine would be right on the money. If you was to race the same machine with your same setup and a matched clutch kit, you would be surprised how badly you would get spanked. The engine turning only 6300 during shift out is pretty far off the pipe's power peak. Since the pipe makes it's max power at a higher rpm, that is why it will climb over the high line ratio until it reaches 6800. Sounds like you need a clutch kit to me. Bubba

 

Thanks again Bubba! I sure say that a lot. Sound's like you think the tach is right. hm... I'll test more tomorrow, looking for slip in particular.

Any idea's on how to validate that tach? If that tach is right I may not do anything. With the trail pipe I'm leaving VERY little horsepower on the table between those rpm's. Remember, this one is the utility machine for me. If'n I decide I wanta get racy I break out the banshee. It's been set up just the way I want it and it's the flyer. For this one it's about perfect. I dont WANT to run around @ peak RPM. Its an odd objective. Based on the stock pipe powerband I'd expected to see 5500 rpm and that was leaving too much power on the table. I wasn't sure it would ever pull that. Maybe the preload did that. Sure was a big change.

I think I'll add the double angle helix and see if I can more rpm on the mid-range. I'm OK with the bottom, but we'll see.

You heard about the all-knowing alien that gave some guy a machine that cured world hunger and brought peace on earth?


He took it apart....

More after I test. See ya.

dan

 

My sunpro tach was tested against a SnapOn multi meter that had a tach built into it. Their was only a 200 rpm difference between the two. This is close enough for me to make good use of the tach.
Did you do the RCR air box mod? You said you removed the snorkle but, that's all. The air box mod really does make a big difference. Big enough, that if you did the air box mod without re-jetting, you would surely blow it up.
I think you'd be happier if you did raise the shift out rpms. My 300 has the RCR 400 mid pipe on it. My engagement is at 3300 rpms.
My shift out is at 6900 rpms.
It will rev out to about 7300 after full shift out.
I could pull more HP out of it if I wanted to let my engine turn about 500 rpms more at shift out and wound out. My air cooled/piston port motor couldn't take those kind of rpms without over heating.

 

Mucho's gracias on the tach test info. After much testing and some math games I came to trust it too. Its VERY nice to know you've got hard data to back it up.

I'll hafta look at the airbox, but I also pulled the rubber donuts the snorkle mounted into. Hard to believe I'm not flowing more air then the carb can take, but I'll talk to him.

I did change the helix and that made it even better. I also swapped the secondary to HPD's purple, but that change would need a dyno to see. I MAY be slipping at launch on concrete for perhaps 5 feet, but the first 20 feet are pretty busy trying to hit it just hard enough. On anything else it spins the tires.

Given its purpose its great as is.

As an aside, today's retest of yesterday's config showed an engage of 2600 and 3000 to get over the 2x4. Same top speeds and same rpm's @ shift.

More later. And yes, I know, nobody like my shift-out. Yet, I'm happier than could be. In fact, its what I wanted to get.

Thanks again.

dan