Sled: Polaris

Hi all - I'm new at modding sleds, thus I have a lot of newbie questions.  I'm asphalt racing (1/4 mile) my 97 Ultra SPX.  It has a stock motor and clutch.  I put PSi pipes on it today, and it's not going any faster than it was with stock pipes - possibly even slower.  With the stock pipes it was revving to 8000 rpms pretty quick, dropping to 7800 and then quickly getting back up to 8000.

The PSI pipes are supposed to run at 8600rpms.  I made a few passes today - it revs to 7500 at a medium pace, and then very slowly climbs to 8100 by the stripe.  I stayed in it a little past the stripe and it climbed a little more before I shut it down.

>>Edit:  on the jackstand it pulls to 8800

Being new to mods, I'm not sure where to start.  Lighter weights in the primary?  If so, how radical of a change should I make?  Stock is a 10-54 (which I assume is 54 grams)

I also think I want to increase the engagement to get it out of the hole faster - it seems more sluggish with the pipes - I think this makes sense - I assume the pipes move the powerband up, so I'll want a higher engagement.  Is my thinking right?  It's engaging at 4800rpm right now.

I asked about my gearing last week, but a few guys told me they was just right.

Thoughts?  Suggestions?

As with tuning any sled not pulling its target rpm, you can try a combination of things. You can install lighter weights, or cut the tips on the weights you have a couple grams each. You can install a different primary spring of stiffer rates for engagement and running rpm using the weights you now have, or use the same final rate spring with a higher engagement with lighter weights. Different rate secondary helix's can even come into play also, but for now just concentrate on the primary clutch spring and weights,and make one change at a time, noting what it does. 

get your final rpm set first tune 1 thing at a time there is no magic list of what 2 run just put ur time in and figure it out ,sounds like u should be running 10.90 s or so

First off, you need to service your driveline. I.E. you have springs that have miles or are old, that is your biggest problem right there. 90% of the time when you have a motor that wicks up to a certain rpm and then starts falling off and then back up is a spring problem. Yours are old. Put new ones in it and check your rollers, pins, buttons, etc. replace anything that is worn. You are trying to tune a dead horse. It wont work. You will have to do everything twice. Also, make sure everything is lined up properly and at spec.

Did you put the pipes on and not change anything else at all?  What is your jetting?  Where are your needles set (which clip), and what is your clutching besides the 10-54 weights?  No matter what, I would not go any lower on the clutch weights... If anything I would like to see you run more.  Its tough to say what those pipes are doing for your motor if you didnt change jetting or anything else in the carbs.  It might be wanting more fuel on top so that is why it is falling on its face up top (given you didnt change anything else).

I had a 1996 Ultra asphalt sled.  This was my set-up that I ran...  10-58 weights, Polaris Almond Black primary spring, 44-34 or something close helix, and EPI Black Secondary spring.  This was for 8100 SLP torque pipes (which I ran a little higher because it e/t'd better, somewhere around 8400)... little different than those PSI's...  you should still be close other than you can get your weights to probably 10-56's.  IMO the spike that you are seeing is an overshift because of your already high engagement.  Engagement that high is OK for asphalt, but if it will leave lower, then give it to it.  .020 belt to sheave clearance in the primary (i think that this is more common problem for too much width there than people tend to see... if it is too wide then it grabs hard to begin with, loses the belt somewhere in the middle of the shift because of load, then gets it back again one the load lessens with speed and RPM's come back.  With tight clearance it loads the clutch and stays with the belt all the way.)  Of course, if you are running a trail helix like a 48-36 or 50-36 then an overshift is almost expected with a helix like that.

If you need more fuel then give it, but I would try a Polaris Almond Black (or something close to 165-320) with 10-56's, an 42-34, 44-34 helix (something close to that), and a secondary spring close to 50-90.  This should be a pretty basic set-up to get you close to what you need.

After three years of running my Ultra it would run 10.70's... 15" wide track, and no lightweight parts, all stock except for pipes and some porting.  Just to give you an idea.