Well, Im getting my motor back together this weekend, and Im going to put my HPD pipe back on until I get the rings seated in. Then Im going to try to dial in this CPI outframe. Mike at CPI told me that in order for this pipe to make peak hp, it needs to rev 8600 rpm.
So, what do ya think? Rick already told me that he would be a little scared that it would come apart. My cases are new, bearings and crank are fresh, case saver tig'd and got the girdle.
Daryll at HPD told me that he really beefed up his lower end for N02, maybe Ill call him, and look into this.
What do you fellas think?
Thanks

 

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sorry cousin, i just couldnt resist [img]i/expressions/face-icon-small-smile.gif[/img]

 

If the pipe is made to turn that RPMs, then do it. I think you'll find tuning the clutch to be easier as you can get more stall and shift patterns the way you want it. The polaris 400 stroke is the same as a 250R Honda and they turn a lot more than 8600 (9500 give or take some). You can also get them with a big top end. They hold up with the small rod in comparison to the beefier Polaris rod. I wouldnt be afraid of it one bit myself. You even have 2 bearings on each side of the engine instead of one. You exhaust duration for the HPD pipe should be fine for turning 8600. I dont know if Darryl would tell you or not, but I believe they have it at 200-202* exhaust duration. Call CPI and find out what they recommend. They may tell you 204-205*. If that's the case then it will need to be that to work the best. CPI knows their stuff when it comes to their pipes. Good luck and keep us posted.

 

Hey thanks for the reply Bubba. When I had my HPD pipe on, it would rev approx 7600. When I put the CPI on, it killed the bottom end, and the top rev was only 7000. I called CPI and he told me to clutch it to rev 8600. So I went from 58's to 53's. With the almond primary. It was too dark to run this setup tonite, but I did notice my stall wasnt any higher. This kinda suprised me. I would have thought that a 5 gram difference would be measurable on the tach at engagement.

 

Since the weights aren't at the point where they are really working the best at engagement, the difference is minimal unless you make a huge jump. You will see a difference in top RPM as well as where it will shift out.

OK, you made me break out the book on this one. I had to look it up as it's been awhile. The calculation on weight changes are this.... F=MRV(2) Force = mass X radius X speed(2)
So given that we can take a calculated assumption on your new setup. With 7000RPMs and and 58 gram weights to the new 8600RPMs. We need to see what the force difference is between the 2 RPMs. So we take the 8600(2) and divide it by the 7000(2). That comes to 1.509, or we'll say 1.51 or almost 17% (of 8600). So 17% less than 58 grams will be only 50.5 grams. Now that is only the mathmatics of it. If the pipe makes more power higher up in the RPMs, then it may take more weight than that also. Field testing will be your only true method to get the results you want. Hope that helped. I am hitting the bed, check back with you later,Bubba

 

whitedog,i'm running almost 53 g of weights at 7600 rpm,
i guess to rev 8600 rpm you'll need to drop weight in the higher 40's
grams of weights,running at least 340 pre-load top primary spring,swap helix to a 34 for the most part and with over drive belt.

 

Well folks, heres an update, on thursday I put in a set of "C" weights in it (48.5) with the almond primary and I got 8000 out of it, so saturday i took them out, and ground the sides on a set of G weights to roughly 43.5. These are S profile weights that I also tucked under. This setup is a little bit too much, cause it starts to over rev (8900) at about 250 feet. But the stall is pretty nice. I can actually blip the throttle rev it to 5 grand, almost like its in neutral. Today I ordered a set of notched 47 gram weights, that Im going to cut down to 44-45. Maybe this will get me where I need to be.
Dam, this "trial and error" tends to get pricey if theres too much "error" LOL
Brent

 

whitedog,i'll tell you an old tuners trick wich is normally mean a drop
of 1 g of weights rev 500 rpm increase so,get back the weight at 47.4 or 47.3 g and you should get the peak rpm you're looking for...
words of scramblereD.

 

hey scramblered what do you mean when you say an overdrive belt? just curious.