Slightly shorter belt, any advantages?

Mad Powersports

Mad Powersports

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My RX1 improver seems to be leaving a lot on the table as far as I think.

When I got it there was a 89L belt on it. She started to let go on the second run I made with it. I had a brand new spare 89L off my 600 I put on it. Sat I noticed that after the first run it was creeping forward at idle. 1,500 rpms. But edge the idle up and it won't move until the primary engages. Well after sitting in line to stage I got a whiff of burning belt. Sure as cats have hairballs the primary sheave was hot.

Put a used 89L on it and the creeping stopped. Sheaves cool. So after doing some research Yamaha calls for an 8DN belt. But Geez thats only like an 1/4 inch longer at 44 1/2" where the 89L is 44 7/32". Is that small amount going to make a noticable difference?

I'm now thinking that someone just slapped a belt on it to sell it but it's too short The SOB pulls like a train but just seems to lack the top end. I can't seem to crack the 105 mark. Constant 103's and one good launch with a 104 and change. To be perfectly honest I haven't seen the peak RPMs as I've been busy watching where I'm going. But by my ears it's nowhere near 13,000.

I have yet to see the inside of the chaincase so I have no idea what the gears are there.

Or am I asking to much out of her? This thing seems to have low end grunt up the wazoo but it just doesn't seem to wind out.
 

Hey I'd definately stick with stock 8DN Yamaha RX-1 belt as for one they are a very hard compound belt as compared to say an 8BU V-4 belt which should help pull some additional rpm, I wouldn't be chincing in the clutching department with something as simple as a belt.

As far as mph on that I.S. RX-1 @ 105 mph in 1000', with Hauck's 200 h.p. I.S. 4-stroke engine, you should be able to run to run around 115 or so in 1000' with the weight of the sled, but with you driving...just need some tune. Now I don't know if your shooting for 13,000 rpms, but you should be looking for around that 10,300 rpm mark. If you bought that sled from Jack Henrick's as a drag sled, then that is what you have not a speed run sled, changes will be required. Let me know what you have for gears, driver diameter i.e. 6.90", 7.07" or larger. Also that is is reducted engine so it is actually turning around 9000 rpm's (give or take) when tach is reading 10,300 rpm so this must be figured into your mph calculations as it will significantly reduce mph calculations. Let me know when you dig into that chaincase and measure drivers, that should let you know where you stand.

EDIT!!! Also after the gear ratio has been correctly calculated and you have a target mph in 1000' that you want to gear for, you can work on various helix profiles and possible weight profiles to pull a consistant 10,000 rpm+ in 1000'

Good Luck Ron.
 
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If you bought that sled from Jack Henrick's as a drag sled
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Justin, Thats the problem. I'm not sure what Jack had it setup for drags or 1,000'.

I'm going to document all the variables today that I can and start from scratch with setup.

Tustin is this weekend and I want to test both the Improver and the Judge so I'm ready for the Weenie roast.
 
Well I have some specs to post.

Stock 9 tooth drivers
25 top gear
38 bottom gear
Hauck VP "Lights" primary weights with a screw in the outter hole
Black primary spring, no shims
Hauck "N" secondary helix
Silver secondary spring wrapped @ 70 degrees
 
THAT 89L BELT AIN,T STANDARD ON THE RX-1. THATS SPEC,S TO A 500 PHAZER. NO DOUBT USE THE 8DN. NOW WITH THAT SAID, I HAVE TRYED TO USE THE 89L BELT ON MY SRX FOR GRASS RACING, THINKING AGAIN SOFTER COMPOUND BETTER GRIP. BUT LIKE YOU POSTED, CLUTCHES MUST BE RE=ALIGNED TO RUN THAT BELT. 3:16 (yammie tony)
 
Run the 8DN belt, that will be more consistant and faster speed wise as well. You likely do need to be in that 11,000-12,000 rpm area for sure as I'm sure it has R1 spec cams & porting in it to push that many rpm.
 
Ya I was going to run it this weekend in Tustin but I'm not comfortable with the gearing in it. Plus I need to get that 8DN yet.

I'm just going to run the Judge and see what she can do in stock form.

Back to the RX1, that has a 25 top and a 38 bottom which is a 1.52 ratio.

Correct me if I'm talkin' outta my arse here but I thought I remember reading (hearing) from one of the more knowledgable race oriented folks either here or on TY that the optimum ratio is 1.75 - 2.0.

That was many moons ago or I may drempt it, but it was something that I remember as, something to remember.

Also, i'm having a bit of brain fade as too which is the way to go on gearing.

All things the same except for gears, and the ratio staying close.

Example: 25/39 @ 1.56 or 23/36 @ 1.57

The 23 top is going to unload the engine and the 25 top is going to work it harder, correct? Yet both are going to have the same theroretical top speed?


I haven't done this for so long I kinda forgot...:beathead:

You likely do need to be in that 11,000-12,000 rpm area for sure as I'm sure it has R1 spec cams & porting in it to push that many rpm.
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From what I was told there was nothing spared when this engine was built. Hauck built from custom cases out. Supposed to have a 13,500 CDI box. I have the number of the CDI unit and can not find ANY information on it.

I just don't think it is reaching the proper RPM's. But then again I'm used to listening to two strokes scream. And then Justin mentioned something about the reduction of the crank to the primary shaft. I had forgot all about that.

Ron
 
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