Rotrex belt slip at high rpm
 

finally got my c30-74 rotrex setup running and dyno'd.

https://cimg1.ibsrv.net/gimg/www.mia...d14dff6f91.jpg


At the dyno, the car shredded a belt but i had another and we pushed on. Ended up with this even with the belt slipping past 7k.. Flamesuit on for low torque.
https://cimg8.ibsrv.net/gimg/www.mia...347e16d2ea.jpg


I guess the question i have i can i convert to a 6 rib setup with a supermiata s/c damper? 949racing says it wont work, but my pulley has 2 more ribs on the front side and the spm sc pulley says its the same alignment as a stock pulley but with two more ribs out front. my basic math tells me it would work. ill just need a new pulley for the rotrex aswell.

Good results! What size pulley are you running on the Rotrex?

By the way, diggin' the intercooler set up ;-)

Blower has a 80mm pulley. About 9 psi before it slips. slip indicated by the rubber everywhere/hot belt and the belt breaking and the psi tapering off at high rpm

Your pics make the ic look like its supposed to fit there.. this is also a much bigger ic hence the pain in the ass to make fit

With the four rib set up they can slip when you go too small on the pulley, but I've only heard of problems with the 75mm pulley. I've never moved on from my 85mm pulley and have never experienced any issues with it. Are you running A/C and P/S? What size belt?

no a/c or p/s. the belt is a 4pk1160, its the smallest i could fit for maximum wrap. im starting to think the no PS is the issue. there is no guidance up there by the blower and the belt being longer stays cooler.

Damn 312 whp on the smallest Rotrex? Good stuff.

You say you have 2 more ribs on both the SC and the crank, and they go the proper direction? That kinda sounds like a no-brainer to me. You can space the autotensioner forward, and get a different pulley for it.

Edit: i have no experience with Rotrex, but I DIY superchargers.... an additional bracket on the back of the SC makes a world of difference.

It’s fixed
 

Also...
 

Tbh I want to see more pics of that engine bay from engine to bumper. That's such a beautiful setup.

i have a build thread! or check out my IG thetwibs

use exhaust to spin it up. problem solved.

i was actually gonna use the exhaust to spin up a pinwheel with an extra flywheel i have so even when im not accelerating the pinwheel can propel me in a forward direction to make me faster.

Out with the turbo talk please.

Twibs,

I want to go to a six-rib setup for my Rotrex C30-74. I have the same problem--80mm pulley, no p/s or a/c, and I can only get to 9.3 psi before I get belt slippage.

Could you be more specific about the parts you used?

I'd be interested in anybody else running a six-rib setup on their Rotrex for the track, as well.

Thanks much,

I thought I was pretty specific.

Bhj supercharger pulley and overlay. No longer avalible As far as I know. You could substitute for a stock pulley overlay. Make sure it’s one that retains a damper

i tossed out the plastic idler pulley and used a full metal wide bearing 2009? Hyundai Elantra timing belt idler

used washers behind the tensioner pulley to get it closer to the bracket. I also had to use a trimmed down bolt to hold the sc bracket on. You’ll know it when you see it.

Also to note. This setup has been 100% solid. Still on the original belt I put on there. Many dyno pulls and some track hours on it. Zero issues with this part of my car.

Twibs,

I'm wicked confused. You say this...

But also this...

I can't find spm supercharger pulleys in the google machine. Did you replace the pulley on the Rotrex? Mine already has a six rib pulley. What I need is an overlay for the crank pulley. If your Rotrex came with a four-rib pulley that lined up with the stock crank pulley, how were you able to use a new six-rib supercharger pulley that had an extra rib on each end without spacing it out at least one rib's thickness from the Rotrex?

You used an overlay for your crank pulley. Doesn't that mean you should have used a larger pulley for the Rotrex as well? I thought 80mm with the stock crank pulley would take the Rotrex to its max rpm of 120,000, so a larger overlay would overspin the Rotrex when you get up into the higher engine rpms.

I did check out your IG page. Beautiful car.

Thanks,

The spm pulley is it’s own beast with its own issues. And things with it weren’t as advertised. I would disregard anything you read about it because I don’t think there were even a handful of them made.

Iirc all the rotrex pulleys come in 6-8 rib. There no issues with this side of the equation. Figure out what crank pulley diameter you’ll be running and then give kraftwerks a call and They can set you up.

BTW @poormxdad , the 75mm rotrex pulley will put the c30-74 just under 120k RPM at 7000rpm with the stock miata BP pulley, not the 80mm one.

Irregardfull, that doesn't mean he's not overspinning the Rotrex. I should be at about 10psi with the OEM crank pulley and 80mm s/c pulley, but I've got some belt slippage as well. If he's got an overlay, he should be making more than 10 psi.

Twibs, did you see an increase in boost when you got it all sorted out?

If I remember right I was slipping about .5 of a psi before the belt broke on the dyno.

My before the overlay and after had similar max blower rpm. So no measureable difference except not breaking belts.

I did see an increase In boost with my bigger exhaust.

@poormxdad if you dont have P/S, it might be worth looking into an ATI Damper, they have 6 rib support so they might line up correctly with the rotrex (since they align with the stock PS, and just have more rib space forward, its likely you can just bolt it on and add a 6 rib belt, and be done with it)

https://www.flyinmiata.com/ati-dampe...-kit-36-2.html

Probably better to talk with FM about it to confirm though.

Update: Installed 75mm pulley and am using a very cheap weird brand belt at the moment while waiting for the Gates RPM belt. The current belt is also a tiny bit too long as my static tensioner is almost touching the P/S pulley.

I have not seen any slip yet, even with this garbage belt not being tensioned that much (auto-tensioner is a bit away from the optimal position)

I have measured 0.84 bar (12psi) @ 7200rpm with MAT of 21C (70f). With a MAT of 38C (100f) with ambient temp of 33C (91f) I was seeing 0.75bar (10.8psi) @ 7200rpm

The boost the 85mm pulley was giving me at 7200rpm (0.64bar) I am now making at 6000rpm

With the new belt I should have a bit of slip margin hopefully. I have yet to track the car in this spec so slippage during consistent hard conditions is unknown as of yet.

I installed the Elantra timing belt idler. That was a great find. It gave me a little more tightening adjustment with the 40457 belt. It's 60mm. 62mm or so would be even better.

Have any of you found a significantly better tensioner assembly than what comes with the kit(s)?

Thanks,

Audi ones *could* work; need to get my hands on one to measure how much load it can apply.

Can you give us a part# for this? does it fit perfectly in the kraftwerks bracket?

Also for future reference, and everyone on the internet trying to figure this out:
The part numbers for the stuff that comes with the kraftwerks kit, as best as I can tell
Auto-tensioner - Gates 38164
Tensioner Idler - Dayco 89003

The auto-tensioner looks to have the same mounting pattern, but the pulley wheel is obviously different, so I dont know if this one has more tension than the one I have.

The part numbers are indeed correct; the Gates autotensioner gives about 450NM of torque. The Audi one I have been mentioning as a possible replacement is from an Audi A4 2.0 2009-2011, part no. 06H903133F, which I need to measure in terms of load that it can apply.

Feedback on Gates RPM belt: its awesome.

After initial tensioning with engine off, it didnt seem to lose any tension that I could tell (I have witness marks on the autotensioner)
After the first 20-30km it stopped dusting completely (not even a HINT of dust anywhere, after I cleaned the bracket and everything else, and after driving 200km with a lot of pulls)

It also doesnt squeal when cold.

No change in peak pressure that I can tell as of now but with some careful custom functions in MLV can confirm im not losing boost to slip (boost per rpm gain is a straight line)

TBD how it holds up to daily and track use

What size? I need a 457.

Thanks,

I used a K040476RPM, since I have P/S. Their website shows all the sizes, seems the step down from mine is 440.
https://www.gates.com/us/en/power-tr...-000000-000002