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