Rotrex install loses boost
 

Hi

This is my first post on this forum, and it's regarding a Rotrex equipped car. Please be gentle.

My car is a '93 1.6, equipped with a Rotrex C15-60 charger. I'm just finishing the install right now. My problem is that the car won't hold boost. Instead, the boost vanishes completely, when the car reaches 6.5 psi (145kPa in new plots), typically at 6000rpm.

Please see the three log screenshots below from my Megasquirt. What might cause such a repetitive and total boost loss?

Very likely it's an issue with your bypass valve.

I thought the same, so earlier today I borrowed a valve from a friend who has the same kit. Didn't chance anything.

The potential issues as I see it

1. Belt slip. However, there is no dust anywhere near the belt.

2. Boost leak. Can a leak be this systematic, causing complete boost drop at a given boost level, and then cure itself for the next pull?

3. Something wrong with the charger. I not 100% sure how it works, but is it possible for the Rotrex charger to simply stall at a certain output pressure?

4. Hose collapse. I've read stories of people experiencing inlet hoses collapsing under boost. I don't understand how that would happen.

5. ???

Take the hood off and strap on a go-pro.

That or eliminate the bypass valve completely.

Rotrex is mechanically driven, it can't "stall". Belt slip might take a while to show, how much rotation are you getting out of your tensioner?

Sounds kinda like the inlet hose collapsing . I had this on another vehicle before. Is that red hose one that came with the kit or just an aftermarket piece that fit your needs? I would hope that the one that came with the kit was rigid enough to prevent collapsing.

I would doing a pull without that "S" intake. It would eliminate collapse and the BPV circuit. Dimes to dollars that's the area of your problems.

Its not belt slip.

The hose collapsing thing would only happen before the charger right? All the black hoses came with the kit, and the red 180deg hose is one I had sitting. I'll try to remove the red piece and see what happens.

Regarding the valve, if I just plug up the recirc circuit, would I not risk damaging the charger?

Edit, I just did a few pulls without the red hose. No change.

I just looked at the logs from the pulls with my friends valve. With his valve the two drops recorded happened at 5.6 and 5.5psi, whereas with my own valve the drops happened at 6.5, 6.4 and 6.5psi.

It's small datasets, but there seems to be a difference. This could be due to different climate conditions on two different days (?), or an actual influence of the valve itself.

there could be 2 problems
valve leak and belt slip

I diagnosed belt slip on a MP62 NB a couple years back, it did the same thing at 6k: made a huge "whoosh" sound and just stopped building any boost

new belt and tightened tensioner, and it was all good

This is my guess too. The whole intake looks like its made of the silicone piping.

I'd be really surprised if a 180hp Miata would be huffing enough air to collapse a silicone inlet, but maybe

Yeah that's probably not it, I just saw the update where he took the red tubing off, and still had the issue. But perhaps the filter is over oiled, or just not flowing the 260ish cfm needed? Thats all i got lol.

True, all hoses in the kit is silicone, photo of the kit for your reference below.

The car has been away for a few days for a clutch change and ABS diagnostics, tomorrow I'll try to do repeated pulls with the two valves back to back. If the numbers mentioned above are repeated, I'll conclude that the valve is the culprit. Let's see.

https://cimg0.ibsrv.net/gimg/www.mia...7c61d94fab.jpg

I did the back to back runs today, and the two valves behaved the same. So I'm not able to conclude it is valve related.

I have discussed the issue with the company who invented the Rotrex charger, and based on the plots, they strongly suspect belt slip. The belt setup looks like this, with the tensioner being the topmost pulley. Any suggestions for how to eliminate slip? I have sufficient tensioner travel, so that's not the problem.

https://cimg4.ibsrv.net/gimg/www.mia...0474340950.jpg
https://cimg8.ibsrv.net/gimg/www.mia...f2ec709f9b.jpg

To rule out the valve as the culprit, I'll do a few pulls with a strong Blow off valve later today.

To clear something up real quick, the Rotrex uses a "hi-speed planetary traction drive" and from the documentation "The Rotrex supercharger has a dedicated traction oil circuit which ensures both lubrication, cooling and actual torque transfer." There is no direct drive inside the unit like an MP62, Paxton or Vortech and it absolutely can slip. Its got a set of rollers inside the unit that rub against each other, there is a reason the magic Rotrex juice is called "traction fluid" in the documentation. BUT you'd have to do something incredibly silly like run it with no oil to make it slip, and I suspect it wouldn't last long and you'd know it pretty quickly.

On a related note, isn't the top of the fluid reservoir supposed to be above the top of the head unit? I may be wrong, but it looks like its below in some of the pics.

The charger is supposed to be the highest point of the oil circuit. Screenshot from the Rotrex manual below:
https://cimg7.ibsrv.net/gimg/www.mia...779bed5ff.jpeg

Valve is officially ruled out. I tested with a strong blow off valve (vent to atmosphere, not recirc), and the issue persisted.

Interesting, I can't say I've ever seen that document. I also noticed that they now say its self priming. Then again its been a number of years since I've pawed through any of this, or the information I was given was bad (entirely plausible)


Is the C15-60 inlet in this kit restricted like the old Kraftwerks kits?

Self priming is a little misleading; you really have to prime and level the traction fluid before driving the car, but this is done by running the system at idle until fluid comes out the compressor outlet. Also, most owners I've talked to about this fill the inlet hose with fluid before starting the car so you are not running it dry until fluid reaches the compressor.

Post Project G group buys circa 2013, the compressor was the C30-74 and was not restricted. I've since replaced that compressor with the C30-94 and is also not restricted.

I have a hard time accepting belt slip as the culprit for the OP but he does have a different tensioner setup than the Kraftwerks kit so I couldn't rule it out. The other (more obvious) cause could be a loose hose clamp or silicone coupler. At a particular boost pressure it bleeds off and doesn't "re-seal" until a lower pressure. How consistent it is might not support this theory but it's not hard to check and re-tighten every clamp in the loop.

The outlet for that traction fluid line, is it free of kinks and stuff? It looks like it could be in that one pic.

The kit does come with a restrictor. It is the black circular thing next to the pulley in the kit overview photo further up. It is required to have the restrictor fitted, for the kit to be legal in Denmark. Somehow I must have forgotten to put it in. Let's hope I don't keep forgetting it :)

I haven't done any boost leak testing. I'll try to make a tool, and get it done.

You're right, in one of the pictures, the outlet hose looks squashed. That's not the case, there is a nice gap between the charger and the bracket :)

Any chance your belt has become glazed? Or your pulleys?

i took off the belt to check. This is how it looks after 200-300 miles
https://cimg1.ibsrv.net/gimg/www.mia...76c1bbb502.jpg
That looks very worn, doesn't it? Almost like the teeth have been ground down.

I've indicated the belt routing in this photo. Note that the three center pulleys are flat, and the belt runs teeth in on two of the three pulleys. That's probably not ideal, but would it cause belt slip? I've also indicated the tensioner direction with an arrow.
https://cimg6.ibsrv.net/gimg/www.mia...c7b5543296.jpg

Any suggestions?

I have no experience with this, but maybe switching the bottom smooth pulley with the center ribbed pulley would help? Just a thought.

All three pulleys in the center of the photo are flat. Only the charger and the crank pulleys are ribbed.

That might be part of your problem.
Flat pulleys are OK on the outside of your belt, but not really on the inside I think.
The important thing here is belt tension: you need tension to prevent the belt to slip.
I am afraid the flat idler pulleys sort of squash the high ribs of the belt and prevent you from getting proper tension.

without any prior knowledge, that sounds right. :)

I have tried changing the belt routing by rotating the mounting of the tensioner, so the tensioner movement is more downwards. Illustrated here.

https://cimg5.ibsrv.net/gimg/www.mia...b81235a61f.jpg

This setup also doesn't seem to work, since the tensioner doesn't move sufficiently down to take out the slack, even with the shortest possible belt.

I'm lost here. Help.

If it's a cheap hose, a stock Miata at idle will collapse a silicone inlet. My old MP62 setup used to do it. I would hope the kit the OP has included a quality hose.


Something's really weird here. Did you buy this kit new or used? It almost seems like the bracket and tensioner system is not compatible with your setup...like the kit is for AC or No AC and you have the opposite.

Do you have proper check valves on all the vac lines? Could have one going bad that burps at ~6.5psi

Also, what kit is this? Every other one I've ever seen has the SC mounted significantly higher, plus I notice the one tensioner pulley in your system seems to be a good 6-7cm below the main crank pulley...

All the charge tubing and intake are silicone. Looking back over this thread, I'm still sayin its those hoses collapsing at 6000rpm.

Do you, or someone you know, have a go-pro or something similar? Would be easy to see if it is the hoses that way.

Kit was bought new, some 25-30 cars run this kit in Denmark. However, almost all run with a chunky restrictor in the inlet, and noone is facing the same issues. The charger is mounted in place of the AC compressor. So no mixups there. But the setup is probably not ideal for belt wear, given that the belt ribs are running on the flat pulleys in two locations.
https://cimg6.ibsrv.net/gimg/www.mia...c7b5543296.jpg
I have no valves in the system, except for the recirc valve seen in the photo below. Which vac line would I be concerend about?
The kit is a Danish offering from small company CCR Racing. You are right, it is a very low mount. The tentioner pulley is the top one in the photo above, with the tensioning direction marked with an arrow.
https://cimg1.ibsrv.net/gimg/www.mia...bbb4299948.jpg
Just so we are on the same page here, only the hose between the filter and the charger would be capable of collapsing at full boost right?

I have a gopro, I guess I could fit it and see what happens. Are you suggesting I remove the hood for the trial? Or put some light under there?

Nope, pretty sure it could happen on any of them. Not likely in the charge pipe, but if there is some issue with supercharger response... who knows.

honestly why would you run without the restrictor if thats how its supposed to be installed?

Put it on, no more hose collapse. I cant believe this problem has persisted so long lol.

I also cant believe a company can sell a kit of such terrible quality. When i first saw this thread, i thought you had cobbled together random cars silicone inlets, and done a diy bracket and pulley setup.

I would think that you'd need check/one-way valves on most of your vac lines and PCV, otherwise when the manifold goes into boost, you'll be pressurizing the entire vac system and the crankcase. Plus, you are missing the crankcase vent hose in this picture, so you're boost is probably just getting blown through the valvecover. I'm guessing right around the 6k mark is where the SC just runs out of puff after pressurizing the charge pipe, intercooler, manifold, crankcase, and the whole vac system. Try capping off the vac lines and the PCV port and I bet it fixes your issues.

Also this, I can't believe they would decide to mount the SC so low, when 1)everyone else mounts it much higher and 2) the company themselves stress the importance of having the SC be the highest point in an oiling system that is critical to its function.

Background info: In Denmark we have this lovely rule, than any changed component on a car is illegal, unless it has been verified by the German testing lab TÜV. And I mean everything, wheels, air filters, steering wheels. The lot. For example, I run 1.8 brakes on my 1.6 car = illegal. As you can appreciate, running a boosted car in Denmark is not easy. CCR has put the kit together and has had it tested at TÜV at great effort and cost. As such, this one kit is the only legal way to boost a Miata in Denmark.

For the TÜV approval to be valid, the car has to run with the restrictor, the stock ECU and the stock injectors. This gives a lift of 116->150 flywheel hp. This of course sucks. Therefore, I have chosen to run this kit without the restrictor using a ms2 and bigger injectors. It will then look legal, but I can hope to make maybe 210 fly hp when everything is tuned properly.

I appreciate your comments about the kit, but they only add to my frustration about the Danish laws.

I never came across anybody mentioning the need to run additional valves even with high boost Rotrex installs. I don't believe the come supplied with the American kits? The photo above was from when I was finishing the install. The crankcase line was connected before first start of the car with the kit. Looks like this now:

https://cimg0.ibsrv.net/gimg/www.mia...7687b7f745.jpg

^ah ok. But I still feel like there was more than one reason they used the restrictor. Did you try running with it back in to see if the problem persisted? You could still tune it for more than the kit legally can make, even with the restrictor.