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.

 

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.




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:

 

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.