Teach me: Big power Rotrex on small-ish motors

As some of you know, i'm building another Miata.

It's going to have a 2.2 litre 4 cylinder motor.

I'm intrigued by centrifugal superchargers, and my power goal is north of 400whp. I can EASILY achieve this with a turbocharger, and right now that's the plan. The downside to the turbocharger is the way it will build power on this motor, that being huge amounts of scary low end torque, which is FUN, but not necessarily FAST.

Centrifugals intrigue me due to their power delivery, how much "easier" they are on motors, and just because they're something i haven't messed with.

My main questions at the moment:

1) I see people making over 300whp using these on 1.8 Miata motors. What are the big obstacles to overcome if these guys were to want to push another 150whp?

2) It's unlikely that i'll be revving this motor over 6500rpms. I'm sure i can swap pullies to reach target supercharger speed, but are there other concerns about driveability or general effective-ness when using one of these on a motor that doesn't rev out real high?

3) Because i don't know much about sizing of these things... is there even a Rotrex big enough to do what i'm wanting on this fairly ill-flowing motor?

Inspiration. Think this, but 2x or more the power.

http://youtu.be/poR3NSgGG5E

Pretty sure Wonrgwheeldrive has a rotrex on his CRX. He's pushing around 350whp I believe, but that's on a Honda motor - so it flows better than the boat anchor you have.

And revs better...

His is the K-powered SMF car, right?

Turbo may very well the only halfway logical choice, i'm just intrigued and would like to try it if there's even the faintest chance of success.

And then if it's awful, i take it off, build a motor for the other Miata, and turn my Mazdaspeed into a supercharged Miata and piss the fanbois off.

I can make my motor flow better if that helps appreciably. Relatively simple matter of putting an FE3 head on my F2T block.

Rotrex's are the bees knees.

If you want to get over 400 out of a 1.8, then my suggestion is that you go turbo.

I have a C30-94 Rotrex on my S2000, it made 385 whp on a dyno dynamics. I think that SC might even be too big for the Miata motor, so you would end up with weird power curve.

I went with the rotrex because I knew 350-375 was more than enough for me, otherwise it would have been straight to a turbo.

Mind you, that much power on an S2000 was more than enough. The linear delivery was great and kept the character of the motor intact. It would click low 12 second passes at the quarter mile all day long. Driving it at the dragon was a lot of fun with all that added low end power. With that said, I would think 3xxhp on a lighter Miata should be more than enough, otherwise go to an LS motor.

I'm using a 2.2.

The C30-94 seems to be working pretty well on the 1.6 powered Miata in the OP.

400whp is the minimum goal. I'd eventually like more, but i may very well end up being limited by my motor choice. At which point i'll switch my bellhousing from B2600 to TII RX7 and start messing with a bridgeport rotary.

There's no logical reasoning for the power levels i want. Nor is there a logical reason for not wanting a V8 in a Miata. But it is what it is.

In reply to Swank Force One:

Yes K20 from the JDM Civic R that has been worked over.

Guy on a forum I visit has one on a 2-liter 16v VW and found that it was surging at low RPM. Solution - bleed hole in the charge pipe. Not only did the bottom end smooth out but it made 50 more horsepower at the top end.

Sizing is key, and it seems like it's not an exact science.

Swank Force One wrote: I'm using a 2.2. The C30-94 seems to be working pretty well on the 1.6 powered Miata in the OP. 400whp is the minimum goal. I'd eventually like more, but i may very well end up being limited by my motor choice. At which point i'll switch my bellhousing from B2600 to TII RX7 and start messing with a bridgeport rotary. There's no logical reasoning for the power levels i want. Nor is there a logical reason for not wanting a V8 in a Miata. But it is what it is.

If you have a 2.2 and the space, then the C38 will put you over 400.

My main point is to not to worry so much about the final number. Go for a C30 and I am sure it will be more than enough to have a lot of fun.

I made a custom pulley for mine and was overspinning it. I never had a problem but they are finicky if you are pushing a lot of RPMs. My S2000 at 8600 rpms and spinning the Rotrex 10% over allowable was fine, but an AP1 doing the same at 9300 rpms only lasted me 5k miles.

Rotrex also have a lifespan and the factory will not rebuild them. They are considered throwaways by them. There is a guy in Tx that rebuilt one for me though, I used it for 1k mile with no problems and then sold it.

have you asked Rotrex yet???

DaveEstey wrote: In reply to Swank Force One: that has been worked over.

Nope, stock unopened K20A with a C30-94. Low amount of street miles but like a gazillion dual-driven autocrosses a year. Thing still works great, and it hasn't made the motor go boom despite it spending most of its time at or near redline :D

There are some other K series guys using the big C38 units that are well north of 400HP, I have no idea if the miata motor will flow well enough to reach 400.

In reply to wrongwheeldrive:

He is talking about an F2T being fed by a rotrex instead of a turbo. Not a miata's BP.

derp, saw miata and assumed BP. Either way, that statement stands. I don't think the F2T is a particularly well flowing motor either

In reply to wrongwheeldrive:

I stand corrected. Makes the numbers even more impressive!

Rotrex. Me rikey.

I've heard of these but never seriously considered one. One dumb question: is anyone out there using them with intercoolers? Didn't see any links etc.

wrongwheeldrive wrote: derp, saw miata and assumed BP. Either way, that statement stands. I don't think the F2T is a particularly well flowing motor either

It's not... but what's the difference between cramming boost through it with a turbo vs. The same with a rotrex?

If the flow is really a problem I can put an fe3 head on it, will pump more air than a BP.

Curmudgeon wrote: I've heard of these but never seriously considered one. One dumb question: is anyone out there using them with intercoolers? Didn't see any links etc.

Mine is intercooled. I can post some pictures when I get home. It will be in an S2000, though.

The Track Dog Racing kits are intercooled.

I suppose you are right, SFO.

Mine is intercooled. The guys over at Bell fabbed up something that would work perfect for the size of the rotrex.

So basically it sounds like I'd need a c38. Is my relatively low redline going to cause problems?

So my next question is: are these limited really by rpm, and psi being secondary? Whatever I get at 100krpms is what I get, period?

Or will the fact that my motor flows like crap cause heat issues due to sky high pressure? (Not uncommon to push 30psi on a holset on a stock motor... then make 350whp.)

I'd say rpm is what kills them.

What about two C30s? ... But that starts getting pricey.

It's weird Skunk2/Oscar Jackson was doing the miata kits then suddenly they dropped off and barely anyone talks about them anymore. They just relaunched their kits but the gains did not seem worth the price? Maybe it's easy to exceed their kit?

170hp/125 torque on 1.6 185/144 on 1.8 94-97 195/150 on 1.8 99-05

The M45 kits? Blargh.

Slippery wrote: I'd say rpm is what kills them. What about two C30s? ... But that starts getting pricey.

I think a C38 running full bore should do it. I need to look at some maps.