211whp on 6.7psi
 

Cross posted from this thread on m.net.. CoralDoc's Kraftwerks C15-60 (baby Rotrex) DIY kit. 99 engine, MS PnP, TDR I/C, 420 RX8 injectors, 43.5psi (NA6) 93 pump gas

211whp on pump gas, 6.7psi running 28° timing. Not bad for a blower the size of a grapefruit.

That spark map looks like something from an N/A motor with the MAP scale inverted. That tuners can run that much timing, that lean on pump gas with these is a real paradigm shift. It matches what we have seen here. I'm starting to see more and more intercooled Rotrex tunes that have timing optimized for MBT at every MAP/RPM without being past detonation threshold.

On paper at least, the Rotrex should only be a tiny bit better in det resistance than a turbo flowing similar CFM & pressure differential. In practice however, we keep leaning them out, adding timing, making more power and they don't knock. Other S/C options aren't even in the same league. More CFM, less boost = Win.

I see this as due to two main factors:

- Exhaust back pressure. While a turbo and Rotrex compressor may have identical compressor maps, one is pushing against the exhaust back pressure created by the turbine where the other does not. The turbo blocking the exhaust flow raises the boost level relative to a Rotrex, which means greater heating of the air mass. The turbo then requires more fuel mass, less timing to control detonation. I think disrupted exhaust scavenging with turbos using stock n/a cams also contributes to lower charge efficiency and mixture burning.

- Compressor housing heat. The water cooled CHRA of a modern turbo does an excellent job of insulating the compressor from the 1200° heat just 2" away but you still have several hundred degree compressor housing temps. In contrast, Rotrex housings run 110~130° on a street car and transients not much past 160° even in race conditions.

Even after all this time, the marvelous efficiency is still fun to look at

Edited 12/27/2010
My rough calcs for BSFC (Brake Specific Fuel Consumption)
196whp @ 6000rpm torque peak +
26 drivetrain losses
222bhp

420cc @ 43.5psi (40 lbs/hr) 195500-4450 Denso RX8 injectors x 4 cylinders
65% DC at 6000RPM torque peak.
120 lbs/hr

104/222 = .47 BSFC roughly - Torque peak

137.6/237bhp roughly .58 BSFC - Power peak

I know my calcs are not dead on but even allowing for some fudge factor.. that's amazing.

That buttery smooth and linear torque curve is familiar. So easy to drive fast at the limit of traction.

Inline linked the images so we can see them clearer

http://forum.miata.net/vb/attachment...7&d=1293329663
http://forum.miata.net/vb/attachment...3&d=1293367919
http://forum.miata.net/vb/attachment...7&d=1293379388

35% for drivetrain loss seems steep. Has this number been backed up with hard data? I could use this info to easily make a clutch decision.

Back on topic: Are there any setups that are ready to push 300+ HP. If so, would this be a more reliable alternative to some of the proven track setups by members on this site?

35hp, not 35% and yes that numbers is widely accepted.

Not sure what you are asking for "setups ready to push 300whp". We don't offer a 300whp in a box if that's what you mean.There is at least one Miata I know of making a conservatively tuned 400+ whp on race gas with a big C38 series blower. The only complete Kraftwerks kit available now is a non-intercooled C30-74 kit making about 160whp for the NB. C15-60 based intercooled kits making around the same power for the NA are just around the corner.

For power levels above that, we offer DIY kits for the C15 and C30 series. It's up to you to plan, build and tune though. We just supply the blower, brackets and drive system. You supply all intake plumbing and fuel management.

what motor is this on?

Edited OP but you could have followed the link you lazy bum.

:) figured since you said it was a cross thread you started teh same post over there... my bad. Congrats!

This is what I was asking. I wanted to know if there was a rotrex style charger that could support more than that I have seen advertised.

I'll check it out on your site.

Edit: After looking at the diy kits; If you have an intercooler and engine management. What are the downsides to this? One diy kit supports 400Hp. What do the dyno plots look like for the large supercharger. (built engine of course)

That is a ton of timing (almost double what most of us run), but pretty impressive nonetheless.

DIY kits don't have dyno plots as they are just a blower and drive system. You have to plan and build the rest of the installation. We don't provide step by step instructions for that part. At the big end, assuming a BP series block with BP4W/BP6D head, unlimited budget and a C30-94 DIY based kit, maybe 470whp running E100 on a built 2.0L.

Being a belt driven centrifugal S/C, boost will generally rise linearly with RPM. So the shape of the plot here is fairly typical. In short, I can't give you a few sentence answer to the basic question you have. You'll have to do more research to begin planning your build.

Tech specs on the C30 series Rotrex

Fixed;)

I am betting it's the former vs. the latter. Going from my stock 8.8:1 '94 motor to the 9.5:1 BP4W motor, I was able to add in two degrees of timing straight across the torque peak despite the higher compression - exhaust flow is huge for timing. Hustler proved this again with the .86 A/R housings - huge timing numbers from unrestricting the exhaust and dropping the compression a little.

Compressor heat MIGHT effect the efficiency a bit, but I don't think it has anything to do with our ability to run timing. 110*F in the manifold is 110*F in the manifold no matter what puts the air there.

I'm surprised the tuner didn't catch the timing drop at high RPM - as soon as the MAP goes over 140 you can watch the timing tank in the datalog, down to probably ~25 degrees at ~7k and 148kpa. If Josh is tuned for MBT he's probably only giving up a horsepower or two, but if he's got it dialed it back from MBT for safety then he may be giving up more.

211 at 150kpa is huge power for the boost, though. Big flow at low pressure is something you just can't achieve without a BIG turbo.

Digging through some old notes and I think I have the estimated drivetrain loss value wrong. Should be 26hp. Not sure where I got 35hp from, sorry.

That would bump the BSFC at Torque peak to .54 and about .58 at power peak. Still good :)

Those are solid numbers. The interpolation on the top is really hurting 6000rpm+ output; if you've got the piston speed, use the spark angle. I don't understand the logic in running more spark at 4000rpm than 7000rpm...unless he's at MBT. I'd like to know where MBT is on this tune, and how far out that spark table is in terms of safety.

I found that in the cruise cells it pays off to run less spark angle after hearing some phantom-detonation with the Polish det-cans and I'm still getting 32-34mpg on cruise, 26mpg on 85-90mph with the 400lb trailer. I also so a large jump in torque by pulling spark and leaning out 3000-4500rpm cells, but I have a different animal of couse. Mustang Dyno = love

Agreed. I think all the difference is lack of exhaust back pressure. After thinking about it a bit, the difference in IAT due to compressor housing temp would be infinitesimal.

I wondered about the timing on top too. Maybe the tuner got nervous seeing 85% DC and dump timing for safety? Hopefully the Dr will chime in.

Thinking about it again, the exhaust backpressure has something to do with it, but I think it also might just be the simple fact that you guys are adding boost with RPM, and RPM is a detonation deterrent. Even on my 2554R I was able to find MBT at 11-12psi above 6000rpm. The same high boost/cylinder pressures that produce big torque at 4000rpm also make it more prone to detonation for obvious reasons.

Very nice numbers!

Emilio, I'm curious about the ideal CR with the rotrex. I remember reading somewhere that you were going to run 11:1 on the OGK.

I've got a 99 head w/ an 01 block and was wondering if I could see similar results on a c30-74. Or is the c15-60 recommended for stock internals?

He's probably going to run corn through it.

The more compression you throw at it, the more torque you make for a given boost level. No "ideal" CR, just whatever will work with the rest of your system.

Match blower size to hp goals. What power are you trying to make with the hybrid motor?

Planned for race gas. No corn nearby unfortunately.

Oh I see.

I'd like to see 230-250 rwhp. Running a MS3 and a DIY FMIC. Wondering if the motor will benefit from sequential fuel and ignition at those power lvls.

c30-74