Noob, Rotrex SC options
 

Hello all,
Just a noob here with the need for speed! Although this sight is mostly for discussion about turbo power, yes, I've gone to the dark side and decided to install a Rotrex Supercharger on my 96 Miata.
My plans are the following for the vehicle- Install 99 NB engine w/ stock bottom end, ported head, 1mm oversize valves, BP5a intake cam, adjustable cam gears. Exhaust exits through a RB header,
2.5 inch exhaust. Catalyst currently still on the vehicle. Ms2pnp still in the box ready to go on, get setup, go through the learning curve (whoa) before the SC install. Intake manifold is a skunk2 with 64mm
throttle body. Coolant bypass going on as soon as the 949 radiator is installed.
Anyway, that is just the baseline of engine mods for a vehicle that is currently a DD with second duty as a track car. My automotive experience is vast, but never with FI aside from being involved from
a distance with my son's Miata turbo install. So as far as goals for the system, 250-300 whp is probably what I'm looking to achieve currently. Does it make sense to use the C30-74, or is the C30-94 a
better option, with room for higher HP if wanted in the future? Hoping someone's been down this road and can share their experience and advise.

The -94 will be easier to get near 300whp. Make your decision about power now and stick to it. Turbo would be easier to change your mind on power, but Rotrex has it's place for some applications (i.e. easy to install, track car FI)

Sounds like you are reasonably well researched... read my build for some advice on what not to do.

Does your son have a build thread here on MT.net?

I suppose the thought is that the Rotrex will have low enough torque at low RPM that it can boost up to 300 whp at high RPM without bending stock rods?

Thanks for the response. I wasn't as clear as I should have been in my opening of this thread. 250-300 whp is what I would like to see at some point, that's why I questioned if the -94 wasn't the best option. To begin with, yes with stock internals, an untuned system, the lower end of that HP range would be my desired starting point. I hate to admit to ignorance but here you have it; I'm not sure what the difference in HP I would be starting using the Kraftwerks Kit for the NB which comes with the -74 as opposed to the -94. They state that the -74 on a stock engine would be in the 190-200 hp. They can tell me what percentage of added air the -94 would flow, but that was it. I also have to wonder if the intercooler for the base system would be sufficient to keep intake air temps in check on a 90 degree plus track day. The more I think about it, the more questions I have!
By the way, DN, the quote is great! I'll keep it in mind. To answer your questions, no and yes! What's your thoughts on max HP the stock rods can handle?

You can go with either the 74 or the 94. The 74 should give you about 250 with that config. See oregonmon's thread.

Hey DN, just noticed the link to your build thread, I'm on my way to it now. Cheers

My build is just opposite of what you have in mind. Tiny turbo for fun street, early boost, low end torque. I’m not familiar with the centrifugal supers, but others are.

You can see my mods in my sig block.

With an 85mm pulley and a gutted cat, my Kraftwerks C74 kit dyno'd at 211hp/170tq. The max boost I've seen on track is 8.8 psi. I think there may be another 10 horses to be had if the spark table were more aggressive, but I asked to keep it conservative so I can beat on her on track.

I had originally installed the Rotrex on a ~134,000 mile engine. At ~144,000 miles, she was using three quarts of oil per two day event, down on power and smoking badly during downshifts. I replaced the bottom end with one from a Japanese Domestic Market used import motor that had about 60k on it. I re-used my 25,000 mile rebuilt head. That's the combo making the 211/170 numbers. The odometer now reads about 153k.

I've had her on track in temps above 100 degrees. I usually short shift at 6600 or so when it's that hot, and I can usually complete a full 30 minute session. I did four days straight at VIR in early November in high 50s low 60s temps, and the coolant barely crossed 200. I still have the a/c hooked up, but never use it. It's coming out over the winter and I suspect all will be well with track temps next Summer.

Enjoy,

I'd suggest going for the 94 Rotrex. Keep in mind you're on the ragged edge for stock block. Keep boost modest and torque below 200 and you should be good.

I made 247 whp and 191 ft/lbs on a mustang dyno with my 225k mile 1.6L, a c30-94, and a custom intercooler. I spin the supercharger to about 90k rpm (c30-94 has a 100k limit while c30-74 has 120k limit) @ 7200 rpm. After 5k miles of track and street abuse, the motor is starting to smoke on decel, so I am building a similar 1.8 to you, minus the head work. I am hoping for 300whp on the same dyno. Currently the -94 makes about 14.5 psi at redline. I could imagine it would be significantly less with the better flowing 1.8.

Thanks for the advise k24madness, yes I already have the -94.
bschonman, sounds like quite a fun little 1.6. It's understandable that a higher mileage motor may start to smoke pushing that kind of HP and being pushed hard! My plans have changed since my last post. I've been tuning my 96's NA 1.8 with the ms2pnp. I've decided to use the bottom end of this motor with the 99 cylinder head that I'm in the process of porting right now. This should flow quite well and I'll have a good testbed for the mods that I'm doing. For what I had planned on selling the motor for, it didn't make sense to not use it! I have a donor, wrecked 2000 NB with 150k that I'm going to remove and rebuild the motor with forged internals, then switch it over down the road. I do still have questions on running a hybrid engine like this, which I do still have to research. What compression ratio will be without shaving the head except for a clean-up, then decide how much to shave the head. If anyone has any thoughts on this set-up, please let me know!
As poormxdad did, I'll tune for longevity in the beginning, not sure how long that will last...The Kraftwerks kit came with the 350 injectors and their cookie cutter intercooler, my son says for the gusto, I'll need to get bigger injectors and a bigger intercooler, any thoughts? He's running a turbo on his NB. with 550 cc injectors and a huge intercooler.

I am amazed how similar your build is to mine. I have an already built 94 bottom end with 8.5:1 forged pistons and forged rods. I got a 99 head and am researching how much I can safely deck it. Because of the lack of low-end the rotrex has, I understand you can run higher compression than a similar boost turbo setup. I think I am leaning toward somewhere between 9.5-10:1 compression, with something like a .04-.06 decking. Since my pistons are below stock compression ratio, I should have a little more room to play with, theoretically. This is my first time assembling a motor that is not stock, so my knowledge is quite limited. Please someone correct me if any of my information is wrong.

Also, if from my understanding, you should have no issues with the hybrid motor. You can use your CAS with the 1.8 head.

Also, my rx8 injectors (~440cc) were maxed out at this power level. I got an adjustable fuel pressure regulator to add a little extra flow and get the duty cycles down to a more reliable level. That should put into perspective how inadequate your injectors are for your goal. I have a set of flow force injectors that will hopefully do the job with the 1.8 and my higher goals.

Sounds like you've been doing your homework bschonman. Higher compression on the SC build has been one of the questions that I was wondering about. I had read several months ago about Quinn Motors taking .100 off the bp4w head. He was running ITB's on the car and started off with taking off much less, and gradually, if my memory serves me, worked up to .100. The car and the build was on one of the other Miata forums, although if you see the car on youtube by looking for Miata ITB.
The KSC also came with the DeatschWerks 255 LPH fuel pump. Are you familiar with it and how that will help over the stock pump? Hope to discuss it further very soon, the next few days are going to be 24Hrs of Lemons!

I think I remember seeing that thread when he said he decked .06 and wished he went for more, but I guess I never finished reading it. .10 is a LOT.

As far as fuel pump, I went with a simple walbro 255, which should be good until ~400 whp on pump gas, so it will meet our needs.

And to continue our similarities, while you are doing 24 Hours of Lemons, I will be doing ChumpCar at VIR. Amazing.

I believe that's what he ended up taking off, please don't quote me, because that does sound crazy! That kind of valve to piston clearance and compression ratio, bring up a whole new set of problems.
Chump Car is the next series that I'm going to start entering, they race at Laguna Seca, which Lemons does not. This weekend is Sonoma. If you'd care to check the car out sometime on youtube, lookup
FauxLorean. It's a Ford Focus that is a gas to drive considering it a low dollar car. Enjoy the weekend!

High compression with a Rotrex is a good plan. Even better is you use cams with shorter seat to seat duration, more lift and more duration at .020+

I am running 11:1 on mine. The biggest challenge you'll have is fuel. I run E85. No way that setup will run on pump fuel. Keep that in mind as you work on potential setups.

I'm personally trying to keep the car streetable and therefore have as much low end torque as a rotrex car can have. Any recommendations for pump gas? No e85 around here. And my want for low end torque rules out cams, right?

Also, what blower do you run and how much power does it make with that setup?

295 WHP, CM30-74 Rotrex, pro built motor so it's tough to compare.

Skip bumping compression on street car. Maybe clip the head .020 and call it good. Run the bigger 94 blower though. Should be able to get good power before detonation sets in.

Depending on on where you are in the build process you should consider passing on the Rotrex and get a TSE turbo kit. Honestly it's a better setup on the street. Seems to be better on track too.

On a stock vvt head, forged 9.5/1 pistons, 2.5” exhaust, smallest pulley for 120000rpm @ 7200rpm, we are seeing 270hp (crank, because that’s how we measure it in Europe) power delivery is so smooth, I would say. 74 is a waste of time. Looking for options to hybrid it to a 94.

BTW, from the original Kraftwerks kit, nothing is left from the kit, at this power level.

Use stock cams. Consider the TSE Turbo kit if you want torque. Personally I'm going with Rotrex for the ironic lack of torque, in hopes of keeping a motor alive for more than two seasons per rebuild.

>wants low end torque
>considering hands down least low end torque providing f/I application

lol

I don't see the problem. he can spool his rotrex with compressed air.

you know you can do this crazy thing called: tuning.

Guys are keeping this entertaining

OP, what about your son’s set-up that you don’t like?

Exactly what problem are you trying to solve?

I enjoy rotrex for it's lack of torque as well. Notice how I said "as much torque as a rotrex can have". I'm not looking for the 300wtq a efr would easily give me. I find my rotrex infinitely easier to drive on track than my FM2 car making a similar amount of power. Every time I push the pedal, I immediately get the same response. Maybe it's because I'm a novice driver, but I just prefer that. 250whp is 250whp however you get there.

A motor making 220wtq will always have a longer lifespan than the same motor making 300wtq. Tuning fuckups can melt a rotrex car the same way they would a turbo car.

This may be a silly question but why don't people ever run the C38 size units on Miatas?

Heads don't flow, so no need. Plus weak transmissions are always an issue.

Back to the injector question. I have the options of 750cc or 1000cc at the same price. Does it make sense to just run the 1000's and not look back? I'm not sure, but I've been told that idle can sometimes be a problem with the bigger injectors. Seems to me that with the ms2 less on time should be fine.

again: tuning

https://cimg8.ibsrv.net/gimg/www.mia...e4d807c855.jpg

If they are ev14 injectors the 1000cc will idle fine

https://cimg5.ibsrv.net/gimg/www.mia...461bce5f8f.jpg
https://cimg8.ibsrv.net/gimg/www.mia...c11fc00946.jpg
Never followed though with a build thread, in fact I think this is my first post :party:
essentially I have a nice churbo build. Lots of influence from previous builds i.e. 18psi style intercooler routing.

What are those graphs showing? Is that controlling boost so it builds gradually to redline? Why would that be preferable over a centrifugal supercharger? Wouldn't the torque still be as low?

I'm just saying, if youre worried about tq, you can tune torque.

Brain,

Your plots show that the tune increased boost on a turbo'd car, which increased hp and torque. On a Rotrex equipped car, would a superior tune increase BOOST over an average tune?

Thanks,

a turbo doesnt have to run full boost at all times. If you have an EBC, you can tune the boost output. If you're worried about too much tq, dont let the turbo produce too much torque.

No. The boost that a Rotrex unit produces is a direct relation to the engine speed (rpm) and pulley size (ratio). No tune will change the amount of boost you make on a Rotrex.

Can tuning change the laws of thermodynamics to fix the inherent massive heat issues that accompanies turbochargers? No doubt, I think turbocharging is better for the OP and anyone would plans to do more street stuff than track stuff. But between turbos falling off (fixed by inconel studs and better hardware), cracked manifolds, High CLT's and oil pressure, high IAT's, wastegate issues etc. you have to at least admit that the Rotrex systems have some appeal to the track only guys. People that want to just stick it on, tune it once, and never have to worry about anything at the track except for suspension/tire setup and driver mod. I was able to hop in a Rotrex car and go extremely fast within a lap, and I'm not the only one that has that same story. Rotrex cars are just easy to drive fast on track without issues.

:jerkit:

So

I feel I have valid contributions to this discussion, being a) a driver of a rotrex C-74 car @210whp for 5 years and b) currently a driver of a 250whp TSE EFR 6258 car.

1) You don't have to run the EFR at 300wtq. The great advantage of a turbo over the rotrex is variable boost under variable conditions. Currently I have my EBC set to give me about 200wtq from 4000-7200. When I get on it on track, it just pulls.

2) the EFR spools quickly, and the integrated recirculating BOV helps to keep it spinning off throttle. Between the two, yes the Rotrex gave crisp definitive absolutely no lag throttle response - but the EFR response is such that if you had not previously driven a Rotrexed car of a similar power level, you would say the response is not noticeable.

3) the EFR gives me torque from down there to up there. I can change that response as I wish with EBC control. I've currently limited it to 200wtq to save the trans ... I'm now thinking that's overly conservative, and will probably bump that to 230 wtq. That flexibility is another advantage of the turbo over the rotrex.

4) I enjoyed my rotrex setup. It was simple, easy, and light on heat management. I also enjoy my EFR setup. It is somewhat simple, not as easy, not nearly as light on heat management. Under hood temps are significantly hotter. Water and oil lines had to be run. But the the power flexibility and usable power potential is so much greater with a 6258 compared to a C30-74. Even a -94, really.

So here's my tl;dr. If you want ultimate easy boosted reliability, go rotrex. If you want boosted reliability with flexible power management, with a vastly greater torque band, but with corresponding increases in needs to deal with heat rejection, go TSE 6258. Other turbo kits have no place in this discussion, really, as they were not originally designed for track use. Apples to oranges.

I 100% do not regret moving from C30-74 to TSE EFR 6258. But, I will also say that I enjoyed the shit out of my C30-74 and the simplicity of its installation.

Coincidentally, this does not change for a belt driven turbo either.

there's some appeal here, but everything you've listed at this point is a non-issue and not mutually exclusive to a turbo.

I drove fast on the track with my turbo and lived to tell the tale.

again: the only thing I was commenting on was "too much tq" with a turbo. If you have "too much tq" then make it not.

It's always so amusing to see how hard people will continue to repeat silly statements to justify their bad or unpopular decisions. Tell yourself whatever makes you sleep better at night =, but at the end of the day if you were right this place would be called miatarotrex.net or at least have enough rotrex Miata's to justify having a subsection for em.

Meanwhile we're enjoying torque :)

Nailed it. prop cat deserved

I think Mobius hit the nail on the head. There's merit to both setups. If I had unlimited money and a trailer it would be TSE EFR all the way.

rotrex Miata is still infinitely better than n/a Miata so... :)

Now that we can agree on.

I also enjoy the shit out of my Kraftwerks C30-74 kit. I went Rotrex three years ago because I got the complete kit, new, shipped, tax free for $3000 as an Indiegogo perk for donating to a Skunk2 effort. I couldn't resist. I have had zero Rotrex-related issues. None, after more than three dozen track days and more than 17,000 miles. And, as 18psi said, it's infinitely better than an n/a Miata. A 211hp/170tq Miata is a surprise to a lot of people.

hey we all agree!

You have your preference for a Rotrex, which is fine, but their shit hardly smells like roses. Belt and tensioner issues are a relatively common S/C problem that few people like to talk about. They also can suffer from broken supercharger brackets, completely separate oiling system filled with extremely expensive oil that must be configured in a specific way, and extremely expensive replacement units if required are all things that can be issues with Rotrex issues.

From your list of "issues" with turbocharger setups, five of your six items* are easily solvable with off-the-shelf parts (studs, good manifold, good radiator+ducting, good IC, and an EFR IWG or any turbo with an EWG). All of those issues are a result of people being cheapskates when trying to put a track car together. If you buy cheap shit, cheap shit breaks. There is no "cheap shit" Rotrex kit. No eBay bracket, no knockoff supercharger, no shitty off-brand tensioners. If you buy a Rotrex, you're getting nice stuff, and it all works. If you buy a nice turbo kit (like mine), it all works. There are half a dozen dedicated race cars built in the last 6 months using my kit, and all of them work. Probably another dozen guys using the kit in road/HPDE configurations, all of those work too. None of them suffer from the supposed cornucopia of issues you've laid out.

Rotrexes are easy to drive in part because they have great response, and in part because they make much, much less torque than a turbocharged car with the same peak output. If you tune an EFR car to run the same as a Rotrex, it would be (nearly) just as easy to drive. The driveability is not inherent to the FI solution, it's inherent to the powerband. If you have a big, high-power Rotrex car, it will arguably be HARDER to drive than a high-power EFR car, since the Rotrex's throttle will be incredibly touchy (boost based on RPM and nothing else, for better or for worse), whereas the turbo can be tuned to use a TPS sensor to alter boost levels and deliver less boost at lower throttle positions (more driveable). The saving grace is that, again, a high-power Rotrex car makes way less torque than a high-power turbo car.

Rotrexes are generally easier to get set up because they make less power. Period. Look at the dyno chart for any Rotrex setup and compare it to a chart of a turbo car making the same power and you'll see what I mean. If you make power, you create heat. Rotrexes create less power, so they create less heat. Because of the high average power output of a turbo car, heat management can be difficult, but again, there are known strategies for dealing with those heat issues that are easily implementable for the average enthusiast. Aluminum heat shields, reflective heat wraps, firesleeve, etc. is all inexpensive and effective.

So yes, Rotrex kits have their appeal in simplicity and reliability, but so do good turbo kits. It comes down to response vs powerband and which is more important to you. I have driven good Rotrex cars, I know what they are capable of, and they are the right solution for some people, but a good turbo kit is far, far, far better than you make it out to be.

(* - The sixth (higher oil pressure) is just not a thing, at all, so I'll ignore it entirely and assume you made a typo or something. As in, turbos don't substantially alter oil pressure in any way, and even if they did, raising it would not be a bad thing within reason, but they don't, so it's not, so ????)

well put.

You guys are starting to sell me on an EFR, although it'll likely be years from now.