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Discussion Starter · #1 ·
Hi folks,
I've in the process of building a 2zz and have been waiting on MRW for 2 years to put there Eaton based supercharger(Katana) kit up for sale but every time I ask about it's status I get the same "It'll be soon.." answer, so Rotrex seams to be a better solution. The ability to use a water/air cooler for one and the possibility to mount it on the exhaust side is another.

The biggest reason for posting this is I'm going to be building this from scratch and the higher N/A HP(230+) of what I'm building is pushing the numbers too far to the right of the C30 compressor charts and puts me right in the C38s 70%+ zone which in turn have boost that can break my rods(stock) and transaxle(C60 modified)!

So here are the best questions I can think of right now to, hopefully, put me on the right track.

1. I've done the air flow and PR calculations and with a max HP of 300 to 350. The efficiency falls in the 60-65% zone on the C30-94 where as on the C38-71 and C38-81 it falls the 70+ zone. So is falling into the 60-65% still something that's workable?
2. Will a C38 fit on the exhaust side of the engine? It is very big! I have PPE exhaust headers which does give me more room near the idler pulley mount.
3. If I do use a C38 will a 115mm pulley and a blow-off valve set for, say, 10lbs. keep me from blowing up my engine?

Basic specs are: Mahle 10.5:1 forged pistons, Darton sleeves, stage 2 MRW cams, stock rods, MRW valves and springs, PPE merged exhaust headers, etc...

Please excuse my inexperience as it's a new field for me.

Any of you old compressor dawngs out there have any sage advise?

Thanks in advance!
 

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A few years ago I hi-jacked someone's thread here on this forum and showed in detail how to make the calculations of boost, torque, and HP vs. RPM with a Rotrex on a 2zz. This has nothing to do with drawing one line for PR and another for flowrate and looking where they intersect - this simplified method completely disregards the turbine speed, which is a critical parameter. Anyone with a background in mechanical or chemical engineering should be able to understand what I presented in that thread - well maybe I'm over-optimistic about what undergraduates take away from their thermodynamics courses, maybe just master's level engineers would get it. For the rest, their response to detailed calculations that give an accurate result is literally: "Well even a blind squirrel can find a nut sometimes." To paraphrase Arthur C. Clarke, any sufficiently complex calculation appears to the ignorant as BS.

With the pre-amble out of the way, centrifugal superchargers combine all of the worst features of supercharging and turbocharging. A centrifugal supercharger has to spool, just like a turbo turbine. However, unlike a turbo, its rotation speed is limited by the engine speed, because they are connected by a belt. So by the time you get to full spool, you are at the engine's rev limit. And below that, the boost production is sub-optimal. A modern turbo gets to full spool at a relatively low rpm and maintains it throught the rev range.

In case you are wondering, I do want to discourage you from using a Rotrex. As far as I am concerned, this is a dead end, how bad of a dead end I did not realize until I invested time and money in exploring it myself.
 

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Discussion Starter · #3 ·
I did see your YouTube video about your Rotrex install. You didn't say anything negative about it so I assumed all was well.

So turbo? What unit?

Hope I can sell my headers!
 

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The beauty of centrifugal superchargers is how linear they keep the motor, which would probably work for someone that is seeking a balance and finesse in their build. Makes the motor have a naturally-aspirated feel to it.

Outside of that, a turbocharger is better at everything.
 

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Hi folks,
I've in the process of building a 2zz and have been waiting on MRW for 2 years to put there Eaton based supercharger(Katana) kit up for sale but every time I ask about it's status I get the same "It'll be soon.." answer, so Rotrex seams to be a better solution. The ability to use a water/air cooler for one and the possibility to mount it on the exhaust side is another.

The biggest reason for posting this is I'm going to be building this from scratch and the higher N/A HP(230+) of what I'm building is pushing the numbers too far to the right of the C30 compressor charts and puts me right in the C38s 70%+ zone which in turn have boost that can break my rods(stock) and transaxle(C60 modified)!

So here are the best questions I can think of right now to, hopefully, put me on the right track.

1. I've done the air flow and PR calculations and with a max HP of 300 to 350. The efficiency falls in the 60-65% zone on the C30-94 where as on the C38-71 and C38-81 it falls the 70+ zone. So is falling into the 60-65% still something that's workable?
2. Will a C38 fit on the exhaust side of the engine? It is very big! I have PPE exhaust headers which does give me more room near the idler pulley mount.
3. If I do use a C38 will a 115mm pulley and a blow-off valve set for, say, 10lbs. keep me from blowing up my engine?

Basic specs are: Mahle 10.5:1 forged pistons, Darton sleeves, stage 2 MRW cams, stock rods, MRW valves and springs, PPE merged exhaust headers, etc...

Please excuse my inexperience as it's a new field for me.

Any of you old compressor dawngs out there have any sage advise?

Thanks in advance!
For a given speed and boost level, the lower the compressor efficiency, the hotter the delivered air will be.

Dave
 

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MR-2 ZZW30 2001 RHD
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The Rotrex does have some advantages:
  • Less heat build-up in the exhaust system
  • Easier to install than a turbo system
  • Better throttle response as a turbo system
  • Easier on the engine and gearbox (due to lack of torque)
But on a 2ZZ-GE, the power curve is a bit silly. Even with a C60 gearbox you will not have consistent average power across the top-end (i.e. from 6500 - 8000 rpm).

The better alternative would be a positive displacement supercharger like on the Lotus Elise / Exige. But I think there is not enough space in the Spyder engine bay for such a thing.
 
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