Rotrex anyone?
Coming from the turbo camp but trying to be very un-biased when looking at new boost packages of any kind, I really don't think the dyno number is the biggest factor for guys searching for a blower for track applications.. turbos are reliable for a DD, but there are a TON of things that can go wrong with them under sustained abuse at the track. Sure with deep enough pockets, who cares, and some people have not had problems with their turbos at the track, mostly a product of meticulous maintenance, and luck. Something like this Rotrex, if it was puting down a clean 200+ whp, would probably be a better choice for a track miata than a turbo in terms of how many parts there are that might break... trust me, I know the turbos can outperform them, but that's not the point really. Yes, a turbo can also be done pretty reliably, but I guess what I'm saying is the SC has a higher chance of being reliable and not having issues.
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Nobody will argue that a turbo system with the same peak CFM as a Rotrex won't make torque sooner. Given the same CFM output, the Rotrex will run cooler IAT's, underhood temps and EGT's though, guaranteed. So everything else being equal, you'll see more peak power with the Rotrex at the same boost. Peak torque remains about the same with the Rotrex but more area under the curve with a turbo having the same peak CFM.
Everyone wants maximum torque so we have experimenting with reducing top end CFM and spinning a larger Rotrex unit faster, to get more CFM down low. The boost number is low but CFM very high. While in theory, reducing the top end CFM might increase IAT's, in practice we see only mild increases.
The characteristic that tells the story is that the production 165whp non-intercooled Kraftwerks kit running stock injectors and an inlet restrictor requires no timing retard. You can't do that without low IAT's. That same basic C30-74, belt tensioner and intake side piping make up the core components for the base intercooled and big boost intercooled kits to come later. On a strong enough 1.8 motor with a good flowing head, I think 300whp on race gas will be possible from the exact same C30-74. That, is an upgrade path
Everyone wants maximum torque so we have experimenting with reducing top end CFM and spinning a larger Rotrex unit faster, to get more CFM down low. The boost number is low but CFM very high. While in theory, reducing the top end CFM might increase IAT's, in practice we see only mild increases.
The characteristic that tells the story is that the production 165whp non-intercooled Kraftwerks kit running stock injectors and an inlet restrictor requires no timing retard. You can't do that without low IAT's. That same basic C30-74, belt tensioner and intake side piping make up the core components for the base intercooled and big boost intercooled kits to come later. On a strong enough 1.8 motor with a good flowing head, I think 300whp on race gas will be possible from the exact same C30-74. That, is an upgrade path
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From: Queensland Australia
ITA's and SC speed
Excuse my ignorance, ? what is a ITA
Maximum safe SC speed is 120000 rpm
With my 95mm pulley it is spinning at a lazy 104900 rpm at 7000rpm
with a 90mm, 110600 rpm @ 7000rpm
With a 85mm, 117250 rpm @ 7000rpm, ? can I pull enough timing out to stop detonation and what power increase would I expect.
ps It is a DD no track work and I am looking for more torque in the lower rev range.
Cheers OD
Maximum safe SC speed is 120000 rpm
With my 95mm pulley it is spinning at a lazy 104900 rpm at 7000rpm
with a 90mm, 110600 rpm @ 7000rpm
With a 85mm, 117250 rpm @ 7000rpm, ? can I pull enough timing out to stop detonation and what power increase would I expect.
ps It is a DD no track work and I am looking for more torque in the lower rev range.
Cheers OD
Nobody will argue that a turbo system with the same peak CFM as a Rotrex won't make torque sooner. Given the same CFM output, the Rotrex will run cooler IAT's, underhood temps and EGT's though, guaranteed. So everything else being equal, you'll see more peak power with the Rotrex at the same boost. Peak torque remains about the same with the Rotrex but more area under the curve with a turbo having the same peak CFM.
Everyone wants maximum torque so we have experimenting with reducing top end CFM and spinning a larger Rotrex unit faster, to get more CFM down low. The boost number is low but CFM very high. While in theory, reducing the top end CFM might increase IAT's, in practice we see only mild increases.
The characteristic that tells the story is that the production 165whp non-intercooled Kraftwerks kit running stock injectors and an inlet restrictor requires no timing retard. You can't do that without low IAT's. That same basic C30-74, belt tensioner and intake side piping make up the core components for the base intercooled and big boost intercooled kits to come later. On a strong enough 1.8 motor with a good flowing head, I think 300whp on race gas will be possible from the exact same C30-74. That, is an upgrade path
Everyone wants maximum torque so we have experimenting with reducing top end CFM and spinning a larger Rotrex unit faster, to get more CFM down low. The boost number is low but CFM very high. While in theory, reducing the top end CFM might increase IAT's, in practice we see only mild increases.
The characteristic that tells the story is that the production 165whp non-intercooled Kraftwerks kit running stock injectors and an inlet restrictor requires no timing retard. You can't do that without low IAT's. That same basic C30-74, belt tensioner and intake side piping make up the core components for the base intercooled and big boost intercooled kits to come later. On a strong enough 1.8 motor with a good flowing head, I think 300whp on race gas will be possible from the exact same C30-74. That, is an upgrade path
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Excuse my ignorance, ? what is a ITA
Maximum safe SC speed is 120000 rpm
With my 95mm pulley it is spinning at a lazy 104900 rpm at 7000rpm
with a 90mm, 110600 rpm @ 7000rpm
With a 85mm, 117250 rpm @ 7000rpm, ? can I pull enough timing out to stop detonation and what power increase would I expect.
ps It is a DD no track work and I am looking for more torque in the lower rev range.
Cheers OD
Maximum safe SC speed is 120000 rpm
With my 95mm pulley it is spinning at a lazy 104900 rpm at 7000rpm
with a 90mm, 110600 rpm @ 7000rpm
With a 85mm, 117250 rpm @ 7000rpm, ? can I pull enough timing out to stop detonation and what power increase would I expect.
ps It is a DD no track work and I am looking for more torque in the lower rev range.
Cheers OD
What has BulletCars suggested?
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I don't know anything and I'm just adding an observation. At the track days I do I've seen a lot more BMWs, S2000s and other cars people spend significant upgrade money on running Rotrex units than any other single FI system. It's very popular among the big buck crowd. Don't know what that means, just an observation.
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From: Rancho Santa Fe, CA
Restricted Rotrex Dyno Sheet
Here is a dyno sheet from the Black Super Spec Miata. The Rotrex unit has been fitted with an inlet restrictor, much like the early Indy Car restrictors. The end result is a shift to the left for the torque and HP curves, and a significant drop in the curves post max value ( this is when the inlet restrictor does its job).
The black lines are prior to tuning the Omnitek ECU, the red lines represent final values. The peak Boost is 10PSI @5900rpm, nominal (average) boost 2k-6k of 7PSI
Also attached is dyno sheet from a Greddy kit at 7 PSI for comparison. This is the kit that is also being considered.
Below that is a dyno sheet from the Rotrex without the restrictor, and with a slightly different pulley size (less max boost).
The black lines are prior to tuning the Omnitek ECU, the red lines represent final values. The peak Boost is 10PSI @5900rpm, nominal (average) boost 2k-6k of 7PSI
Also attached is dyno sheet from a Greddy kit at 7 PSI for comparison. This is the kit that is also being considered.
Below that is a dyno sheet from the Rotrex without the restrictor, and with a slightly different pulley size (less max boost).
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From: Phoenix
The guys running centri's on the LS V-8's have been using restrictors for a while to get better low/mid range for a while. People are also starting to run a wastegate on cetri blowers without the restrictor to limit peak boost also.
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If you work at it, you can get serious power from a Rotrex 
[NA] DIY Rotrex Miata Challenge Build - MX-5 Miata Forum
[NA] DIY Rotrex Miata Challenge Build - MX-5 Miata Forum
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Seems a little bitter, don't you think?
On a street car, if you don't like to shift and want peak torque at 4K, sure. But for a track car with a 6 speed it makes a lot of torque over a bigger rev range than the gear shift covers, so no downside.
On a street car, if you don't like to shift and want peak torque at 4K, sure. But for a track car with a 6 speed it makes a lot of torque over a bigger rev range than the gear shift covers, so no downside.
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bitter, not at all...
but this is what I mean by area under curve fail. All other things being equal, I'm sure one of these cars will accelerate out of corners faster...
but this is what I mean by area under curve fail. All other things being equal, I'm sure one of these cars will accelerate out of corners faster...
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Rotrex $1500 (craigslist)
TDR IC $1100
Intake manifold parts $350
Tubing & Hoses $150
Ebay BOV $32
Total $3132
This ignores the built motor, etc. since you'd have to do those things for any high power setup.
5 deg F above ambient is amazing. And completely impossible except at low boost and only one pull. If you had a 100% efficient compressor (no such thing) and a 90% efficient intercooler (not likely), you could have at most 5.5 psi of boost and still run only 5F above ambient. That calculation applies to sustained power, not one squirt.
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