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Old 12-15-2015, 08:10 AM   #81
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Quote:
Originally Posted by emilio700 View Post

Perez, Scott, 18psi, et, al: "trubos are better becuz torques!!"
It's more like: TQ is better cause I drive an average of 20mph. And I dont want to have to drop a miata into 1st gear to be able to pass a minivan on the highway...
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Old 12-15-2015, 08:17 AM   #82
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The dyno graph two posts up only looks flatter because the rpm scaling is stretched out horizontally. If overlayed with one of the turbo graph lines Sav posted, it would show how peaked the Rotrex graph is in actuality.
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Old 12-15-2015, 02:33 PM   #83
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Quote:
Originally Posted by Joe Perez View Post
I asked a serious question, you responded with an ad homimem attack.

If you don't believe me vis-a-vis the "which pros are using it" test, do some searching of my past posts. I've used this precise wording in the inquisition of electric superchargers, magic oil filters, magic oil treatments, HHO generators, things involving magnets and perpetual motion, and a number of other technologies which just didn't seem to pass the sniff test.

I've sometimes been wrong. Occasionally you've been the one to illuminate me.

But I apply the same logic to a sacred cow, and suddenly I'm an antagonist?

No. Being offended isn't a "get out of logic free" card. You're a smart guy whose opinion I genuinely respect, and you can do better than this.
"I can only listen to people say "The Rotrex supercharger is best for [application] because it produces the smallest area under the curve" so many times..."

I am referring to this embellished faux "quote" . You have a preconceived notion that due to the particular performance envelope of the Rotrex compared to a turbo of similar peak power, it is innately inferior for all uses. Thus, you, like others hear, post facetious arguments like this. In another thread, you stated how you didn't understand why anyone would want a blower that makes "peak torque at redline", when clearly not all Rotrex installations do so. It's a false stereotype. I expect more from such an adept observer as yourself.

I'm not offended, just frustrated that Rotrex threads get polluted with these stupid debates. Honestly, I think all the turbo proponents are genuinely threatened by the advent of Rotrex builds. Otherwise, why even bother following the threads and post arguments against them? If the Rotrex was a truly bad idea like say, a Miata with 15x9 +0 and 185/55/15's at -4, you wouldn't argue. You would just make jokes and ban hammer like you do to the stance kids.

You ask for specific data to validate the Rotrex, on your terms; OEM's and race teams. I am genuinely disappointed that the thousands of words myself and others and have posted about our BP Rotrex builds does not hold merit with you but, I don't need to validate it otherwise.

Quote:
Originally Posted by Savington View Post
That chart is from a car that bleeds boost at higher RPM, and as a result, the torque curve falls to redline because boost does not continue to rise. You can look above for the results when you try to "scale it up" and build full boost like you want to. When boost rises with RPM, so does torque.
There was no boost bleed on the setup in this plot. About 9.5psi on top. We did design a boost bleed with a WG on the IM. That dyno will be published when JR releases their Rotrex kit for the BP.

Key factor is a VVT engine with full standalone. Thus good midrange and peak torque coming well shy of peak revs.


Last edited by emilio700; 12-15-2015 at 04:13 PM. Reason: because doh
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Old 12-15-2015, 02:50 PM   #84
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I don't think that last dyno plot was posted to prove a point...

























it looks like a *****
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Old 12-15-2015, 02:50 PM   #85
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Quote:
Originally Posted by Madjak View Post

Also your comparison isn't really how I'd do it. I mean why match RPM's?.. I'm not arguing that a Rotrex can generate more power than a turbo at set rpm points so why limit the RPM to suit your turbo?
Why limit the RPM of the turbo car to suit your Rotrex? The same breathing mods that allow a Rotrex to make big high-RPM power will do the exact same thing to a turbo car.

Quote:
Rotrex vs Turbo
230whp @ 6000rpm vs 230whp @ 5000rpm
280whp @ 7000rpm vs 280whp @ 6000rpm
290whp @ 8000rpm vs 290whp @ 7000rpm

If the gearing is correct on these two cars they would have very similar track performance.
Even if you did elevate the RPM on the Rotrex car with a custom rear end ratio ($$$), you would need custom gearbox ratios to put the same average power to the ground. Shift a Rotrex at 8000rpm from 3rd to 4th in a Miata 6-speed, for instance, and you drop to 6110rpm. Shift a turbo car at 7000rpm from 3rd to 4th and you drop to 5350rpm. This gets worse the higher you rev the Rotrex. On every shift, the turbo car will be further up in its powerband than the Rotrex would be.


Quote:
Doesn't that validate my argument that a Rotrex can have torque and can be an excellent choice for a track car? Whether my magical build is realistic or not.
I don't think it does, no. You need to do an awful lot of work to the Rotrex (intake manifold, headwork, cams, etc), AND rev it 1000rpm+ harder, to make it match the powerband of a turbo car. Do the same breathing mods to the turbo car and it will eclipse the Rotrex all over again.
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Old 12-15-2015, 03:01 PM   #86
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Quote:
Originally Posted by emilio700 View Post
There was no boost bleed on the setup in this plot. About 9.5psi on top. We did design a boost bleed with a WG on the IM. That dyno will be published when JR releases their Rotrex kit for the BP.
Aha, ok. The post that accompanied said that it was using an ECU-controlled wastegate that wasn't fully dialed in, so I assumed it was dumping something.

Quote:
Anyway, that plot looks atrocious. Huge dip at 4500, then a great whack at 5000.
There's a "dip and whack" joke to be made here (that dyno chart is a *****)
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Old 12-15-2015, 03:07 PM   #87
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There are 2 different arguments going on here.

1 is the rotrex is better because its better.

2 is the rotrex is better because its more reliable easier to setup more linear etc.

Just pointing this out.
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Old 12-15-2015, 03:18 PM   #88
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Why do Rotrex suck at torque?-80-a4ba979b76f5a90cc9d5d106cba7df86_4445b905adf74b8a099534e14209e7dc8b7898bd.jpg  
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Old 12-15-2015, 04:06 PM   #89
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We need to get fae fae in here to discuss a proper torque/hp curve. Of course that would require a fae fae decoder ring cause i dont read in fael.
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Old 12-15-2015, 04:10 PM   #90
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Quote:
Originally Posted by aidandj View Post
There are 2 different arguments going on here.

1 is the rotrex is better because its better.

2 is the rotrex is better because its more reliable easier to setup more linear etc.

Just pointing this out.
Neither. Pretty sure no one ever said the Rotrex was "better".

Personally, I am an IPA drinker although I have been drinking a lot of porters lately, Maybe its a winter thing. But clearly, IPA's are better.

Quote:
Originally Posted by Savington View Post
..There's a "dip and whack" joke to be made here (that dyno chart is a *****)
doh. Missed that.
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Old 12-15-2015, 04:57 PM   #91
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Someone tell me why this is wrong.


The ideal dyno plot for any car is going to be a flat 10 ft lb shy of one of the following.

-Traction limits in the most used gear.
-Drivetrain strength limit
-Conrod strength limit
-Driver skill limit


And that setup would have smooth delivery leading to that torque band, and it would have really easy to modulate torque.

As much as I love turbo's is this not a rotrex with carefully selected head components?

Dann
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Old 12-15-2015, 06:13 PM   #92
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Quote:
Originally Posted by nitrodann View Post
Someone tell me why this is wrong.


The ideal dyno plot for any car is going to be a flat 10 ft lb shy of one of the following.

-Traction limits in the most used gear.
-Drivetrain strength limit
-Conrod strength limit
-Driver skill limit


And that setup would have smooth delivery leading to that torque band, and it would have really easy to modulate torque.

As much as I love turbo's is this not a rotrex with carefully selected head components?

Dann
Not natively. You can perhaps manipulate it into something like this by playing games with restricting boost or venting boost, or whatnot, but the natural torque curve of a centrifugal is more like the plots that Savington posted.

If you want flat torque across the rev band without playing games, then you get that with a twin screw positive displacement supercharger. Look at tntuba's "old" dyno plot in this thread:

https://www.miataturbo.net/general-m...2/#post1287065

There's a reason why the old FM Ubercharger setups are desired for SSM cars.

--Ian
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Old 12-15-2015, 06:19 PM   #93
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Quote:
Originally Posted by nitrodann View Post
Someone tell me why this is wrong.


The ideal dyno plot for any car is going to be a flat 10 ft lb shy of one of the following.

-Traction limits in the most used gear.
-Drivetrain strength limit
-Conrod strength limit
-Driver skill limit


And that setup would have smooth delivery leading to that torque band, and it would have really easy to modulate torque.

As much as I love turbo's is this not a rotrex with carefully selected head components?

Dann
It's easier to accomplish that with a Rotrex but it can also be done with a turbo. Few have though. Problem is balancing boost lag with peak power. AZ-6 wants to stay below about 280 lbs tq for it to last a few years. That much torque requires a huge Rotrex that will make 400whp on top. Medium sized turbos will hit that easily but aren't made bombproof or lag free quite so easily as a Rotrex.

About 10 years ago I put together a GT2554R based system on a 10.0:1 BP4W. Zero lag at anything above about 2800rpm but that was limited to about 230whp on pump gas. My only complaint then was PTFB. It made boost so quickly that it would get too much boost as you modulated mid corner. The answer was a 4 port boost solenoid with a standalone ECU and some careful tuning. I threw in the towel after the 11th time the turbo fell off and went N/A.

The new small Borg EFR turbos promise that same freaky sharp boost response but with another 100whp or so of flow. Again, no one in the Miata worlds has published such a build. TSE's kit holds great promise here though. I think it'll tick all the boxes and end up costing about the same, $6-7k for everything excluding beefed up long block. ~280whp and 280tq on pump gas with instant response at anything above about 2800rpm with fine modulation of torque by TPS. That's my personal happy place.
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Old 12-15-2015, 06:38 PM   #94
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Quote:
Originally Posted by aidandj View Post
I don't think that last dyno plot was posted to prove a point...

























it looks like a *****
Quote:
Originally Posted by Savington View Post
There's a "dip and whack" joke to be made here (that dyno chart is a *****)
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Old 12-15-2015, 08:28 PM   #95
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Emilio, for the most part we completely agree on every point.

If your 10:1 build was at 11.5, on E85 and used a bigger turbo it would have been capable of being a lot closer to the stated goals.

I do my best to convince all of my customers that this is the way to go, but I get almost exclusively stock engine turbo builds.

Dann
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Old 12-15-2015, 08:51 PM   #96
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Quote:
Originally Posted by aidandj View Post
A CVT drive setup inside the supercharger would work better I bet.
Quote:
Originally Posted by codrus View Post
Sure, but you're burning more gas, making more heat to get rid of, etc. It's much better not to make the pressure in the first place than to make it and then vent it.

I'm not saying it won't work, just that a variable-ratio pulley would be much better, if it could be made light and reliable.

--Ian
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Originally Posted by aidandj View Post
Why drive the compressor with electric when you could just get an electric supercharger?!
It's two, two, two things in one!

Rotrex A/S
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Old 12-15-2015, 10:31 PM   #97
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That is quite interesting


Edit: the vc8 supports up to 50bhp. Not interesting
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Old 12-15-2015, 10:36 PM   #98
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Originally Posted by glade View Post
That is quite interesting
Isn't it?

A little reading shows their first unit is far too small for even a 1.6...

...but give Rotrex a little time.
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Old 12-15-2015, 10:38 PM   #99
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Originally Posted by Savington View Post
Why limit the RPM of the turbo car to suit your Rotrex? The same breathing mods that allow a Rotrex to make big high-RPM power will do the exact same thing to a turbo car.

Even if you did elevate the RPM on the Rotrex car with a custom rear end ratio ($$$), you would need custom gearbox ratios to put the same average power to the ground. Shift a Rotrex at 8000rpm from 3rd to 4th in a Miata 6-speed, for instance, and you drop to 6110rpm. Shift a turbo car at 7000rpm from 3rd to 4th and you drop to 5350rpm. This gets worse the higher you rev the Rotrex. On every shift, the turbo car will be further up in its powerband than the Rotrex would be.
Yes, there is a little difference between the two but not a lot, and certainly no need for custom ratios. I run a 6-speed with a 4.78 rear diff specifically for that reason as my powerband is up high and narrow.

Also 4th to 5th has much less drop and 5th to 6th is even closer again. The main difference though is because the revs are higher, you can actually generate 50hp more over that entire range whilst maintaining the same torque limit, that's if you can manage to get the Rotrex to the required boost level.

Quote:
Originally Posted by Savington View Post
I don't think it does, no. You need to do an awful lot of work to the Rotrex (intake manifold, headwork, cams, etc), AND rev it 1000rpm+ harder, to make it match the powerband of a turbo car. Do the same breathing mods to the turbo car and it will eclipse the Rotrex all over again.
If you push the turbo car much further you'll be in zone for gearbox failure. Sure this can be fixed with a different box but there is a reason most turbo builds sit at 350hp. I'm sure you could build a 700hp turbo miata with a non-stock drivetrain... but that's not what this discussion is about. You could also do what I propose and preserve the stock gearbox but push the powerband up the rev range as fas as possible so that you can push the power up in turn.

The whole point of this discussion and my 'magical Rotrex' concept is to not match the powerband of a turbo... it's to move the powerband as high as possible so that the torque doesn't pass 280-300ft lbs. I don't think I've once said that you could do this on a stock engine. You need something equivalent to a 949 Whammy to even get close to 400hp with a Rotrex. Built bottom end, 70mm throttle body, high flow intake manifold, ported head, oversized valves, high lift cams, free flowing exhaust. An engine that can rev to 8500rpm and do it whilst holding onto 400hp isn't going to be cheap.
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Old 12-15-2015, 11:15 PM   #100
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Quote:
Originally Posted by Madjak View Post
You need something equivalent to a 949 Whammy to even get close to 400hp with a Rotrex. Built bottom end, 70mm throttle body, high flow intake manifold, ported head, oversized valves, high lift cams, free flowing exhaust. An engine that can rev to 8500rpm and do it whilst holding onto 400hp isn't going to be cheap.
Actually no. As stated earlier in this thread, you can bolt a stupid big Rotrex (C38-74) to a basically stock BP and make about 460bhp. The resultant powerband isn't great but response is. Sorta like what you get by sticking say an EFR 6758 on a basically stock engine. Lotsa lag down low, midrange torque if you wait for it, huge power on top.

By putting a much smaller (C30-74) Rotrex on a built engine, you can get a great powerband in a useful rev range. Splitting the difference would be a C30-94 on forged engine with no flow improvements. That's the best of both worlds, 240-270lbs tq depending on fuel, 290-330whp.
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