Fastest spooling 6PSI ish turbo
 

So, lets say someone only wanted to make 6-8PSI and wanted it to spool as fast as humanly possible. What would be the best turbo and how fast could one expect it to spool on a built 1.6L with cams/ headwork etc.

I'm thinking GT2550 ish? Or go smaller?

2554. They can be had for cheap and will spool like it is telepathic.

Super fun for low end torque, around town driving.

Dibs on the Rotrex.

Seriously though. Is the rotrex not doing it for ya? You have a built 1.6 with head work. Are you thinking of changing it up? Disappointed with the power? Don't like the torque curve, or the lack there of? Whats going on here?

Who says I am getting rid of the rotrex? ;)

It's all a game for me. I love working on my car and now that it's basically done I need to figure something else out to do.

The Rotrex pumps a 2.0PR at 8k RPM on my motor. 4PSI = 1.272PR. So that times that = 2.544 = 22PSI. I could also put my old pulley on which would equate to about 12PSI at redline with the rotrex or about 21PSI compounded with 4PSI on a turbo. I know my motor will take more than the 15PSI it's getting right now. I'm just just brainstorming on how to do it without stepping up to a C38. Power Enterprise has done a twincharged S15 240SX as well as the R35.

I assume you'll have it like this?:

Supercharger -> Turbo -> Engine

How do you read a compressor map for a compound supercharging situation? Some maps are in units of volume and some are in units of mass and feeding compressed air into the compressor will alter the relationship between mass and volume.

a turbo to spool a SCer....who would of thought.

I bought a turbo one time that the guy told me was from an SR20. It wasn't. It actually was from a 80's Sunbird turbo coupe, I think. It was a garrett with a .48 turbine/ .49 compressor. It spooled stupid fast and made decent power and torque, but anything over 8 psi and it would fall on it's face after 6,000 RPM. Might be what you're looking for.

Thinking out loud here. Wouldn't the small turbine choke off the flow of the supercharger?

they are talking about a no-torque-rex.

I am still confused. But even at high rpm when the Rotrex is on boil, the 2554 turbine is going to be maxed out and chocking off power. Unless of course there is a huge wastegate allowing a lot of air to bypass the turbine housing.

yeah, you'd need some sort of complete turbo bypass.

Ok, that makes more sence. I wast trying to figure out how to get 22 psi out of a 2554 turbine at high revs.

Oh lawdy, compound boost sounds like a good idea. Judging by your build thread you'll do it right too, I'll be exited to see results

*and a bypass around the compressor, which will also be maxed out at 240 hp.

The turbine won't choke til past 260 hp, and even then the wastegate will flow some % more.

does the compressor need to be bypassed? if it's only compressing 6psi until the wastegate/bypass opens and the rotrex takes over, the compressor wheel wouldn't be overloaded.


I'm imagining a Begi S6 style manifold with an IWG turbo. There's a HUGE EWG on the collector back to the DP. The turbo boosts into the Rotrex inlet.

turbo runs on IWG, when you want to turn it off, open the EWG dump straight to exhaust.

More cubes helps all….

These are the problems with compound supercharging. The logistics of getting everybody to work together is a huge pain in the ass.

To answer the original question, a Garret GT15V would likely be the smallest turbo that would make any sort of reasonable compression ratio at your peak flow rate, but you're going to over run any small compressor like that at high rpm. You can get them for stupid cheap on ebay pretty regularly, though, as Garret used to give one to every FSAE team who asked for one each year. The VNT will likely be problematic as you put miles on it, as they don't like gasoline EGTs very much.

Further, you're really going about this backward using a micro turbo to fill in the torque lacking with the stupid centrifugal supercharger. Traditionally 'twincharging' is used to add to the top end of a restrictive roots or twin screw blower that will be peachy at low rpm, but doesn't make a peak power target. You're going to have to figure out some sort of boost activated compressor bypass that won't make the turbo freewheel over it's rated speed.

here:

https://www.miataturbo.net/attachmen...1&d=1311957470


now time for Chipotle.

Not to say I don't like the power the Rotrex is putting down, I do. The car is 4 seconds faster than last year at our track without the wilwoods I had last year. With some aero and brakes (and driving skill) the car is capible of 1:15's which if you knew our track that's very fast. I just want a new project and the whole reason I did a 1.6L Rotrex was to do something different. This would be an addition to that idea.

No... Intake -> Turbo -> Super -> Engine

At this point I'm ball parking based on what kind of boost my motor makes. It makes 15PSI at redline which is just over a 2.0PR. 5PSI is 1.34. You take the 1.34 and multiply it by 2.0 which is 2.68. Then remove atmospheric pressure (14.7) and you get 24.6PSI of boost at redline. It would be less in the lower RPMS and work off the same idea that the rotrex already does. Since boost rises with RPM, you will only be hitting 14-15PSI at peak VE. I'm running 26* of timing on 91octane right now with zero hint of detonation... going with this theory since 6PSI is fairly low and won't be too hot... the rotrex dosen't heat air up as much as a turbo it should still run pretty cool.

Just need to think if I need v-bands even for 6PSI. I doubt it. Some inconel hardware should be enough I think...? I do track the car so...


Would I really though? I'm trying to understand the concept here, but I guess I have it a bit off. I figured that the turbo would be run on an electronic boost control system with it's feed taken from the compressor housing. That way when the Rotrex starts pulling enough air to bring what is essentially 6PSI down to 2-3PSI and eventually start choking, the boost control would adapt, and hold the boost steady at 5-6PSI in relation to whatever vacuum the Rotrex is pulling.



That's another way to do it, however this way you are not getting any benefit from the turbo in the upper RPMS through the pressure ratio multiplication of the Rotrex.

The only thing I'm trying to figure out is the logistics of fitting a turbo. I would need a log style manifold with a bottom mount turbo on the 3/4 runners. Clock the turbo towards the shock tower and run the turbo directly into the supercharger inlet. Brain, your picture is pretty much exactly what I was thinking. I'm quite impressed with your paint skillz BTW... lol

How to compound turbo set ups work? Would the smaller turbo not choke the larger compressor? I think if I can figure out how that works, then I should be able to make it work since they are both compressor based and similar.

The way I look at it, it will be like a compound turbo set up but without the added heat that a turbo gives off VS. a rotrex. That, and fitting an actual compound turbo set up on a 4 cyl Miata with it able to create enough pressure would be difficult.

paint is for noobs.

What program is that? It looked too good to be paint.

ON compound turbo setups the smaller turbo is after the larger one, so it never sees atmospheric pressure after the larger turbo spools. Since the smaller turbo is force fed the boost from the larger, and never chokes. It just chugs along at a relatively low PR and doesn't know that it's actually moving a significantly larger VOLUME of air.

So wouldn't the same idea work with the Rotrex PULLING all the air through the smaller turbo?

https://www.miataturbo.net/attachmen...ine=1311962164

Looks interesting... Baby turbo gets it's exhaust gases from the big turbo, but feeds it's charge air into the big turbo which then feeds it to the motor. Or is it the other way around? Hard to tell on this set up because the turbos look very close in size.

This on the other hand is a bit more clear...

https://www.miataturbo.net/attachmen...ine=1311962219
http://i68.photobucket.com/albums/i1...k/P8140077.jpg

Not really what we are talking about, but has some similar ideas. Might help clear things up if some one doesn't understand compound turbocharging.

Centrifugal compressors are better than roots blowers at drawing air in, but your flow issue is going to be an area choke flow limitation at the small compressor inlet, as only so much air will flow through the area of the compressor inlet before reaching near mach/ choke flow.


Now, if you wanted to put a 3076 or larger on it and blow from the turbo into the Rotrex, you could make a really horrible peaky pain in the butt that would make astronomical pressure ratios between 7000 and 8000 rpm, and pretty much suck to drive, lol.

Ok, so theoredically you spool a small GT25 to whatever it has to go to to see your target boost as fast as possible through the Rotrex. When the intake manifold sees 20 PSI (due to the multiplication PR of the Rotrex) the wastegate opens however much it needs to to keep the boost at 20PSI.

If I go off my current Boost/PR plot... if I boost 12PSI as a base on the turbo I should see 19PSI at the manifold by 3300-3400RPM. Since it would work on a ramp up type rate it's hard to get the exact measurement. I based it off a static measurement of 4PSI the rotrex gives out at about 3600RPM right now. Most turbos these days can hit 12PSI by 3600RPM I would think.

And if I want to see, say 13-14PSI, boost the turbo to 10PSI and I should hit 13.35PSI by approx 3000RPM. That's going off 10PSI (1.68PR)x 2PSI (1.136PR) at 2963RPM. And again, since it would be working on a ramp I would likely see it sooner since as the turbo is spooling 6-8-10PSI it would be multiplying as it spooled.

https://www.miataturbo.net/attachmen...ine=1311625300

So I guess what you would do is feed the small turbo into the Rotrex, and run the boost controller off the intake manifold with whatever you want your peak boost to be.

This is a pretty standard compound setup. Here, the exhaust goes small turbine --> large turbine, but compressor flow goes large compressor --> small compressor. The small compressor will still pull air through the large compressor at low boost, and stuff will get most real as the larger compressor spools.


https://www.miataturbo.net/attachmen...ine=1311962164

voila.


https://www.miataturbo.net/attachmen...1&d=1311963362


so lol.

haha. you show off.


I could make it even more interesting by using RPM based boost control. :P

I think I found my winter project.

So since were talking 10-12PSI now... I'd think a GT2554R should be enough? OR step it up to a 2560R? What exhaust housing would be ideal for spool without choking too much up high?

This is the same way Caterpillar does it on the over the road truck engines that need a broader powerband than a construction machine or stationary engine.

well I'd control the large bypass by RPM, to more or less divert all exhaust around the turbo.

The thing is…going compound…add up all the weight, specially made bits and cooling/tuning issues, etc. Some swapped alloy V6 engines may even weigh less! More cubes than 1.6 is suggested too. But it would certainly be fun to build either way.

That wouldn't be too hard to do either. The Haltech has a few general purpose outs and RPM switches. Instead of using a boost control table, switch the EBC with the RPM based out.

That's not what it's about. For me it's about doing something different and trying new things. I already have a built motor, Rotrex and well set up car... why would I pull the engine? :jerkit:

This idea literally came out of the blue and you know it may not happen. But where would we be as a group if no one ever tried new things to help progress the way we build our cars?

I'd do it just to troll the SCer folk. the turbo for low end is a brilliant play.

Lol,... well I like the Rotrex and I like how it makes good power up top without much heat. It's just lacking a bit down low which can sometimes be frustrating. On the track I don't really notice it since I have a 4.3 and run 13's but on the street an extra punch down low would be great.


And we all know how fun it is to troll S/C folk.

hey!!! thats the turbo i have, its a TB2522 nice to know someone on here has messed with it.

https://www.miataturbo.net/attachmen...ine=1311968329https://www.miataturbo.net/attachmen...ine=1311968506http://www.turbobygarrett.com/turbob...14-3comp_e.jpg

The GT22 looks like it would actually do the job fairly well VS. the GT2554R.

I basically need a turbo that will make 10PSI as fast as possible without choking on the compressor side at 300+whp. I'm thinking a hybrid small turbine/large compressor is really the only answer. Since most of the exhaust gasses would be bypassing the turbine in the upper RPMs through a giant wastegate... a small turbine may not be a bad idea.

Any ideas?

Then there is the smaller GT2560R which seems to have a decent efficiency towards the right of the map.
http://www.turbobygarrett.com/turbob...-1&4comp_e.jpg
I don't think I would be going over a 2.5PR ratio anyhow. The PR on the turbo will lower significantly at higher RPM with the blower pulling air through the compressor.

Dood the smallest fastest turbo for 300 hp is the GT2860RS with 0.48 hotside.

That's not what I'm asking, but thanks anyways.



Looks like this guy is the only other person I can find who has twin charged a car with a Rotrex. However he is doing it different and has the Rotrex feeding a huge turbo.

http://www.mr2forum.org/forum/index....-rotrex-power/

http://www.youtube.com/watch?v=96QbY...mbedded#t=106s

I know this may be missing the whole point, of compounding the two. But would this work?

Normal Rotrex setup and mount. A turbo tim bottom mount type set up. Both flowing into a collector with a flapper valve. At lower rpm the little turbo is spooled up and pushing more air than the rotrex, as the rotrex comes into it's prime it pushes the flapper valve down closing or mostly closing the turbo side of the collector. This then flows into the IC with the map sensor post IC.

Would this work?

Crappy paint drawing

https://www.miataturbo.net/attachmen...ine=1312002087

If this is hyperish, flame away.

I don't like that idea because you're basically throwing away boost. My idea is to make the most boost as fast as possible, without taxing either compressor at all. That will only work if you compound

falcon,

unfortunately, the way you're considering this has a bunch of practical roadblocks to making it work well. The most significant probably is you will have to bypass the turbo compressor at some point, as the amount of flow will completely choke it once you have the rotrex really going. At that point you will lose a lot of boost anyway because of the effective restriction through the turbo compressor and likely the excessive temp rise because you'll fall off the cliff on comp efficiency. Not to mention a good chance you'll be overspeeding the compressor wheel causing damage to it and probably the bearing.
Which aspect is likely to be worse would depend mostly on how you try to calibrate it. If you don't wastegate enough flow, overspeed and temp will be the main issues, along with high turbine inlet pressures, and if you do wastegate the flow enough so you don't overspeed the compressor, you will just choke the rotrex.
The only way it will function reasonably well sticking with the plan you describe, is to completely bypass the turbo on both ends once the rotrex is making good boost. Depending on the comp map for it, you might be able to re-pulley the rotrex for the higher boost and use the turbo to compensate for the soggy bottom end. Something very small would be best I think, in the GT15 range. One of the OEM turbos off the Ford 3.5L would probably be a good choice if you can find one cheap, they are GT1549.

That article is pretty stupid in regards to what they're saying about F1 cars because they don't allow F1 cars to be timed at Goodwood anymore. Nick Heidfeld's 1999 record still stands at 41.6 with the MP4-13 as the fastest ever up the hill (officially). A modern F1 car would go much quicker than 48.07. :)

Exactly like my first car, but mine had pop up headlights. Plus the turbo was a wee bit smaller..

I am going to hook up a boost gauge to the rotrex intake and log how much vaccum it pulls through the whole rev range. I should be able to match a compressor on a turbo that will allow it to flow that much at a low 1.3-1.5 PR.

why not just tune the rotrex for low and the turbo to take over when the rotrex runs out of steam

Because if I gear it any lower it would be massivley overspinning it in the high RPM.

To prevent the turbo compressor from choking out the rotrex, how about a big ass one way valve between the two? this way the rotrex can pull from that air and not necessarily from the turbo?

Dann

I cant tell if you guys are joking or not...

joking about what? twin charging? It's been done before with a Rotrex.

I think the best way to do it is like a compound turbo set up where the big turbo (in this case the rotrex) feeds the small turbo's inlet. Then when the big turbo (rotrex) takes over it blows through the little turbo. That's how must compound turbo set ups are made.

I see two misconceptions in the arguments against this setup. The first is that the small turbo will be out of its efficiency range due to high pressure after the Rotrex starts moving air. The thing to remember about the compressor maps is that it is a pressure ratio and not an absolute pressure being portrayed on the maps. If you add, say, one BAR of pressure to the inlet of the turbo compressor, that will be 1 PR on your compressor map and not 2 PR as a starting point.

The second is that some of you are confusing mass of air on the compressor map with volume. When the Rotrex is making positive pressure the mass of pre-compressed air entering the turbo will be far greater than the mass if it was simply atmospheric air entering the turbo. I'm no engineer, but I believe this will effect the mass calculations when reading the compressor map as well. You are essentially moving the base calculations for atmospheric conditions of pressure and mass of air by changing the pressure and mass of the air by volume that enters the compressor inlet. The compressor "sees" different atmospheric conditions than ambient.

Have you ever seen a shop air compressor with a multi-cylinder compound design that uses a very large piston feeding a smaller one and then going to the tank? The smaller one is not choking the larger one's ability to feed the tank. The large volume entering the big cylinder is a much smaller volume when leaving it and can easily fit into the smaller cylinder to be compressed even further. This idea is nothing new.

Thats what I was originally thinking...

After thinking about it for a while, I think you're on the right track, except that falcon keeps mentioning blowing the turbo into the Rotrex, making the small turbo compressor inlet the choke point in the system. If You were to blow from the Rotrex into the turbo, then you would get exactly the sort of system you want. Just like in the case of compound turbos, the small turbo will pull air through the restriction of the Rotrex compressor (less efficiently than it would from open atmosphere, but not too badly, as the Rotrex will be moving SOME air at low rpm, if not enough to force feed the turbo) until the blower spins up to an rpm where it can add to the mass flow rate, and multiplicative pressure ratios will begin to take over. You wouldn't have to use any sort of silly check valves/ bypass nonsense, or any boost control other than a well designed Hytech style wastegate biased exhaust manifold and a big gate. You'd also get most of the advantages of the compound turbos, without the complicated exhaust routing, multiple wastegates, complex boost control strategies, or most of the packaging tom foolery...

The question I can't answer for certain is what will happen when you try to move 33ish lbs/ min through that GT2252 compressor, even at a really low pressure ratio. That's still a ways right of the choke line.