Pure response.

I know about weight, I know about heat.

From a pure response perspective, does anything match the BNR stage 3?

EFR 7670?

Not interested in: GT35R, T04, etc.

 

https://www.rx7club.com/build-thread...build-1013942/

 

Thank you, I'd seen that build, but it didn't manage the >200hp at 3,000 rpm that I'd seen from others, so I'm not quite sure how I feel about it.

 

I haven't seen anything that matches the response of optimized stock(ish) sequential twins without killing the top end power.

I mean, obviously you could run a single turbo the size of the stock primary turbo optimized with better intake, manifold and downpipe and it will have better response, but it will max around 200rwhp.

With the stock(ish) twins you have a tiny primary turbo for low end and then with the seconday online it not only adds the second compressor, but opens up large exhaust area so the high overlap rotary isn't bottle necked with high exhaust manifold pressure.

I think perhaps it could be done, but it might look something like an EFR 7670 with the T4 1.04AR adapted to the stock sequential manifold acting as a quick spool valve (sending all exhaust through one exhaust scroll for low end and both for top end like S4 RX-7).

Still, you have the huge mass and leverage disadvantage of the larger single turbo compressor wheel in the very low rpm.

This may be able to be overcome though being able to use huge straight intake and huge downpipe for an extreme pressure ratio delta between exhaust turbine sides.

Instead of working on this optimized single turbo set up to match the current level of sequential twins we could instead optimize a sequential twin set up further.

This could be as simple as putting some tiny EFR CHRA and compressors into the stock twins exhaust manifolds for the lower mass and higher pressure ratio capable compressors.

Or it could be complex, addressing the issues with top end power the stock sequential layout has (pinched 2ndary turbo inlet, dead headed turbine exhaust flow with 90 degree downpipe outlet, lack of WG area, etc).

 

In my experience you cannot possibly get 200hp @ 3000rpms on a single turbo. That link above already has what most would consider an undersized single turbo, and it still cannot make what you ask( and based on the photos, who is involved etc, everything is maximized).

I agree the EFR 7670 is your best bet. If you used our new shorty manifold, and a 4" exhaust system, you could probably get to the 185/190hp range @ 3000rpms.

BorgWarner EFR IWG FD3S Turbo System

 

There was a greddy single setup on my fd when I bought it. It is a TD06H-20g. I bought the car with a blown motor, so I can't speak from first hand experience on response. From what I have read, it spools very fast, comparable to the twins (in power and response). I'm not saying it is or isn't the best one for your application, but it may be one to look at. I have a few pics if you want. If your looking for a used setup shoot me a pm.

 

I'm sorry, I typed 200hp and obviously meant 200 ft/lbs. 200 hp @ 3000 would be quite the achievement.

That 7670 dyno is pretty close to awesome, given the torque is pretty flat from ~3200-7800. It is, however, a very odd setup. The BW turbos are optimized for 20-30 psi, and that was only at 12. Why was that?

 

You know I was curious if you meant 200 ft lbs, as I was thinking man I don't think I have ever dyno tuned a set of twins that made that much HP at that RPM LOL.

You can ask the owner here why he is only running 12 psi;

https://www.rx7club.com/build-thread...032831/page11/

I am dyno tuning another car in 2/3 weeks with the same turbo system @ 30psi.

Here is a screen shot of his current powerband @ 30psi( Our TDX61 T4 1.0 system). We ran out of injectors on this run, and had to stop short. I turned the boost down to 22psi and finished it. As you can see in both runs its near 240rwtq @ 3000rpms.

He now has 4 ID2000s, and this new EFR IWG 8374 kit( almost done, just waiting on me)..

 

I have to say, the torque curve (lack there of) is amazing on that TDX61. It's transitional response that really matters to me though, and that's where the gamma wheels of the EFR are supposed to really shine.

Odd that I'm not seeing much spool difference between the 7670 and 8374 on your dynos though.

 

Holy Mother of God that youtube video just made my day...

How soon can we expect some 7670 dyno results?

I really like the fact that you added the dual EGT bungs option in the drop down menu on the webiste

Keep up the good work and really looking forward to the 7670 results!

 

We don't have any dyno results for the 7670. I have one customer out of state running one, but he hasn't hit the dyno. I have another in house job that is getting the 7670 IWG, but the engine needs to be finished first.

And yes you are correct you cannot see transitional response from a 4th gear dyno pull, especially one that starts at 1200rpms.

As soon as we are caught up with old work, I intend to play on the dyno for 2 to 3 straight days doing back to back tests against everything you can imagine;
short vs long runners, open vs divided turbine housings, small vs big a/r, 3" vs 3.5" vs 4" downpipes, journal vs ball bearing, small vs large turbos, etc etc etc. Basically the holy grail of rotary dyno comparisons. I will also be including a video on transitional response etc etc...

 

flame suit on.

perhaps you should be looking at superchargers for the best low end response for autocross, they just are not extremely common due to the complexity of making one work and work well on a rotary engine. not to mention their rather limited peak power capability.

the other alternative is to run higher compression and lower your boost level with a mid size turbo(the current setup i am building, but my turbo is still considered a mid/large frame and somewhat inefficient).

 

That's wonderful, thank you. Definitely in to see how wide of a powerband the 7670 can give, say 250 tq or more from x to y, and where it hits 200.

 

I'm cross-posting this in two threads because I think the point is valid in both cases.

The FD is old, and so is the 13B-REW. It's port injected. It has fixed port timing and poor combustion. Even in steady state flywheel torque it can't compete with turbo piston engines anymore. I'm not saying this to be a downer, just to give people a little context. I'm going to compare manufacturer rated torque curves for a series 6 FD, series 5 FC turbo, and a vehicle that is in the same price range as the FD was back in the day--the Daimler AMG A45.

For those of you who aren't familiar with manufacturer rated torque and power curves, they are run on an engine dyno in quasi steady-state. Basically, the flywheel is bolted right to the dyno. The engine is held for roughly 30 seconds at each speed and load point, and then the line "connects the dots." So spool is not an issue--it's basically the max torque available at a given rpm.



Here's the FC and FD torque curve as published by Mazda back in 1993 in a technical paper.



Here's the torque and power curve of the Daimler M133 engine. Note that these are metric units so horsepower and torque don't cross at 5252rpm.



Here is a chart I made comparing the two (using a tracer program to dump the torque curves to Excel). It's not even close. There is absolutely nothing you can do to a 2 rotor engine to get it anywhere near that at low speeds unless you drastically cut off the high end torque (and therefore power).

The A45 has a 345 horsepower 2.0 liter turbo with the most advanced gasoline direct injection system available today, and a single twin scroll turbo. It runs a small turbo at about 26psi of boost to get the low end torque. The FD was rated at 255 horsepower using sequential twins, and the series 5 was rated at 200 horsepower using a twin scroll turbo just like the AMG.

The key to the modern direct injection turbo piston engines is the direct injection in combination with variable valve timing (and sometimes variable lift). So the piston engines dial in overlap to spool the turbo and increase mass flow, while being able to run good spark advance at full boost. The rotary needs this kind of technology to make torque close to what a piston engine can do.

 

The car in the link I posted is a 2 time national champion at exactly the same thing you are doing. Yet,you are hung up over 200ftlbs at 3k Rpms?

The answer is right in front of you. The guys competing at the top aren't running sequential twins.

 

https://www.rx7club.com/single-turbo...d-dyno-956766/

Same setup with a clearer dyno graph. Hits 250rwtq at 3k Rpms on the stock ports.

 

It's a bit silly to say 'I'm hung up on power that comes on low, look at the winners' then post a graph of the winners doing exactly what I was asking about...

But yes, over 250 ft/lbs at 3000 is wonderful in this application. Thank you for the graph.

 

An interesting read that attempts to objectively quantify the response of the twins vs. a small (RX6) single with the time domain added. (As opposed to just boost vs. RPM, which doesn't tell the whole story.)

TurboRX7.com > Apexi RX-6 vs. Stock Twins

It sure would be interesting to see how the EFR stacks up.

 

what you need is electric charger off a new bmw, plumb it in series downstream the compressor of the efr, then use one or 2 of the check valves found on the audi 3.0 tdi biturbo. if you want I have the pressure loss of the valve at certain flow of air. it really flows well!

Sequential turbos: Bypass HP turbo compressor - TDIClub Forums

this will also work well using 2 aftermarket turbos in sequential setup but the big and only issue is making the HP charger turbine bypass valve to flow well and stand the EGT's of a rotary

 

edit:
seems these electric supercharger from cpt is not yet in series.. damn, I saw it last year already on a motorsport expo in köln..

other alternative is clutched belt driven charger, either positive displacement or centrifual, use boost/rpm to declutch it and have the check valves and single turbo do the rest

 

Arghx, think you could redo this graph with some of the more recent efr dyno plots at similar boost levels to the A45? A 2.0 liter at 26 psi vs a 1.3 (2.6) at 7.5 psi doesn't really seem like a fair comparison. I know the REW will still fall short but just curious what we'll see.

 

From everything I have seen with speed junkies 7640 efr that is probably the closest single turbo to the stock twins in terms of building boost fast and having decent topend. You can hear the turbo spooling while he is parking the car with very little throttle input.

 

You can get an idea of response from this video, it even out pulls V8s instantly!

 

Just saw this post. I don't think there's much point in redoing the graph. Those are engine dyno curves like the ones used when an engine receives a horsepower rating from a manufacturer. You can't compare those quasi steady state tests to chassis dyno pulls people are posting. The engine is loaded down in a different way.

The manufacturer curves are under much more controlled conditions and the actual dyno is "correct" in the sense that they're lab-grade, calibrated and maintained much better than a shop's Dynojet. However the nature of the engine dyno tests exaggerate the low end torque, because the engine has more than enough time to spool up and stabilize at these low engine speeds.

 

Wow, that spool is very impressive. I don't think the twins at any boost level could contend with that. I need to ride in one someday to see how it feels on the street tho.