Single Turbo RX-7's Questions about all aspects of single turbo setups.

EFR internal wastegate turbos

Old 10-13-16, 03:05 PM
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Thanks BLUE, but I'm not sure I 100% follow.

I mean.. I know there's going to be high-RPM torque drop. It looks like the torque would be fine until 7000 rpm with the 7163, then drop toward redline.

What do you consider an acceptable EMP for a car you want to do track runs with fun with?

Check this, for example: BorgWarner MatchBot I THINK I input the numbers about right, there. And I'm assuming an a2w intercooler that doesn't have much pressure drop.

As you say, torque drops at the high end. Well, that's expected. 212lb-ft @ 8000 RPM is still much better than you get on stock twins.
The [email protected], [email protected], [email protected], [email protected] are the more interesting numbers to me. That's assuming I've got the VE set correctly, and BSFC correctly. Honestly, I might not. Maybe those BSFC for the higher end should be 1-1.5 higher if not more.

At 8000rpm the 25.7 psi EMP does seem high, but that's still a 2.25:1 ratio.
Or would you say that ratio of boost to EMP doesn't matter? I'd say that sounds right. What matters is simply the CFM of the turbo and the EMP, right? And a 25 EMP is just plain high, isn't it? Also, as you can see, the wastegate is choked just barely there.

Right so what you're saying is that you need higher EMP for certain boost levels in these smaller turbos. You can't just wastegate it away, as while you lower EMP you also lower boost. The question is what is an acceptable EMP for a race track? When I look around, it seems like 25 is to people.

Are you aware of what the stock EMP is @ 8000 rpm? That'd be a fantastic number to know.

And most of the power drop is simply due to the BSFC... which is going to happen no matter what past 7500rpm. Besides that, have almost as much torque at 2000 RPM as there'd be at 8000, and a very strong amount from 3000-7500, which is pretty crazy if the EMP is acceptable, right? Well, again, assuming those BSFC numbers are right for pump gas and this turbo.

If I compare to a 8374, okay yeah, it can do 13psi @7000rpm and 8000rpm while having lower EMP. And the compressor outlet temps are 232.93 versus 237.39 despite moving more air. (258deg F for the 7163 @13psi @7000RPM)
I was expecting more than just at 18.3 vs 21.8 EMP @7000rpm, though. Granted it's at 11psi @7000RPM for the 7163 and 13 for the 8374. http://tinyurl.com/j8bbtuf. At 13psi for the 7163 it'd be 24.3psi EMP, a difference of being 25% lower for the 8374.

Last edited by zaque; 10-13-16 at 04:32 PM.
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Old 10-13-16, 05:16 PM
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Your matchbot looks good to me except the engine VE is not set by RPM alone and will decrease rather quickly as EMP increases on the relatively high overlap rotary.

I don't believe the matchbot factors this in.

The question is what is an acceptable EMP for a race track?

That is a judgement call that depends on many factors. Coolant, oil, EGT, octane of fuel and reliability are all factors to be weighed.

I didn't concern myself with EMP too much since I built my car for sprints on race gas and the car I modeled my set-up off ran a similar compressor with a much smaller exhaust side.

Still, I wouldn't run EFR 7163 0.85AR at 14.7psi on 91 octane pump gas. I ran my 7670 1.05AR at 12psi on pump gas and 8.5:1CR.
I would run the 7163 at 10psi on pump gas and 9:1CR.

Remember it has a less exhaust wheel area and tighter A/R than stock twins by far so you will have to run lower boost to have the same knock threshold.
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Old 10-13-16, 06:28 PM
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MatchBot definitely doesn't factor that in. You have to figure the BSFC and VE yourself. But I think what I input is close enough to right.
The are some more downsides to EMP as well. It increases the exhaust-intake overlap. A little bit of that is good and lowers temps, but too much is not.

It does seem like the 7163 is a similar size though to some SM2 turbos people run. Like: https://www.rx7club.com/single-turbo...d-dyno-956766/

You also have to factor in that the 7163 is quite different than the 7670. While the 7670 and 8374 are roughly the same design and the later is just larger on both ends.

Looking at tests like Borg Warner EFR-7163 Test and Tune PERRIN Performance Official Blog it doesn't seem like the 7163 sacrifices much top end compared to the 7670.
Indeed, going by MatchBot, it seems it's just a sacrifice of 8-10% greater EMT for a gain of the greater response and like max boost 500-800rpm sooner.

So, if others were running turbos even smaller than 7163 for AutoX, well I'm not seeing why the 7163 is bad it's they're superior in every way to those other small turbos and EMPs will be better than it is for those other small turbos.

And if it means I ought to shift 300-400 rpm sooner, is that so bad when I'm getting power 500-800rpm sooner? That seems like a big net gain, a lot of which comes down to that wasn't the 7163 a more advanced turbo that came out later than the other EFRs?

I 100% agree about your point with the small 63mm 0.85a/r. It's just there aren't ideal options for these turbos for our engines. But yeah, I would prefer if I could have the 7163 compressor, but with a greater a/r from the housing on it... It'd spool later that way, of course, but very low rotating mass for better response and the more advanced turbine wheel design.

Now, in all likelihood, after this mod the next thing I'd do is set up for flex fuel so it'd not only monitor if it's E85 or pump gas, but also if the 91 octane is really 91 octane, which would give me a lot more leeway. Before I do that, I'm only looking for like 325-350rwhp. It looks like 420 should be possible on e85 or race gas from the 7163.


All that said... yes EMP is a big issue for me. Rotaries like low exhaust manifold pressure more than pretty much any engine. But I can't figure out what the EMP is for the stock twins...

Last edited by zaque; 10-13-16 at 06:30 PM.
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Old 10-14-16, 03:43 PM
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Okay some additions..

The stock turbos are two 51mm 0.6a/r turbines that work together at higher RPM.
I would not be surprised if stock EMP is actually closer to 30 EMP, which would make the 7163 about

Obviously if you want near or above 400 hp on pump gas, the 7163 is not the choice, just like stock twins aren't. But the 7163 seems to be better than the stock twins in every single way, which is what I'm looking for. If it's a difference of 30EMP @ 10psi for stock twins, and 20EMP @ 10psi for the 7163, that's damn significant.

Someone told me it's 32psi for the stock twins at their peak. 32psi EMP for 10psi sounds like a lot but... 1992 tech, and two 51mm 0.60a/r turbines, I guess that doesn't sound wrong, really?

Maybe if I contact Petit or another tuner, they'd know. I would have thought that information would already be on this forums or some other site on the internet, though!

Btw, BLUE, what was your plan for your twin set up with those two 7163s you got?
I plugged those in because I was curious..
BorgWarner MatchBot Parallel 7163s.
BorgWarner MatchBot 8374 0.83a/r.
BorgWarner MatchBot 8374 0.92a/r.

Interestingly, at 6000 RPM the 7163's working together have 10% better exhaust flow than the 0.92a/r 8374. 20 psi IMT @ only 18.6 EMT!
But the compressor is not efficient and intake temps are high. And no low or even mid range.
I'd assume you're going to do some sequential set up to make the low end work, but what's your plan?

Really the 8374 0.83a/r would seem the way to go if you want decent response but still high end power on a large track. Its compressor is so much more efficient up there. Or a 7163 for the low end (or smaller, really) with 8374 in sequence.

Last edited by zaque; 10-14-16 at 04:10 PM.
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Old 10-15-16, 12:47 AM
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Btw, BLUE, what was your plan for your twin set up with those two 7163s you got?

My plan is to keep it simple by keeping it close to the stock system in operation.

I will use the stock sequential manifold since it is durable even with the tighter stock turbos AR and little exhaust wheels and it includes the switching valve.

I will put a IWG 0.85AR exhaust housing on the primary turbo.

I will keep the non-wastegate 0.85 exhaust housing on the 2ndary turbo, but place the turbo forward facing up where the air pump would have been (but behind the primary turbo) and use a EWG for its pre-spool actuator.

I will swap both front covers out for the 90 outlet versions with BOV for the primary and use the BOV as the recirc valve on the 2ndary.

I will use the stock 2ndary blocker valve between the 2ndary turbo and IC.

Not sure if I will use an IC with dual inlets or use two ICs stacked front/back. I kind of like the idea of dual ICs with the 2ndary turbos IC out front keeping cool when not in use and keeping the primary turbos IC volume down for best response.

I plan on dual 3" ebay exhausts (downpipe/midpipe) to a dual 3" inlet single 3.5" outlet OBX-R muffler for a midpipe and then into my 3.5" OBX-R cat back.

I will use hallman pro RX MBC for wastegate and pre-spool control as I was able to get perfect, smooth transition that way which I wasn't able to achieve with EBC.

Last edited by BLUE TII; 10-15-16 at 12:50 AM.
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Old 10-15-16, 01:36 AM
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Originally Posted by BLUE TII View Post
Btw, BLUE, what was your plan for your twin set up with those two 7163s you got?

My plan is to keep it simple by keeping it close to the stock system in operation.

I will use the stock sequential manifold since it is durable even with the tighter stock turbos AR and little exhaust wheels and it includes the switching valve.

I will put a IWG 0.85AR exhaust housing on the primary turbo.

I will keep the non-wastegate 0.85 exhaust housing on the 2ndary turbo, but place the turbo forward facing up where the air pump would have been (but behind the primary turbo) and use a EWG for its pre-spool actuator.

I will swap both front covers out for the 90 outlet versions with BOV for the primary and use the BOV as the recirc valve on the 2ndary.

I will use the stock 2ndary blocker valve between the 2ndary turbo and IC.

Not sure if I will use an IC with dual inlets or use two ICs stacked front/back. I kind of like the idea of dual ICs with the 2ndary turbos IC out front keeping cool when not in use and keeping the primary turbos IC volume down for best response.

I plan on dual 3" ebay exhausts (downpipe/midpipe) to a dual 3" inlet single 3.5" outlet OBX-R muffler for a midpipe and then into my 3.5" OBX-R cat back.

I will use hallman pro RX MBC for wastegate and pre-spool control as I was able to get perfect, smooth transition that way which I wasn't able to achieve with EBC.
look into the stock 20b twins y pipe. seems like a much better design, and starting point.. i got one
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Old 10-15-16, 03:05 AM
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The stock system wasn't simple, though! :P

It had a wastegate behind the second turbo, then a smaller wastegate on a split pipe to let a little exhaust in there to "prespool", then another actuator behind the second turbos compressor to stop it from putting out air and keep it from choking off.
And so many vacuum lines... Though you say you only plan to use the manifold and not all that perse'.

Personally, I always hated the having 2 separate air intake pipes and filters, as well.

Simple would be just a Y pipe with a valve on one of the splits to start opening up when the first turbo has already made 20psi, or whatever you're shooting for, and using the IWG on both behind that. Another valve behind the second turbo as well so the first turbo doesn't try to suck backwards through it. But that can probably be simplified by always keeping a bit of positive pressure from the second turbo by never fully closing its exhaust off, at the cost of slower initial spooling, no?
Also, wouldn't just one BoV and having closing the valve behind the 2nd compressor open up a valve to vent to the atmosphere be sufficient?

Should be a very interesting race set up either way if it works out.
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Old 10-17-16, 11:20 AM
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Oh, and something else to consider with the EFR 7163 compared to say a GT3076R is that the 7163 still has the larger 3" turbine exducer compared to the 2.5" on the GT3076R.

I think people overblow considering it too small. Too small for 400+ hp on pump gas, sure. I'm surprised no one has tried it.
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