zaque

So I know that the stock twins are 51mm turbines with 0.60a/r each.

Stock, at 7000 rpm, they output 25lb/min of air.

What I can't find is what the stock exhaust manifold pressure is at various RPM. Particularly 7000rpm, which is a good peak number to know.

I would guess, since it peaks at 4000rpm and the compressors are only 49% efficient, and it's 25 year old tech, that it's probably around 15psi EMP at peak. But for those that have them tuned to continue to output 10psi at 7000rpm, I wouldn't be surprised if it's in the low 30psi EMP instead.

Does anyone know? This is such an important spec, I'm surprised it's not cataloged anywhere. I've been searching and searching, and can't find it.

arghx

iTrader: (3)

One of the reasons why it's not catalogued is because it's not easy to get instrumentation in there. You have to drill the turbo manifold in two places, and you need equipment that can actually record it (an analog gauge isn't going to read fast enough). That kind of measurement is usually done on an engine dyno because there's a lot more space to fit everything in a lab environment.

We can only speculate, but I would say ~2 bar relative (3 bar absolute) at 7000rpm as you are suggesting is probably on the low side.

zaque

Yeah, I get that. You'd have to drill into the stock manifold, and install a fitting, and something to measure from there. I still would have figured that someone would have bothered to do that...

43.5psi EMP stock sounds absurdly high, though. That's more than a 3:1 EMP:IMP ratio.

BLUE TII

iTrader: (9)

zaque
43.5psi EMP stock sounds absurdly high, though. That's more than a 3:1 EMP:IMP ratio.

Well, Exhaust Manifold Pressure really depends on how much boost pressure you are trying to push.

Here are some claims from someone who has said he tested EMPs on various set-ups.


Using Ht12 std turbine wheel with exhaust housing extremely ported
Manifold pressure 20psi and the exhaust back pressure = 52psi

Using Ht12 std turbine with exhaust housing unported manifold pressure 20psi and the exhaust back pressure = 52psi

BNRs 3 with 20psi manifold pressure , exhaust housing ported to the extreme , exhaust back pressure = 54psi , because the garrett turbine wheel was too wide this had increased the back pressure higher than oem wheel .

Bathurst sp 650ps version , exhaust housing un ported , manifold pressure 22psi , the exhaust back pressure = 38 psi .

From this thread-
http://https://www.rx7club.com/time-...1099206/page3/

arghx

iTrader: (3)

Yeah to understand that better we need to see exactly where the pressure transducers were installed. The turbine outlet pressure has to be lower than the turbine inlet pressure, so there's something a little off with those numbers quoted.

Also, you really need crank angle based measurements inside the manifold, which costs more than your car is worth (high speed data acquisition using something like AVL Indicom or A&D CAS with Kistler or AVL pressure transducers, water cooled in that configuration).

BLUE TII

iTrader: (9)

That is *inlet manifold pressure* (boost pressure)

arghx

iTrader: (3)

ah ok thanks

zaque

Well that's at 20psi. EMP shouldn't change linearly with IMP.

So if EMP was 52psi for 20psi from the stock Ht12s, I would think that at 10psi it would be in the low 30s.
Presumably those measurements were at peak, so about 7000rpm.

Someone did tell me it was 32psi EMP stock. I guess that lines up with the other's claims.

edit:
More specifically, going from 10psi to 20psi IMP should generally be around a 66% increase in EMP. So 52psi:20psi should drop to ~31.35:10psi.
So either both our sources were right, or this is a strange coincidence. In my head I was imagining it was in the upper 20s or lower 30s just figuring 25 year old tech, 2 61mm 0.60a/r turbines, so I guess that's probably it.

Now this leaves me wondering why people consider the EFR 7163 to be too small of a turbo, when it should flow 35% better than stock. I haven't seen what EMPs people are getting on 7670s, though, which should give an idea.

BLUE TII

iTrader: (9)

Now this leaves me wondering why people consider the EFR 7163 to be too small of a turbo, when it should flow 35% better than stock. I haven't seen what EMPs people are getting on 7670s, though, which should give an idea.

35% more than the stock primary turbo which is good for 225rwhp?

The stock twin turbos have 51mm exhaust wheel and 0.60AR each.

For A/R when you have two turbos (or two passages in a single turbo) you add them as shown in the both the 2nd gen and 3rd gen Yamaguchi RX-7 books.

So, the stock twin turbos not only have the added exhaust area of two 51mm exhaust wheels, they have a 1.20AR.


----
Bathurst sp 650ps version , exhaust housing un ported , manifold pressure 22psi , the exhaust back pressure = 38 psi .

These turbos have the 63mm exhaust wheel of the HT18 (from TII) which is the same as the 7163 exhaust wheel size.

So, two 63mm exhaust wheels in 1.20AR instead of a single 63mm exhaust wheel in an 0.85AR as you are proposing to use.

BLUE TII

iTrader: (9)

Now this leaves me wondering why people consider the EFR 7163 to be too small of a turbo.

It is a subjective thing depending on how much power you want.

7163 is a great size turbo for 250-300rwhp on a rotary.

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It will be able to be pushed to 350rwhp+. Maybe to 400rwhp if EMP/overlap doesn't end the party before that.

But this is a race gas only, torturing engine with heat/EMP kind of tune.

SA3R

I think the OP might be trying to read too far into something that's not widely used. "Exhaust manifold pressure" is not typically used/sought out by most people.
Nor do most people drill holes in the turbo exhaust manifold to try and find out (for what gain, I really don't know..)

If you're trying to use the pressure in the exhaust manifold to spec what size turbo to go with, there are better ways and proven setups that don't require that sort of measurement.

Also, I don't know of much in the way of measuring equipment or instrumentation that's available to read such a pressure reliably, and at the sorts of violently hot temperatures that manifold can reach inside. I wouldn't be overly interested in the pressure in the exhaust manifold when there is volumes of proven turbo combinations to go with already.

arghx

iTrader: (3)

It's not something used on home projects because of the cost involved. All the turbo suppliers use it as part of their design process for OEM applications, but that's in an engine dyno lab or a gas stand. You can't correctly calculate turbine expansion ratio (the X axis of a turbine map) without inlet pressure. You should see the gigantic spreadsheets that these turbo suppliers use to calculate turbo parameters (static and dynamic pressures, temperature correction factors, etc). Also, from an engine design perspective, manifold pressure/turbine inlet pressure gets too high, it can cause valve float in piston engines if the valvesprings aren't stiff enough. You can use this data for example to spec out backpressure vs flow curve with different exhaust components.

You can't fit the instrumentation in a vehicle very easily, but it can be done. If you have high speed data acquisition (crank angle based) you can see exhaust pulsation and dynamic tuning effects at each degree of crank rotation, to understand scavenging and residual effects. Setting this up costs more than your car though. What OP is asking about is a basic static pressure kind of measurement which needs a pressure transducer of the correct range and something to record the signal.

Yup. Rule of thumb is a lot cheaper than a lab full of equipment, and lot of times all those calculations are used in a lab setting because the engineers don't have the time to put the turbo on a vehicle and actually drive it around before they have to make a design decision.

The individual enthusiast (myself included) can't afford the equipment. Only research labs at OEMs and suppliers use this. I've done my share of work with exhaust manifold pressures in my day job, but in my home projects it is of limited use because I don't have a $50,000 system to record the data at high speed, or a staff of people to model new exhaust manifold designs based on the data.

zaque

EMP is the second most limited factor to creating the power you want in a rotary next to the compressor map operating in the range you need and efficiently, is it not?
Largely because high EMP hurts reliability a lot, mostly by increasing engine temps.

I know with the Spirit R, which does have a bit more efficient turbos, a simple tune would give 300rwhp reliably.

That is in the range I'm looking for. 300-350rwhp.
Again, just stock but better. Faster spooling than stock, less complication, smoother (less spiky) boost delivery, lighter weight.

So is there something about BW MatchBot that is wildly inaccurate with calculating EMP?

Because those calculations show that with effectively 63mm 1.20a/r, dropping from 22psi IMP to 10psi should be around 21 EMP, the exact same that d MatchBot says the 7163 will get with its 63mm 0.85a/r.
The Bathurst SP surely doesn't have more efficient compressors, so it won't have lower outlet temps, either. Two smaller ones is worse than one larger one for that, especially considering the tech difference.

So, what is it, then?

There are many ways that something like MatchBot can be wrong on when theory comes to practice. But the EMP, or the CFM, needed to drive the compressor wheel the amount needed for the air flow you're looking for is not going to be wrong. Knowing how much to wastegate out in order to create the desired output is extremely straight forward and it shouldn't be wrong, there.

I'm inclined to believe, as has been seen time and time again, that the EFR turbos turbine wheel size and a/r are not directly comparable to old turbos. They flow over the turbine wheel much better and they're less restrictive for a given size than you'd figure.