IHI RHB5 VJ11 Compressor Map and PSI plots

SixSick6 · 9-26-05, 13:07

I figured since the compressor map only shows lbs/min that I'd convert to CFM as well as plot Pr (psi) on the map for everyone to see.

Here it is:

I know that Pr is correct

This belongs to n20_matt:

matt- I'm not sure how you factored in RPM but your Pr are off. You have 12 psi at 1.9 Pr which 12 psi is 1.81 Pr. Looking at the rest they're a little off as well. Pr is calculated by boost pressure+14.7/14.7

The map is broken up in groups of 5 and groups of 10. Your 7.5 mark would be 1.6 Pr which is roughly 8.8 psi.

SixSick6 · 9-26-05, 13:29

I also resized the Pr chart I found for the RHB5 series as well as RHC6 (My GM3):

**n2o_matt** · 9-26-05, 14:24

Quote:

matt- I'm not sure how you factored in RPM but your Pr are off. You have 12 psi at 1.9 Pr which 12 psi is 1.81 Pr. Looking at the rest they're a little off as well. Pr is calculated by boost pressure+14.7/14.

The map is broken up in groups of 5 and groups of 10. Your 7.5 mark would be 1.6 Pr which is roughly 8.8 psi.

If you look at my spread sheet on my web page, you would understand that the rpms represent the amount of air in m^3/min our engine takes in. That plot i made was specificaly for the f2T. An engine at a specific rpm will take in the same VOLUME of air at any boost pressure.

Yes, Pr = boost pressure+14.7/14. On your map you are using boost numbers strait from the turbo. In my spread sheet it says to input the amout of boost you want to see on your gauge, which is not the same as the boost from the turbo. My sheet has a field for pressure drop across the ic and piping(i used 1.5 as the pressure drop). So my formula is:

[boost(12) + 14.7 + ic pressure drop(1.5)]/14.7 = 1.918367

You add the pressure drop to the boost you see at the gauge b/c the the turbo is actualy puting out more boost than the gauge reads (unless you gauge is tied in at the nozle of the turbo - i hope not)

any more questions?

O BTW - my spread sheet also converts m^3/min to cfm. Not to mention that it already outputs in in m^3/min so no conversion is needed for IHI maps - thats why i made it in the first place.

SixSick6 · 9-26-05, 14:31

Fair enough.

I also did the same thing with the T Bird, and as it appears, up to 14 psi is where the turbo is most efficient as it pushes roughly 264.8 cfm at 76% compressor efficiency:

At 18 psi, it would be pushing roughly 317.8 cfm at roughly 72% efficiency but is also at the choke line.

The choke line is described as the maximum centrifugal compressor volume flow rate that is normally limited by the cross section at the compressor inlet. When flow at the wheel inlet reaches sonic velocity, no further flow rate increase is possible. the choke line can be recognised by the steeply descending speed lines at the right of the compressor map.

This is a case where bigger isn't always better. You've already seen my comparison of the T Bird wheel and Vj11 wheel. This is a case where people think that the turbo is bigger so "I must be able to push higher boost" They forget that just the same as other turbos, the larger turbo is capable of flowing the more at less boost.

Case in point the T Bird is capable of 264.8 cfm at 14 psi and 76% efficiency where the Vj11 is capable of 264.8 cfm at 18 psi and barely 70% efficiency, it is also at the choke line at that point. The T bird on the other hand is capable of 320 cfm at 18 psi but is on the choke line itself.

So as far as sizing wise, you should yield the best results at between 8 and 14 psi at roughly 76% efficiency and 14-16 psi puts you in the 74% catagory but you'll probably find that 14-15 psi feels best.

**Mr.JasonBH** · 9-26-05, 14:42

I really wish this all made sense to me.
I can semi-under stand it.
It pretty much outlines.

Stock Turbo - no higher than 16 PSI.
Based on the plot. 15.5.

The HP #'s are a little off.

SixSick6 · 9-26-05, 14:55

Quote:

Originally Posted by Mr.JasonBH

I really wish this all made sense to me.
I can semi-under stand it.
It pretty much outlines.

Stock Turbo - no higher than 16 PSI.
Based on the plot. 15.5.

The HP #'s are a little off.

It's all math and theory, not absolute as there are plenty of variables. But the stock T Bird hybrid pushes at 14-15 psi what the Vj11 takes roughly 18-20 psi to do.

The way that this was explained is that-"The compressor in the Probe and MX6 is biased toward elimination of surge and high pressure ratios at relatively low flow. It is rated for 300-325cfm, about the same as a DSM T25, but it can actually put out 325cfm at a pressure ratio of 2.7 (23-25psi of boost)"-which doesn't mean that you should go that high. I changed some numbers around because the person who explained it had the numbers a little higher than they should have been.

Look on the right side of the VJ11 map (the choke line) and you'll see that if you went further, that it could make it this high. However, if you look at my last dyno sheets you'll see that the Vj11 made about 2 hp per lb of boost increase. This is a case where the T Bird would have probably made the same numbers on a minimal 14-16 psi. There have been plenty of people who have run 200+ hp with 16 psi on the T Bird, it took me 20-22 psi to get 195hp on the Vj11. This could have been a complete disaster on the dyno.

This could also be a reason that Terri (MSGT-R) pulled such low numbers on the dyno (140hp) with a T Bird, stock air box with filter and stock boost solenoid. She'd in theory only be pushing what the T Bird is capable of at 8 psi where the Vj11 would be at around 10-12 psi. She didn't have a boost guage hooked up so nobody has any idea what boost level she was at. For all we know she could have been at 6 psi.

The compressor in the thunderbird turbo coupe is biased heavily toward flow and much less for "high" pressure ratios - it actually is outside of spec at anything above a 2.4 pressure ratio (wheelspeed exceeds design limits) This is one of the reasons people with the tbird IHI turbos complain that they "blow up" if you run more than 16-18 psi.

At 18 psi it is capable of 320cfm, but it is on the choke line. It is for this reason that it should be kept less than 16 psi rather than boosting it to 18 psi thinking that you must be able to because it is larger, and asking for your money back when it is your own fault.

Look at this for more insight on flow of our motor:
http://www.mx6.com/forums/showthread.php?t=107278 (Exhaust Flow Calculator)

SixSick6 · 9-27-05, 5:35

Quote:

Originally Posted by n2o_matt

any more questions?

I also made 176.6 HP at 4,370 rpm at 10 psi:
http://www.mx6.com/forums/showpost.p...2&postcount=56

Your plots say 174HP at 4,500 rpm. Regardless it is all theory and there are too many variables.

**n2o_matt** · 9-27-05, 10:28

Quote:

At 18 psi, it would be pushing roughly 317.8 cfm at roughly 72% efficiency but is also at the choke line.

so do you know what that means?

Quote:

So as far as sizing wise, you should yield the best results at between 8 and 14 psi at roughly 76% efficiency and 14-16 psi puts you in the 74% catagory but you'll probably find that 14-15 psi feels best.

So are you saying when ever i run 14-16psi i'm at 74%?? - b/c thats what it sounds like. hmm... you're missing something.

**n2o_matt** · 9-27-05, 10:32

Mr.Jason - the hp numbers are off. In the thread sick took that map from I state that they are nimbers based only on the amount of air coming in the turbo - i do not take in consideration the change in VE of the engine through the rpm's. I simply use a flat VE of 85%

**n2o_matt** · 9-29-05, 18:06

so... its open sick. Are you still going to finish?

**n2o_matt** · 9-29-05, 23:40

test post

**n2o_matt** · 9-30-05, 16:33

test post

SixSick6 · 9-30-05, 18:42

Matt- I'm also curious where you got your 1.5 psi of pressure drop at the intercooler? Every reference I have seen for the MX6/Probe intercooler (which is not many) and I believe was posted by magik8 or SleepCounter showed less than a 1psi drop from if any at all.

I got curious today and hooked up three McMaster/Carr vaccum/boost gauges plus my Autometer which is tapped at the dynamic chamber behind the throttle body.

I tested one gauge at the turbo outlet line to boost solenoid, one after the stock bypass before the intercooler, and one after the intercooler on the way to the throttle body and went for a drive.

I had 10 psi on all 4 gauges with no kind of drop whatsoever.

Now keeping in mind that you did no actual testing, rather just threw a number in and called it a day, this says one thing and one thing only. Your calculations are flawed.

This isn't a perfect world and all of this isn't even an absolute, it would be impossible to say that it was as there are so many variables. But, you can cut down on the variables if you don't add in your own variables.

As said, I got 10 psi on all 4 gauges. How much did you get?

**Samol_hok** · 9-30-05, 19:20

AR ratio = (atmospheric pressure 14.6 x boost pressure)/(atmospherice pressure 14.7)

SixSick6 · 9-30-05, 20:50

Quote:

Originally Posted by Samol_hok

AR ratio = (atmospheric pressure 14.6 x boost pressure)/(atmospherice pressure 14.7)

Dood, WHAT are you talking about? AR and Pr are two entirely different things. A/R is the area of the scroll divided by the radius from the center of the scroll to the shaft centerline.

PR, is the ratio of the air pressure at the discharge opening divided by the ambient air pressure at the inlet, P2C/P1C.

The equation is set up as 14.7+boost pressure/14.7