2nd Gear Peak Boost - T04E
 

So my FD has 4.77 gears and I autox it. I have a used single turbo kit (modified HKS single kit) as follows:

HKS/Garrett TO4E
* 0.84 Turbine A/R
* 0.60 Compressor A/R
* Divided Turbine Housing
* Upgraded 360* Journal Bearing
HKS External Wastegate (8 lbs spring)
HKS Downpipe w/ O2 Bung
HKS Exhaust Manifold w/ Divided Turbine Inlet

The previous owner says it's was a TO4E 57 trim from the HKS turbo kit and now it's a TO4E 60 trim with the upgraded compressor.

My experience is that the turbo can spool up in higher gear to the 17-18 psi or 1.2kg/cm^2, however, I need the power in 2nd gear for autox. The load is dramatically lower in 2nd due to the gearing and as a result, even with the wastegate completely disconnected, 2nd gear will only spool to 1.01 kg/cm^2.

I think this is a mechanical limit to the turbo itself (assuming a free flowing exhaust and intake). What would need to be change mechanically with the turbo to create higher 2nd gear boost (and as a bonus also increase low end response)? Or is it possible the turbo is damaged. I don't know what other people are able to peak in second with similar turbos.

Checking for exhaust restrictions
Verify engine health ie 100+ psi compression
Checking for boost leaks
Checking wastegate does not leak
Checking for exhaust leaks between engine and turbine housing
Testing with a stronger wastegate spring



Changine turbine housing to 0.7A/R
Refresh turbo
Replace compressor wheel with a wheel actually suited to the rotary engines airflow requirements (flow @ low boost not flow @ high boost).

What wheel specifically would be a suitable replacement for my application? (I know very little about compressor maps and turbo sizing)

I would check everything else before blaming the turbo. I doubt the the T04E wheel will make it spool slower. I don't like them because they have larger wheels than T04B wheels for the same flow. To me it looks like all changes are for low rpm high boost low flow engines (pist-on).

Btw the 60-trim isn't too bad regarding flow at low boost, I just checked the maps, and it stands to reason because it has a 60-trim wheel. Have a read of this, and remember you want response go as small as possible.

http://fc3spro.com/TECH/TURBO/compmap.html

I bet you have a boost leak; the compressor size is not the issue. With the w/g disconnected you should be able to see an easy 2 bar...

I don't think it has a boost leak considering it made 377 whp at 1.19 kg/cm^2 in 4th gear on the dyno. This was at 75% wastegate duty PFC setting controlling a MAC 3 way solenoid valve.

The fact is, there is a high-flow metallic substrate cat, that is a serious bottle neck. But due to sound restrictions with SCCA now, I can't have the car back firing or I will get dsq'ed. The fact that the turbo hits the target boost fine in 4th gear, but short in 2nd leads me to think it is a load issue.

How do you test to see if the wastegate is bypassing exhaust without a triggered opening (ie leaking exhaust past the turbine)?

You have a weak wastegate spring. I wonder if the exhaust backpressure is pushing it open.

Run a line from the compressor housing to the top port only. ONLY to the top port, leave the side port open and do not install any form of boost controller. Be VERY CAREFUL when you do this as it could dramatically increase boost. The pressure supplied from the compressor housing will push on the diaphragm in the wastegate in order to help fight exhaust backpressure which may be forcing the valve open. This is a test to determine whether your spring is too weak.

Never under normal circumstances should you run an uninterrupted pressure source to the top of an external wastegate. This is only a test.

Thanks Raymond!

http://i175.photobucket.com/albums/w...pressorMap.jpg

So this is my compressor map huh....


^^^^ This is my 1000 post! I'm a nerd.

Also, the spring is fully preloaded at the moment.

EDIT: Raymond, what if I run the MAC Valve vent port to the upper portion of the wastegate, and leave the feed routed to the lower portion? Would this do the same as stiffening the wastegate spring?.

I'm not entirely following what you are suggesting because I don't know exactly which ports on the solenoid you are referring to. But perhaps you meant something like this configuration?

https://www.rx7club.com/attachment.p...1&d=1283205978

It's definitely worth a shot. That's one of the configurations in the TurboSmart E-boost manual. The Turbosmart uses a similar solenoid. Very little air will be fed to the side port of the gate in that configuration, and the side port is what actually opens the gate up. If that doesn't raise the boost I'd start looking for boost and exhaust leaks next.

I've been around the block a bit and I have NEVER heard boost expressed in kg/cm^2. Why not psi/bar? You're in the US, shun the metric system like the rest of us!

Is the car in question 'hamfisted racing' number 1? Nice work!!!

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You haven't used Apex'i boost control much then. AVC-R and Power FC use kg/cm^2, where 1.0 kg/cm^2 = 14.22 psi. And there's no way to change the units on these devices. Some oldschool boost gauges also use kg/cm^2.

Compression test numbers from Mazda testers are also in kg/cm^2. That's why perfect compression is usually considered to be between 8.2 and 8.5 depending on cranking speed etc.

https://www.rx7club.com/attachment.p...1&d=1283261920

It's still an oddball Japanese unit though.

To add to what arghx said, kg/cm^2 is fairly close to bar, (14.2 psi vs 14.5 psi equals 1) so you don't need to hurt your head too much trying to differentiate :)

I would think the amount of pressurized air routed to the side port (the port I am currently using) would be the same in that configuration, however, the net effect would be reduced because pressurized air would be fighting/counter-acting that pressure on the other side of the diaphragm from the vent-feed.

As a result, I would anticipate this to build significant more boost at a given wastegate duty, as you mentioned (versus my current setup). The benefit here is that the added pressure of the opposite side of the diaphragm would help resist the exhaust forcing the wastegate open. I certainly would like to try this setup and see if it helps.

Thanks again Raymond.

Perfect answer. Thanks, that clears that up! :)

I could see 22-23psi in 2nd with my T04E 57trim and tubular manifold no worries, plenty of torque.

What Wg/spring combo?