Stapped RHB32 shaft..solution and VAF questions
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Author:  Steen [ Mon Jan 30, 2017 11:11 pm ]
Post subject:  Stapped RHB32 shaft..solution and VAF questions

I recently swapped over the drivetrain from my 91 turbo firefly (Non existent body) into a rust free 90 sprint.
before taking the car out for a drive I decided to install one of the 3tech camshafts.

after getting the timing where I thought it was right, I was able to take it out and let it fly in 2nd gear.. and I was VERY impressed with the power. Judging by the boost gauge the car was making somewhere around 8psi. I turned around to come back home and gave it some steam in first gear, it immediately shutdown (some sort of fuel cut around 6k) and proceeded to have no power. I assumed something was amiss with the coldside piping maybe, but I babied it home, as it idled I looked and looked for an issue with none to be found.

I came back a few hours later, started the car and heard a rattle.. long story short I figured out the turbine had separated from the compressor in the turbo. (PS the car has a well operating slightly crushed DSM bov to avoid compressor surge)
If I had to guess I'd bet I've only put around 20KM on this little motor, I have absolutely no idea as to what caused the shaft to snap.. But here are my quick questions that I hope somebody can help me with, PS thanks for taking your time to read my wall of text! I've searched and searched but every question seems to have 2 totally different answers.

#1) How different are the RHB31 and the RHB32 turbos? Is the only difference the exhaust housing? I have found a new shaft and turbine for less than $100 dollars for the rhb31, is this a direct replacement for the rhb32? What is my best option to fixing this turbo, or replacing it?
#2) How does one avoid what seemed to be a very harsh fuel cut which likely was the cause of the broken turbo shaft? I do not plan on cranking the boost. The camshaft was put in to avoid having to turn it up and put a stress on the little turbo.. well that didn't work very well. Is there something inside of the VAF that can be modified with no ill effects which causes no power cut?

Thanks again everyone.

PS. I have a little Mitsubishi turbo that when not compared to the original turbo seemed usable, but now that I have them both sitting on the bench here.. I'm not sure the little 3 banger would ever spool it.

Author:  JamalSpelling [ Tue Jan 31, 2017 12:18 am ]
Post subject:  Re: Stapped RHB32 shaft..solution and VAF questions

I have a much larger K04 Turbo on my MK1 T3, and the G10 has no problem spooling it,
however there is considerable lag, there is no comparison to the spool time Vs. the RHB32,
however a programmable electronic boost controller does provide some tailoring on the
spool time.
That said I have no idea what the direct differences on the RHB31 vs. the RHB32 other
than I believe the RBH32 to be water cooled.
The RHB32 VZ5 is the expensive hard to find (someone said it was out of production),
where there is many versions of the RHB31 available on line, whether they be genuine
IHI or knockof. Take a look at the tag on your turbo, particularly the numbers after
RHB31... these will help you identify your specific turbo and help you determine
and source replacement parts.
As far as fuel cut being the culprit of a broken shaft..the turbine shaft runs on a cushion
of oil. It's likely over time, your shaft has worn due to insufficient lubrication, neglected
maintenance of the oil system, poor choice of oil, coking, lack of use, improper cooldown
procedures or just plain normal wear and tear. These little turbos can take a beating and
perform quite well up until the moment of death. Worn shafts, play and impeller/compressor
wear due to shaft play are common as well as just plain 'seized' shafts, and many failures
are contributed to improper never change the oil, or use crappy oil.
If you're using a VAF, fuel cut is caused by the vane moving more or less to the
'fully open' position and not necessarily the boost pressure. When boost pressure is sufficient
enough that you have enough airflow that moves the vane in the VAF to roughly more than 90%
of travel
, it will typically cut fuel and illuminate the check engine light momentarily.
Other triggers can be larger diameter cold piping, efficient air filters, larger diameter exhaust,
ported intake or exhaust, cold weather/denser air mixtures and excessive boost.
Keep in mind also a binding wastegate can also cause a boost spike.
Typically boost pressures in excess of about 10.5psi will trigger the fuel cut, but since
the earlier generation models using the VAF, don't actually monitor boost, this figure is
more or less the point at which the factory blow off valve will open to release pressure.
If you're lucky enough to reach these boost pressures on a well tuned motor, you will
also trigger the fuel cut indicated by the extreme movement of the vane in the VAF.
So pretty much your stuck with removing the plastic cover on the bottom side of the
VAF to reveal the finicky spring mechanism inside, which with care, you can reset
the spring tension to a greater value. Use care and mark the original position as a
reference point and only do a few notches at a time as the ECM does respond well
to drastic changes. If you tighten it too much, you will not have enough airflow at idle
to move the vane and you will start lean and not be able to operate your car at low
speeds, you can however drill out the idle air bypass plug to access the idle air adjustment
screw and allow more bypass air for a sufficient idle on a tighter spring, but only so much
as if you tighten the spring too much your screwed. There is a happy medium.
And a warning if you get everything dialed in and you don't drive the car for a days,
weeks or months, temp changes can affect spring tension and you can have a driveability
issue after the car sits too long, but pretty much only on extreme tension, like close
to a full turn.
Hope that helps, this is more geared to MK1, but if you're running a VAF this should help
you understand. Also really helps to have an accurate A/F gauge to make sure your fueling
is up to par if you're doing the VAF mod thing.

Author:  mxmikie [ Tue Jan 31, 2017 5:32 am ]
Post subject:  Re: Stapped RHB32 shaft..solution and VAF questions

i have some RHB32 turbo shafts if you still need one

Author:  Steen [ Wed Feb 01, 2017 9:18 pm ]
Post subject:  Re: Stapped RHB32 shaft..solution and VAF questions

I'm having an extremely difficult time trying to figure out these part numbers. Here are the numbers stamped into the front of the compressor housing on the turbo that came off of my '91 firefly turbo.
vz13 9005
2(4 or A) 3908

when I look these up i'm finding the IHI rhb31... even though it says rhb32 right on the compressor housing.
It would be ideal if my compressor and turbine housing were to bolt onto a new rhb31 cartridge, but there is no info on this particular question. I appreciate the replies, this is a nightmare.

EDIT: I've found a seasoned turbo locally for the right price. Fingers crossed that another failure wont happen for awhile.
I WILL make sure I order one of the rhb31 cartridges, hopefully it works and I can "rebuild" my original turbo. There has to be a better solution out there for us.
And before any modification happens with the VAF I'll definitely throw the wideband on it and monitor closely.

New turbo for future reference
vz13 9010
15 405B

Author:  Woodie [ Thu Feb 02, 2017 6:32 am ]
Post subject:  Re: Stapped RHB32 shaft..solution and VAF questions

Here's mine in case it may be of some help, also from a 91:

I'm pretty sure the RHB 31 and 32 use the same rebuild kit, but don't know if that means the same cartridge. I had mine rebuilt by

Comp Turbo Technology, Inc.
3214 Producer Way
Pomona, CA 91768

but it was just a rebuild. Was working fine but spewing some oil. They did everything fine except documenting the clocking before they disassembled it. When I got it back EVERYTHING was pointing the wrong direction, it was quite a puzzle. Took about two hours of fiddling to get it all straight.

I think that last number is a Suzuki part #, it's in the right format.

Author:  t3 ragtop [ Thu Feb 02, 2017 5:36 pm ]
Post subject:  Re: Stapped RHB32 shaft..solution and VAF questions

it has been a really long time since i had an rhb31 but as i recall, the rhb31 and rhb32 shared parts but the body of the rhb31 had a different body with a smaller inlet to the hot side which fit the isuzu and early turbo3 engines. the inlet flange had shorter center to center measurements on the flange bolt holes.

that made the rhb31 a non-fit for the suzuki turbo3 engines unless it was an early 88 model. actually, i think that the rhb31 in the suzuki line was designated for the 600 cc engines they used in the kei cars, cappucino and the like.

i also recall that the shaft, impeller, and cold side snail and fan seemed the same between the rhb31 and rhb32.

again, it has been many years but i did stop buying the rhb31 turbos as direct replacements for the suzuki turbo3 cars because they didn't bolt up properly.

Author:  turbohull [ Fri Feb 03, 2017 6:28 pm ]
Post subject:  Re: Stapped RHB32 shaft..solution and VAF questions

There are so many good turbos out there to try, it may be cheaper in the long run to just make yourself a new manifold and use a commonly available turbo.

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