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PorschOz 12-14-2006 02:29 PM

Upgraded TPC supercharger and stalls
Hey guys,

I recently upgraded my TPC supercharger to the latest version (changed to a smaller pulley/ belt, change the injector, and re-wired everything) as well as had a new SPEC clutch and lightened flywheel installed.

Runs like a champ but every now and then when I need to stop for a red light or stop sign, it stalls as I engage the clutch and come to a stop.

I know the kinetic energy is a lot less with this flywheel vs. stock so do I need to take it to a tuning shop to change my idle position or is there something they can do to the computer to alleviate this problem?

BTW - I have a black 1998 911 Cabriolet (all Gemballa upgrades)


onefstm 12-14-2006 04:05 PM

Did you upgrade to their Unichip? Are you running an intercooler? What are your impressions of the upgrade? I recently puchased a car with the non-intercooled setup and was wondering about the upgrade to the Unichip. I was told by TPC that it is a 25hp increase in peak hp with improvements in driveability and also better protection against detonation. I'm anxious to hear your opinion.

WydRyd 12-14-2006 04:52 PM

Stunning car! Congrats!

I'd say you need to get your Motronics idle programming looked into. If I were you, I'd contact Todd Knighton of Protomotive. He's a guru when it comes to re-coding the BOSCH Motronics software, especially for aftermarket forced induction applications.

RarlyL8 12-14-2006 09:14 PM

Your problem is most likely the lightened flywheel.
The engine will decellerate faster and may stall before the idle can recover. This can be cured by adding a throttle bipass that will allow exta air around the trottle when it is chopped. If that is not an option you may simply increase the idle a bit and see how it reacts.

Beautiful car by the way.

PorschOz 12-16-2006 08:47 AM

Thanks for the options
Sorry for the late reply,

I went from the older style pulley which was a bit larger than the existing one I had on the supercharger. I haven't put the intercooler in yet. I wanted to get this setup dialed in before I took the next step.

The TPC upgrade included a new injector, smaller pulley, new belt and required moving and re-wiring the "brains" to the new location of piggy backing the stock CPU under the seat.

I did this upgrade at the same time I had the clutch/flywheel installed so I saw a huge difference once I was able to break the clutch in (which took forever).

I agree in that the flywheel is the reason it is not recovering in time. I will ask my mechanic about adding a throttle bipass. I am not sure what that would entail.

Thanks again for the help and the nice comments. Here's another pic:


onefstm 12-16-2006 09:14 AM


Are you running 5 or 6 psi? Do you notice most of the difference with driveability or do feel a substantial power increase?

RarlyL8 12-16-2006 06:23 PM

This car is a '98?
There should be some provision in the electronic tuning to allow the idle to "hang" a bit longer during chop throttle events. A vacuum operated bipass valve most likely is used for that function. If so it needs to see the signal a little differently or for a bit longer.

97c4s 01-05-2007 10:21 AM

Did you get the Uni-Q box with your SC?

You might want to join onefstm and others on the Rennlist board for a couple of threads on the TPC system.

Like others who have a pre Uni-Q system, I have the dreaded CEL (check engine light) problem. OBDII codes show random misfires. A total re-do of the secondary ignition system at TPC's suggestion did not make the problem go away. I've been trying to find someone who has a setup similar to mine who does have the Uni-T box to see if that really clears up the problem as I'm not to keen to spend another $2500 incl. labor just to make the problem go away (oh yeah and pick up another 25HP).

Any help?


Craig 930 RS 01-05-2007 10:36 AM

Hate to mention the obvious........but I assumed you called and spoke with TPC about this?

97c4s 01-05-2007 10:40 AM

On several occasions. Their response is to buy the upgrade. I'm trying to find out if the *&^^^%$ thing works!

PorschOz 01-05-2007 12:54 PM

Hey Dick,

When I bought the car a couple years ago, it already had the sc installed. I had some misfire issues as well and I took it to a shop for them to change out all the plugs and clean all connections and injectors. After that, it ran pretty good but the old belt was not wearing properly and slipping. I didn't get the power I should have.

I am not sure if I have the "Uni-T box" or not. Describe it and I will check.

I also upgraded to the latest sc kit at the same time I upgraded my clutch/flywheel so combine all that and I noticed a huge difference in power. Just now have this stalling problem every now and then. The new SPEC clutch supports up to 700HP so it's a lot more difficult to drive. Very short release point and grabs extremely hard.

Oh yeah, I shredded 2 belts to get to the right pulley alignment that would handle all the load. Really helps to have a good guy as your main mechanic!

So being a sc novice, have you had the error codes from the time of the sc instalation or did they increase over time? I ask because with the sc installed, the plugs work twice as hard and in essence get dirty and go bad twice as fast. you could have someone check them like I did.

Hope any of this helps.

onefstm - sorry, not really sure about the boost level.


onefstm 01-05-2007 01:31 PM


Based on your description of the installation (unit now piggybacking ECU, new injector, just purchased), I am 99% sure that you have the Uni-T or Unichip. Since I just ordered the same setup, I would say that you went from the original 3.0 inch (4.5 lb) pulley to the 2.8 inch (6 lb) pulley.


I would imagine that will pick up significant power by switching to the uni-T and the smaller pulley. You should be able to go a 6or 7 psi with the intercooler.

Have you tried actually taking the bulb out of the check engine light on the back of the instrument gauge? I understand that you want to rid yourself of the actual issue...but as they say "out of sight, out of mind"

Also, have you called TPC lately to confirm the uni-chip price? $2,500 seems $1,000 high to me.

PorschOz 01-05-2007 02:28 PM

That is correct and Tom gave me a break on the upgrade price and overnighted it to me as well.

97c4s 01-08-2007 01:47 PM


THanks for the reply. I'm forwarding all the comments to my wrench who is excellent by the way.

You asked if the CEL's increased with time...nope -- had them each time after a reset in just a couple of miles. Didn't matter whether I drove conservatively or hammered it (the usual mode).

Also had a slight alignment problem with the belts but was resolved with a little grinding. Did have a horrible belt squeal for a while as well but that was resolved with some magic lubricant of some sort.

I can't really describe what the Uni-Q looks like, but when did you buy the upgrade and all. The Uni-Q wasn' available until some time in mid summer I believe.

Here' a pic of the installation on my car.

Jim2 01-08-2007 07:25 PM

97C4S I notice your car is water to air intercooled. Would you happen to have any pictures of the water heat exchangers which you could post for us to see?

There is another thread in the turbo forum called Intercooler 101 where they are currently discussing the topic.


97c4s 01-09-2007 07:47 AM


Here are four pics for you to check out. These show the water exchanger before and after installation. You will notice that the water exhchanger is mounted in front of the oil cooler. The plumbing runs across the front of the car then down the drivers side to the engine compartment.

Hope these help.


onefstm 01-09-2007 08:05 AM

Dick ,

Thanks for the pictures. I always thought that the heat exchanger was mounted in the tail on the TPC kit. No wonder it takes 12 hours to install. It all makes sense now.

97c4s 01-09-2007 09:03 AM

Not a job for the timid or faint of heart -- lot's of plumbing involved! Not something one would try at home. I sing the praises of really good Pcar wrenches.

rsquad911 01-15-2007 11:37 AM

Mine had the same problem with stalling coming to a stop. It was fixed through street tuning. You can do it with either the split sec box or the Unichip.

I have the Unichip (custom tuned to my setup) My kit and overall car setup is differnt than that of TPC. So to get the Unichip for 500-800 and spend another 500-800 on custom personalized tuning was cheaper than the "one size fits all" TPC unit.

Even with the unichip I get teh CEL. I just pulled the bulb out.

SC993c4 01-15-2007 07:35 PM

What's the expected HP of a TPC supercharger on a 95 c4 cab?

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