Problem with high revs - 16v turbo - PeachParts Mercedes-Benz Forum

Joreto · #1 06-26-2003, 12:40 PM

As many of you know I have had problems with the high revs, the car would start to hesitate after 5900 - 6000 rev. Today during the instalation of bigger pipes from the turbo to the throttlebody box I did the following experiment :

The car is not moving in neutral gear, the pipes from the turbo to the throttlebody box are disconnected and only the box over the throttle body is in place. The car would rev freely (and very quickly) all the to 7200 - 7500 revs.

After that I connected the pipes from the turbo to the throttlebody and when I reved the car it would rev to 6000 rpm ?? To get it to 7200 - 7500 I would have to hold the throttle quite a bit longer then without the pipe work.

Is this normal, if not where should I look for the problem ?? Also the Air/fuel meter indicated a leaner mixture with the pipe work disconnected then with the pipes connected ??

Any suggestions ??

Benzmac · #2 06-26-2003, 07:38 PM

How much boost are you running? What type of fuel management?

Maddog · #3 06-26-2003, 11:08 PM

what are you using for fuel enrichment?

Joreto · #4 06-27-2003, 02:22 AM

For enrichment I'm currently using a ajustable pressure switch to activate the coldstart injector at 0.3 bars. I'm running maximum of 0.5 bars of boost. Acutally the Air/fuel ratio meter shows that there is enough fuel. The turbo is a garret TB25 rated at A/R 48 ( I know that it's small for big Hp gains but low down torque is incredible

)

Is there any way that I could measure the amount of air coming into the engine ?

Maddog · #5 06-27-2003, 10:27 AM

That's what the boost gauge is for. Does your boost gauge on your intake manifold read any boost at high rpms?

Joreto · #6 06-27-2003, 11:32 AM

The boost gauge reads 0.5 bars of pressure from 2500 revs on up (at WOT when the car is moveing), but the reading is taken at the turbo (the same place that gets the pressure for the integrated wastegate). Is there any place thats after the throttlebody where I can tie into to read the pressure ??

P.S. You can see pics of the setup in the turbo folder at:
Turbo install pics

What is different on the current setup is that the pipes from the turbo to the throttlebody are 63mm, before they were 50mm and the intercooler is removed since it was to small.

Maddog · #7 06-27-2003, 01:42 PM

Just remove a vacuum line off of the intake manifold temporarily and hook the boost gauge up there. We just need to see this to determine what your problem is.

Joreto · #8 06-29-2003, 07:15 AM

Maddog, I'll be sure to do that. However I found a big crack in the exhaust manifold on the pipe connected to the first cylinder, could this cause the problem I described ?? Part of the exhaust gases excape through the crack without spining the turbo i which case at high rpm the turbo can't supply enough air ??

Maddog · #9 06-29-2003, 02:12 PM

Its possible and the test I have suggested will tell if that is in fact the problem.

Speedtek · #10 07-03-2003, 01:40 AM

You are going to have a lot of problems with your manifold design.
The way it is the hot exhaust gases will be hitting each other and creating excessive heat. which will create cracks in the manifold all the time.

Do you have a EGT gauge installed? if you do not you will need to get one and not exceed 1350F degrees. Mount the probe on the collector of the turbo. (Entrance to the exhaust housing, manifold side)

Your turbo looks very small. What was the specs?
(never mind I see them)
YOUR TURBO IS TOO SMALL! you will have great low end but no top end.

Yeah I think your exhaust leak is causing one of your boost problems.

Joreto · #11 07-03-2003, 03:15 AM

SpeedTek, thanks for the reply ! All along I suppected that the turbo is too small, so now I've decided to switch to a bigger turbo. Also I'll be making a different exaust manifold. I'll try to make it something like this one (sorry for the big pics ) :

What kind of turbo should I use ? I know that the t3/t4 would be perfect but it'll be hard to find one here, however I have a couple of Garrett T3's from which I can choose (they are second hand but in good condition). What compressor/turbine trim should I look for ?

P.S. This is not my exhaust manifold, the pics are linked from the
www.powerpage.dk/turbomanifold.htm

Speedtek · #12 07-03-2003, 04:32 AM

If you plan to stay with blowing thru the CIS meter you will need to get a T3 with a Super 60 Compressor Trim and a .69 exhaust housing.

If you plan to go to EFI then I will recommend a different turbo.

The pic of the 4-1 header is better, but you really need to use steam weld pipe, which is easy to find in your country. The thin wall header will crack every few months. It can not take the expansion and contraction of everyday use well. Also try to use 1/2" thick flange for the turbo and head side. Minimum is 3/8"
The steam weld pipe I am talking about is 1/8" thick cast steel easily welded by heli-arc.

Joreto · #13 07-03-2003, 04:12 PM

Speedtek, thanks again for your help ! l'll have the new manifold and the new turbo installed hopefully by the end of this month. I plan on useing the standard CIS (with an additional injector controller for fuel enrichment ), since switching to an EFI seems beyond my mechanical abilites at the moment.

Joreto · #14 07-14-2003, 04:18 AM

Speedtek, what are steam weld pipes ?? Where can i find them, in what industry are they used ??