Turbo question - PeachParts Mercedes-Benz Forum

kollas2 · #1 05-04-2002, 09:16 AM

Turbo related question
Since I lately installed a turbo system in my 230.4 I have a problem adjusting right the carburator which is a 32/36 DGAV Weber .The carb is closed firmly and is taking compressed air only from the turbo.The power from stop is great , but as soon as the whole carb is opened the engine drops dead...I tried several different configurations about the second part of the carb changing the little screws through air and fuel passes,but I had no luck...I suspect the carburator is small.
Any ideas ?

Robby Ackerman · #2 05-06-2002, 09:56 PM

The carb is plenty big. You are pulling air through it under pressure. I have a supercharger and it is placed between the carb and the intake manifold so it pulls air through the carb. Is this how your's is setup or are you pushing air into the carb under pressure? How many pounds of boost are you running? Are the throttle plates or shafts binding due to the pressure?

Does it remain running if you slowly depress the throttle to its maximum or does it die only when you floor it quickly?

kollas2 · #3 05-07-2002, 09:54 AM

Actually the turbo is installed in the outake manifold and gives compressed air (hot until I put a intercooler) to the carburator .The engine with the turbo runs fine -car parked- in
full range rpm ,but as soon as I seat in to drive it the problem comes up with the carb...
When the second part of the carb opens the engine tends to shut down.
The turbo is taken from a Seat Ibiza 1.8TD or 1.9TD .The pressure -according to the mechanik- is set temporarily to 0.2-0.3bar,until the problem with the carb is fixed ,later on we see.I should check the throttle plates for bending!

Jim Villers · #4 05-07-2002, 02:57 PM

I installed a supercharger on my 2.3-16. This engine is injected but some of the symptoms might be similar. First, does the engine run fine without the turbocharger pipe attached? Second, is the fuel bowl vent port enclosed in the intake duct? I am not familiar with your specific carb, but my DCOE Weber has a port next to the venturi that vents the fuel bowl. This must receive the same pressure as the venturi or pressure across the jets will be negative and no fuel will flow.

kollas2 · #5 05-08-2002, 05:32 PM

Great tip! Thanks.
As I think I understood ,the fuel bowl must have the atmospheric pressure,otherwise it cannot send fuel to the carb , is it right?
So I must find a way so the fuel bowl receives atmospheric air.Is a bit difficult to configure as the whole upper carb is firmly closed...
Any ideas and suggestions are pretty welcome.

Speedtek · #6 05-08-2002, 06:14 PM

There are 2 types of systems for using carbs for turbocharging.
1. Draw Through. (Carb is before turbo)
2. Pressurized. (Carb is after turbo compressor)

Sounds like you are #2. You may have to build a box around the carb. this is the pressurize the fuel bowl and also prevent fives from leaking shafts. Maserati did this look at an early non-injected car. Lotus used special Dellorto carbs that had shaft seals a nd a port for pressurizing the fuel bowl. Mikuni made a sidedraft carb also. You can upgrade any Dellorto DHLA carb to do this.
The DGAV is a great carb. but the shafts are not sealed. so be careful. If you need help jetting it let me know. there are a lot of emulsion tubes you can change to for better response.

good luck.

Jim Villers · #7 05-09-2002, 08:56 AM

The float bowl needs to be at the same pressure as the air passage so that the jets will meter the correct fuel. I have not seen the DGAV carb but in the drawing, I annotated what looks like the bowl vent. If this is the fuel bowl port, then it needs to be inside the turbo duct.

kollas2 · #8 05-09-2002, 10:04 AM

Hi Jim !
Thank you for your suggestions,though I must say that my currant config is exactly like you reccomended...
The filter box from the carb has been modified and now is air-proof completely ,except a big whole in the upper surface in the center where fits the tube from the turbo.It is a week now
I ve finished the job with the turbo and cannot tune the carb!
I should check again if the air from the turbo duct bends the shafts and chokes like this the carb and the engine...

Jim Villers · #9 05-09-2002, 10:10 AM

Robby got the shaft bending from my 2.3-16 project and I doubt that it applies to your engine since you are not experiencing throttle bind. The stock Mercedes throttle body would bind when under boost. I solved my problem by switching to a Mustang 5.0 throttle body. I also converted to an aftermarket SDS Injection system. Good luck, that is about all of the advice I can provide.

jasondew · #10 05-09-2002, 11:26 AM

jim,

what's different about the mustang throttle body compared to the 16v? i remember you describing the car sticking in WOT and getting some boost creep a while ago. did that new TB fix it. also, did you switch injections systems for more performance or was that part of the solution for the throttle problem too?

thanks

Jim Villers · #11 05-09-2002, 11:46 AM

Jason .. The throttle body was definitely the problem. The difference is that the stock unit utilized roller bearings and the Mustang TB used ball bearings. I changed out the injection system partly because of the throttle body and partly because it appeared that the engine was running lean at full throttle. The injection has taken a lot more time and effort than I thought it would. The most difficult was building a fuel rail that did not leak. The most time consuming is programming the fuel map (still in progress). If I were doing it over, I would have spent more time either modifying the stock throttle body to ball bearings or finding a shorter aftermarket TB. I would have evaluated the stock injection system with a functioning TB before jumping into a total replacement. As it is, I am VERY happy with the results even though I still have a few "driveability" tweaks to make.

jasondew · #12 05-09-2002, 06:33 PM

what do you think it was about the roller bearings that caused the leaflet to stay open that the ball bearings fixed?

Jim Villers · #13 05-10-2002, 07:06 AM

The only thing that I can think of is a minor flex in the shaft. It is a very thin shaft, about 5/16 inch or so and it is split in the center for the buterfly. The Mustang shaft was significantly larger. A small mis-alignment of roller bearings can cause the shaft to bind; not so with ball bearings. I did not do an engineering investigation but I did spend $350 for a new Mercedes throttle body that did not solve the binding. The price of a little knowledge is sometimes high.

jasondew · #14 05-10-2002, 08:40 AM

jim,

what boost level have you end up running? what's your comp ratio? 9.7:1?

thanks

Jim Villers · #15 05-10-2002, 08:54 AM

I think that that my compression is 9.7 (standard US). I am running 3-4 psi. I need to do more testing and tuning. With the boost set higher, I had a lot of ignition ping and when I retarded the ignition, I lost the free spirited high revs. This seems to be a good "seat-of-the-pants" setting. It is hard to tune without a dyno and I can't drive and revise the fuel map at the same time. I need to get my son to drive and hold full throttle, constant RPM by using the brake. I could then adjust the fuel and ignition map using the air/fuel ration gauge and the sound of engine knock. A little crude but it should work. After I am satisfied that I have it the best I can make it, I will have a local dyno guy see if he can improve it.