Car - 93, 300D, 2.5T.

Problem is I am getting what feels like inconsistent air flow when cruising on the freeway. It feels like the car is hitting a wall of wind or something (even when no wind). I don't notice an RPM change nor do I hear the motor lug down. I assume it's the wastegate and/or the actuator after the turbo before the intake crossover piece. So I have two things I plan to do. First i have original vac lines and I am replacing and mending those. That is a short term fix. I'd like to do the wholesale changeover to pressure actuator and ****can the EGR, vacuum actuator on the wastegate (and put the pressure actuator on) and the delete the 2nd vac actuator after the turbo. Maybe I have another problem too, but this can only help I would guess.

Questions.

• I want to drop in a boost guage now to see if I can notice any intake presssure changes. Can I tap into either of the two plugged ports just above and the the left respectively of the hose that goes to the ALDA. I don't want to T the alda line if I can avoid it but that is my back-up plan I guess. See the pic below for the two plugs I mention. Anyone got any pictures of their boost guage installation results both under the hood, where you went thru the firewall and how you mounted the guage?

• Second, can I eliminate the EGR valve, cap off the exhaust stub of course and use the orignal EGR flange on the turbo for my pressure line to the new pressure driven actuator on the wastegate? I figure I need to make a plate to cap off the EGR mount anyway and why not just tap and put a nipple in there (with an RTV or some other kind of gasket between the flange on the turbo and the homemade cover plate with nipple) This would avoid having to pull the turbo and drill and tap the actual housing (like GSXR's original DIY article). Any reason using the EGR port won't work for this? Have others done this and any pics would be great if you have.

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1) It will help if the flapper is a problem because you'll wire the flapper open when you convert to a pressure actuator.

2) Why don't you want to tee into the ALDA line for a boost gauge? That's where I get a boost gauge signal.

3) There is a grommet between the brake booster mounting boss the cabin heater coolant supply line under the wiper arm. The lines for engine shutoff, ACC vacuum, headrest actuators and some wires go through the grommet. There's room for more lines. Cut through a nib and feed your boost gauge line. I'm pretty sure you can fish out the line from below the dash but it's easier to remove the gauge cluster to fish out the line.

4) You can tap the same location for a pressure actuator signal. You can fabricate a cover plate for the EGR port with a nipple as you described. No need to fabricate a gasket if you don't mind buying another EGR gasket.

Sixto
87 300D

Thanks Sixto. Good point on just using a new EGR gasket - Duh! As for tieing into the ALDA line, I may do that but it just seemed like a nipple onto one of those plugged ports would be cleaner and pretty simple if I can find the right fitting. Eitherway it looks like a fairly straight forward job. I jacked up the car and took a look at the wastegate actuator and it will be a tight fit to get to it from the bottom but it looks doable. There is a darn oil line/hose right in the way and my hands are not exactly small. I hope the vac lines help but eitherway I'll convert it over eventually.

I know it's been discussed in the conversion thread but I am still trying to get my head around the pressure actuator vs. the vacuum one as far as when it opens and closes the wastegate. It is opposite and intrinically that seems like it wouldn't work but I'm going on faith here but if anyone can further explain the difference for when it is under boost and non-boost in these two systems and why the backwards set up works OK I would appreciate it. Anything to get that EGR and rats nest of vacuum lines and electric solenoids for flapper, wastegate actuator and EGR out of there seems like it's well worth doing. pardon my lack of understanding of the system here.

If this doesn't fix my drag/loss of power issue do any other thoughts pop into anyone's mind? My intake has the typical sludge coating in it from the EGR so I am not sure that isn't a problem too plugging up the ALDA line??? If I make the changeover, the next time I have to replace the glowplugs I'll have the intake boiled out to really clean it up. The last time I took it off to change the GP's it was a friggin mess of oily residue in there.

Pressure actuator (as nature intended) = wastegate is normally closed. Manifold pressure overwhelms the spring and pushes the wastegate flap open so some exhaust flow bypasses the turbine which reduces compressor rpm.

Vacuum actuator (the devil's own work) = wastegate is normally open. Government commission determines when wastegate should close to allow exhaust flow to turbine which increases compressor rpm.

For a preview of what you're missing, rig a line directly between the engine vacuum pump and wastegate actuator. That'll effectively wedge the wastegate closed. Go for a drive keeping in mind that there is no mechanism to prevent an overboost situation. C'mon, it's a T25. It's not going to produce more than 1.1 bar long enough to destroy the engine unless you try to climb Pike's Peak at WOT. Just don't hold the pedal to the floor and you'll be fine during the test.

The nipple for the ALDA signal line is 603 098 03 04 with washer N 007603 008109 or any crush washer that'll fit. That said, I don't know if the other ports are tapped with the same thread. Jeremy can answer that if the ports are the same between the 602 and 603.

I don't recall that anyone who cleaned the intake manifold noticed a performance improvement for the effort. Sure feels good, though

Sixto
87 300D

Thanks again Sixto. Awesome information. It's clicking in my head now after I ready you post. Makes sense, boost when you need it and the pressure shuts it down and prevents the overboost/ continued boost as a result. Great point on using an ALDA port fitting on one of the other ports. I hadn't thought of that. Was having trouble finding the right metric fitting at my FLAPS. Really a good idea since I actually have a 91 300D parts car sitting behind the darn shop anyway! I'll see if it fits one of the other ports on the 93 300D intake manifold (help me make a few bucks back from the parts car investment )