Porsche-O-Phile

As part of my efforts to return the boost to my 951 "n/a", I'm dropping the crossover pipe this morning. Since I've checked or replaced everything else in the turbo system (including the turbo), I'm suspecting the inside of the crossover pipe is collapsed; I simply don't know what else it can be. I'll know for sure later today, but if anyone has an extra one they're willing to part with, PM me with what you want for it.

Obviously due to shipping costs, local pickup in SoCal would be best, but I'll consider anything. Trades also considered, just let me know what you need.

Ski

Unless there is damage to the crossover pipe, I don't see it collasping - I think this is wasting your time, I could be wrong but unless you see damage...I've pulled 7 or 8 of these and I've never seen one collasped - first time for everything though.

I would still pull the cat section off and drive the car around the block - eliminate or confirm the cat is free/plugged.

The car we turned into a track car, the turbo was damaged and the wastegate was toast. We hit it with air and the valve started fluttering at 4psi, at 6 it was open and staying that way.

Porsche-O-Phile

Any of the double-walled pipes certainly can collapse. Here's a pic someone posted recently of one:



I had the cat pipe off last weekend and got a very good look inside it. I noted nothing wrong. The problem is there's no way to really check the flow capacity of the pipes or to see past where the bends are, so if it was collapsed / blocked up inside past the bends, you'd never know it. I'm not about to go hacking apart a $500 pipe just to find out!

I'm really hesitant to run the car without the downpipe / cat pipe installed also. The "elbow" off the back of the turbocharger only goes down about a foot before the cat pipe bolts onto it, so running without it means the hot turbo exhaust gases go out the down pipe and (1) into the cabin (CO poisoning) and (2) could melt or ignite the plastic stuff near there. It just doesn't seem like a really bright idea. If you've done it and it's not a problem for a short (and I mean SHORT) trip, I'll roll down all the windows and do it quickly.

I suppose I could buy a used cat pipe off someone (so I can pass emissions) and dremel out the cats from this one and make a test pipe out of it by getting a piece welded back into it. I was kind of hoping for a non-destructive testing method that wouldn't cost a fortune though. . .

Ski

Jeff, like I said about driving it on an earlier post, around the block( or shorter) because of the exhaust gases, just see if she would boost over 1.2. Great photo - never seen that before but that is part of the exhaust piping and not the crossover from seeing the wastegate dump pipe there beside it.

Peckster

What about running a golf ball through it?

Porsche-O-Phile

I'll probably do that with the crossover pipe (or a tennis ball); as for the cat pipe. . . doesn't work because the cat is in the way.

Yea, that photo kind of made me go "yikes" and maybe become a little paranoid. I know it's part of the cat pipe (dunno, maybe the guy cut it or something), but the point is it can happen to any of those "double wall" pipes. Since I've pretty much checked everything else, maybe checking the crossover pipe is in order. I guess I'll drop the cat pipe off again and give it a shot; if you've done it for a short time I guess it'll be okay. It'd certainly be nice if that was the problem!

FWIW - there's a "plug" in the bottom of the cat that I removed when I had the assembly dropped out; looking inside I saw a whitish (due to heat, I'm guessing) screen / mesh that is most likely the catylist material. The screen was a little finer than a standard window screen (so maybe it is restricting the flow, who knows?) It did not look broken, melted or crumbled in any way though.

Porsche-O-Phile

You know, a way of testing that cat pipe just popped into my head. I'll try this. I need to find a ball like a tennis ball or something like we discussed above for the crossover pipe that's close to the inside diameter of the pipe. I'll drill a hole in it through the middle and attach a length of string that's pre-measured to be about the length of the pipe from the end to where the cat starts (including all the bends). Standing the pipe on end, I'll try to feed this down the pipe. If it goes all the way down (string is taut), there's no blockage / collapse. If it doesn't, there's the problem. Obviously this will have to be done for both ends so I'll need two strings (different lengths) and it doesn't really "test" the cat itself for flow through it.

Running the car should pretty much let me know too. Obviously if I get boost with the pipe off, there was something screwed up with the pipe, I'd just need to find out what.

It seems like everyone on here is suspicious of the cat pipe, so I'll try it. If it ends up being that, I'll get a spare / replacement from someone for emissions testing every couple of years and end up chopping out the "bad part and converting it into a test pipe.

J Chen

But Jeff, that photo shot is of a down pipe
& not the crossover. As far as I can tell,
the crossover have heat shields over the
pipes. They aren't double wall like the
turbo down pipe.

Ski

There is ceramic disc, plus the steel wool, then ceramic disc again in the cat. You can see the ceramic from the back of the cat. The openings in the ceramic are about 1mm square.

As these cars run rich, APE chips and others at the onset of boost, the soot tends to clog the ceramic openings and then start closing off the steel wool. I originally cleaned mine out in one afternoon with a 31" crow bar and 5# shop hammer; now with SFR full 3" exhaust and a removable cat section all is well.

fortysixandtwo

I just tried the golf ball test on my, known to be good, cat and crossunder pipes. The ball will not go all the way though, it stops where the pipes are flattened out. Something a little smaller in diameter will have to be used. I tried paintballs also but I think they may be too small. A ping pong ball might work, but I don't have one of those to try. Hmm...what other sporting goods will fit through there?

I forgot if you have the two piece crossunder pipe not, but you might be able to look around the corner, where the tube leading to the wastegate connects, with one of those small round inspection mirrors. Just trying to throw some ideas out.

dhallilama

Use a shop-vac.
Seriously, works great for ghetto-flow testing an exhaust....
Drop your exhaust out, put the shop-vac on the end, and listen for it struggling to draw air through the exhaust.
You can use a flow meter to measure if you wanted to get "technical"... but you can hear pretty well if the exhaust is overly restricting.

Porsche-O-Phile

Well, there's a 12-gauge I've been eyeing. . .



As far as the shop vac test - not a bad idea. I might try and rig up something like that. I only have the upstairs vaccum though - not a "shop vac" per se, but it does have a hose attachment on it. It's actually down in the garage because I used it to vaccum all the billion tiny shards of shattered brittle plastic hoses, ignition wire wraps, clips, and other assorted plastic junk that has failed over the years from off the top of the head and balance shaft cover. Just don't tell the wife. :O

I'm still leaning towards the idea of something being blocked or collapsed. The turbo spools pretty quick and then just stops at 1.1-1.2 bar. The car accelerates pretty well (just like an n/a) but after about 5,000-ish or maybe 5,500 RPM you have to give it a lot of gas to keep the RPMs building - pretty much what I'd expect if something was restricted. I'll do the cat pipe removal test this afternoon; right now I have to replace ANOTHER brittle hose (this time it's the one from the brake booster to the venturi). It was so brittle when I removed it it snapped in two. Off to find a replacement!

Porsche-O-Phile

Something else odd I've noticed - all the "big" hoses / vaccum lines are actually 15/32" (non-metric) designation. This makes me wonder whether the Euro-spec cars came without all that octopus crap under the intake. Probably not, I'm guessing. . .

For now I'll keep it (nothing wrong with it, no leaks or anything) but I'll probably end up ditching it at some point.

Danno

I've got a couple spare crossover pipes you can try out. I'm still betting on the wastegate as being the culprit though...

Tom M'Guinn

Just thinking out loud. How about taking a little piece of aluminum, drilling three holes in it, and blocking the connection coming off the wastegate dump tube? For quick testing anyway, that would force the exhaust through the turbo even if the wastegate is opening, no?