Mark J

Bugger was hoping to be reporting back today saying how great the new CAT bypass sounded but alas i have just returned from a wasted journey

It appears the 'simple' job of replacing the CAT is going to be nothing like simple. The guys at HP Motorsports said the flange of the heat exchanger that the CAT connects to is so corroded that they would not be able to bolt the new bypass upto it and didnt dare unbolt the old one in case i was left with a blowing exhaust. So now my bypass thats already cost me £286 all in, will need another couple of hundred quid spent on getting a secondhand heat exchanger & fitting

Really cant believe my poor luck when it comes to things like this. If i had known i wouldnt have flipping bothered with a bypass, its not really worth a £400+ cost for such a minor mod.
HPM says i should be able to pick up a 2nd hand nearside heat exchanger for about £120-£150 so will just have to look about.
Anyone got one laying around they no longer need ?

The good news is they said i have a very tidy good example 964 and its all in good condition underside. Except that bastich heat exchanger naturally
and i got the thicker rear anti roll bar fitted.

boxsey911

These are for sale in Surrey:

ebay link

Mark J

nice one Boxsey, have bid for them. Lets hope aye, otherwise i can see my danske pipe sitting in a cupboard for a long while.

edit oh crap, just read the rest of the ad and it says left side corroded with holes in it ! bugger and ive bid now. Was too impulsive.

boxsey911

I'm sure you can get it welded up. Just don't go mad on any subsequent bidding.

Mark J

welded up ? is that feasible for a heat exchange? Thought the temps would be too high for any patching.

964russ

Weld is way higher than exhaust temp, molten metal is v.hot.
The only problem with weld is that you need good metal to weld too, so depends on the amount of rust ect.
Ive heard a car running a dansk bypass-cup pipe+standard back box and there slightly queiter than mine.
My car was 107db at oulton last year. But the noise amount seems to differ from car to car.

Mark J

i spoke to the guy selling the heat exchanger and he said the only corrosion is on the heat exchanger itself meaning it would suck in a bit more air via the few small holes from the engine bay as well as the engine itself for heat. He said the actual manifold and flanges etc were in pretty good shape. Should i pursue this or not? He kindly offered to allow me to pull out of the bidding, obviously another nice 964 owner
Or should i pursue a better example via the 2nd hand parts dealers about? Just how good shape is a near 20yr old heat exchanger going to be in from any 964 ??
I assume my current one must have similar corrosion to the one being offered, with the exception that my flange is fooked, so i wouldnt really be compromising what i have lived with since i owned the car ? I am guessing we would all have similar corrosion around the heat exchanger itself due to the harsh life that particular part has to live.

mrmoots

Hi Mark

I have a spare pair of heat exchangers in the garage I no longer need. One has some corrosion to the heat exchanger element itself and I think its the right side, i.e not the side the CAT bolts to.

I will drag them out later today, photo any damage and post some pics later on.

Ross

ThomasC2

Hang in there Mark, there's always a light in the end of the tunnel! And most of the time it's not a train :-)

boxsey911

I was thinking about this earlier when you first mentioned the garage hilighting the potential problem of undoing the cat. In theory the cat is removed every 12,000 miles when serviced. The service kit even includes a flange gasket and replacement nuts and bolts for removing the cat (this is done to get good access for a valve adjust in case you were wondering). Therefore if the cat has been removed at each service there should not be enough time for heavy corrosion to set in to the bolts. Maybe in your case the cat has not been removed for a very long time and the garage think it is now too corroded? Alternatively get an opinion from another garage about fitting your bypass? You don't necessarily have to go to a Porsche specialist, it's only an exhaust after all so you could try an exhaust centre. They blow out corroded bolts and clean up flanges every day.

mrmoots

The flange for the cross over pipe and CAT are pretty substantial, I would have thought that it would take a lot for these to rust beyond use.

If the CAT flange is bad, it would be worth checking what your exhaust studs and nuts are like before you go much further. These can rust up badly and become really awkward to remove.

Do you know when the last valve adjustment was done? As boxsey says, the CAT has to come off for this.

These are the pics of the one from my garage. It’s a bit oily but sound enough.

Mark J

Hmm, you have me guessing now. I also wondered how a flange that thick could have corroded so much that it couldnt be re-bolted too. Took the wheel off and had a look, the bottom half of the flange of the heat exchanger has rotted away. HPM tried to use washers but no joy, it will need another exchanger unit put on.

Just checked comprehensive service history (all done at JZM) last valve adjustment was done 20k Miles ago. How come none of my services since have flagged this up, both at JZM and La Rose ?? or is it on a need-to-do basis rather than every 12k ?

MrMoots, how much would you like for the heat exchanger ? Can pm.

The garage said the rest of my exhaust bolts were all in good shape and had been renewed at some point but i can see the bolted flange that joins the two units in the centre (cross over?) looks pretty heat welded/rusted together.

Thanks again for your help gents.

Mark J

two shots of the offending flange:-

This appears to show the flange still in reasonable enough shape to bolt to:-



and the worst part, the one bolt HPM tried to use washers on to see if it could fix properly.



i take it 2 of 3 bolts wouldnt be enough to secure the bypass to the heat exchanger? I guess risk of future blowing etc. In my bodge mans eyes i would have tightened that bolt right up with the washers and think it would have stayed strong enough for a good while, assuming the other two bolts secured properly, and looking at top half of flange where it looked a lot more solid, have no reason to think it wouldnt have held. But it would only have been a reasonably short term solution.

The rusty flange connecting the cross overs, i wouldnt fancy trying to get them undone ! but guess standard work for a garage.

boxsey911

Although your pics are a bit blurred, I have to agree that the flange looks in shocking condition. They normally look like the flanges on Mr Moot's pics.

BTW little jobs on 964s often turn into bigger jobs so don't feel too bad about it.

Mark J

yeah sorry about blurred pics, they were from me sliding under the car 9am this morning and clicking away with arm outstretched

I dont know why my exhaust flange would be any more corroded than anyone else's car of similar vintage. (Other than sods law ) I've had the car 3 years now and alway garaged overnight and that last valve adjustment was done just before i got the car. All the heat shields etc are in good condition and when i swapped out the primary box for the cup bypass, that was all in good health too and came out easily enough. Strange one.