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alfadriver
alfadriver MegaDork
12/16/16 7:07 a.m.

In reply to scottsrods:

Diesel and gas catalysts are very, very different.

dean1484
dean1484 MegaDork
12/16/16 7:20 a.m.

Unless the oe cat is damaged you will not see any improved performance by modifying the exhaust on a 944. Porsche put an excellent system on the car. Most aftermarket cat back systems will have serious drone to them. The stock cat is a honeycomb unit that flows excellent. The only reason to change the cat back on these cars is if you need to save weight but I found it not worth I both time and money wise. If it is a track only car take the cat back off and just put a strait pipe after the cat. It will be extremely loud but you pick up a couple hp. And by a couple I mean 5-7 hp and only at the top end.

Where these cars are limited is in the factory timing maps. The timing map from the factory starts pulling timing at about 5800rpm. I found that most chip makers increase the overall timing across the whole map but still have it fall off at the top end. The best performance pickup I made was to take timing control away from the dme and use timing maps of my own design. I spent some quality time on the dyno. I only netted about 12 hp max gain but I was able to flatten out the hp and torque curves and in some places on the map the gains were more than 18/18. The key to a 944 is applying the power over much more of the rpm scale. If you can pull an average of 10% gain across the entire rpm range you will be that much quicker for a much longer period of time than the guy that focuses on peak numbers in a 944. With a 944 it is all about making improvements under the curve.

dean1484
dean1484 MegaDork
12/16/16 7:27 a.m.

Oh and my 944 taught me how to actually drive fast. It is a car that rewards being smooth and precise. It does not like abrupt changes on track. Driving becomes almost fluid in nature. It I a car that at first you will be much faster driving at 9/10 learning that last 1/10th in a Porsche is what made me a much better driver that carried on to all the other cars I drove as well.

spitfirebill
spitfirebill UltimaDork
12/16/16 7:27 a.m.

The cat in my Nissan truck is original and 400k miles on it. Do you think I need to replace it?

dean1484
dean1484 MegaDork
12/16/16 7:31 a.m.

Only if it is broken. If you keep a car running properly a cat will last. Cats don't generally fail. Cats are damaged/killed by somthing else going wrong with the car.

alfadriver
alfadriver MegaDork
12/16/16 7:32 a.m.

guys- this is an old thread- and I was responding to what appears to be a canoe.

bill- how old is your truck? If it's post '96, I'd say you are ok, as the car should be able to tell if the cat is bad.

scottsrods
scottsrods New Reader
12/19/16 1:09 a.m.

In reply to Dusterbd13:

i made the account specifically to reply to this topic, so this is why the names are the same. Anyway thanks for the reply to you and all the others bellow you, much appreciated!

Knurled
Knurled MegaDork
12/19/16 7:55 a.m.
Brett_Murphy wrote: I was looking on Special Stage to see what they run. I'm not sure how they would work for ODBII inspections, but I figure if they can stand up to a rally car, they'll be alright on my beaters.

Thousand-dollar motorsports cats mounted under the rear bumper.

Technically they are converters!

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