illegal exhuast

Guest · Post by **Guest** » 31 Oct 2003, 01:36

I have a '94 850 turbo. I took out my cat converter and ran a 3 inch pipe all the way through to a performance muffler at the back which is obviously illegal but given me a significant gain in horsepower. I like it's performance as is but know that I will eventually have to pass emissions and was wondering if all I had to do was put a cat back on that will fit the new pipe. The only downside to this was losing a lot of low end torque, will this also be solved by re-installing a cat converter?

potroast · Post by **potroast** » 16 Jun 2004, 13:05

you will gain some low-end back by replacing the cat. However, since you also increased the pipe diameter, you won't get back to a "stock" low-end, but you will still have an improved high-end -- which is where our engines really shine, anyway.

I do not recommend running without a cat, simply because it is illigal, and although I am not a tree-hugger, it seems the gains of running w/o a cat do not outweigh the environmental concerns.

However, it is common for people to replace their cats to get smogged, then remove them again for the next 2 years.

Of course, this is only applicable to states where they use the sniffer -- such as california, the smog-nazi state. Other states, such as oregon, will simply read your codes and as long as you're clean, you'll pass...

Volvord · Post by **Volvord** » 16 Jun 2004, 19:51

Your question on legality of your exhaust really depends on your location, In some states your entire exhaust system has to be th eoriginal style and type which includes the same diameter and number, type and location of mufflers and cat. In other states they just look at tailpipe emmisions.

Post by **matthew1** » 16 Jun 2004, 20:45

A little off-topic here, but remember about noise. Even a small increase in pipe diameter is going to add drone to your drive. The guy who wrote this nice piece on exhausts found the drone to be a little noticible:
https://www.matthewsvolvosite.com/exhaust.php

wdw · Post by **wdw** » 03 Mar 2005, 06:49

Svensson · Post by **Svensson** » 03 Mar 2005, 06:57

Ok now i know i don't need to register =)..

I'm writing from Sweden.. I just had to remind you that the turbine in your turbosystem demands a bit of resistance, if you remove cat and mufflers - your turbo will eventually fail.. In my car (Opel Calibra T) the .. ehm.. pressureclock (i don't know the accurate english word) didn't open due to lack of resistance in the exhaustsystem. The turbinewheel didn't gain rotation in low rpm and the bearings failed..

At least that's what the repairman said..

Volvord · Post by **Volvord** » 03 Mar 2005, 19:56

You turbo failure is not from a lack of backpressure. Turbochargers work best with little to no resistence or backpressure. In fact all engines will work best with no backpressure, the problem is that installing an open exhaust does not always reduce backpressure, properly tuned exhaust manifolds and exhaust systems will actually scavenge of "draw" exhaust out of the engine whereas an open exhaust may create turbulence which will cause backpressure

The "pressureclock" you speak of, the only thing that makes sense is the wastegate which opens to allow exhaust to bypass the turbin which limits the total amount of boost. The wastegate is actuated by a vacuum/pressure diaphram connected to the intake, exhaust will not have any effect of this.

Guest · Post by **Guest** » 07 Mar 2005, 02:29

Ok, thank you for your answer.

I guess the repairman didn't know what he was talking about. The word i was looking for was "vakuum diaphram", it's called "vakuumklocka" in swedish.

But I still think removing the cat is a bad idea =)