I have a mostly stock (apart from a Vitesse chip and LBE) 1989 Turbo and am considering doing an exhaust upgrade, plus maybe a Tial wastegate "while I'm in there."

I'm not trying to go mod-crazy and make huge power, just sort of an OEM+ thing, so what kind of realistic gains should I expect from a high-flow cat exhaust (was thinking Fabspeed) by itself? The current cat was replaced a few years ago so it's probably not all blocked up, although the car came from CA so I'm not sure if the previous owner had to put an extra restrictive cat on at the time.

The car is strong enough for me as-is so my thought process is basically, do I want to drop $2000 on this stuff if it's just going to give me another 10-20hp, or does it make a night and day difference?

 

I would suggest a full 3” turbo back exhaust along with Tial F38 wastegate.

The exhaust will help the engine breathe better and help the boost come on sooner.

The WG will help prevent the boost from bleeding off at higher RPM.

 

I installed a Magnaflow muffler and sport cat but still keeping rest of exhaust stock. I immediately noticed the turbo spool up much faster. That alone made it worth it and would do it again every time. It relieved a lot of turbo back pressure. No idea if added any horsepower.

Exhaust is a science. You have to make sure you understand EVERYTHING else on the engine because it all works together. Read up on gas heat and velocity and turbo back pressure. Then decide how an aftermarket exhaust would affect your horsepower.

That being said, this might help….

https://rennlist.com/forums/944-turb...ispreloading=1

 

I got my car with the cat deleted, a custom exhaust (still need to caliper it, think it's a 3"), and no muffler. It has some kind of glass pack or resonator instead of a muffler, but it sounds like straight exhaust. I actually don't like it, as it is annoyingly loud. But that's a personal thing. Fart cannons are for Honda.

I think most sites will tell you 20-30 HP for a good exhaust. Or at least in their ad material. I don't know if you'd see that on the dyno. But I've never seen a single post on here where someone couldn't tell a difference with an upgraded exhaust. Porsche really choked these things stock. The fact we never see anyone say "I couldn't tell a difference" or "I was unhappy with the upgrade" tells you all you need to know. There is a reason it's almost always the first thing everyone does.

I would say research dual-port vs single-port waste gates. Deeply. Before you decide on a wastegate. I'm not going to point you one way or the other, as I haven't tried both myself. But I will say that for a long time I thought dual-port = better in every way, in every case. Everyone upgrades to duel port for a reason, right? But it's more complicated than that. Worth researching.

 

It will definitely sound a lot faster.

 

I’ve debated this quite a bit myself. Assuming there’s no extra restriction like a clogged cat or collapsed pipe, I’ve seen it stated many times that the factory exhaust is not restrictive below around 300 whp. Though a bigger exhaust would probably reduce lag, which I’d be interested in. It’s my understanding that the factory muffler is essentially a straight through design.

My car has a K26-8, Lindsey A Tune, Tial wastegate, and a hogged out cat with factory exhaust and muffler. It sounds good and pulls hard at 18psi. Given the cost of a good exhaust, I think I’d rather spend my money on a Vitesse MAF, then on a bigger, more efficient turbo, then finally a good turbo back exhaust with high flow cat. Now, where’s that big bag of money I had sitting around?

 

Do you have mandatory emissions testing in your area? If not, try clearing out the cat first. Of course, any "try" requires about $300 worth of exhaust seal rings oh gawwwd

 

Good question, I'm also looking around for a complete exhaust (probably including, at some point, the exhaust headers).

 

Way back when...
I talked to Autothority about installing a so-called 'test pipe' cat replacement.
They said "7 HP on our dyno", rest of the system stock. They also said "Zero HP for a K&N".
Biggest difference was how much faster the turbo spooled up. Totally woke the car up.
Don't really know how restrictive the rest of the exhaust is though.
Fabspeed 3" with Magnaflow straight through muffler on the race car. A little louder than I prefer on the street, but that's probably just me.
I can't stand a loud car... it's just annoying, and I really don't want to announce my misdeeds to everyone in the county.

 

That's definitely one of the reasons I'm asking directly. It seems like a lot of previous threads involve highly modded cars pushing 350+ hp so it's not too informative in my case with a relatively stock 951. On the other hand, the consensus also seems to be that the first and best bang-for-the-buck mods should usually be chip, exhaust and wastegate.



I don't (Texas), but the PO put a new cat on a few years/5k miles ago so I'd imagine it's in pretty good shape. As mentioned, he was in CA so I'm not sure if they force you to put on an extra-restrictive cat, though. If I upgrade the exhaust I'd probably do a high-flow cat, as I've gathered catless is pretty stinky and I think it would annoy me.

 

My low mile 86 with Autothority chips and 'test pipe' was clean enough tosail throughthe CA tailpipe smog test.
Wouldn't have passed if they had been checking NOx at the time. and would have failed the visual test miserably.
Not stinky... but higher mile examples might have more HC and be more smelly.

 

I put on a FabSpeed system and noticed a definite gain in spooling and acceleration... also, the stock cat was still in decent shape. So, between the larger pipe and the cat delete, would say this was a good gain, also while reducing a fair amount of weight. The cost though was significant at more than $1300 if I recall correctly. I also installed a Lindsey dual port waste gate that helped, but upgrading to a larger Tial 44mm to accommodate all my other mods.

A middle ground approach is installing a Bursch 2.5" cat delete head pipe and tie into your existing system. I may have one sitting in the parts garage if interested.

rick

 

With a K26/6 or K26/8 (even K27/6) the stock exhaust (if in good condition) is fine. Going to a larger 3" exhaust will not yield much.
Ask people selling the 3" exhaust to show you before/after dyno charts!!

The stock cat is a restriction, most are 30+ years old and are no longer efficient. A bursch 2.5" test pipe is a good upgrade, you will notice quicker spoolup.

If you think you will upgrade turbos in the future, then a 3" exhaust makes sense.

If sticking with the K26 turbo, try to maximize the area under the power curve. A dual port WG with a good boost controller make a nice addition, which you can keep using down the road if you ever upgrade turbos.

Once you start modifying the exhaust and/or alter boost, you must address the engine management.

 

What are the brands to look at for a complete exhaust system make over?

 

Fabspeed does nice work. Lindsey is a crap shoot. TurboTim may get you your parts, once you've paid in full, in about a year or ten...