Anyone got no cat?

[Subaru ETA]

Just wanting to hear from people who have taken the cat out.
The placement of therear turbo is quite close to the cat so one would think that by getting rid of the cat it would decrease the backpressure to the rear turbo causing less life?
is there a noticable power difference with 3inch exhaust with no cat?

[Nick Mann]

Just wanting to hear from people who have taken the cat out.
/Wyhy


The placement of therear turbo is quite close to the cat so one would think that by getting rid of the cat it would decrease the backpressure to the rear turbo causing less life?
I know of a couple of rear turbo failures, but I don't follow the logic. The back pressure will be the same to both turbos, as the cat is after the two downpipes join. If it's any consolation, both failures involve abused cars!


is there a noticable power difference with 3inch exhaust with no cat?/yes The standard exhaust system strangles the engine at high revs. A de-cat and back box should solve the problem to a large extent, but a full system has the potential to do it better.

[Roadrunner]

The standard exhaust system strangles the engine at high revs. A de-cat and back box should solve the problem to a large extent, but a full system has the potential to do it better.
On the other hand, increasing the bore of the exhaust reduces the torque so, if you don't up the boost to gain the benefit of the freer-flowing gases, you might feel that the car is slower because it won't be accelerating as hard.

I've removed the cat, retained the rest of the original exhaust and upped the boost by around 0.2 bar and it feels quick compared to my last car which had the same mods but a 3" cat-back and 4" tail-pipe.

Brian

[Paul C]

I've removed cat and the car seems really smooth on accelleration with about 230lbs of torque. Dont know what standard torque is for vr4 any ideas?

[stuey]

Just removed the cat on mine on saturday, haven't noticed any difference yet (still on standard boost and exhaust).

[Kenneth]

On the other hand, increasing the bore of the exhaust reduces the torque so, if you don't up the boost to gain the benefit of the freer-flowing gases, you might feel that the car is slower because it won't be accelerating as hard.


Not true. It IS possible to drop some torque down low, but with a turbo car the turbine usually provides some back pressure once the revs rise a little. (And with our small turbos, the turbos provide plenty of impedence)

After the turbos are making boost, torque loss is absolutely irrelivent. And in our cars, this is from about 2000rpm onwards.

I have attached a dyno graph in which the difference (apart from the electrical misfires on the blue line) is the exaust. The blue is standard exaust (with decat), standard boost etc and the red is with the exaust that can be seen in my photo gallery (2.5" from turbos into 3")

With a turbo car, the bigger your exaust the better. Obviously the law of deminishing returns does apply.

As you can see on the dyno plot, the red line pulls away in torque from just over 2000rpm.

[Roadrunner]

Not true
So can you explain why my current car is significantly faster than my old one where the only difference is that the old one has a 3" cat-back and the current one retains the standard exhaust ... ? (the works Evo rally cars use a 2½" exhaust front to back for improved torque, btw)

[Kenneth]

So can you explain why my current car is significantly faster than my old one where the only difference is that the old one has a 3" cat-back and the current one retains the standard exhaust ... ? (the works Evo rally cars use a 2½" exhaust front to back for improved torque, btw)

No, and I am not even going to try hard. Just look at the dyno result, the evidence is there. I dont care what the Evo results are, because I dont drive one... Our cars are different and you cant apply the same logic.
I suspect that the turbo size has a lot to do with it. With a 2.5" down pipe on each turbo I can make 7psi of boost (with STANDARD BOOST CONTROL) at 2500rpm, 3psi at 2000.

Anyway, it is possible that with the standard down pipes you didn't get any gains with boost response... I know that even You See's car has poor boost response compared to mine (with the full exaust system in)

To be honest, you could be right according to your setup... but without any evidence its hard to say. I have dyno proof of the performance gain of my exaust, and thats basically the end of that.
Obviously with a different setup, you will get different results... Mine shows clear improvement from 2000rpm and so I base my opinions on that.

Oh, and before I go dont forget that there may be more differences between 2 cars than just the exaust. for example, if the AFR on the slower one was far to rich, that would also affect performance. The benefit of my dyno results is that the rest of the car is the same and the AFR is essentially the same on both runs (apart from the misfires) (oh, and the boost... but thats because there was a leak when they tapped into the manifold boost reference...)