Why relocate it? You're talking about the cat in the downpipe right and not that secondary cat they supply. I would just cut out that secondary cat. It's not even monitored by the ECU.

 

Double post.

 

I am talking about the cat in the downpipe. I have already removed the secondary cat. The reason for relocating the one in the downpipe is due to fluid dynamics. Ill try to explain.

On a N/A car the exhaust gas exiting the combustion chamber cause a vacuum. Atmospheric pressure then pushes fresh air into the cylinders. The higher the velocity of the gasses leaving the combustion chamber the higher the velocity of the gasses going in. Now this works until velocity of the exciting gases exceeds the velocity of atmospheric pressure. Luckily we have turbos.

On a turbo car this matters when the car is cruising due to vacuum in the manifold. However since the exhaust has to be adequate while boosting the dynamics are incorrect for vacuum. This is part of the reason there is drone. Since turbo cars have pressure forcing air into the cylinders the exhaust gas velocity is not as important. The thing that is more important is that the exhaust flow is not impeded. When the flow is impeded it causes the turbo to work harder.

A cat works by having a materiel that is heated up from exhaust gasses and uses this heat to burn any excess fuel and any other crap it can. However it impedes exhaust flow. How much depends on the cat.

The reason for relocating is due to removing this flow impingement. By doing so you cause the exhaust gasses to have a higher flow then if the cat was in place, this make it easier for the turbos exhaust gasses to vacate the area and then the turbo doesn't work as hard pushing the fresh air in. It could also push it in faster since there are no gasses in the way.

Now removing it completely is ideal but that is smelly and illegal. Relocating it while probably still being somewhat illegal (not totally sure) it will be less noticeable, due to smell. When it is relocated downstream you give the gasses time to cool and expand. Pressure is inversely proportionate to volume. Since the volume between the turbo and the cat is greater than before the pressure is less. While the cat may be less efficient at cleaning the gasses due to it being cooler the turbo won't be working as hard and this can be tuned to give us more power.

That was long sorry, its not as simple as backpressure like people think.

 

My BA in History brain is reeling but I comprehend.

 

I should add that if you do this without a tune the fuel injector will pulse to soon, and with the increased gas velocity some of the fuel will exit the chamber. This will cause a lean A/F ratio witch is not good.

Melangell, it's ok I'm sure my grammar is driving you crazy. I do science not english.

 

I'm also very interested in this thread. Enjoying learning from everything posted. Keep it up!

 

So the high flow cat in my Akrapovic is not doing me any favors until I do get a tune? I know it's not really helping but I want the freer flowing exhaust manifold before I pull the NM tune trigger.

Your grammar is fine. Trust me, there's much worse on NAM!

 

Basically, it might help in minuscule amount. If anything your turbo is working less for the same amount of power. Thats never bad. A new header is not a bad idea, upgrade to the JCW manifold you could even port and polish it if you really wanted to.

 

That has kinda been my overall plan. Not having the engineering knowledge you have, I decided to get ready for an eventual tune by opening up the system on both ends, ie: easier flowing, cooler air in and easier flowing exhaust out. I'm going to hold off on the P&P. I'm already $4k+ into the Dread Pirate and really haven't even look at suspension yet. I can only imagine how much you're spending!

 

Definitely a freer flowing intake and exhaust on a turbo car will have an increase in power. Same boost pressure while increasing air flow = more power. Unfortunately, in my case, with the R53, my boost is mechanically driven, so more air flow won't necessarily increase power...as shown by the negligible increases with freer flowing exhausts on my supercharged brethren. Thanks to wastegates you have a much better capacity to increase airflow and maintain boost which equals MUCH more power.

 

Just ordered CP 77.5mm bore and 10.5:1CR pistons to replace the supertech ones.

 

Guess what everyone, a discovery has been made! The cause of my engine problems was a clogged 3" high flow cat. The cat was done, clogged and loose in the housing. This caused my EGT to rise causing my pistons to over heat. The over heating fried a ring or something. Not sure what part fried, still need to measure them all.

 

Glad you were able to figure that one out.

 

Good to know you found the reason for the failure. Do you think it was a quality issue with the cat or did the car produce excess EGT and melt it down? Did you ever take EGT measurements and at which part (pre turbo, post turbo)?.

I also like the idea of relocating the cat further down the exhaust, however you need to work where to locate it, the specs of the cat (optimum/ minimum working temp).
As you may already know a cat is efficient as long as it gets up to a proper temp. If you relocate it too far from the turbine, the exhaust gases will cool down prior entering the cat and efficiency will be lost. You may also find that wrapping the downpipe or thermal coating it to contain heat produced will be beneficial.
It's no secret that the Countryman WRC has a twin exit thermal coated exhaust with two cats at the end (literally inside the back tips of the exhaust). This way the exhaust gases remain hot through the whole length of the pipe (maximum thermal expansion, maximum efficiency, maximum gas speed) with additional gains...

 

I do not know what my EGT were, I never had any check engine lights though. I'm not sure if it was a quality issue or not. I will have to see that it looks like when It is cut it open.

I was aware that WRC cars had the cat in the very back. I noticed them glowing when watching races. That full coating would be spend! You can buy FIA homologated cats, I will have to research them a bit to see what temp they require.

 

I installed the limited slip today. It wasn't to hard. The only part that sucked was reverse came out of the transmission when I separated the cases. After some inspecting I figured out how it went back in. There were three little ball detents that had to be pushed in at the same time. Finally about an hour later and a gash in my thumb I got it back in place. thumbs are important. Here are a few pics for you.

Stock dif / LDS


The gear on the right is reverse and those three little T shaped things were all the trouble.


Here is the inside of the gearbox, the spot on the bottom left is where reverse gear was supposed to stay, total pain.


One more of it all put back together.

 

Great Stuff!

 

Sorry you had bad luck with your engine, but this should be awesome once it's all finished!

 

thank God im catless... lol

 

I used to be catless, then I drove across country and put it back before the trip. But for some good news my new pistons arrived today.

CP 77.5mm 10.5:1 CR They are a little bit heavier than the Supertech ones but the quality is much much higher. The weight would be expected with a denser alloy. Other than that I am very happy with them.

Box


Inside


Close up

 

Hi, I'm curious.
Since you are changing the stock pistons to forged ones, why not try the ones with compression 9.5:1?

 

Simple answer, decreasing compression decreases power, kinda.
Lower compression = higher boost ability
Higher compression = lower boost ability

Im going to cheat in my example, and it isn't totally correct since there are a lot more factors. Basically lets say you have a car with 10:1 compression ratio and are boosting 5lbs. Theoretically that would have the same cylinder pressure as running 5:1 compression and boosting 10lbs. To much cylinder presser and your gas will ignite premature causing bad things to happen, really bad things.

 

Ok, roughly understood that.
And regarding the bore size. You opt for the 77.5mm over the standard size of 77mm because the forged pistons expand lesser than the stock ones?

Try to understand why as I might be ordering these soon.

 

Forged pistions expand a lot more than stock ones. I got a bigger bore because it will give me a few extra CC's and more CC equal more power. Before you order anything, read as much info as you can or have a performance shop do everything for you.

 

I'm in for more info on the turbo