Exhaust question

[nordcore]

Hi, I am new to the forum so now i have some questions - I have seen that on kam racing site there are 2 versions of the Supersprint exhaust :
1. Catback exhaust 63mm
2. Decat exhaust 63mm

Now my exhaust system is in very bad condition, so i would like to replace it, so will there be any difference catback - decat, in power output and noise etc., my engine is standard, no mods.
i have a ph1 2000 and i noticed i have some kind of a twin-chamber catalytic converter with 1 lambda. i think it's 60mm...so if i took a catback system would there be much difference (noise, power) than a decat system?

One more thing, does anyone now what kind of a cat (twin-chamber) is this, i've seen later versions have a single one, and my friend in germany said that they used these twin cats for their clio race cars.

Thanks!

 

[Sam@NP]

You will only see about 2 bhp increase with a remap and decat. The main difference is noise, decat is a fair bit louder.

 

[nordcore]

Ok Sam, but what about this twin cat, would it be better to replace it with some sport cat or leave it as it is?
For now : twin cat + centre and back section - 63mm exhaust system (supersprint)
Will the supersprint be enough loud even with the twin cat?

 

[Sam@NP]

A supersprint will be loud enough, twin chamber cats are actually pretty efficient so Id keep it over a sports cat.

 

[nordcore]

Thanks a lot Sam, if the twin chamber cat is good i will then keep it, also i think the cat is needed for some backpressure (if you have a straight through gr. N or A exhaust system like the supersprint or OMP), correct?

 

[Kam.]

you dont need backpressure. Backpressure is a by-product of high gas speed.
With a normally aspirated engine you want the exhaust gases to exit as fast as possible to help exhaust scavenging. You want to get the gas speed optimised to the engine so it produces the maximum power gain without the backpressure strangling the car. Your exhaust bore choice can affect where you make peak power, can optimise certain rpm points and so on.
Very basic description but it gives you an idea...

I would keep the twin cat design. You are not going to notice too much in the way of gains despite some ugly angles as it flows well. Keeps your car road legal as well. If I was venturing on track then i'd probably fit a decat but its not the simplest of swaps due to the decat pipe going right up into the engine bay.

Kev

 

[wentworthmeister]

Your exhaust bore choice can affect where you make peak power, can optimise certain rpm points and so on.

With a larger bore moving the peak power delivery higher up the rev range, correct? Or is that too much of a generalisation?

 

[nordcore]

As i said i have a completely standard engine with no mods so i think this will be the best setup :
1. Twin chamber cat (i think it's 60mm)
2. Straight through middle section 63mm
3. Group A/N backbox 63 mm
+ maybe a remap

I think it will be good for performance, and it will be still loud enough despite the cat.
Any opinions about this? Thanks

 

[Kam.]

looks good to me

 

[Kam.]

With a larger bore moving the peak power delivery higher up the rev range, correct? Or is that too much of a generalisation?

thats about there, but you can go too big. Many other things can affect the peak power such as bends and joins in the system so it can get complex. Our Citroen Saxo one when compared to its nearest rival produces a touch more power 400rpm higher but the bore is the same. Clio exhausts follow a simpler route though

 

[nordcore]

Today i fitted the exhaust and made a remap, i am very satisfied.
The exhaust setup is : PH1 twin cat - Straight through middle pipe gr.A 63,5mm - Straight through backbox gr.A 63,5mm
The idle is fine, it's getting loud at 3000-3500, at 4000 it begins to be f****** loud, from 5500 till end maybe little quieter but it gets raspy as hell.
When the car is fully warmed up i think it is even more loud, maybe because of the inox.
Inside it's ok till 3000-3500 rpm, than it gets loud.
When i mapped it i tried the decat pipe 63,5mm i got also, and then the cat and the car was heavily lacking of low-middle torque with the decat, then i fitted the twin cat and the car was like wild, much more responsive...and in terms loudness it's the same decat-cat, i didn't notice any difference, maybe in car 1-2db quiter with cat. Yep and it's not so easy to refit the decat-cat on ph1.


Thanks once again for the help regarding the exhaust setup to all of you!

 

[Kam.]

what exhaust did you buy then?

 

[nordcore]

i got the old supersprint, i think it's the same as the new in your shop. i took it off from a trashed sport ph1, i got a good price for it.

i have a question regarding the remap - i had a debate with my mechanic, the car is mapped with the twin cat, so if i took the cat off and put the decat pipe
will i have to make a remap again...regarding the fuel mixture, lambda , etc., because with the remap the fuel mixture is richer, so could it theoretically happen when you put the pipe it will become leaner, and could it also put some pressure on the valves, because the pipe has no restriction as the cat the twin chambers (meaning that the exhaust will be too open/big for a standard engine) ?

Thanks!

 

[xoldog400]

I have the same similar exhaust (from a german company powersprint) as you, and the car is also mapped. When i took my twin barrel cat off (the car was already mapped with it) the car didn't feel much responsive in low and middle range, also the fuel mixture that you are reffering to got leaner...i had it for a while and then on 200 km/h two of my exhaust valves got burned, so i had to rebuild my engine again. I think you need some little backpressure on a N/A engine, and if you got 63mm from manifold to the backbox i think it is little to open (on a standard engine)
I drove the car 5 years with this map and no problems, and then when i replaced it with the decat this happened...so if you really want to try the decat i advise you to do a remap. The difference in power is none, and i see you have a gr.a exhaust that is already enough loud even with the twin cat.
In my opinion keep this cat on the car, i also had my doubts about it-the twin barrel cat + 63mm exhaust i think is a very good combination on a ph1.

 

[nordcore]

Ok thanks, i've searched the forum and many guys (Fred, Danny...) said that the twin cat is very good for flow.
And as you said if the car is mapped with twin cat it certainly won't be running good with the decat (and the current map).