Tuning Custom exhaust help

[RotoraNL]

I'm thinking about making a custom exhaust for my Seicento 1.1 SPI. Would like some more sporty sounds from the exhaust. Now I'm considering my options and hopefully someone could give some feedback on what to do.

I'm currently thinking about making it with a silencer in the middle and dropping the rear silencer, just welding a nice exhaust tip onto it. Don't know if anyone ever done an exhaust like that and , if someone did it, how the sound would be.

I'm also still thinking if I should get rid of the cat. This would usually give a bit more power, but I don't know if it would really have a significant effect on the Seicento.

Hope someone could help me out with a few of these points.

 

[woj]

Not sure about the rest of your exhaust system, but in NL I had problems pushing my Cinq through APK without the CAT. There will be tons of people here that will tell you it should still pass, but my readings were waaaaay off without the cat, with the cat they were waaaaay on so to say.

 

[RotoraNL]

The exhaust system is original. I could test mine at work without cat to see if it'll still pass the mot. But if it doesn't pass it isn't a big problem. I'm going to make an replacement that'll fit in like the cat, so I have the posibilitie to just simply bolt the cat back in for the mot.

But did you notice any powergains or isn't it really worth the work?

 

[woj]

I am a different case. My cat is a high flow one and for up to 200 bhp. I did not notice any difference on my turbo after mounting it. I have never tried removing the cat on the stock engine.

 

[cc1]

Removing the Cat makes no real difference except for a more raspy exhaust note.
The reason to remove them on a highly tuned engine is they will be destroyed due to excess fuel from wild cams.
The only exhaust mod to give better gains is to fit a tubular manifold unless you have a race spec or bigger CC engine.

 

[fingers99]

:yeahthat:

Unless the stock exhaust is hopelessly bad (wrong diameter, blockages, malformed bends) -- and the stock ones are pretty good -- you'll not see any real gains on an n/a engine. The best you can hope for is something that lasts longer, sounds nicer. You might pick up a little if you can smooth the flow into and out of the cat (mods described in the A Graham Bell books) by fabricating a new box for the cat.

The biggest gains I've seen from an 8v SPI FIRE engine (without going overboard) were a P75 cam a 40mm throttle body and a Uno 45 inlet manifold (nrvrt got round to playing with the exhaust manifold). Port matching on the inlet side is worthwhile, on the exhaust side it's likely to do more damage than good.

 

[RotoraNL]

Well in that case I'll just leave the cat on it.
But how about the exhaust? What would give a better (and still legal) sound? Making one without the rear silencer and only the middle or no middle but a rear silencer?

 

[Jd801]

I removed centre silencer on mine and left standard rear box. Made slight difference but not enough to notice whilst in the car

 

[jatkinson]

i only have a back box in mine

 

[RotoraNL]

Do you have a standard back box or did you replace it? And how's the sound?

I wont be using standard silencers because I'm going to weld a custom 'catback' exhaust.Guess otherwise I'll just have to buy some iron and just try it with different silencers.

At least I'm sure now that I'm going to make a custom one and not just cut the centre silencer out of the standard exhaust

 

[seicentoceeney]

I've taken out the cat on the standard manifold on my MPI SEI and I have a sportex "race" middle and rear (straight through to a back box) and I found it revved a lot easier, maybe slight increase in power but nothing overly noticeable