I got a question on my Rear engined Renault 5 fitted with a KV6 2.5.

I am just looking at making the exhaust up at the moment and I was originally going to reuse the manifolds and weld up the rest in mild steel. Bit i am limited for space so need to alter the manifolds. I have a few bits of stainless tube left from when I turboed my Mk so I will make some new manifolds up out of that. The original exhaust is 1.5” manifold tubes into 2” down pipes into 2.5” after the starter cat, I am guessing that the rest of the system is 2.5” to the tail pipe on the original car (MG ZS).

I don’t have any 2.5” stainless tube and plenty of 1.5 and 2”, if I make the system from this with a straight thru muffler will It restrict the engine power? Do I ‘need’ to keep it 2.5” after the manifolds? I know the larger the better on a turbo car but this is a high revving V6 and don’t want to mess it up with this exhaust.

I am removing the starter cat.

The exhaust length is about 1.5 meters from manifolds to tail pipe. VERY SHORT. I have a universal straight through stainless muffler from demon thieves.

Any comments?

Size is important! I would say that you will need a min of 2" to get enough flow from each bank to the cat and then go up to something bigger. You might find that it will sound awful with such a short system and ideally you need to get some more length if at all possible.
I went through several design changes with my V6 and found that the sound improved (deeper sound) with a larger bore and more length - it was very 'waspy' with the previous 2.25" bore.

[Edited on 18-1-08 by RazMan]

search on here for dave ashurst - he wrote an excel spreadsheet for calculating exhaust size. I'm sure he posted it as well.

I like the new avatar raz