5 replies to this topic

[rusimir]

Hi!
What bore is standard for 998 engine exhaust system 1.75'' or 2''??

Is it 2'' much for standard 998 engine? Is it 2'' better for 998 +.20 or +.40 or it can be set on standard 998 engine?

Thanks

[newdawn1st]

I believe its 1.625" for 998 and 1.75" for 1275, Cooperman is one for these Q's I think.

Edit:

I'm sorry to have to tell you, but a 2" diameter exhaust is way, way too large a for a 998. In fact it's too big even for a road-going 1275 unless you are going to be pulling a sustained 7000 rpm plus at full throttle.
For a good 998 the optimum exhaust pipe diameter is 1.625" internal diameter from the lcb 'Y-piece' right to the end of the tailpipe. That has been posted on here a lot in the past by several people.
To explain, the exhaust gases need to travel down the pipe at a good speed to make the molecules of gas get some inertia so that they exit at the right velocity and pressure which then 'draws' the gas out more easily. A 2" diameter means that the exhaust gases are going too slowly, so the gas inertia is too low and there is then too much back pressure. As the gas velocity increases, the pressure decreases. Go too small in diameter and that's another situation as you are then trying to get too much gas down a restricted pipe. 1.625" is the best size.

Edited by newdawn1st, 22 October 2009 - 02:29 PM.

[jaydee]

Hi!
What bore is standard for 998 engine exhaust system 1.75'' or 2''??

Is it 2'' much for standard 998 engine? Is it 2'' better for 998 +.20 or +.40 or it can be set on standard 998 engine?

Thanks

As standard 998 came out the factory with a 1,5" internal diameter system. Later coopers had a different exhaust with 1,62" int. diam.
About optimal size, follow Peter/Cooperman advise.

[Paul Wiginton]

Standard 998 exhaust is 1 1/8" ID I have just measured one.

Paul

[lrostoke]

thats why they get nicknamed peashooters

[rusimir]

Thanks!
So, 1.75'' and 2'' bore are to big for 998 engine!