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i am going to be making a complete stainless exhaust for my project car and i was wondering what size the downpipe and exhaust piping needs to be for a 2.3 liter engine with a 284 cam in it. other slight mods will be done to the engine as well.

3.5" - 4" would be good!!


J

You need to be careful not to go to big, this is as bad as going to small. I would advise not straying to far from the standard diameter, just increase this slightly.
The best thing you can do is eliminate as many bends and consrictions in the path of the pipe as poss.

Exhuast sizing is difficult and an optimum can only be really found through testing.

What is the standard diameter?

Steve

i take it its a 2.3 m20 engine - 6 cylinder

the header pipes should be the same size as your exhaust ports and ensuring that they are matched to the head is essential

Now using a little bit of maths, by finding the tube iternal area of the existing port and multipling x3 for each bank of tubes this gives the toal gas flow area this can then be knocked down to find the suggested pipe diameter of 69.28mm

69.28mm is the maximum it should be as 2.5 " is quite large. obviously not all ports are firing at once so that much gas wont be traveling in at one time but this is where manifold tuning comes into play. i would suggest a 2 1/4 inch stainless tube for each bank off 3 and equal length primarys

A cross over pipe is not needed but i think makes a nice edition and should help if you have messed up the lengths of the headers a little