Anybody know the diameter of the 1.8L downpipe/ frontpipe coming off the manifold?

it looks like 2-2.25 inch.

i actually think its 1.75" but that might be just south of the downpipe

This post has been edited by playr158: Sep 27, 2006 - 10:47 AM

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from the manifold to the cat its a larger pipe, the just after the cat the size is reduced to damned tiny, but keep in mind that its ONLY a 1.8L engine and that most of its power is made at lower rpms, so having a smaller diameter pipe isnt as as hurtful as you'd think. i'd say any exhaust on the 7afe thats larger than 2.5 is going to start being too large and will slowdown the exhaust flow and harm the scavenging effect.

i just measured, its about 2". just to be clear, the pipe between the stock manifold and the cat converter is 2 inches.

This post has been edited by Bitter: Sep 27, 2006 - 11:45 AM

what would happen, if you expand it maybe, the entire header and downpipe by .25"? would you loose or gain HP?

well thats hard to say, the stock manifold is cast iron and would be hard to do anything to without it cracking (which its already prone to do). cast iron is hard to work with, difficult to weld, very weak when thin, it has a porus structure which makes grinding it easy but because of its porosity when it gets thin it'll crack alot easier. also, you'd only be able to port the inlets/outlet. the inside of it is like 4 short fingers that flow into a large open void. its pretty bad for scaveneging at higher engine speeds but good to keep costs low and good for....well im not sure what its good for from a performance standpoint.

making the downpipe between the cat and manifold larger with the stock header wouldnt do much..since the cat, rest of the exhaust, and the manifold before it will be restrictions.

but say I put an after market header on my 7afe... would it be worth the while to look into expanding the rest of my exhaust system, if so, would removing the catylitic converter do that much for me. yes i do know this is illega, im just trying to figure out how much of a difference it makes.

the only header for the 7afe that i know of includes the downpipe.

i have the ebay header with most of the stock exhaust, i dont know if i i would see any benefit from dropping the cat. possibly a small one but not enough to make the work worth it for me.

if you do want to ditch the cat, look on ebay, i saw a 'test pipe' for sale that bolts inplace of the cat.

what size is the header downpipe that you bought?