Hello, group - While crawling under my XJ 4.0L, I have been amazed by the degree to which the downpipe from the exhaust manifold is collapsed. It is 2/3 shut at the bend.
I have mentioned this at both the local 4WD shop and at the dealership parts counter, and the replies have been something to the effect that "Those 4 Litres seem to like the restriction", to "That's normal. They're all formed like that".
When I read about modifications for power, those most popular seem to be (not necessarily in their order):
- Replace cat-back
- Headers
- Bored-out throttle body
- low-restriction intake
What do the experts on this board think? Does this engine really benefit from headers,since it seems as though it was engineered for significant back-pressure?
Thanks.
jim