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Old February 15th, 2008, 06:43
NAXJA Forum User
Join Date: May 2004
Location: Des Moines, Iowa
Posts: 4,647
Re: 0331 head swap, mpg change?

Originally Posted by indy_xj
2000 XJ
54,xxx miles

I swapped my cracked 0331 head for a '98 630 and an 'aftermarket' header. The one with the acordian expansion chambers.

That was about 1100 miles ago. Since then, my milage has gone down the drain. I used to average about 17.5 mpg and 230-240 miles / tank.

Now I am getting about 13.5 mpg, and my last tank was a tiny 180 miles.

Its mostly city driving, but it was before the change also. No check engine lights or codes since the swap.

Anyone else have similar experiences, results?


I can't give you much insight on the head swap, but I know those "headers" with the expansion joints are pretty much a copy of the stock manifolds, and they crack almost as fast. As long as yours isn't cracked though, I would look past that. I honestly can't think why swapping heads would be the problem other than the fact that the 0630 has bigger exhaust ports and thus possibly produces more power since you have the 99+ intake and 99- exhaust. Just a thought, I can tell you that's about what my 99 XJ gets mpg wise. I forgot to ask...what did you do about the dual cats coming off your '00 exhaust manifold, did you hook them back up somehow or delete them?
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