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Discussion Starter · #1 ·
I have a 82 258 and I noticed that the exhaust ports are smaller than the exhaust manifold.
If I was to enlarge the exhaust ports & clean up the intake would this take away from the low
end???? Using stock cam, 2 barrel BBD carb and HEI ???????

 
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Discussion Starter · #2 ·
Head porting shouldn't hurt low end, but it wouldn't help either. Most head porting and polishing is done for high end horse power. With a stock setup you probable wouldn't even notice the difference because of so many other limiting factors(like exhaust and carburation). The real big improvement would come from using a 4.0 head on your 258. I haven't done it, but the port design on the intake side is more direct and doesn't take a 90 degree bend like the 258 head and you can put on the MPI at the same time/wwwthreads_images/icons/cool.gif.

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Randy 80 CJ5
 
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Discussion Starter · #3 ·
I saw a guy who tried to open up those ports and ended up grinding into the water jacket....there is not enough meat there to take off. However, you can help by smoothing out the short side radius of the intakes and exhaust. You can also take about a 1/16 off the inside radius of the valve seat....lots of meat there. I did that and it helped the upper end about 20%. While u are at it, have them do a 3 angle valve cut. It tends to seal and last longer. In the case of a jeep, it won't help performance.

John......southern CA
84CJ7, 3"lift, 32"BFG, 4.10's, ARB Locker, Solid Axle's, Durabak
 
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Discussion Starter · #4 ·
I tried the porting and polishing of the 258; even increased valve sizes. It helped, but ended up putting a 4.0 head. Given the expense involved in working on the 258 head and what you get in the end - I'll not even think of working on the 4.2 head. The 4.0 head breathes so much better. Save your money, pick up a 4.0 head from a early 90s and then do your porting, polishing and value modifications. You will not be disappointed with this investment. This of course means that you are a committed I6er.

Mindbender
CJ7 258
 
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