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Well crud, I wish I had seen this thread and knew about this solution before pulling the trigger on my own recent concoction. I have been disappointed in the results. <br />
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To summarize what I did: I've got a 4.2L ATK reman, installed about 10k miles ago. It also has a 2bbl Weber carb. I just added a DUI HEI, Hedman 6-in-1 headers, a Flowmaster Super 50, and a 2.5" pipe width all the way back. <br />
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My specific areas of disappointment in the solution:<br />
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I didn't find any power increase; instead, I've got a possible power decrease. If I hold throttle steady (driving down the road) and then accelerate (passing someone) there can be a momentary pause, followed by a little surging... The guys at my shop said that the increased pipe size could have released too much backpressure, causing this problem. Your thoughts? Was 2.5" too big?<br />
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Second issue = too loud. My neighbor 3 doors down says she can tell when I'm going for a ride in the jeep. WTF? From my research, the Flowmaster Super 50 appeared to be the quietest muffler beyond stock. Someone in the CJ-8 forums piped in again about the 2.5" being "like a sewer pipe" for the 258, increasing sound... Again, thoughts?<br />
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So I'm thinking that I should have done the 4.0L head swap. I suppose its not too late. However, it would SUK if the near $1k I just invested in headers, exhaust, install, etc are totally wasted. I've tried to absorb as much from this thread as possible, however I get lost in details.<br />
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Optimally, I can just slap the 4.0 head on, reusing my existing carb, headers, and 2.5" exhaust system and be good-to-go. But things arent generally optimal... Anyone care to set me straight? <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f615.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":confused:" title="Confused :confused:" data-smilie="5"data-shortname=":confused:" /><br />
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(Other relevant info: T-5, 3.31 TracLoc)
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Like the others have said, you'll need to get a manifold for a 4.0, but the good news is you can buy a brand new one from ebay for around $75 delivered, and it's actually a good flowing tubular header instead of restrictive cast iron. People go out and spend a fortune on expensive exhaust because the manufaturers promise all kinds of increased hp, but the truth is, exhaust does very little on an engine that size because they just don't flow that much, especially in the RPM range that 258's run. You can use the intake and webber, but you'll have to do a little modding to get the intake to clear the manifold. I had to dent one of the exhaust manifold tubes a little, but not enough to restrict flow. You'll also have to fabricate some larger keeper washers to bridge the gap between the intake and exhaust manifolds where the center bolts hold both. The stock 258 thick round washers diameter is too small.<br />
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P.S. Just checking in. My 258 is still running perfect with the 4.0 head. I decided I wanted even more hp last year and started in on a 4.7L stroker, but I got side tracked by a lot of things including a big boat project so the 4.7 went on the back burner. Currently I have a 4.0 block sitting on the stand freshly bored .030 over. I have a new set of pistons with coated skirts, a Comp cam, and a high volume oil pump. What's missing is I still have to canibalize my good running 258 for the crank and rods. I hate doing that but I haven't been able to locate a good pre 1981 258 crank and rods for a reasonable price. Going from 110hp to 150 with the 4.0 was great. I can't wait to have 250 hp with the stroker! 35" tires will be next on the list since I'll have the power to push them. <img src="/community/smilies/biggrin.gif" class="smilie" loading="lazy" alt=":D" title="Grin :D" data-shortname=":D" /></div>
