258 rebuild or 302 conversion advice.

uglyjeepoffroad said:
I actually have a factory 4.0 header as well.

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Damn your making it hard for me to say no. It'll be a few weeks before I can get up there to get that out of your way. Unless your coming to Raleigh anytime soon.
 
I can come part of the way. Jut let me know and we can work out a deal on part or all of the parts.

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Ok. That may work. Or it might be easier if I just rode out there. That way I don't have to haul a cherry picker with me. Pm me if you have paypal. I'll get you a deposit this weekend for holding it. Thx. I could probably use whatever you have. 4.0 block and head and 4.2 rotating assembly and the 4.0 exhaust manifold. Guess I better get on my honey do list. So I don't end up sleeping on the streets with my two wore out jeep motors lol
Edit: if the 4.0 is together I'd like to try and use the cam too, if it's any good.

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josh m said:
Well if I do the stroker and get everything balanced well to spin a little faster. I've read that I can bolt up the 4.2 intake to the 4.0 head with a little modifying. Maybe upgrade to a offy duel plane intake and 4.0 exhaust manifold. It sounds like it'll breath better at higher rpms. Do y'all agree that this is a sound plan?


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No. I would use the factory 4.0 EFI. Fuck a carburetor.
 
josh m said:
08-7001J258
Haters!!


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I hate Weber Carbs, but that's another story. It seems you would have to build a hell of a motor to use both of those carbs. And I agree with the above, carbs suck as a whole. That being said, I have a Weber or two that I can sell if you are interestedo_O
 
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josh m said:
Well if I do the stroker and get everything balanced well to spin a little faster. I've read that I can bolt up the 4.2 intake to the 4.0 head with a little modifying. Maybe upgrade to a offy duel plane intake and 4.0 exhaust manifold. It sounds like it'll breath better at higher rpms. Do y'all agree that this is a sound plan?


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Not exactly. If you want it rev happy don't stroke it. If high Rpm's are what you are after,

Port the head, rods and rod bolts, big cam and solid lifters, big valves.

Or boost.

None of that is cheap.

A dual plane intake isn't build for high rpm use.

Pretty sure the port heights are different on 4.2 vs 4.0HO and mismatched ports between intake and head will kill higher rpm flow.


If you want good cheap power, build a stroker, put a decent cam in it, and run fuel injection for good driveability.

A quick revving stroker uses the 89/90 crank as it's the lightest, and already has the snout for the serpentine belt.

Port the head to improve high rpm flow.

Don't run a huge cam as the the stock valves,rods, springs (with shim for cam) , and injection are good for the 5200 rpm red line.

Also too big of a cam will have a poor vacuum signal at idle due to the overlap.

Run some bigger injectors and disconnect the vacuum line to the FPR and done.

Then match your gearing, tire size, and cruise rpm to you cam.

Too much carb on any motor will cause poor driveability and poor throttle response as airflow through the carb will slow, even at WOT.

Building a high rpm motor will not be budget friendly.

Is your desired rpm range out of the range of most engines?

Why not regear or change tire size?
Both are cheaper than a high $$ high rpm build.
 
3.55 gears and 31s are not out of proportion IMO I could go 33 and drop my highway rpms but without a low first gear my town driving would suffer. I'm not needing a high revving motor, one that will pull well to 3500-4000 rpm will be good. I'm going to pick up Chris's 4.0 and 4.2 next weekend and see if I can't make something out of the two. Hopefully the stock cam in the 4.0 is GTG. I'll see where to go when I tear them down. I'm hoping I can reuse the cam, go thru and use the 4.0 head. I'll see how the bores look on the 4.0 and go based on that. Use the 4.0 header and possibly get a offy intake. Shoot for reliable, long lasting and happy @3200rpm and under as that is pushing 80mph and plenty fast for a cj. My current 2100 is 1.14 venture so that might be killing some power. Might switch to a Webber or something, depending on what intake. Again no FI. Wanna keep my engine bay clean and simple.


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justjeepin86 said:
I hate Weber Carbs, but that's another story. It seems you would have to build a hell of a motor to use both of those carbs. And I agree with the above, carbs suck as a whole. That being said, I have a Weber or two that I can sell if you are interestedo_O
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What Weber do you have? I picked up a 4.0 and 4.2 a week ago, I'm gonna start tearing them down and get them to the machine shop. I'm thinking about doing the 99+ intake with the carb adapter for now. This will make it easier to FI if I ever decide to. If you have a 38 Weber I'd be interested in buying it from you. Or a 32/36. It would be easy to swap em around and see what works. Thx
 
josh m said:
What Weber do you have? I picked up a 4.0 and 4.2 a week ago, I'm gonna start tearing them down and get them to the machine shop. I'm thinking about doing the 99+ intake with the carb adapter for now. This will make it easier to FI if I ever decide to. If you have a 38 Weber I'd be interested in buying it from you. Or a 32/36. It would be easy to swap em around and see what works. Thx
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I sold one and have the one left that's on my YJ currently. I think it's a 32/36, I would have to look. I don't really want to make the jeep undrivable until I start my motor swap though. It shouldn't be long.
 
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