4.6L Stroker

[Cecil14]

My 258 is getting pretty tired and I'm going to need something reliable to drive back and forth to school this winter, hense, I have decided to build a stroker! I got the 4.0L for $100 and am taking it to the machine shop piece by piece. Got a few questions though:

Do I just need to get regular .030 over pistons for the 4.0L? And I use the crank and rods out of my '79 258, right? Anything else special I need to do? I need to have the crank shortened a bit don't I? Either that or a spacer?

Anybody know what a good size carb would be for a 4.6? I was thinking maybe a 500cfm 4bbl? Probably go with a clifford 4bbl intake...maybe and offy...not real sure. Gonna be doing this motor real soon (within the next month).

Also wondering about exhaust...I didn't get the stock manifold with the 4.0L and the one from my 258 won't work. I was thinking about going with a header and new highflow exhaust all the way back. Any suggestions there? Money is a concern but I'm willing to spend a bit to get something good.

Thanks,
Anthony

[K-Centre]

Anthony -

I know that Scotty is the resident expert on that build-up, I know that he has done a lot of research on it. I don't know of anyone that has put one of theose in an FSJ, though. I've done a lot of research on it as well since both of my rigs are 258's. You're correct that you use the crank and connecting rods from the 258. If you're going to bore the 4.0L block, then you will need the oversize pistons for the 4.0. If I can remember correctly, there is a portion of the rear of the 258 crank that will need to be machined off to work correctly. Sorry to be vague, can't recall correctly.

Try this site for more info: Rockcrawler Stroker (http://www.rockcrawler.com/techreports/stroker40/index.asp)

Also, I'd just go with a stock 4.0L exaust manifold if you're not looking for the high RPM horses from a header. The stock manifold is tube style and, IIRC is made from stainless or another repairable metal. To save some money, I'd look for a junkyard manifold, but then again, I'm really cheap.

500 cfm should be plenty. That's what I was looking at for a 4.0L head swap on my rig. It also helps that I have a 500 cfm Edlebrock laying around from another project. The 4 barrel intake is a little too pricey for me, I'm going to put a 4 barrel adapter on my 2 barrel intake. Then again, I'm not going all the way with the stoker either.

Hope this helps. If anyone disagrees, feel free, I've just researched and don't have any practical experience with this.

[grimgaunt]

Go to http://groups.yahoo.com/group/strokers/
these guys are a real nice group and great resource.
All they yak about is 6-cyl stroker buildups

[Cecil14]

Thanks guys, I'll check out those sites.

Keep the help coming!

Anthony

[scotty]

dont have much to add,cept that you will only have to shorten the 4.0 crank if you are using a serpentine belt.if you will be retaining the v belt setup from your 258,pretty much just drop the crank in there. smile.gif using the 4.0 pistons will net you about 9.4 to 1 compression,wich may be alittle high for some folks on pump gas. custom pistons are available that will give you alittle lower-in the 9 to 1 range.if you can live with the high compression, then .030 over 4.0 pistons will be fine.

only reason ive got a 258 instead of a stroker is that the 4.0 i have needs about $1000 worth of machine work :mad: ,and that number doesnt include the cam :eek: eventually ill find one in alittle better shape or have the extra $$ to build a really nice motor.

on the carb,i am running a Q jet 4bbl on my stock 258(prolly 650cfm?) so im sure a built motor can handle a 500cfm carb no prollem.

on the headers,some headers may have clearance issues with te carb intake,as may the non-ho factroy header with the aluminum intake. i modified a cast iron intake to fit over the non-ho exhaust,so in a worse case scenario you may need to dig up an iron intake. its prolly just as well you didnt get the factory header,as 99% of them are cracked and warped anyway. sorry i cant be of more help in that dept,some trial and error may be needed to find a header/intake combo that works for you...

one last thing is to plan on a good electric fuel pump,as there is no provision for a mechanical one on the 4.0 block. :eek: that is the only difference i can see with the 4.0/4.2 cams. the 4.0 cam has no pump lobe.

also,the motor mounts,conventional duraspark distributor,and all the 258 v belt brackets will fit the 4.0 block.

further questions? smile.gif

[Cecil14]

Was waiting for you to chime in scotty, smile.gif , couple things come to mind right now. Can I use the starter from my 258? Can I use my HEI dist from my 258? (I assume yes if the stock one will fit.) I've got all my wiring down fairly well and would like to keep it now. No biggy on the fuel pump.

With that compression do I need to run premium? I think my 258 has about 9.2:1 or so stock and I run 87 octane in that.

Would a stock exhaust manifold and a clifford 4bbl intake work you think? Hmmm....maybe I'll call them monday and see what they can tell me.

Thanks,
Anthony

[PhilSine]

A 500 CFM carb would be perfect. Any bigger and the carb's potential would go un-used.

[scotty]

yes on the starter and distributor. you will be reusing your 258 flywheel.

on the compression,9.4 is getting up there,prolly on the borderline for premium gas. ive known lots of guys that run 10 to 1 and 11 to 1 on pump gas with octane booster and fuel injection,so i prolly wouldnt go any higher than 9.4 with a carb,specially if youre gonna be drivig it daily.

thats prolly what ill be doing- i think the 9.4 compression will be fine for me. smile.gif

id think the 4bbl intake would fit,specially with the HO manifold,wich tucks in by the block alittle more,but id think it to fit with the non ho manifold,too. where you will have clearance prollems with any intake is with the pipes comig out of cyls 3 and 4 hitting the intake where the carb bolts on. if you call cliffors,let me know what they say. smile.gif

[ September 14, 2002, 04:41 AM: Message edited by: scotty ]

[FSJeeper]

I would definitely not go holley 500 cfm carb or the clifford intake manifold. You will kill your low rpm torque.

From experience I can tell you that the Offy dual port is one of the best mode you can do to the 6 cylinder. Many say it is the single best mod you can make to that engine. Secondly, a q-jet has smaller primarries than the stock jeep and a lot smaller than the Holly 500. The smaller primaries, and the small primary runners in the offy give good low end and the big secondaries on the q-jet as well as the offy kick in with a venturi ram effect because of the high velocity of the primary fuel/air mixture. If properly setup, the q-jet will not over carburate. It is all based on vacuum and engine need. It also flow from almost nothing to over 750 cfm. They used the Q-Jet with great success on the hot Buick V-6's and the Pontiac OHC 6 cylinders of the late 60's, both close to the size of you engine.

[scotty]

can you still get an offy,other than finding a used one? id agree that would be the way to go. also hafta agree on the q jet. as i mentioned,my engine is stock,and i dont have any prollems with the carb being too big. and he will run darn near on his side :D

[tomd]

My JCWhitney Jeep catalog has 4bbl Offy intakes for

73LS7650X 64-80 199", 232", 258" engines.
73LS7651N 81-90 258" engines

Not sure if thats what your looking for though.