low buck 4.2L stroker

[Plechtan]

Anybody thought of using a 232 crank to make a 4.2L stroker? For those of us not lucky enough to find a 258 crank in the bone yard for $30.00, the price of a 258 kit on ebay is in the $300.00 range. Currently there is a 232 crank kit for less than $100. this includes a re ground crank and the bearings.

Os the 232 crank is very cost effective. the 232 used the same length rods as the 4.0 The difference in stroke is 3.5-3.41 = 0.090 this would put the piston .045 higher up in the bore than the stock crank. The 4.2L assumes a .060 overbore on the block, so new pistons would be required anyway. Maybe somebody could chime in on what pistons might work.

An normal low buck stroker goes form a 3.41 stroke to a 3.90" stroke, an increase of .490 or almost half an inch. The 4.2 would have a stroke increase 0only 20% of the 4.6L. With the bigger bore and increased stroke it would give more power, but i don't know if the performance gain would be worth the investment vs going with a 4.6

[gradon]

I played with the calc and that 232 crank with the 4.0 rods and either the 2229 silvolites or the sealed power 677cps(due to their smaller comp height). There would be no decking of the block necessary to achieve a zero deck or up to .005" out of the hole. Anyhow, the numbers looked good and would be better than a stock 4.0 rebuild, imo. The SCRs would be mid9s-10:1(less if you dish out the 2229s like others have).

[oletshot]

My first attempt at getting a 4.2 crank yielded a 232 crank instead. The block #'s were unreadable, so I took the guy's word that it was an '80 4.2L. Crank # proved him wrong. I ended up throwing it away. I researched using it, but decided not to change my build plans and nobody else wanted it. I do regret it, as it was a 12 weight crank and probably would have made a nice build. If only foresight was 20/20.

[jsawduste]

Some of the better JeepSpeed teams are using this combination. They are having great success with it.

[Only In A Jeep Xj]

A new 258 Crank from Orielly's is only $180

[heartlandoffroad]

Some of the better JeepSpeed teams are using this combination. They are having great success with it.

If they are they are cheating. Engine rules are to use stock stroke and max of .060 over bore.

[1bolt]

I thought Jeep speed was anything goes as long as it's off the shelf or was in a Jeep originally?

Do they do post race tear downs or engine claiming? I can't imagine they do considering its such a grass roots sort of setup...

[1bolt]

An normal low buck stroker goes form a 3.41 stroke to a 3.90" stroke, an increase of .490 or almost half an inch. The 4.2 would have a stroke increase 0only 20% of the 4.6L. With the bigger bore and increased stroke it would give more power, but i don't know if the performance gain would be worth the investment vs going with a 4.6

Nice find Pete! If I was going to build a racing Jeep I6 and I wanted RPM and horse power, this setup would be one to seriously consider IMO. The longer stroke squares the bore/stroke ratio, gets rid of the loose factory quench, ups compression, and is ultra low buck all in one shot.

Without digging into the numbers, if you could find a good crank, and just hone on a stock 4.0 bore... re ring, throw some gaskets on and with no machining you've got a longer stroke higher compression tight quench budget stroker that with a little head machining (more compression) might be the perfect basis for an ultra cheap E85 build...

Only one thing something is not adding up... are you sure of that stroke? The 258 has a stroke of 3.895 right? The 258 crank puts the 4.0 rod/piston up out of the hole by a considerable amount nearly a quarter of an inch IIRC... Last time I looked at it I was looking for chevy flat top pistons with a higher pin height that would allow me to use the 4.0 rods and 258 crank to make a ultra high compression low buck E85 build with... So either I'm missing something (which is probably the case, it's late and I'm worn out) or that 232 stroke has to be lower than 3.90 that's .005 more than the 258.

[Plechtan]

Os the 232 crank is very cost effective. the 232 used the same length rods as the 4.0 The difference in stroke is 3.5-3.41 = 0.090

See above, the 232 crank has a 3.5" stroke. vs 3.895 on the 258.

[1bolt]

Doh now I see what I was missing, you were comparing the 258 stroker crank when you said 3.90.

So accourding to http://www.jeeptech.com/engine/amc232.html the 232 is 3.50 stroke or .09 more stroke than a stock 4.0

[1bolt]

Looks like with bone stock everything (no overbore just drill honing a good block) factory sized 13cc dish this nets a 9.47:1 CR at zero deck putting quench below head gasket thickness if you wanted a higher performance 4.0 (4.05L) with higher compression and quench could be up near .030 to base a build off this would be ultra low buck.

I can see why Jeep Speed teams might play with something like this... The crank looks the same, the chances someone's going to tear you down and measure stroke are probably worth risking. If It were me, my crank would be all aero and lightened anyway so the casting numbers would be gone... It saves you buying custom pistons to get tighter quench.

This is kind of one of those things that makes you scratch your head... WTF did AMC shorten the stroke of the 4.0 by .09" and worsen quench when all they had to do was reuse the 232 crank and deepen the dish and alter the piston top a bit to get somewhere around .050 or .040 quench? I guess in the late 70's early 80's they wanted .080-ish quench... maybe due to rod stretch and notoriously sloppy 1970's factory tolerances that most of those engineers would have been used to dealing with in those days... who knows.

[oletshot]

With the 2229 pistons you end up about .003" above the deck at TDC, on paper anyway.

I think we have some bad info in the FAQ section. Info on an '89 4.0 is listed as 9.429-9.435 block height in the "Block FAQ section", 3.44 stroke in the "Crankshaft FAQ" section, 1.651-1.655" piston height in the "Block FAQ" section (Piston FAQ section says 1.601" for all years). If we add all this up you end up with the piston coming out of the bore by .066".
I'm pretty sure that's not going to work. The info that I think is questionable (block height, stroke, and piston height) comes from the "Mopar Jeep Engines 3rd edition" book. Maybe there is a misprint?

[Plechtan]

Stroke on the 4.0 is 3.41 not sure about the rest of the numbers, sounds like a question for Dino

[oletshot]

Stroke on the 4.0 is 3.41 not sure about the rest of the numbers, sounds like a question for Dino

I've always thought:

Block height = 9.452"
Stroke= 3.410"
Rod length = 6.125"
Piston height = 1.601"
For all years.

Add it all up and you end up with .021" deck clearance. How this relates to a low buck 4.2 stroker, I'm not sure, so I'll unhijack your original thread. Sorry.

[Plechtan]

the stroke difference is 3.5-3.41= .090 the piston will move up higher in the bore by half the stroke, so .045