Jeep Strokers

Planning all the parts for my 4.0 rebuild for some more torque and need a check on my SCR and DCR and if it's compatible with 87 octane:

Polish 4.0 crank and new Mopar bearings and gaskets.
Cloyes adjustable double roller timing set
New stock valve parts and lifters
Mopar 28 cam, 240/199 with .43 lift and 48 deg intake closing, with 24 overlap and 108 LSA
No decking, stock mopar head gasket with quench at .072
Bore .020 over with Icon 945 pistons with 10cc dish

Running the specs through the compression calculator my static compression would be 9.06, dynamic is 8.04
If I use a performance head gasket to drop the quench to .064 the static becomes 9.22, dynamic is 8.18

Am I looking at rampant detonation with these numbers?
Local altitude makes negligible difference (.2) and local fuels are almost exclusively 10% ethanol. Every 2 degrees of cam timing changes compression .1, while switching to 944 pistons with 21cc dish drops the compression almost a full point.

To many other variables.
How hard will this engine have to work based on gearing, tire size, trans type, vehiclec weight etc.

I don't like building engines to run 87. Leaves so much on the table with little room for error.

I've tried researching what octane can be used for a certain SCR or DCR. Primary changes are slightly smaller piston dish volume, shorter duration cam with less overlap, slight increase in valve lift, all other specs are unchanged.

98 TJ has 4.10 gears, 33" tires, 32rh 3 speed (1:1 in 3rd gear), and couple hundred pounds of armor and skids. Typical RPM's are extended creeping at idle, cruising at 2500-3000, shifts at 3500-4000. Not looking to make a hot rod, just want a bit more grunt in the bottom end at the sacrifice of top end power that never gets used. Would prefer to keep it on 87 or 89 octane, since premium is easily 25% more in this area.

GASnBRASS wrote:Bore .020 over with Icon 945 pistons with 10cc dish

Those pistons are only suitable for a stroker. You'll need taller pistons for a stock 4.0 rebuild.

DOH! Totally missed the compression height spec on those, thanks for catching my error.

GASnBRASS wrote:DOH! Totally missed the compression height spec on those, thanks for catching my error.

You should consider a 3.500 stroke utilizing a late 72-79 232 crankshaft. Many refer to this as the "Mini Stroker".

The advantage of this stroker build is that it allows you to use the components of a economical 4.0 engine kit and allow you to retain your stock 4.0 rods as opposed to the shorter and less desirable to 258 conecting rod.

This kit with upgrades will be under 1K

Russ Pottenger
Bishop-Buehl Racing Engines
531 N. Lyall Avenue
West Covina, California 91790
(626) 967-1000
Email/PayPal: [email protected]

Here's an example of a mini-stroker build that could work for you if a diet of 87 octane is an absolute requirement:

4.2L Milder mini-stroker

AMC 232 3.500" stroke crank
Jeep 4.0L 6.125" rods
Silvolite UEM-2229 +0.060" bore pistons
Increase piston dish volume to 24cc
8.8:1 CR
CompCams 68-115-4 192/200 degree camshaft
DIY ported HO 1.91"/1.50" 57cc cylinder head
Mopar/Victor 0.043" head gasket
0.040" quench height
Bosch 0280155703 injectors for '96-'04 engines
241hp @ 5000rpm, 293lbft @ 3500rpm

Considering that I've completely struck out on finding .001 undersized main or thrust bearings for my stock crank it'll need to be ground .010 for new bearings, and it needs an overbore with new pistons anyways. But the mention now of a 4.2 mini stroker with mostly off the shelf parts and minimal machining is interesting. What piston compression height am I looking for with a 232 crank? Stroke difference between the cranks appears to be .090 / 2 and stock piston compression height at 1.592 so am I looking for a piston compression .045 shorter? The 2229 listed is only .011 shorter, or is that to tighten the quench height? And what is the standard dish volume of those pistons?

Opps, I think I looked at the wrong spec for the stock pistons, should be 1.601
New pistons at 1.581 with the .043 head gasket should leave quench at .042

Screw it, I'm done farting around with this stock motor, just ordered a 232 crank. Might as well join the stroker club (albeit in a small way).
And I've dropped the 87 octane requirement; this is just a summer toy so I'll run 91+ octane and a higher compression.
Just need to decide if I'll run a Mopar 28 or 29 cam on stock springs and rockers.
Piston recommendations that don't need machining and work with premium fuel?

GASnBRASS wrote:And I've dropped the 87 octane requirement; this is just a summer toy so I'll run 91+ octane and a higher compression.

In that case, here's an alternative mini-stroker build spec:

4.2L Wilder mini-stroker

AMC 232 3.500" stroke crank
Jeep 4.0L 6.125" rods
Silvolite UEM-2229 +0.060" bore pistons
9.6:1 CR
CompCams 68-235-4 210/218 degree camshaft
Russ Pottenger ported HO 2.00"/1.55" 62cc cylinder head
Mopar/Victor 0.043" head gasket
0.040" quench height
Ford 24lb/hr injectors for '96-'04 engines
268hp @ 5300rpm, 303lbft @ 3900rpm

Thanks for that build list, and I just found your tech specs page and it's very useful!
I plan to overbore .020 for a 250ci/4.1L displacement, Mopar 28 cam, and unported head. Not going wild with this.
Just a few questions though:

I already have a new head gasket 53010587AA, is this the correct HG for proper quench when you refer to using a mopar/victor HG?
For the high compression version I assume the 2229 11cc piston dish can be left as is?
My '98 has the gray 53030778 23.2 lb/hr injectors, are these enough with a mild cam or does it really need ford 24 lb/hr injectors?

Thank you very much for all the help!

GASnBRASS wrote:I already have a new head gasket 53010587AA, is this the correct HG for proper quench when you refer to using a mopar/victor HG? Yes, it's the same MLS gasket.
For the high compression version I assume the 2229 11cc piston dish can be left as is? Yes
My '98 has the gray 53030778 23.2 lb/hr injectors, are these enough with a mild cam or does it really need ford 24 lb/hr injectors? The stock injectors might just be enough.

Awesome, thanks a bunch! Time to gather all the parts and get this motor built.

Cheromaniac wrote:

GASnBRASS wrote:And I've dropped the 87 octane requirement; this is just a summer toy so I'll run 91+ octane and a higher compression.

In that case, here's an alternative mini-stroker build spec:

4.2L Wilder mini-stroker

AMC 232 3.500" stroke crank
Jeep 4.0L 6.125" rods
Silvolite UEM-2229 +0.060" bore pistons
9.6:1 CR
CompCams 68-235-4 210/218 degree camshaft
Russ Pottenger ported HO 2.00"/1.55" 62cc cylinder head
Mopar/Victor 0.043" head gasket
0.040" quench height
Ford 24lb/hr injectors for '96-'04 engines
268hp @ 5300rpm, 303lbft @ 3900rpm

Would you have to run 91+ in this set up? What would running 87 do?

I'm new here and to all of this. I'm just trying to learn as much as I can before i potentially stroke my 4.0.