Stroking the 4.0 :)

[72'CaminoKid]

alright, some of yall saw where i've been looking for new motors for the jeep. finally i decided to call my dads budy who owns a salvage yard, he's gonna find me a rebuildable 4.0 for my yj so i can build it while still using mine, this will minimize down time of my vehicle.... i was originally going to just rebuild it a stock 4.0 (which would already be a vast improvement over my dying 4.0) but then i decided, heck, it'll take the same amount of work to stroke it. so thats what i'm gonna do. i'll be using the crank out of an older jeep 4.2L but not sure what i wanna do about the bore (30 over = 4.6L, 60 over = 4.7L if i'm not mistaken) i may steer clear of the 4.7 bc i think you may need to run higher octane fuel with that (dependent on the CR) and with gas like it is, i dont wanna have to pay more. but anyways, i just thought i'd let yall know where i'm at with this and if any of yall have any hints/tips/advice/ideas/ any input is welcome. once i start getting into this project i'll be doing a write up thread. with pictures and all.

[75K30]

What an idea. This should be fun. Do try to find a 91 to 95 engine, as these will produce the best power. The head has larger intake runners and will outperform the later head.
The 4.0L engine has a 3.411" stroke, 3.875" bore, 6 cylinders, and a displacement of 241.5ci (3956cc). You can increase the displacement of your 4.0L engine by installing a stroker crank (complete kits are available). At the heart of tany kit is the 3.895" stroke crankshaft that was used in the AMC/Jeep 258ci (4.2L) I6 engine.

On an engine with the stock 3.875" bore, the stroker crank increases displacement to 276ci (4517cc or 4.5L). Add 30 thousandths or 60 thousandths overbored pistons, and displacement is increased to 280ci (4587cc or 4.6L) and 284ci (4657cc or 4.7L) respectively.

If you're feeling really brave, you can overbore your engine to 4.00" and use custom forged pistons. The block must be sonic-tested to ensure that there's adequate cylinder wall thickness before overboring this far, though. Displacement with the 3.895" stroker crank is increased to 294ci (4812cc or 4.8L). The next step up the ladder includes an offset-ground 3.98" stroker crank that increases displacement to 300.1ci (4917cc or 4.9L). The ultimate stroker includes an offset-ground 4.06" stroker crank producing a displacement of 306.1ci (5016cc or 5.0L).
Now I am justgetting too excited!
Another thing that is often underestimated is the injector sizing. You will run into detonation problems with injectors that are too small.
Stroker engines require oversize injectors to provide adequate fuel flow rates and prevent pinging due to lean air/fuel mixtures.

To calculate optimum injector size, use the following formula:

Injector flow rate (lb/hr) = [Expected HP x 0.5 (BSFC)] / [no. of cylinders x 0.8 (injector duty cycle)]

The actual injector flow rate from each injector depends on the fuel pressure (FP) in the injector rail. Most injectors have rated flows at 43.5psi fuel pressure. The actual flow rate from each injector is:

Actual injector flow rate = Rated injector flow rate at 43.5psi x square root of (FP/43.5)

You can expect approx 265 HP from your 4.6L engine, and this will require Ford Motorsport 24lb/hr injectors, stock intake, and 62mm TB.
This is a potent little combo when you use this CompCams #68-231-4 206/214 degree cam.

Rod length is important here.
If the Jeep 4.2L 5.875" rods and stock Jeep 4.0L pistons are used, the pistons will be 0.008" further down the bore at TDC than those in the stock Jeep 4.0L engine. The deck clearance is thus increased to 0.030" and the quench height is increased to 0.081". The resultant CR is 9.7:1 with stock bore pistons and 9.9:1 with 0.060" overbore pistons. If the block is decked 0.010" to return the quench height to stock, the combustion volume is reduced by 2.0ml and the CR is increased to 9.9:1 and 10.1:1 respectively. Premium fuel will be required to prevent detonation.

If the stock Jeep 4.0L 6.125" rods are used, expensive custom forged pistons with a shorter pin height than stock (1.380") are required to achieve zero deck clearance. Using longer rods does enable you to choose pistons with a larger dish volume than stock. These reduce the CR and allow the use of low octane fuel without detonation. You can also use a shorter duration camshaft for increased low-rev torque, and select the head gasket thickness required to achieve the desired 0.040"-0.060" quench height.
If you use the shorter Jeep 4.2L rods with cheaper cast aluminium or hypereutectic pistons, the quench height can be reduced by milling the block deck and installing a thinner head gasket. The CR can be reduced by increasing the combustion chamber volume and the piston dish volume.
*For each 0.010" milled from the block deck (or taken from head gasket thickness) to reduce quench height, the combustion volume decreases by ~2.0ml and the CR increases by ~0.2*.


A little more junk to totally confuse you, since I am on a roll here, lol.
1. Deck height = Rod length + stroke/2 + piston pin height + deck clearance

9.453" = 6.125" + 1.705" + 1.601" + 0.022"

2. Combustion volume = Combustion chamber volume + head gasket volume + deck clearance volume + piston dish volume

84.6cc = 56.7cc + 10.5cc + 4.3cc + 13.1cc

3. Compression ratio (CR) = Cylinder volume/combustion volume + 1.0

CR = 660/84.6 + 1.0 = 7.80 + 1.0 = 8.80

4. Quench height = Deck clearance + compressed head gasket thickness

0.073" = 0.022" + 0.051"

I have made over 300 Hp from these little mills, and have pleanty of combos that should take all of the guess work out. Dyno results to back them up.
Good luck on this upgrade, you will love it!!!!!!

75

[72'CaminoKid]

i'd read a good bit of that in an article eariler. i've gotta question about compression ratios though. i may be wrong, but i think that the CR is pretty much what decides what octane fuel i'll have to run. with gas being so high i'm trying to stay at regular 87. whats a good CR i could set up to use regular, at what point would i have to step up the fuel octane..... also what exactly is the "quench height"

[75K30]

This is a tough question, because "deck heigth" and quench are common terms that are used improperly. This is also where the static, and dynamic compression ratios come into play, and where the point of detonation becomes real interesting.
Higher CR's can be achieved with lower octane requirements when the quench area is effecient.
Here is how I understand quench.
Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench.
If you look at a combustion chamber, you will usually see these flat areas, and they will have the volume of the actual combustion chamber between them. When the piston is compressing the mixture, as the piston nears the head, the flat areas on the head and piston come together and force the mixture from those areas to "squish" into the chamber, where the spark plug and burning mixture reside, so you achieve a more complete burn.
The quench area also runs cooler than the rest of the chamber / piston. These lower temperatures are where the "quench" comes from.
When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.
Bottom line is "properly designed, quench is good".

With a good quench area, your 4.6 stroker can run approx 9.5:1 without agreat deal of ping, as long as you upgrade the injectors, and fuel pressure regulator. You will need an adjustable unit from an early jeep. Along with this, and the injectors, you can obtain decent results with low grade pump gas.

Many factors are present, so not every example is accurate. You area will have different factors, altitude, barametric pressures, fuel quality, ignition timing, piston material, etc, etc can have an effect on this this.

[72'CaminoKid]

i was planning on mustang 5.0 injectors (i think 24lb/hr) and i was reading about the adjustable fuel pressure regulator, would i need that or an adjustable map sensor. i got a little confused when getting into that.

you say 9.5 to 1 is an acceptable CR, is that approximnately the limit at which i could go before needing to use higher octane fuel? bc honestly i dont want to push it and end up killing the engine from running right on the edge of parameters.

i'm sure you can tell by now that what i'm looking to build is a mild, "semi-low-budget" stoker. it will still be my DD so it will see lots of miles, main reason for not wanting to push it to the limit, but i definately want the gains of a bigger displacement motor. i'm in no rush for answers on anything at the moment as i'm just in the very beginning stages of planning this, but i want o have everything planned out before i get into the project.

i've done some research and found that the crank i want is from a 72'-80' AMC 258, this era has 12 counterweights compared to the others with only 4. its makes it heavier, but should help the engine better balance itself and run smoother. and should make it sturdier off road. just looking over e-bay i'm having trouble finding this timeframe crank shaft except ones that have already had work done to them. i'd like to find one stock to my machinest can do the work for me. any help in locating one of these would be great. and the rods to go along with it as well

[75K30]

Right on man, I respect what you are trying to do, and, if you cant tell, I get a little excited about this.
About the crank, is that crank the best alternative? I question the use of it because of simple rotational mass. Reciprocating weight is not our friend when we are building an engine. "Light is right."
I have always used aftermarket cranks. I am fortunate to have built many engines over the years, and have a source to have anything I want made for me. Yeah, good to have friends. Great machinists that dont understand suspension technology, or electricity, so we trade a bunch of work. The old barter system at its best.
Let me look at some notes from other builds. I even built a 5.0 L super stroker that used small block chevy pistons. Used an offset ground crank (4.06, or .09), 5.875" H-beam rods, solid lifter cam, 2.02" / 1.60" valves, and big 30lb/hr injectors.
This bad boy was bad! It made a little over 330 hp @ 5200 rpm. Did require the good fuel, but it was a bad mamma jamma.

Again i will look into some notes and post some combos for you. I have probably built 4 or 5 of these lil strokers. I used to be really into the Jeep thing.

Here is an interesting little article on quench. It may help you make a little sense of it. It is tough to understand. Especially when a knucklehead like me is trying to explain.
Dumb cavemen do not make good teachers, lol.
Piston Head Clearance Guide - Tech Article - Chevy High Performance Magazine

[72'CaminoKid]

i read about the 5.0, whats that take a .125 bore or something like that. and i'm not positive this is the best crank but based on all that i've read its the top choice. and since i dont have the same oppurtunites to get something made and am trying to keep it low budget i think it might be better/easier than going aftermarket on the crank chaft. i do plan on an aftermarket cam. not sure exactly what yet though. and the reciprocating weight issue has been in the back of my head the whole time, bc i understand that it isnt the best thing to have, but the arguement for the extra counterweights to balance the engine and durability off-road make a lot of sense to me. guess i need to do some more research and weigh the pros and cons. of the 12 or 4 conterweight cranks

[75K30]

Here is a decent low dollar build
This is a proven combo that makes 230 HP @ 4500 rpm and 320 ft/lbs @ 2000 rpm
Man, that is right where you want it. This baby has some crawl power.
~ Jeep 4.2L 3.895" stroke crank
~ Jeep 4.2L 5.875" rods
~ Keith-Black Silvolite UEM-2229 +0.030" bore pistons
~ Increase piston dish volume to 30cc
8.8:1 CR
~ CompCams #68-115-4 192/200 degree cam
~ Ported HO 1.91"/1.50" cylinder head
~ Mill block deck 0.035"
~ Mopar Performance 0.043" head gasket
~ 0.058" quench height
~ 2.25" exhaust
~ Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines


Guarantee this will run very well on pump gas no matter where you build it, or where you run it. This lil guy has got some thump down low. Perfect for a DD that will see plenty of miles.


Could try this too:
~ Jeep 4.2L 3.895" stroke crank
~ Jeep 4.2L 5.875" rods
~ Jeep 4.0L 3.875" standard bore pistons
9.7:1 CR
~ CompCams #68-231-4 206/214 degree camshaft
~ Ported HO 1.91"/1.50" cylinder head
~ Stock 0.051" head gasket
~ 0.081" quench height
~ Ford 24lb/hr injectors with adjustable FPR or MAP adjuster for '87-'95 engines, Ford 24lb/hr injectors with stock 49psi FPR for '96 and later engines

This is only a 4.5L with a little larger cam. It makes 250 HP @ 4800 rpm, and the torque is about the same as the above, 320 but not until 3200 rpm

You could change this last one to a +.030 piston, like the first engine, and get a higher CR. The Hp's will go up, but you have to buzz the engine a bit more without a real big gain in torque.
The first engine looks like the one for your application.
Nice header and a 2.25" free flowing exhaust, and you will be moving man.

[72'CaminoKid]

thanks for that help there 75. i'm sure you'll be providing me with lots more through this project. i was also thinking the first one, mainly bc the torque is available at lower rpms where i'll need it most.

do you think that 2.25" exhaust is enough, aint that the stock size pipe? also, what type muffler (obviously high-flow cat) but i'm wondering if this engine would sound good or should i just try and keep it quite. i absolutely hate the little 6cyl jeeps and toyotas runnin flowmaster and what not bc it's so high pitched. if this stroker will sound good and have a deep rumble i'd like to make it noticeable not obnoxious, but at least let it be heard a little

[75K30]

Yeah, you know it is going to sound like an angry bee with a bad attitude if you install the wrong muffler, and I do feel the the 2 1/2" exhaust is plenty, even with a tailpipe. With a header, and a good flowing system, the pipe diameter will keep velocities up, and will maximize the torque down low. You probably will not be buzzing this thing way up in the upper rpm ranges to require a larger pipe diameter. You may experiment with 2.75" pipe, but I cant see too many advantages here.
This should even pass emissions if it is required. This lil plant should be a real wolf in sheeps clothing. Should have plenty of pop when you want it, and with that first cam, will have great throttle response.
The sound is going to come from the head, and the sligtly larger bore, but do not expect too much more than the original tone. A Magna Flow will help tone it down, and give it a rich sound without sounding "ricey" or having that "Turdmaster" sound, lol.
Let me know what else you come up with, I have a few calls out regarding that crank issue we were discussing. Most seem to lean towards the light side, but my machinist suggested a heavier crank would have more material to work with so a "knife cut" can be done to the counter weights. This way much of the heavy material can be removed, and the sharp edges of the counter weights can cut through the oil. This will free up a few extra HP's.I will research this to see journal sizes and so forth to make sure this is a reasonable solution.
I will even ask around to see if we can come up with a crank for you.


75