4.2 with 4.0 head or stroker?

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#1
The title says it all. What makes a stroker better than a 4.2 with a 4.0 head? Assuming all ignition, injection, and cams are the same, what's really the difference?
 

tower210

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Olathe
State
KS
#2
I know the stroker bumps it to 4.6 or 4.7 or 4.9 liters; so there is added displacement....
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#3
I know the stroker bumps it to 4.6 or 4.7 or 4.9 liters; so there is added displacement....
That's a fair answer. I didn't mention displacement. The 4.2 can be bored bigger also. I don't understand why the stroked and bored 4.0 would be so much better than a bored 4.2.
 

CJ7Pilot

18436572
LIFETIME
CJ-8.com Member
City
Yuba City
State
CA
#4
It's probably not better. The engine you build probably depends on the engine you start out with.

I had a 258 with a 4.0HO head, and I loved it! If I had another 258, I'd do the same thing again.

If I had a 4.0 though, I probably wouldn't look for a 258 to swap in... I'd just work with the 4.0.

What are you working on?
 
Last edited:

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#5
It's probably not better. The engine you build probably depends on the engine you start out with.

I had a 258 with a 4.0HO head, and I loved it! If I had another 258, I'd do the same thing again.

If I had a 4.0 though, I probably wouldn't look for a 258 to swap in... I'd just work with the 4.0.

What are you working on?
1981 scrambler. Currently has a 258, with a 4 speed. I have another jeep with a 258 with 10,000 miles on it and an ax15 with the same miles. I have a 302 ford I was going to put in my scrambler, but some of these strokers people speak of are pretty comparable to the 302.

I just don't see how starting with a 258 would yield less of an engine than a 4.0 with a stroke.
 

tower210

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Olathe
State
KS
#7
My perception is that boring any modern engine yields very little displacement since most of them can only be bored about 60 thou. Not sure why it is; but strokers seem to increase torque more. I know Jake White (cartotracks on bookFace) has a 4.7 stroker and loves it; with a 4:1 tcase he can put it in 1st and let it idle; doesn't matter how hard you stop on the brakes you can't kill the stroker....

He might be a good one to talk to...
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#8
I appreciate the input Tower. I am looking at as many places as I can research and am getting zero answers. I know Jake really likes his stroker, but no one so far can actually explain the difference. They both have the same stroke and similar bore. I don't see the advantage of the 4.0 build and would love to see the actual mechanical proof.
 

HighSierra CJ

Scrambler Enthusiast
LIFETIME
CJ-8.com Member
SOA Member
City
Ducor
State
Ca
#9
I appreciate the input Tower. I am looking at as many places as I can research and am getting zero answers. I know Jake really likes his stroker, but no one so far can actually explain the difference. They both have the same stroke and similar bore. I don't see the advantage of the 4.0 build and would love to see the actual mechanical proof.
I bought a 4.6 stroker from Golen a couple of years ago, and installed Mopar FI. Golen sent me a dyno print out on my motor, and while I do not remember the specs, I do know that it has a lot more power than either of my other two jeeps, with the stock 4.2/Mopar FI. seems like the stroker was rated around 270 HP. You should call Chad Golen and talk to him about the strokers. He is a super nice guy, and an authority on these motors.
 

ag4ever

Average Nut
LIFETIME
CJ-8.com Member
City
Richmond
State
TX
#10
Have you visited the stroker forum?

https://www.jeepstrokers.com/forum/

The 4.0 (242) has a 3.89" bore, 3.75" stroke.

The 4.2 (258) has a 3.75" bore, 3.90 stroke.

The 4.0 can be bored to 3.935" and up to 3.970" (race)

The 4.2 can be bored to 3.93" and up to 3.95" (race)

So, there is a marginal gain with the 4.0 block, but not much. Most use the 4.0 block due to the the bore being near the final size from the factory and the engines are being used in jeeps that originally came with a 4.0 so accessories and such bolt right up. Also there are slight differences in the 4.2 heads vs the 4.0 on how the intake and exhaust manifold bolt on.

In short, I don't think it matters which way you go, in the end, same bore x same stroke should be similar if using the same head/intake/exhaust and only the block is different.
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#11
I bought a 4.6 stroker from Golen a couple of years ago, and installed Mopar FI. Golen sent me a dyno print out on my motor, and while I do not remember the specs, I do know that it has a lot more power than either of my other two jeeps, with the stock 4.2/Mopar FI. seems like the stroker was rated around 270 HP. You should call Chad Golen and talk to him about the strokers. He is a super nice guy, and an authority on these motors.
Thank you. That is a great idea. I will call him.
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#12
Have you visited the stroker forum?


In short, I don't think it matters which way you go, in the end, same bore x same stroke should be similar if using the same head/intake/exhaust and only the block is different.
That's pretty much what it would seem to me too.
 

Domin8

Scrambler Enthusiast
LIFETIME
CJ-8.com Member
City
Astoria
State
NY
#15
I have been reading up on this question lately, and I am hoping to rebuild my original 4.2 block, and swap in a 4.0 head & intake/exhaust along with the new Gen III Hesco MPFI kit.

I wonder if anyone knows whether or not all the late model 4.0 accessories and pulleys will bolt up to a 4.2?

I'd like to have the late model 4.0 serpentine set up. The one that puts the alternator up top on the passenger side, and the AC compressor down under the power steering pump on the driver's side. Like this one:

https://i0.wp.com/serpentinebelthq..../07/2001-Jeep-Wrangler-4.0L-with-AC.jpg?ssl=1

I think my original 4.2 block with 71k miles might be in good enough shape to keep. If not, then I will probably just go the stroker route.
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
SOA Member
City
Biloxi
State
MS
#16
They should?

I did the opposite, bolted all my old 4.2 brackets/accessories on to a 4.0 block and head. Minimum modifications, maybe a washer as a spacer here or there.

Just keep in mind rotation of the water pump.
 

Domin8

Scrambler Enthusiast
LIFETIME
CJ-8.com Member
City
Astoria
State
NY
#17
They should?

I did the opposite, bolted all my old 4.2 brackets/accessories on to a 4.0 block and head. Minimum modifications, maybe a washer as a spacer here or there.

Just keep in mind rotation of the water pump.
Thanks, I can't wait to try this out. Will probably try to source all the accessories and brackets from salvage yards at some point.

The water pump rotation (assuming I could use a 4.0 water pump) might actually be a plus.

That's because I am hoping to use a seven blade, counterclockwise rotation fan (18.8 inch dia) off a 1995 ford F-150, 5.0 V8, along with a severe duty fan clutch.

Supposedly, that is all supposed to bolt up, and fit inside the factory Jeep "heavy duty cooling" (drivers side offset fill neck radiator) fan shroud.

It will still be a while until I can try this out, but I'm trying to figure out things ahead of time.

Thanks again!
 
Last edited:

CJ-8_Jim

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
NW Chicago Suburb
State
IL
#18
Just saw this OP January post. Probably too late, but here's my 2 cents... I've had the options the OP is asking about.

Caveat 1: My results are driver impression. Nothing was dyno'd
Caveat 2: All the time, changing the specs of each scenario will have a noticeable effect. Powerplants are a "system". If you want max performance, then improve the entire "system", not just some components. I have not wanted to spend the time & $$$s to do that, but I am happy where I ended up with my Sunday driver.
Caveat 3: I discuss I-6 options below. I am NOT providing feedback on other engine swaps. I can't speak to those -- others can and will do that... just wait :)

- Stock 258 with 95 MPI: I had this first. MPI (and I suspect any fuel injection upgrade like TBI) is a HUGE upgrade in performance. It did have little predetonation when I floored it, but usually there was none with 87 octane.
Many (most?) people get a lot of predetonation when putting on MPI. An adjustable fuel pressure regulator didn't help me those times when I floored it.
I don't think TBI has predetonation issues, but some states DMVs won't pass TBI, only MPI (I got the HESCO MPI sticker).
  • NOTE: I can't speak to carb upgrades, but after years fiddling with an OEM carb on my AMC 304 1979 CJ-5, I swore off carbs (not the food)... life is short and I'm not a "Carb Whisperer".

- Stock 258 with 95 MPI and 4.0 HO head and stock exhaust and TJ OEM air intake.
Result: No noticeable difference. And the predetonation did NOT go away. And Yes, I had the 7120 HO head.
  • Upgrading the exhaust would have helped, but then again upgrading the exhaust without the HO head would have helped.

Fast forward 9 years.... then I cracked the block's water jacket at the weakest headbolt found on #6, so off I was to replace engine... cheapest route for my "around town family Sunday driver CJ-8" was a budget stroker:

- "Budget stroker" 4.0L block, 258 long nose crank, +30 over and decked to 0.013" head ported/polished ($2,296 including core and S&H in 2017) with '95 MPI, stock exhaust and TJ OEM air intake.
Result: An even MORE noticeable difference over 4.2 with 4.0HO head, but I definitely need to run 93 octane.
It runs great and I'm quite satisfied, but it is quite clear the TJ intake holds it back significantly.

If I wanted to spend the time and money to improve it further (I don't have a need to improve as this suits us just fine).... I would in this order:
- improve air intake (multiple options)
- improve exhaust (multiple options)
- use a later 4.0 intake manifold that is curved and not squared off like the '95

If I was going the budget stroker route again, I would deck it to 0.0" or close thereof for the sole reason that I might be able to run regular 87 octane. Maybe even as much as -0.010" (but I'd have to think/research that more). But it runs great decked at 0.013"

If you want to spend more $$$ and more time, get a short nose stroker so you can change over to S-belt, and maybe install a later FI system and maybe a later head casting (newer has more advanced engineering... no?).


My 2 cent conclusions:
  • If you are keeping the 258 and it's not tired and you don't want to swap engines, choose FI -- NOT 4.0 Head.
  • If you have MPI and think 4.0HO head will eliminate predetonation, my experience is that it will not. Save your $$$ and just buy premium.
  • If your MPI engine is shot and you are in a hurry to get a new engine so your kids can go to SandBlast (and you are not looking to turn your Sunday driver into a speed demon), then for me it was only $2,296 (including $300 core charge and S&H) to get a stroker.

This is just I-6 options. There are lot's of good guys here with good feedback on other powerplants.

Jim
 
Last edited:

ag4ever

Average Nut
LIFETIME
CJ-8.com Member
City
Richmond
State
TX
#19
Where did you get your stroker?

I’m about to jump in the deep end and have one built locally.

But, then again, I might just get the new sniper efi for the 4.2. I really need to get a Jeep running reliably for the summer.
 

CJ-8_Jim

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
NW Chicago Suburb
State
IL
#20
I have been reading up on this question lately, and I am hoping to rebuild my original 4.2 block, and swap in a 4.0 head & intake/exhaust along with the new Gen III Hesco MPFI kit.

I wonder if anyone knows whether or not all the late model 4.0 accessories and pulleys will bolt up to a 4.2?

I'd like to have the late model 4.0 serpentine set up. The one that puts the alternator up top on the passenger side, and the AC compressor down under the power steering pump on the driver's side. Like this one:

https://i0.wp.com/serpentinebelthq..../07/2001-Jeep-Wrangler-4.0L-with-AC.jpg?ssl=1

I think my original 4.2 block with 71k miles might be in good enough shape to keep. If not, then I will probably just go the stroker route.
1) I once looked into this, but it didn't seem worth the time hassle and $$$ to do the changeover.
I'm sure S-belt has benefits, but I didn't need those incremental benefits on a Sunday driver.

2) FWIW... see my post above. HESCO MPI is a HUGE improvement. When I later did 4.0HO head swap, I experience no improvement.

Maybe 4.0HO with carb (no MPI) has noticeable benefits?

But if I were you, I'd hold-off on the 4.0HO... it's easy enough to do later. Doing it later only costs you the extra time of swapping exhaust manifolds (which is easy). Everything else has to be done either way.
 
Top