What the 4.0 could have been

[JustDandee]

The general consensus is you will gain a few %, like 2-3%, in power output per point of compression ratio gained. So a 200 hp engine moving from 8.5 to 9.5 might gain 5hp, nothing significant. You would never notice that. On a 500hp engine, that % change would become more noticeable.

An engine is a system, so if you were to bump the compression and increase the VE, then you start making noticeable power changes.

So not significant which is what I noticed. I was tracking top end mph At the time-Test loop was to put the pedal to floor- GPS check the speed on a flat piece of interstate. but the head shave for its moderate gain, I recall just felt better with the drivability.

I don't think moving the dynamic compression ratio to 8.0 would require more than 87 octane.

In my opinion this is the biggest problem.

View attachment 425327

The red cells are timing adjustments I made. I don't think throttle position has any influence. The RPMs and absolute pressure are the dominant inputs. With the stock timing the ECM reduces power when you need more power to go up a long hill on the interstate.

I have to ask- horizontal lines are RPM increments/ the vertical is Absolute pressure? not familiar with MAP range inputs- Looks like you made some significant timing changes though in that quadrant -those original numbers look low.
how did you manage that? I have a little experience helping my son get a car up And going on a mega squirt system/ tuner studio- basically auto tune set stoic targets, and tweaking the base line timing on the old OBD I systems. Said another way, enough to get into trouble

 

[TheBoogieman]

Drive a 4.2L Jeep for a week and you'll love the 4.0.

 

[John Cooper]

Drive a 4.2L Jeep for a week and you'll love the 4.0.

But what if the 4.2 had fuel injection??

My 4.2 with an aluminum intake, 390 4 barrel holley and Clifford cam, really performed nicely in my 84 CJ8.

 

[Brianj5600]

Q

Interesting prospective from a Dana 60 equipped TJ guy . My personal D-35 experience has been less then a minuscule failure rate with 2 XJ's and ass kicking 225/75 R 15 tires. The 4.0 goes back to a time where the first version had 177 h.p. and that was more than a Ford 302 or Chevy 305 or dodge 318 had.
Sad times indeed. A 242 is a dog compared to modern engines , but it is reliable and has an exceptionally flat , ( under-powered ) torque curve.
The Dana -35 ranks right up there with the Peugeot BA-10 transmission , it works until it doesn't. Maybe it was solid in a Rambler classic custon six with 180 Gross lb. ft. of torque.
At the end of the day I'm glad we can make mods to make a TJ work in OUR specific application.

Ford and Chevrolet had 200+ HP with the 302 and the 305 before the 4.0 debuted.

 

[TheBoogieman]

But what if the 4.2 had fuel injection??

My 4.2 with an aluminum intake, 390 4 barrel holley and Clifford cam, really performed nicely in my 84 CJ8.

That's cheating. My buddy's 1990 YJ 4.2L put out a breathtaking 112HP. My 4 cylinder Jeep could outrun it.

 

[Brianj5600]

The general consensus is you will gain a few %, like 2-3%, in power output per point of compression ratio gained. So a 200 hp engine moving from 8.5 to 9.5 might gain 5hp, nothing significant. You would never notice that. On a 500hp engine, that % change would become more noticeable.

An engine is a system, so if you were to bump the compression and increase the VE, then you start making noticeable power changes.

How much difference is there in reducing quench from .078" to .040"?

 

[Apparition]

Ford and Chevrolet had 200+ HP with the 302 and the 305 before the 4.0 debuted.

Might as well use a 1980's Ford 2.3L 4 cylinder to keep weight down

Year	Power	Torque
1984	175 hp (130 kW) @ 4400 rpm	210 lb⋅ft (285 N⋅m) @ 3000 rpm
1985	175 hp (130 kW) @ 4400 rpm	210 lb⋅ft (285 N⋅m) @ 3000 rpm
19851⁄2	205 hp (153 kW) @ 5000 rpm	248 lb⋅ft (336 N⋅m) @ 3200 rpm
1986	200 hp (149 kW) @ 5000 rpm	240 lb⋅ft (325 N⋅m) @ 3200 rpm

 

[Brianj5600]

So not significant which is what I noticed. I was tracking top end mph At the time-Test loop was to put the pedal to floor- GPS check the speed on a flat piece of interstate. but the head shave for its moderate gain, I recall just felt better with the drivability.


I have to ask- horizontal lines are RPM increments/ the vertical is Absolute pressure? not familiar with MAP range inputs- Looks like you made some significant timing changes though in that quadrant -those original numbers look low.
how did you manage that? I have a little experience helping my son get a car up And going on a mega squirt system/ tuner studio- basically auto tune set stoic targets, and tweaking the base line timing on the old OBD I systems. Said another way, enough to get into trouble

The tuning software is Syked and the map is in torrs. I don't know why they use torrs and make me convert it to I understand. Hptuners is much easier to work with but not available when I purchased my Syked software.

Stupid autocorrect!

 

[Brianj5600]

Might as well use a 1980's Ford 2.3L 4 cylinder to keep weight down

Year	Power	Torque
1984	175 hp (130 kW) @ 4400 rpm	210 lb⋅ft (285 N⋅m) @ 3000 rpm
1985	175 hp (130 kW) @ 4400 rpm	210 lb⋅ft (285 N⋅m) @ 3000 rpm
19851⁄2	205 hp (153 kW) @ 5000 rpm	248 lb⋅ft (336 N⋅m) @ 3200 rpm
1986	200 hp (149 kW) @ 5000 rpm	240 lb⋅ft (325 N⋅m) @ 3200 rpm

Definitely turbo 2.3L. The OG Ecoboost

 

[BlueC]

So not significant which is what I noticed. I was tracking top end mph At the time-Test loop was to put the pedal to floor- GPS check the speed on a flat piece of interstate. but the head shave for its moderate gain, I recall just felt better with the drivability.

Did you pull a head off of a good running engine just to shave it and put everything back as it was, head gasket and all, with no other changes?

 

[BlueC]

How much difference is there in reducing quench from .078" to .040"?

I don't know that answer. I'm just a backyard hot rodder, not a professional engine builder. I'd be interested to hear an answer with a simple explanation.

 

[Brianj5600]

Here is some reading on quench.

https://www.enginelabs.com/engine-t...ormance-squished-between-the-piston-and-head/

 

[JPHikr]

I might consider a Ford motor. The 4.0L I6 Barra.
https://www.enginelabs.com/engine-tech/an-australian-in-the-states-building-a-ford

“The Barra can trace its roots back to the 2.4-liter (144 cubic inches) ‘Thriftpower 6’ from the North American 1959 Ford Falcon,” says Hilzinger. From there, the six-cylinder design was modified by Ford Australia, and evolved into the iron-headed Cross Flow engine of the 1970s, the aluminum-head Cross Flow engine of the 1980s, and then the single overhead cam I-6 that came on scene in the late ‘80s and carried through until 2002.


Jeep should have done the same with a minimal cost Jeep could have done a Hemi twin cam two valve on the 4.0 block

The Barra is a undersquare Bore 3.632 Stroke 3.910 in

4.0 Oversquare Bore 3.875 in Stroke 3.414

Now if they had gone with 4.6 Bore 3.917 in Stroke 3.895 in. it would have well over 300hp NA.

With the 12 counterweight crank and a heavy flywheel it would be a stump puller which is what you want in a Jeep.

 

[JustDandee]

Did you pull a head off of a good running engine just to shave it and put everything back as it was, head gasket and all, with no other changes?

right in the context that no valve work was done- just check for cracks and shave since I had it off......but the work was done as a leak from a water port to the side of the head- not a leak to a cylinder. So new head gasket/Arp studs- old head with a shave. Gasket thickness would be the only possible variable- I could offer? and I just got the run of mill Felpro.

 

[Rickyd]

But what if the 4.2 had fuel injection??

My 4.2 with an aluminum intake, 390 4 barrel holley and Clifford cam, really performed nicely in my 84 CJ8.

Put that crank in a 4l block and save the heartache

 

[Rickyd]

How much difference is there in reducing quench from .078" to .040"?

Less likely to detonate with tight quench

 

[ColoJeep]

Ford and Chevrolet had 200+ HP with the 302 and the 305 before the 4.0 debuted.

Well I should have said in Midsize SUV's not HO 5.0 Mustangs or Kali equipped 305 pee whiffing Corvettes.
Perhaps to be more accurate , I should have compared apples to apples.
In 1987 in midsize SUVs this is how the comparison sizes up. with highest horsepower engine available.

87 Chevy S-10 Blazer 2.8 V-6 125 h.p.
87 Ford Bronco II 2.9 V-6 140 h.p.
87 Toyota 4runner 2.4 I-4 105 h.p.
87 Jeep Cherokee 4.0 I-6 173 h.p.

So in it's market the 4.0 was powerful compare to the rest of the market at introduction.

Today you can could go way high tech and have a butt load of power but your cost / horsepower ratio goes out the window.
This is why " just LS swap it " pisses so many people off and yet make a ton of sense in the cost / horsepower ratio.

Kinda the same way folks would swap a 327 into a flattie 50 years ago , sure you had to steer with your left hand because your right hand was busy holding the T-90 into 2nd gear....

 

[Squatch]

87 Chevy S-10 Blazer 2.8 V-6 125 h.p.
87 Ford Bronco II 2.9 V-6 140 h.p.
87 Toyota 4runner 2.4 I-4 105 h.p.
87 Jeep Cherokee 4.0 I-6 173 h.p.

Hindsight being 20/20, I know what I would choose for a "New for '87" rig...

 

[RINC]

Well I should have said in Midsize SUV's not HO 5.0 Mustangs or Kali equipped 305 pee whiffing Corvettes.
Perhaps to be more accurate , I should have compared apples to apples.
In 1987 in midsize SUVs this is how the comparison sizes up. with highest horsepower engine available.

87 Chevy S-10 Blazer 2.8 V-6 125 h.p.
87 Ford Bronco II 2.9 V-6 140 h.p.
87 Toyota 4runner 2.4 I-4 105 h.p.
87 Jeep Cherokee 4.0 I-6 173 h.p.

So in it's market the 4.0 was powerful compare to the rest of the market at introduction.

Today you can could go way high tech and have a butt load of power but your cost / horsepower ratio goes out the window.
This is why " just LS swap it " pisses so many people off and yet make a ton of sense in the cost / horsepower ratio.

Kinda the same way folks would swap a 327 into a flattie 50 years ago , sure you had to steer with your left hand because your right hand was busy holding the T-90 into 2nd gear....

This thread has also made me think of the 4.3L 262cu V6 motor that is still in current production as the entry level motor in the full size GM pickups.

 

[ColoJeep]

Hindsight being 20/20, I know what I would choose for a "New for '87" rig...
View attachment 425670

Interesting choice , I believe I would be happier without a 105 h.p. 4 banger and IFS.