GM 4200 Vortec vs AMC/Chrysler 4.0L

[Nick R]

So we have the GM 4.2L 24V DOHC Inline 6 at 291HP, and 277lb/ft of torque, versus the AMC 4.0L 12V OHV Pushrod Inline 6 at 190HP and 230lb/ft of torque. On paper the Vortec 4200 demolishes the venerable 4.0L. But for some reason it hasn't gained much of a foothold. Anyone have thoughts on this?

FWIW, both are extremely smooth (inherent in I-6 configuration) and sound quite nice.

http://www.youtube.com/watch?v=BziG5OjRMwk

http://www.youtube.com/watch?v=bZjrkXa7u04

 

[addyguy]

You can't really compare them at all - TOTALLY different styles of engines. Yes, the torque is higher on the GM 4200, but I think what you'll find is that the 4.0 Jeep I-6 has much more 'useable' torque 'down low' where you need it. You have to wind the 4200 I-6 out to get power from it, and so it won't feel as powerful as a 4.0 I-6.

If you are doing SERIOUS off-roading, you DON'T want the GM 4200 I-6.

 

[JTK]

I owned and loved both engines. Like said, the GM Atlas/Vortec 4.2L needs revs to achieve those number. Revs that a truck application normally doesn't see.

Joel

 

[440Magnum]

If GM had ever put the 4.2 in something that wasn't a big porky mall crawler, it would have gained a better following. (extracting tongue from cheek...)

Seriously, I agree with the comment that the 4.0 had more usable torque for its intended purpose (offroad crawling). It's got scads of torque right off idle. Heck, mine's never even *seen* the high side of 3600 RPM because there's just no need to take it up there (and it doesn't really have anything up there either).

Plus the 4.0 a brutally simple and rugged engine. The 4.2 is significantly more complex. When emissions/crash safety (mostly the latter...) killed the 4.0, I was very glad that Jeep engineers picked the available Chrysler engine that was *the most* similar to the 4.0 in terms of power delivery, ruggedness, and simplicity- the pushrod iron block 3.8 v6- instead of being tempted for the bigger numbers available with the 4.0 SOHC aluminum v6.

 

[Gary Allan]

How old is the 24V DOHC 4.2? I only found it in the Envoy and Trailblazer from 2002 forward. The 4.0 had an almost 40 year plus history with very minor alterations. There's also the fact that for most of the jeep line it was the most installed engine offered over the most chassis.


I could be missing something for lack of detailed research, but where's it going to go with 2 flavors of one chassis out of about 20? Everything else gets the more compact 4.3 V6 or a V8.

 

[Nick R]

Your absolutely right, gary. What I meant was I'm surprised that the 4.2 hasn't been placed in more vehicles. I'm sure with some tweaking, more low end should be easily attainable.

 

[PT1]

Originally Posted By: 440Magnum
If GM had ever put the 4.2 in something that wasn't a big porky mall crawler, it would have gained a better following.

 

[38sho]

I love the 4200, its such a nice smooth engine with some power...

completely different driving experience then the 4.0

I don't know wth you guys are talking about that the 4200 doesn't make good power without winding it out so its useless for offroad...... The kind of off-roading we do down here in south florida.... RPM's are your friend.......


be interesting to compare some dyno charts of the two motors.... sure the 4.2 might make power higher up, but its so much more power that it might even make more power then the 4.0 all across the board.....

 

[MNgopher]

Totally different driving experiences in two different types of vehicles. The 4200 is smooth, and definitely likes to rev, but is in a glorified minivan for practical purposes.

The Jeep 4.0 is perfect for the actual off-road capabilities that until more recently nearly all jeeps were known for. Pulls hard right off idle.

Not sure on the curb weight on other Jeep products, but in the Cherokee (unibody) the 4.0 was mated to a pretty light application, while the 4200 suffers with the full body on frame.

 

[Gary Allan]

Appears so..

2002 Chevrolet TrailBlazer
LS 4dr 4x4

Horsepower:
270 @ 6,000 rpm
Torque:
275 @ 3,600 rpm
Transmission:
4-spd auto w/OD
Curb Weight:
4,600 lbs.
Fuel Type:
NA

Jeep Cherokee Classic 4X4 (2000)

Engine Type OHV 12-valve 4.0 Liter I6 w/SMFI*
Engine Size 242 cid/3956 cc
Horsepower 190 @ 4600 RPM
Torque (lb-ft) 225 @ 3000 RPM
Wheelbase/Width/Length 101.4"/69.4"/167.5"
Transmission Four-speed automatic
Curb Weight 3379 pounds

Here's the Wranglers

Curb weight: 3,092 lb (1,403) with four-cylinder, 3,229 lb (1,465 kg) with I-6

The Grand Cherokee is about 3900 in 1999-2004 which is the last year for the 4.0 in that chassis.


So ..700-1500+lb difference 20-50%+/- more mass to move.

 

[artificialist]

My ex-boss became an expert in GM 4.2 engine repairs. He saw so many cylinder heads with failed valve seats, it baffled his mind.

That combined with the fact that each repair is labor intensive is probably why the 4.2 didn't catch on.

 

[JTK]

I used to be active on GM 4.2L I6 related boards when I owned my 2005 Trailblazer 4x4. Can't say I ever saw failed valve seats as being a common issue (don't recall any actually), but yes, removing the head from that chain driven DOHC would be labor intensive job. Given the smoothness and ease the 4.2L propells a "porky" GM T360 chassis, installed in a vehicle ~1300lbs less it would have power/accelleration and possibly MPG to spare. Like I've said 10x on this board, the worst thing about the Atlas/Vortec 4.2L is the vehicle GM dropped them into.

Joel

 

[Eddie]

It is all about torque and the 4.0 produces usable torque at 1500 rpm. We seem to get hung up on the maximum torque. As addguy states usable torque what the 4.0 has and the GM does not.

 

[440Magnum]

Originally Posted By: 38sho


I don't know wth you guys are talking about that the 4200 doesn't make good power without winding it out so its useless for offroad...... The kind of off-roading we do down here in south florida.... RPM's are your friend.....


That's not offroadin', that's MUDDIN' ;-)

The only kind of offroading I do requires lots of idling over big rocks in 4-low, first gear or maybe 2nd. Sub walking-speed- off-idle torque is essential. Lots of people have blown 4.0s to bits getting carried away with revs in the mud- its definitely not the best powerplant for that.

 

[440Magnum]

Originally Posted By: Gary Allan
The 4.0 had an almost 40 year plus history with very minor alterations


Actually the 4.0 only dates back to around '84. It isn't a derivative of the previous (258?) CID AMC six, it was a clean-sheet design. Never even got sold in a carbureted form. The fact that it happened to keep the 258's bore-center spacing, bearing sizes and bearing spacing does for a very quick and convenient stroker setup though (258 crank in a 4.0 block plus overbore = 4.7L) ;-)

 

[Nick R]

That's interesting becuase offroading, our jeep with the 2.5L 4 cylinder does just fine, without much bottom end torque.

 

[440Magnum]

Originally Posted By: rudolphna
That's interesting becuase offroading, our jeep with the 2.5L 4 cylinder does just fine, without much bottom end torque.


I would actually say that the 2.5 had a LOT of bottom-end torque. Less than a 4.0, but still a lot more than, say, a VTEC Honda.

 

[Gary Allan]

Originally Posted By: 440Magnum
Originally Posted By: Gary Allan
The 4.0 had an almost 40 year plus history with very minor alterations


Actually the 4.0 only dates back to around '84. It isn't a derivative of the previous (258?) CID AMC six, it was a clean-sheet design. Never even got sold in a carbureted form. The fact that it happened to keep the 258's bore-center spacing, bearing sizes and bearing spacing does for a very quick and convenient stroker setup though (258 crank in a 4.0 block plus overbore = 4.7L) ;-)



Quote:
with very minor alterations


The crank got shorter ..the head got configured like the newer designed 2.5 ..which used the same block .. hacking two cylinders off the original.

As I said, minor changes. They could have shortened the crank and left the poorer flowing head to make it even simpler ..but "while you're there".

4.0 head swaps are VERY common on the 4.2 and 4.2 crank swaps into the 4.0 are too.

I believe that there were differences in rod length and wrist pin orientation over the years ..and the deck heights are different between the 4.0 and the 2.5 in at least the 99 versions.

..but clean slate is not something that comes to mind.

 

[Nick R]

Originally Posted By: 440Magnum
Originally Posted By: rudolphna
That's interesting becuase offroading, our jeep with the 2.5L 4 cylinder does just fine, without much bottom end torque.


I would actually say that the 2.5 had a LOT of bottom-end torque. Less than a 4.0, but still a lot more than, say, a VTEC Honda.


This is true. I've never driven a truly gutless car. Even the 2.2L OHV in my cav has good low end torque. I suppose the Jeep does have some.

 

[Gary Allan]

The 2.5 just has no horsepower to move a 3300lb chassis at anything but fractional G's for the butt dyno. While it doesn't have the quick ramp and (relative) flatness of the 4.0 ..it's a torque engine. On reasonably flat ground I can leave from a standstill @ 2000 rpm and the tach never dips until the converter locks up. By the time it returns to 2000 ..you're doing 50-55mph.

If it was in something like a tin can 70's Courier/Madza or Toyota pick up chassis ..it would be marveled as one of whomever's greatest achievements of all time.