What's the most HP for a 4.0?

[j99xj]

How much torque/power can a blueprinted and utmost built/tuned AMC 242 feasibly produce in a reliable manner, fuelled on standard pump gas?

400 reliable NA hp on pump gas?! No way.

I'd say no more than 250 hp. That puts it at a little more than 1.0 hp/cubic inch. Getting 250 hp would require all the bolt ons and a highly ported head with a good camshaft and roller rockers. An increased rev limit would also be necessary. (probably on the order of 5500-6000 rpms)

I've done mostly all the intake mods (except K&n filter because I think they are a joke) and exhaust mods for the 4.0 and I might be making 210-220 hp (at sea level).

Of course I'm taking a 15-18% penalty just being in Colorado. So those numbers put me at about what a stock 4.0 puts out.

But I'm not complaining. If I had 4.10 gears I could be about even with a 5.0 mustang.

 

[NXJ]

I'm thinking more like 700BHP/1000NM +, attained through clever forced induction with sequential twin-turbos and serious intercooling. The limits, as I can see it, lies within the outdated valvetrain.

One must not forget that there are countless BMW, Toyota and Nissan I6-engines (similar factory size and output as the 4.0) that push upwards of 1000 horses.

 

[MudDawg]

The only problem with getting SERIOUS hp from a normally aspirated 4.0 is the upper rpm limit and the modest volumetric efficiency...."modern" small displacement engines make serious hp because of three things...higher thermal efficiency, higher volumetic efficiency, and high upper rpm redlines.

So any comparison is apples to oranges....however, you can use a power adder like a blower or turbo to artificially enhance volumetric efficiency...or a power adder like nitrous oxide or exotic fuel like nitromethane.

As Dino pointed out...incremental increases in power can be gained by the combination of several modifications like porting, throttle body, cold air, better exhaust, cam, etc....but they are each relatively small increases...

If only the magic wish genie would build a DOHC 4 valve, pent roof crossflow head.

 

[BBeach]

Does anyone have specs as far as dimensions of the block, cylinder spacing, cylinder wall thickness, etc.?

 

[Dr. Dyno]

The 4.0 (or stroker) cannot safely be revved past 5600rpm because a cam harmonic at this point can break the timing chain or throw the distributor out of the block. Therefore NA with stock displacement, you're not going to get much more than 250hp (crank) out of it. If you build a 4.7 stroker, you could stretch it to ~280hp. To get more than that you need a power adder.

 

[JohnX]

Not necessarily. If you throw on a bunch of external bolt-on mods, port the head and raise the CR slightly to improve efficiency, and chip tune to optimize the fuel/timing curves, you can have a factory stock reliable motor that puts out a lot more power than stock.
_________________________
1992 XJ Laredo - 4.6L Stroker - 5-speed manual
Dyno - 198hp@4650rpm, 254lbft@3550rpm (wheels) = 245hp@4800rpm, 306lbft@3550rpm (crank)
Performance - 0-60 = 6.2, 1/4 mile = [email protected] in full street trim
Sites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

While I know you have lots of experience and tons of knowledge on motors (4.0 or otherwise), I must disagree.

The way i see it, if stock make 200 ponies, each cylinder is making 35ish.
If a HiPo motor makes 300, then each cylinder is making 50ish.

So how can the same rings and bearings wear the same amount with different amounts of load on them?

It seems to me, that all other things being equal, more load on parts must equal more wear. Maybe not an proportional amount of wear to the extra load, but more none the less.

 

[5-90]

The 4.0 (or stroker) cannot safely be revved past 5600rpm because a cam harmonic at this point can break the timing chain or throw the distributor out of the block. Therefore NA with stock displacement, you're not going to get much more than 250hp (crank) out of it. If you build a 4.7 stroker, you could stretch it to ~280hp. To get more than that you need a power adder.

Interesting. As I understood it, the harmonic issue came around 6000-6500RPM - on either side of that range, you were fine. Within that range, and sustained operation could even snap a crankshaft, due to harmonics.

I may have to recheck that.

 

[JJacobs]

I saw 6400rpm for 2.5 minutes before two rods broke. Of course that was because the oil had just been drained. I didn't feel any undue vibrations before it let go, but it probably wasn't a valid test.

 

[BBeach]

I saw 6400rpm for 2.5 minutes before two rods broke. Of course that was because the oil had just been drained. I didn't feel any undue vibrations before it let go, but it probably wasn't a valid test.

No rev limiter??

 

[JJacobs]

Apparently not on a Renix.

 

[Flash]

Apparently not on a Renix.

That is a question i wouldn't mind haveing answered!!!!!!!

I have no tach in my Renix, and i have revved it pretty high and never hit the rev limiter.......Did the Renix system have a rev limiter or have i been chickening out to soon?

Flash.

 

[Dr. Dyno]

Interesting. As I understood it, the harmonic issue came around 6000-6500RPM - on either side of that range, you were fine. Within that range, and sustained operation could even snap a crankshaft, due to harmonics.

I may have to recheck that.

Yeah, it's the crank harmonic that comes in at around 6200-6500rpm. The cam harmonic comes in at ~5600rpm.

 

[Dr. Dyno]

While I know you have lots of experience and tons of knowledge on motors (4.0 or otherwise), I must disagree.

The way i see it, if stock make 200 ponies, each cylinder is making 35ish.
If a HiPo motor makes 300, then each cylinder is making 50ish.

So how can the same rings and bearings wear the same amount with different amounts of load on them?

It seems to me, that all other things being equal, more load on parts must equal more wear. Maybe not an proportional amount of wear to the extra load, but more none the less.

Good point. With the extra cylinder pressure that comes with the improved volumetric efficiency of the engine, the wear rate of the rod bearings and rings would be accelerated somewhat but I think we're only talking about a 300,000 mile engine lasting maybe 270,000 miles instead.
A stock 4.0 makes ~190hp, a full bolt-on 4.0 with ported head and stock cam will make ~235hp. The 300hp figure that you quoted is a pipe dream from a naturally-aspirated Jeep 4.0 unless you stroke it.

 

[89Daytona]

If only the magic wish genie would build a DOHC 4 valve, pent roof crossflow head.

If you want to put in the time you can design one and get it quoted using software available through EMachineShop

It would probably be easiest to move the intake to the passenger side (using the same bolt pattern so that the stock intake will fit) and leave the exhaust on the drivers side. The real question is how many people would want one and how much would they be willing to pay for it.

 

[j99xj]

It wouldn't be worth it to me. By the time I would want a DOHC 4.0 I would rather just swap a V8 and be done with it.

 

[Flash]

So did the Renix have a rev limiter or not?:dunno:


Flash.

 

[5-90]

Yeah, it's the crank harmonic that comes in at around 6200-6500rpm. The cam harmonic comes in at ~5600rpm.

Ah - thank you. I didn't know about the cam harmonic, but I suppose the idea does make some sense.

 

[Beej]

If only the magic wish genie would build a DOHC 4 valve, pent roof crossflow head.

He did, the only problem is, he built it for Nissan...

 

[MudDawg]

The DOHC head for a 4.0 would be a moot point because of the harmonic problem with the crank (unless there is a way around that) because the whole idea would be to allow the engine to rev to the 7-8K rpm range, therefore allowing much more hp.

But the 2.5 suffers from no such harmonic problem:cheers:

 

[89Daytona]

Can you get the cam/crank balanced to increase the rpm limit, and by how much if any?