Am i asking too much of my 4.0? lack of power

[cal]

Indeed, I didn't even notice the RPM comment.

We hold our motor at 4000+ RPM's for hours at a time without thinking about it. Sometimes we'll go a half hour being over 5K more often than not.

 

[Hoooper]

Doesn't sound sketchy at all, sound about right for it, remember this vehicle came with 28" tires and 3.55 gears.. Hell you got it better that your higher speed at 4500rpm than the stock does
This is where it's Rpms and speed is for the factory size

your chart is wrong. stock tires and gearing dont turn 4500 RPM at just over 50 mph. I think you might have done 4.56s on 28" tire. Stock 3.55 and 28" tire would be turning about 1600 RPM with an AW4 at that speed, not 4500. Hell, even in second gear it would only turn 3300 RPM at 51 MPH.

We hold our motor at 4000+ RPM's for hours at a time without thinking about it. Sometimes we'll go a half hour being over 5K more often than not.

it just doesnt sit right with me that an engine that clearly doesnt like being spun up that high is run at that RPM for several minutes in a row. Ive never seen an engine protest high RPMs as much as this thing does. Maybe im just paranoid because im used to engines with way different balance and performance. Even the turbodiesel in my car redlines higher than the 4.0 :laugh:

 

[cal]

well, i'd agree with you Hooper, but we'd both be wrong.

The 4.0 doesnt protest RPM's at all. *YOURS* may, could be high miles and lack of oil changes has lead to a loose valvetrain.

 

[Hoooper]

well, i'd agree with you Hooper, but we'd both be wrong.

The 4.0 doesnt protest RPM's at all. *YOURS* may, could be high miles and lack of oil changes has lead to a loose valvetrain.

its not that its loose, vibey, or shakey, its that even that high it just doesnt make any more power doesnt seem like. Might be because of the whole 190hp peak thing though. Im a speed guy so when I say it doesnt like it, what I mean is that it couldnt go 80 MPH up that hill even if I asked it nicely and whispered sweet nothings into its ear. The engine actually runs great and drives fine, just not enough powah!

 

[cal]

So what you're saying is your jeep cam is doing what its supposed to, and putting out maximum torque at a usable range.

So you call that protesting high RPM's?

I invite you to come out wheeling with us for a weekend. See if you feel the same way after driving a jeep 6 with a better cam and head

 

[Demonoid369]

your chart is wrong. stock tires and gearing dont turn 4500 RPM at just over 50 mph. I think you might have done 4.56s on 28" tire. Stock 3.55 and 28" tire would be turning about 1600 RPM with an AW4 at that speed, not 4500. Hell, even in second gear it would only turn 3300 RPM at 51 MPH.:

Actually you're wrong, use the calculator yourself and you'll get the same answer as me.
Plus dont you think if I had typed in 4.56(which you say you have yourself) wouldn't the Rpms be MUCH MUCH higher than yours on 33" and 4.56 gears........ Just saying

There is a reason why so many threads state that 4.56 and 33" are close to be the same as stock gearing and tires...

 

[chedisme]

That 50mph at 4500rpm is with the t case in low.

 

[XJLI]

Lol

 

[X E Ryder]

Re: Mill head, port clean up

Speaking as one who is relatively ignorant about this straight six, but has several decades of experience playing with big block Chevys, is there not an option for some head work and a cam?................

This was a question I have been wondering about as well - for those who have built a few of the 4.0 I6's - how much can you mill a (stock) head and be good to go with no higher than 91 octane? How about some light port work?

I only run 91 anyway - I would not mind milling the head, freshening up the top end while it was off. That has historically made a great difference.

And while in there can you knock the pistons out the top and do a hone/ring/rod bearing job?

 

[Demonoid369]

That 50mph at 4500rpm is with the t case in low.

Hahaha just realized that. I hate trying to read tint screens lol

Side note, I'm surprised 4lo can go that fast lol

 

[old_man]

Re: Mill head, port clean up

This was a question I have been wondering about as well - for those who have built a few of the 4.0 I6's - how much can you mill a (stock) head and be good to go with no higher than 91 octane? How about some light port work?

I only run 91 anyway - I would not mind milling the head, freshening up the top end while it was off. That has historically made a great difference.

And while in there can you knock the pistons out the top and do a hone/ring/rod bearing job?

Milling the head does not adjust the quench height, it only raises the compression and only make things worse. You mill the block.

 

[BENZOMATIC]

Quick thought for the OP...

Has it always driven like that on the highway or has power been slowly dropping over time?

You just took her for a swim in a mud hole, maybe you got some mud/trash in your exhaust and are plugging up your catalytic converter or muffler.

Plugged exhaust will behave just like you are describing.

Drop your exhaust after the 02 sensor and run it open pipe for a few miles to see if you gain any significant power.

 

[Digger87xj]

restricted exhaust?

 

[Hoooper]

Actually you're wrong, use the calculator yourself and you'll get the same answer as me.
Plus dont you think if I had typed in 4.56(which you say you have yourself) wouldn't the Rpms be MUCH MUCH higher than yours on 33" and 4.56 gears........ Just saying

you would have realized something was up with your calculator if you had just though about that. When the jeep was stock, did it hit redline in 4th gear before 70 MPH?

 

[cheapcherokee93]

4.56

i took my XJ cross country, almost the same setup as your MJ... 3" lift, 33x10.5s, lots of weight, etc. i had every bolt on... cowl intake, 62mm TB, 99 intake, header, hi flow cat, dynomax muffler, had almost 200k miles on it when i got home. only when i was up in the mountains in colorado did i want more power. i think you'd benefit from a shift kit in the aw4 to firm up shifts and loose some slush going from gear to gear.

pic bc i love this shot..

wow, that is super close to what im running, right down to the Ecco Wheels. i think i'll go 4.88 though since you pretty much cant go wheeling in SoCal without going over some sort of steep grade (probably not 100% accurate but where i wheel its true). gotta spin dat 4 liter up to get anywhere

Quick thought for the OP...

Has it always driven like that on the highway or has power been slowly dropping over time?

You just took her for a swim in a mud hole, maybe you got some mud/trash in your exhaust and are plugging up your catalytic converter or muffler.

Plugged exhaust will behave just like you are describing.

Drop your exhaust after the 02 sensor and run it open pipe for a few miles to see if you gain any significant power.

it hasnt always been that sluggish, but that was also the first time i've ever had that much of a load in it over any significant distance. Used to be able to pull up the Cajon Pass in 3rd the whole way up, but with the added weight and tent i can sorta understand needing 2nd. I've also had this same lift/gear/axle setup since i was running 235/75s, so ive been feeling it get slower each time i moved up a tire size.


the mud hole turned out to be mostly dirty water, when i got it running for the first time it spewed water out the exhaust and that was it. its possible something murky got plugged up on there so i think i'll heed your advice anyways and yank out the cat or something.

restricted exhaust?

I'll be looking into this next.

 

[XJLI]

wow, that is super close to what im running, right down to the Ecco Wheels. i think i'll go 4.88 though since you pretty much cant go wheeling in SoCal without going over some sort of steep grade (probably not 100% accurate but where i wheel its true). gotta spin dat 4 liter up to get

I do recall some giant climb on I8 or I10 (it looked like we were in the hammers... All white rocky desert) and the speed limit was 45 and I couldn't even get up to 35. There were even water stations for people who overheated.

 

[Demonoid369]

you would have realized something was up with your calculator if you had just though about that. When the jeep was stock, did it hit redline in 4th gear before 70 MPH?

Nope mine wasn't stock with stock tires so I wouldn't have known lol

 

[sandsgg]

What app is this?

 

[XJLI]

It's a website

 

[cal]

http://www.grimmjeeper.com/gears.html