What Breaks In A Boosted 4.0L?

[89Patches]

So I have been away from this forum for sometime now and I never finished my MJ because I wasn't happy with the direction it was heading and was bit by the DSM bug. I was going to make it a trail truck but I don't offroad so it didn't make sense for me, lol

 

So basically I want to make the ultimate towing Comanche :yes:  I always like the low end grunt of a 4.0L but in the upper rpm dear good is it slow. So how do you change that? A TURBO!! I have lots of exprience with turbo charged vehicles. So it's not make to the turbo work is what I don't get.

 

So the question is what breaks when a 4.0L is boosted on a stock SHORT BLOCK? Do the rods breaks, Pistons, Crank? I am guessing the rings would be the first thing to let go.

 

 

So I guess I better go over the plans for my truck.

 

Engine

 

- Refreshed Stock short block

- Ported cylinder head

- MLS head gasket

- ARP head studs

- ARP main studs

- ARP rod bolts

 

Turbo/Exhaust 

-GT3076R T3 housing.

-Full 3" exhaust/ 3" down pipe.

- Water to Air intercooler

 

And tuning will be done by a AEM unit 

 

And I already have the 97+ swap done with a 8.8 rear lsd axle and beefed up rear leafs And it will also be airbag'd in the back as well, Oh plus It with be just with a 3" inch lift... And want to run around 20 psi of boost 

 

So basically I am looking for 400+ ft-lbs of torque  . :MJ 1: .

 

And Yes I know what it takes to make horsepower :cheers:

 

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[ComancheKid45]

I have no knowledge to contribute, but I was having the turbo'd 4.0 conversation just this evening with a few friends and am also interested in the answers that will show themselves ;)

[Oyaji]

Will the stock drivetrain handle 400 lb-feet of torque? Does anyone here know  its torque limit? and what the weakest link in it is?

.

Keep in mind that the drivetrain torque limit will reduced by increasing tire size over stock, too...

.

Interesting project - please keep us updated. 

[johnj92131]

400 lb/ft at what rpm?  Turbos need to be relatively small to produce good low end performance that you want for towing.  Guessing you might want 15 lbs of boost at 1800 rpms to double stock torque and a stock cam for towing performance.  My gut tells me that the transmission will be the weak point out side the engine.  My gut also tells me that stock pistions are not up to the kind of boost it will take for 400 lb/ft at the lower end.  You are going to need to lower the compression (bigger dish in forged pistions?).

[mnkyboy]

Ultimate Towing and Comanche don't go together. It could have 1000 ft lbs of torque, it still won't do what a stock full size can do.

 

What would you tow with it?

[zagscrawler]

to be honest man I would love to see a high hp turbo manche but I can't see how it will make a good tow vehicle.  like Oyaji started to say the drivetrain would be so overworked I can't see how you would be able to make it practical.  I'm sure the Aw4 could handle the hp and torque but how to deal with all the added heat from the turbo and the pure cast iron motor would be way more then that puny little radiator ever dreamed of handling in a sustained situation. This package is capable of some serious abuse but its at bursts I'm sure, but planning a gas engine turbo tow rig will cost you some serious money, not just a few week links in the rotating assembly. IMO of coarse.  To put it into perspective... lots of us have overheating issues when simple mods like tire size and 4wd converts (improper gearing for instance), this drive train never quits when used within reason but kramming boost into these things, especially when towing sounds like dangerous ground.  Get bad @$$ LBZ or 7.3 ford if you want to have a specific tow vehicle.  (Ive got both and I suggest the LBZ lmao :D ) ohh crap did I say that....

[mnkyboy]

A boosted 4.0l isn't that uncommon so I don't think that will be much of a problem.

 

The issue is that no matter what you do to the engine an MJ is too small/light to make much of a tow rig.

[zagscrawler]

Not uncommon I'm sure, but boosted tow rig.. that's impressive.  Besides like you said monkey they are to light and don't have the stance for all around towing..  I'm sure some will disagree but ive towed with all types of rigs and my MJ just doesn't strike me as a candidate.  To be honest.. most anything can be done.  With the "to do list" for the truck I don't think its a great idea is all.. 

[reece146]

Go here and start reading/ researching:

 

http://www.naxja.org/forum/forumdisplay.php?f=68

[Tactical Bacon]

DSM? You poor bastard.

 

Getting back to the subject at hand, I'd be looking for a heavy duty water pump (maybe an electric?), power steering cooler, trans fluid cooler and an AW4, and a bigger radiator. A front air dam might help get air to all the cooling bits, if strategically installed.

[89Patches]

A 2500 to 3000 lbs car with a aluminum car hauler. That's probably the most weight it would haul to be honest. But I want to do it with ease..

 

And as for the drive train that's what I did when the plan was just the 97+ swap, So it wouldn't be staying that way. It will be going back to a standard.

I know what it will take for the rest of the truck to make able to tow, It's just the limits of the motor I don't know.

 

Don't get me wrong this isn't 100% set in stone, Just something I want to eventually do. 

[mvusse]

A guy local to me wheels a TJ with a supercharged 4.0. Don't know how much boost he runs, but it's still in one piece.

 

When he gets into the skinny pedal you can hear the whine about a quarter mile away.

[Alexia]

Forged pistons are a good idea. The stock crankshaft and connecting rods are rather strong up to around 400 horsepower. One of the main issues with forced induction is blowing out the head gaskets. Stock replacements, based on a few engines, appear to fail around 12 PSI.

 

http://www.jeepstrokers.com/forum/viewtopic.php?f=15&t=3517

[reece146]

Sounds like we are building the same Jeep for the same purpose. I am building a MJ to tow a track car and have a slide in tent trailer kind of thing for over-nighters. It says it's rated for 5000 lbs so that's what I'm staying under.

 

Brakes!

 

Weight distributing hitch

 

Anti-sway

 

Should be fine if you are patient on the up hills.

 

Btw, have you registered your truck yet? Do you have a blue or black plate? In theory even with black plate we should be exempt from annual inspections (yellow sticker) because truck plus fully loaded trailer falls under 4500 kg. But...

[89Patches]

Forged pistons are a good idea. The stock crankshaft and connecting rods are rather strong up to around 400 horsepower. One of the main issues with forced induction is blowing out the head gaskets. Stock replacements, based on a few engines, appear to fail around 12 PSI.

 

http://www.jeepstrokers.com/forum/viewtopic.php?f=15&t=3517

Thanks that's Something I was looking for! So basically the only thing the bottom end should need is pistons to handle the more realistic 10 to 15psi of boost. 

 

Sounds like we are building the same Jeep for the same purpose. I am building a MJ to tow a track car and have a slide in tent trailer kind of thing for over-nighters. It says it's rated for 5000 lbs so that's what I'm staying under.

 

Brakes!

 

Weight distributing hitch

 

Anti-sway

 

Should be fine if you are patient on the up hills.

 

Btw, have you registered your truck yet? Do you have a blue or black plate? In theory even with black plate we should be exempt from annual inspections (yellow sticker) because truck plus fully loaded trailer falls under 4500 kg. But...

Brake's = something that fits inside a 16" rim.

Truck also retained the 8.8 factory rear sway bar and WJ front.

Hitch is being welded to the frame.

 

As for the stickers I believe they are the black plates, That's on my brothers Comanche, I do not have mine plated.....

[reece146]

I have WJ brakes on the front and vented Suzuki J2 front brakes on the rear axle on my XJ... towing my Starcarft 11RT fully loaded it has no issues braking on the downhills from Maniwaki, Quebec. I'd guess the towed weight is around 3500 lbs and no trailer brakes (I'm lazy).

 

I'm running 16" wheels also to clear the WJ brakes, 265/75-16 Duratracs.

[mvusse]

Please tell you the hitch will be bolted to the frame as well? Even though the bed is body on frame, it is still a unibody style frame made from layers of sheetmetal stacked on top of each other. If you just weld the hitch to the frame, it will just rip the outermost layer off. It needs to be bolted, preferably with a nut strip inside the frame, to distribute the load.

 

There is a reason our track bar brackets are bolted on, unlike the Wranglers where they (I believe) are welded on.

[johnj92131]

Aa long as you are in the block you should think hard about a stroker. Virtually no xtra cost for you and more low end for towing.

I am sure you will have a weight distribuitng hitch and at least a D44 for wider drum brakes.

[89Patches]

Aa long as you are in the block you should think hard about a stroker. Virtually no xtra cost for you and more low end for towing.

I am sure you will have a weight distribuitng hitch and at least a D44 for wider drum brakes.

I have thought about building a stroker. Depends on the cost difference. I have built plenty of engines from all sorts of cars as I am a machinist, But have never done a 4L so I really don't know about availability of parts. 

 

And if I were going to build a forged engine I would probably want 500hp :doh:  As I am a very power hungry person So keeping It Somewhat stock will limit me and save money for other modifications that I want to do in other area of the truck, So I can have a better overall truck not just a POS with a 5k engine. :banana:

[johnj92131]

Extra cost for a stroker should be near zero.  Crank is stock from an AMC/Jeep 258 engine.  You will likely buy forged pistons anyway.  Might have to machine the crank nose - but you are a machinist, so no cost.

If you want 500 hp - just turn up the boost!!

 

Seriously, towing 5000 lbs with a Comanche is one thing - Stopping the Comanche/trailer is WAY more important.  But YOU know this - not sure about others who may read this in 6 months.

 

 

Aa long as you are in the block you should think hard about a stroker. Virtually no xtra cost for you and more low end for towing.
I am sure you will have a weight distribuitng hitch and at least a D44 for wider drum brakes.

I have thought about building a stroker. Depends on the cost difference. I have built plenty of engines from all sorts of cars as I am a machinist, But have never done a 4L so I really don't know about availability of parts. 

 

And if I were going to build a forged engine I would probably want 500hp :doh:  As I am a very power hungry person So keeping It Somewhat stock will limit me and save money for other modifications that I want to do in other area of the truck, So I can have a better overall truck not just a POS with a 5k engine. :banana:

 

 

[ftpiercecracker1]

Everything you ever wanted to know about either stroking and/or boosting a 4.0 can be found/learned over on jeepstrokers.com     I am still a member but havent been on in ages since my dreams of building a stroker for myself were dashed.   :cry:  I still have every single bit and piece needed to build one i just lack the funds for the machining. 

 

Everybody has been spot on so far. Making the power isnt the issue its stopping the load. Whatever you plan on pulling make sure its got a good set of trailer brakes.  :thumbsup:

[89Patches]

As for the brakes I am thinking of stock R32 GTR 4 pots up front, As they fit under 16" rims. And for the rear probably just stock 8.8 disc brakes. 

 

I already have a car hauler, which was built to the max width that's legal in Canada and the MTO doesn't like that and I get harassed for it if they see it. And it's steel and weighs in at around 2000lbs not loaded, :rotfl2:  So I am planning to sell it and buy a brand new aluminum open car hauler that's half the weight and a bit smaller in size.

[mvusse]

This is the blown 4.0.

 

https://www.facebook.com/photo.php?v=10151956418415991&set=vb.747280990&type=2&theater

[zagscrawler]

The stopping power of the four pistons is going to be nice and all but I would think of the rest of the stress placed on all the other components in the front end.  I can't help but think of the four link and not sure I ever seen such load applied with that kind of front end.  all the tow rigs ive seen (real tow rigs) are leaf sprung or independent, I'm thinking its for a reason I can only imagine the stress put on the trackbar and the links stopping a load of that size time and time again.  I get what your trying to do, but if your serious about making a manche a serious tow rig ditch all the ideas of large improvements in small areas and look at it from a larger safer scale.  If I were to do it and I am purely speculating here with an unlimited budget of coarse.   First full size axles and all the goodies that come with it, leaf spring front end, major frame stiffening add ons, air bags in rear, hydro brakes, high sprung (heavy) suspension all around for sure, tightened up trans with major aftermarket coolers and built to the hilt long block(w/major rod journal oiling mods) boosted just enough to tow my shyte...putting a cooling system in that is still up in the air if you don't want to mount something extra in the bed with aux fans.   It sounds like you know the ins and outs of performance parts but they don't have a kit to make the mj into a pulling power house.  think of it like this   Its been done before many many times and who knows maybe they started out with something even less substantial than a compact truck but the end result is sitting next to you at the stoplight. A fullsize truck overbuilt not for the soccer mom but intended for towing a fellow auto behind it with no foreseen issues. Just try to think of everything you need to make it happen not what you can get away with is all.  Edge of your seat is for racers its why they get to have all the fun. towing in a real life situation is not a sport, its a responsibility to everyone around you. When I tow and I tow a lot I never worry about my rig, I worry about everything else around me and what to do if they make me nervous..  I mean no offence but build the baddest tow manche we have seen yet that would be @#$%in sweet.

[Oyaji]

5th wheel on a long bed Metric Ton package maybe? Longer wheelbase would make for a more stable towing platform, and the 5th wheel  hitch would distribute  load weight better.