Hi folks, first time post here. In reading through this forum it looks to have enormous amounts of highly smart engine people, compared to the other jeep forums. (not just "stroking" you guys, really looks that way!)
My 4.0 #5 piston skirt did itself in and its time to rebuild or replace. (from my 99 grand cherokee)
I'm hoping you can help, I've got a couple questions.
I'm considering purchasing a long block from Promar Precision Engines from the east coast. I've looked at their website and ebay feedback.
They rank 100% positive on ebay & at looking through their engine handling/machining process they look to be doing everything right & using all the good top shelf components in their rebuilds. From the looks of it, I dont think I can get it done any cheaper if I did all this myself and paid for the same machining. And they have a 3year unlimited mileage warranty to boot.
(here's their ebay link detailing their mfg. process's)
http://www.ebay.com/itm/390071641342?ru ... 26_rdc%3D1
Anybody here ever use these folks? I know most of you guys & gals likely do your own rebuilds, but I'm hoping for some feedback on these folks.
Question #2: Earler this week I was reading a thread on this forum (today I cant find it) that discussed the issue with 4.0 heads cracking.
If I go with a rebuild I have the option to request which head is used. I no doubt want the one that is not prone to cracking.
Can anyone please direct me to the information that will show me how to tell the correct head to be purchasing. In the rocker area of the head I took off my 99 grand cherokee has "WJ" cast into it, along with NHI & the numbers I999 or 1998 (year made?)
Looking to purchase a 4.0 rebuild from Promar Precision Eng.
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Steve
- Posts: 1
- Joined: March 8th, 2013, 9:34 am
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Desertjr
- BANNED
- Posts: 159
- Joined: December 31st, 2012, 2:12 am
- Vehicle Year: 1990
- Vehicle Make: Jeep
- Vehicle Model: Cherokee
Re: Looking to purchase a 4.0 rebuild from Promar Precision
early 0331 ones crack. There's also a 0331 that's stamped "Tupy", I think it was 2002+. Those are the latter cast and seem to not crack..at least not that I've seen. Alabama cylinder head offers 1 as well as clear water I think? They also seem to be the most desirable from what I've read. Higher exhaust ports or something, thus are best for porting, or more potential? I know the 7120 is the most commonly used and is what I have, that was ported.
Never heard of the company, but some questions to ask yourself. Looking for a stock 4.0? Well then why not up to a 4.1/4.2 pending bore size? Uses a slightly bigger crank that gives a zero deck..thus better quench...thus better efficiency..thus more power and mileage and emissions for almost nothing more!
Off the self "replacement" pistons have a .008-.02x LOWER pin height than stock 4.0, pending the piston that's used. So this puts the piston even further in the hole...thus less quench, worse everything I stated above. The 3.8l crank has a .090 bigger stroker. Stock 4.0l pistons are approximately .025 below deck already. Add in the extra from the lower pin height replacement pistons and your now anywhere from .035-.05 below deck.
Now the cranks .090 bigger stroke. You take half that number (kind like how 31" vs 33" tires only gives you 1" extra diff clearance)..anyway that numbers .045. That's basically how far the pistons in the whole so you end up with a deck height at or just below zero deck with no added machine cost. Polishing a 4.0 crank, new bearings, and decking the block if you wanted it to be zero deck would cost more than a 3.8l crack with bearings...so its kind of pointless to not do it when you think that way. You can get the crank with bearings for clegg engine for around 275-ish I think.
Also I would request the cam be installed 4* advanced. There's a running thread with graphs showing the differences in my personal spec 4.2l stroker. It's roughly 20-30ft lbs more from 2000-3500.. Estimated at 310ft lbs...on 87 octane. Would effect nothing else as long as compression is kept close to stock, would just have more balls (more useable power) all around in a close to stock 4.0 or 4.2l. Free horsepower if you will
In a bigger stroker the gains aren't as drastic because its in a bigger motor.
Also being online things can't be taken back to have it adjusted or fixed to your demands...a local shop "could" be cheaper, easier, less hassle. And again to your spec, you see things getting done ect. That was a big key for me. I chose my smaller motor (much wilder 4.2l) to my specs vs a golden 4.6l because I wanted to be a part of it and wanted to see it take shape.
And also question to ask the company is what's the final deck height..do they zero deck it? What pistons are used? What dish is the pistons at..this could bump compressions a little but(good thing) or could lower it below stock(undesirable). ALOT goes into it..personally a 4.2l bottom end can be done with all stock parts, off the shelf pistons and the key parts the crank. 1200 bucks maybe? The cam being advanced to 4* is free power in our smaller motors so its a given, and a must do I'd say for any stock or close to stock 4.0.
Cleaning up a head with paper rolls in your garage is free and easy. Removing roughness and the casting flaws helps out and is nothing but a few hours and wouldn't hurt you or be to big of a job at all. I did my head and all I did was clean things up, polishing exhaust runners with 320 grit flap wheels, intake done at 80 grit. The intake bowls done at 200 grit. Rougher intake causes slight turbulence, thus better atomization of fuel and air. I did 80 to get better atomization..most do 120, I only had 80 grit rolls so I did 80. I did 200 at the bowls to try and help speed up the flow. maybe make it a bit easier to cause the "vaccum effect" at lower valve lift and to help avoid carbon build up right there.
Never heard of the company, but some questions to ask yourself. Looking for a stock 4.0? Well then why not up to a 4.1/4.2 pending bore size? Uses a slightly bigger crank that gives a zero deck..thus better quench...thus better efficiency..thus more power and mileage and emissions for almost nothing more!
Off the self "replacement" pistons have a .008-.02x LOWER pin height than stock 4.0, pending the piston that's used. So this puts the piston even further in the hole...thus less quench, worse everything I stated above. The 3.8l crank has a .090 bigger stroker. Stock 4.0l pistons are approximately .025 below deck already. Add in the extra from the lower pin height replacement pistons and your now anywhere from .035-.05 below deck.
Now the cranks .090 bigger stroke. You take half that number (kind like how 31" vs 33" tires only gives you 1" extra diff clearance)..anyway that numbers .045. That's basically how far the pistons in the whole so you end up with a deck height at or just below zero deck with no added machine cost. Polishing a 4.0 crank, new bearings, and decking the block if you wanted it to be zero deck would cost more than a 3.8l crack with bearings...so its kind of pointless to not do it when you think that way. You can get the crank with bearings for clegg engine for around 275-ish I think.
Also I would request the cam be installed 4* advanced. There's a running thread with graphs showing the differences in my personal spec 4.2l stroker. It's roughly 20-30ft lbs more from 2000-3500.. Estimated at 310ft lbs...on 87 octane. Would effect nothing else as long as compression is kept close to stock, would just have more balls (more useable power) all around in a close to stock 4.0 or 4.2l. Free horsepower if you will
In a bigger stroker the gains aren't as drastic because its in a bigger motor.Also being online things can't be taken back to have it adjusted or fixed to your demands...a local shop "could" be cheaper, easier, less hassle. And again to your spec, you see things getting done ect. That was a big key for me. I chose my smaller motor (much wilder 4.2l) to my specs vs a golden 4.6l because I wanted to be a part of it and wanted to see it take shape.
And also question to ask the company is what's the final deck height..do they zero deck it? What pistons are used? What dish is the pistons at..this could bump compressions a little but(good thing) or could lower it below stock(undesirable). ALOT goes into it..personally a 4.2l bottom end can be done with all stock parts, off the shelf pistons and the key parts the crank. 1200 bucks maybe? The cam being advanced to 4* is free power in our smaller motors so its a given, and a must do I'd say for any stock or close to stock 4.0.
Cleaning up a head with paper rolls in your garage is free and easy. Removing roughness and the casting flaws helps out and is nothing but a few hours and wouldn't hurt you or be to big of a job at all. I did my head and all I did was clean things up, polishing exhaust runners with 320 grit flap wheels, intake done at 80 grit. The intake bowls done at 200 grit. Rougher intake causes slight turbulence, thus better atomization of fuel and air. I did 80 to get better atomization..most do 120, I only had 80 grit rolls so I did 80. I did 200 at the bowls to try and help speed up the flow. maybe make it a bit easier to cause the "vaccum effect" at lower valve lift and to help avoid carbon build up right there.
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