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Stroke it? Blow it?

Stroke it or blow it

  • Total voters
    265
M

Matt S.

NAXJA Forum User
Location
Fresno, CA
To help future searches and not destroy my other thread....

Which would be more EFFECTIVE in the long run. Considering dependability, price, longevity, repair, etc..

MATT
 
Although personally I would have more fun with a blower (I have honest to God dreams about Kenne Bell's kit), you want to stroke it. You say dependability, price, longetivity, and repair, and the stroker wins hands down in all of these. Don't forget that with a stroker kit you ar pretty much rebuilding the engine anyway, giving it whole new life. Also, a good stroker will prolly run about 1 to 2 g's less moola than a good supercharger kit. If you listed horsies as your main concern, i say blower. But with what youre looking for, the obvious choice is a nice stroker kit. And if you do decide to stroke it, get all the best parts in the process, it will probably save you trouble in the long run. Best of luck!
 
Stroker all the way. If you still want more HP/TQ after you've done the stroker, you can add on a supercharger. If you do that though, be prepared to spend mucho $$$ beefing up the tranny, drivetrain, suspension, brakes. You could easily end up spending $10k doing a supercharged stroker with all the trimmings.
 
The supercharger has the potential to add the most performance...However if you install a blower system that is tuned to produce a LOT more horsepower with no other mods to the engine, the long term durability will go down the tubes...

For reliability under high boost,mechanically speaking you need better pistons, better rods, and improved head gasket seal...these issues can be addressed during the stroker build...keep the overbore to a minimum if you think you may add the blower later...if you have core-shift in the block, you could possibly end up with a thin cylinder wall...the actual wall thickness can be sonic tested to determine existing thickness...have the core crank reworked by someone that specializes in high performance...Eagle Performance builds steel connecting rods that cost about the same money as a complete rework of the stock 4.2 cast rods... also consider cylinder head modification, including porting and better valves...
 
Ok, so here are some better thoughts on this issue.

I am thinking that a SIMPLE yet quality build stroker will be great to start out as. Throw the 4.2 crank in, replace pistons, rings, rods, and everything else that goes with it. I KNOW that the block I am most likly going to be using, does not need any type of work to it. Why do you say that the charger could add 10k onto project price?? I guess I could see that if this was to be put into a DD or already existing XJ. But, in my other post, I think it is pretty clear that the weakest part of the drive train will be tha drivelines! :laugh3:

Is there another tranny that will bolt behind the 4.0 without an adapter that can hold large amounts of power?

MATT
 
Jeep/AMC used GM TH400 units in early Waggy's behind the 304 and 401 V8's.
Also the Chrysler 727 was used in some applications. My 2 cents would be to find a TH400....it is a 3 speed but properly built is one tuff tranny.
 
Ha, that is one tranny I won't even consider to put in. But, I had a revelation last night from my room mate that I took seriously. Put a NV4500 behind it, URF believes in it. So do many others. I just dont know how to wheel with stick, and I have always said auto is better. :eyes: Can that tranny hold that power?

MATT
 
The NV4500 is rated to 410lbft of torque so it'll handle a supercharged stroker. It's very much a truck gearbox with widely spaced ratios and a very short (numerically high ratio) 1st gear that's good for crawling.
It's much bigger and a damn sight heavier than the AW4 so you might have to "massage" the transmission tunnel with a big hammer to create enough clearance for it.
 
I don't have a buttload of knowledge on transmissions, but i'll chime in in the name of being corrected by someone smarter. I would keep the AW4, it's very similar to the tranny in turbo supras and can be built to handle crazy power. I don't know exactly who does it, someone on here will, but there is a shop that has a kit that'll build one of those puppies to support like 900hp (Or lb-ft of torque, if you wanna be picky). That'll prolly actually end up being cheaper than adapting even a cheap older tranny, while keeping the AW4's behaviour, weight, and size. Lata.
 
I think I'm the minority on this one but I'm for maintaining stock bore/stroke and go for high RPM horsepower (maybe just bore .060" over). Make it breathe and use short gears (like 4.11's on stock OD tires).

Correct me if I'm wrong but I believe the '96+ uses lightweight pistons, rods and a different (lighter) crank shaft. My friend just got a '97 and I was amazed how easy it was to run right up to the 5250 rev limiter. With an ASE chip (increasing the rev limiter) a serious cam, head work, headers and the rest, It could pull strong right up to 6000 rpm (or beyond) with the stock crank.

One thing a lot of people forget is the XJ is fairly light and the 4.0 is already torquey. Tall gears makes the acceleration "heavy" therefore requiring more torque. Instead run shorter gears and take advantage of the HP potential.

___________________________________
Now dead '91 XJ (donor vehicle) --> Mods
Coming soon '97 XJ, I-6, 5-speed, 4WD
JeepSpeed East / SCCA RallyCross
The race course
 
Well i got some GREAT news. I am taking an AUTOMATIC specialty calss right now, and the first thing I asked the instructor, was about this. He said that the chrysler 727 came behind the 4.0s and can handle HUGE power with under 800 bucks. he runs one in his 8 sec drag car with a rat motor. So...... he said to try to find a 519??? or a 727. I guess the 519 or 518 whatever it is, has a few beffier parts that would lower the cost in the long run. I REALLY REALLY would like to keep an auto, basically cuz this is ganna be trail only. Highway is the only street it will see.

This is where i am at as of now.
1. Stroke motor and build it as if I were going to charge it.
2. Build a auto tranny to handle it, bump MLP WAY up, with manual valve body and pump.
3. Hopefully try to do this a cheap as possible.

My drivetrain is important to me. If it keeps me out of JV for another two years, I am ok with that. as long as when it is done, I am 110% sure in my rig.


Am I right in any of my thinking?

MATT
 
kreature said:
I think I'm the minority on this one but I'm for maintaining stock bore/stroke and go for high RPM horsepower (maybe just bore .060" over). Make it breathe and use short gears (like 4.11's on stock OD tires).

Correct me if I'm wrong but I believe the '96+ uses lightweight pistons, rods and a different (lighter) crank shaft. My friend just got a '97 and I was amazed how easy it was to run right up to the 5250 rev limiter. With an ASE chip (increasing the rev limiter) a serious cam, head work, headers and the rest, It could pull strong right up to 6000 rpm (or beyond) with the stock crank.

One thing a lot of people forget is the XJ is fairly light and the 4.0 is already torquey. Tall gears makes the acceleration "heavy" therefore requiring more torque. Instead run shorter gears and take advantage of the HP potential.

___________________________________
Now dead '91 XJ (donor vehicle) --> Mods
Coming soon '97 XJ, I-6, 5-speed, 4WD
JeepSpeed East / SCCA RallyCross
The race course
Click to expand...

Your argument does make a lot of sense and I've thought about doing that myself instead of building a stroker.
The stock valvetrain can't handle 6000rpm though so the minimum you'd need is a performance cam like the Crane 753901 with lifters, springs (Crane springs are rated to 6500rpm), and retainers. The stock timing gear and oil pump are also marginal at 6000rpm so a Cloyes dual roller timing set would be a good idea. A higher tension oil spring could be put in the pump to increase the oil pressure a bit.
The '96 and later 4.0's had lighter weight cast aluminium pistons installed but the rods and crank are the same on all 4.0's. The stock crank is OK up to 6200rpm before second order harmonics become an issue. A balanced bottom end would improve smoothness and improve the engine's tolerance of higher rpm.
 
Dr. Dyno said:
Your argument does make a lot of sense and I've thought about doing that myself instead of building a stroker.
The stock valvetrain can't handle 6000rpm though so the minimum you'd need is a performance cam like the Crane 753901 with lifters, springs (Crane springs are rated to 6500rpm), and retainers. The stock timing gear and oil pump are also marginal at 6000rpm so a Cloyes dual roller timing set would be a good idea. A higher tension oil spring could be put in the pump to increase the oil pressure a bit.
The '96 and later 4.0's had lighter weight cast aluminium pistons installed but the rods and crank are the same on all 4.0's. The stock crank is OK up to 6200rpm before second order harmonics become an issue. A balanced bottom end would improve smoothness and improve the engine's tolerance of higher rpm.
Click to expand...

Could you expand on "second order harmonics". What it is, what causes it, how to prevent...
Thanks
 
kreature said:
Could you expand on "second order harmonics". What it is, what causes it, how to prevent...
Thanks
Click to expand...

In a nutshell, these are the torsional vibrations of the crank that are produced by the firing of the cylinders. Second order harmonics are vibrations that occur twice per crank revolution and occur in four cylinder engines. Third order harmonics are vibrations that occur three times per crank revolution and occur in six cylinder engines. In both cases, the vibrations are produced by reciprocating forces in the engine.
Balancing the reciprocating assembly (crank with counterweights, rods, rod caps, rod bolts, pistons, pins) together with the use of a good quality harmonic balancer will reduce torsional vibration of the crank and prevent it from oscillating excessively (and possibly breaking) at certain rpm. This will improve engine smoothness and prolong engine life.
 
Last edited:
kreature said:
I think I'm the minority on this one but I'm for maintaining stock bore/stroke and go for high RPM horsepower (maybe just bore .060" over). Make it breathe and use short gears (like 4.11's on stock OD tires).

Correct me if I'm wrong but I believe the '96+ uses lightweight pistons, rods and a different (lighter) crank shaft. My friend just got a '97 and I was amazed how easy it was to run right up to the 5250 rev limiter. With an ASE chip (increasing the rev limiter) a serious cam, head work, headers and the rest, It could pull strong right up to 6000 rpm (or beyond) with the stock crank.
Click to expand...
I've considered this for my street mj when I do it and another option for this is a crank out of a 199cid they are forged and are pretty stong. they can take 30lbs of boost and make over 600hp and hold up very well witch i don't think the 4.0 crank will do but i does bring you down to i belive 3.5L witch is fine form since that means i can pound it with boost and maybe a NOS.
 
JeepSpeed said:
I don't have a buttload of knowledge on transmissions, but i'll chime in in the name of being corrected by someone smarter. I would keep the AW4, it's very similar to the tranny in turbo supras and can be built to handle crazy power. I don't know exactly who does it, someone on here will, but there is a shop that has a kit that'll build one of those puppies to support like 900hp (Or lb-ft of torque, if you wanna be picky). That'll prolly actually end up being cheaper than adapting even a cheap older tranny, while keeping the AW4's behaviour, weight, and size. Lata.
Click to expand...

www.levelten.com
 
Scrappy said:
He said that the chrysler 727 came behind the 4.0s and can handle HUGE power with under 800 bucks. he runs one in his 8 sec drag car with a rat motor.
MATT
Click to expand...

He runs a 727 behind a big block Chevy?
 
REDXJ4FUN said:
I've considered this for my street mj when I do it and another option for this is a crank out of a 199cid they are forged and are pretty stong. they can take 30lbs of boost and make over 600hp and hold up very well witch i don't think the 4.0 crank will do but i does bring you down to i belive 3.5L witch is fine form since that means i can pound it with boost and maybe a NOS.
Click to expand...

With a .030 over the 199cid crank would bring displacement to 3.6L. On the desktop dyno it makes 226hp@5500 and 257ft/lbs@4000 with the normal performance mods and a port and polish. Thats NA at 8.50:1 CR. That motor would have serious potential when you give it some boost. Iv'e been wanting to build a high reving 4.0L for a while, and this idea is growing on me. What rods and pistons would you use with this? Would 4.0 rods and pistons give you enough height?
 
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