4.0 rebuild question

98zjstroker

98zjstroker

Well-Known Member
Joined
Oct 14, 2009
Location
concord nc
So Its finally time to rebuild the 4.0 in my zj. Already started tearing it down. I had a couple questions I needed help with. Was originally thinking about doing a stroker but for longevity and price I decided against it.

first- Camshaft upgrade is a must. The problem is everything I keep finding wont work. Mostly looked on summit and jegs. Most everything I found said doesn't work with fuel injection even though I clearly typed in my vehicle and that is what it pulled up. I did look on 505 performance. They are a little expensive for the stage 2 and 3 cam kits but does come with everything. Does anyone have any experience with them or other recommendations?

second- fuel injector upgrade will also be needed. So I found 4 hole and 12 hole injectors that say they will work for my 4.0zj. I know that the 4 hole is better for atomization compared to the stock 1 hole. With that theoretically the 12 hole should be better then the four hole, but is this really true? ksuspensionfab.com has a 12 hole injectors for a good price. Any opinions on 12 over 4?

And third- any ideas on bottom end parts like new pistons (brand, bore, compression)? And does anyone know what the stock compression is on the 98 4.0?

Thanks
 
505 performance, specifically Zach the owner. is a douche bag that will sell you shit parts for big coin. Then wont stand by said parts.. Stay away as far as you can.

A big cam may hurt you more then help, unless you are changing the displacement. A stroker will last as long as any other engine as long as you keep it well maintained.

contact Russ Bishop-Buehl Racing Engines a very nice, well rounded in the stroker engine building dept. Sells quality parts and will make sure the parts you buy will fit. Will even work directly with your machinist if you wish.
 
Russ at Bishop Buehl.

IIRC, the Comp 231-4 is the biggest you can run without changing springs and retainers. That adds about $250 in cost if you go to the 235-4.

Stock static compression ratio is 8.8:1. I'd have to do the math on dynamic.
 
Not sure about other brands comparing to this, but I have a crane 753905 in my stroker. Can look at duration at .050” to easily compare other brand cams to this cam card. Heavily ported head. Can’t remember which injectors I have, whether mustang or dodge v8. No other computer mods other than vacuum line pulled off the fpr to get 46 psi IIRC. Factory yj intank pump with remove corvette tpi filter that doesn’t have return line/fpr built in.

Runs fine with the computer, still good idle signal to map sensor, was told anything more would cause it to load up at idle due to low idle vacuum signal.

Only thing I had to do mechanically to run this cam was to add a shim under the valve spring to bring the spring pressure up to 105 lbs with the valve closed. Replaced springs with new ones to reuse all the stock retainers and keepers.

I’m guessing they were pbm springs that matched the mopar performance ones. I was told to stay under .500 lift. Ordered springs thru my machine shop.

There are some crossover parts from 426 hemi stuff for retainers and keepers that match the 4.0 valves.

Again, if I remember correctly it was a .100” shim, but that was 14 years ago haha.



Built and been running this cam since 05. Pulls great. Doesn’t waste any power down low and begins to taper off at 5000.

80d4a48773252312d40fe90e09341bc3.jpg


If I remember correctly, my static compression was 9.7:1. I started with 93 octane only, and try to only buy 93 non ethanol. It will run on 89 non ethanol, but will ping on 87 w/ 10% ethanol.

Ports are significantly opened up to match the gasket and chambers were deburred and polished. Piston tops were also deburred and polished.
 
As far as other concerns, I would never rebuild a 4.0, and not do a stroker. It’s just too easy and cost is pretty much the same.

4.2 crank & rods, 4.0 pistons and done.

Port the crap out of the head and be happy.

If I did it again, I would use 4.2 crank, 4.0 rods, and go for custom pistons.

I like the lighter weight late 4.0 (89/90) crank as it is quicker to rev and is plenty strong.

Just would do forged pistons so I could add n2o or boost later without changing anything internally.

There are some tricks to reduce squish so you can run pump gas and keep the CR up some.

Jody can elaborate on that.

I’ve broken nearly everything behind my stroker being abusive, except for the 14 bolt. It can roast 39” stickies and pull 3rd gear clutch dumps all day in low range. Never really had an issue with power, but a lot of that is with the heavy porting done by my dad.

If I had to rebuild a 4.0 and not stroke it, I’d still without a doubt do a comparable cam to what I have above, and again port the crap out of the head and polish the chambers.
 
I've got a 4ctw 87 4.2 crank (needs spacer for 4.0 serp setup), 4.2 rods, 4.0 block (needs bored/cleaned), 4.0 freeze cracked block complete (in case you want to go custom pistons & 4.0 rods -the better route, about $250 for pistons, so not much more than stock pistons & don't have to deck block). Also have an Eaton m90 could add to it for moPar. pm me if interested.
 
Mac5005 said:
Not sure about other brands comparing to this, but I have a crane 753905 in my stroker.
Click to expand...

Good point on vacuum. Russ Pottenger has versions of the comp cams with 113 lsa (in lieu of 111) to address that.
 
Geez now I wanna build a Stroker. But, LS sounds call my name.
 
I've read about some horror stories on the 12 hole injectors no first hand experience though. I've contemplated a stroker just because I want to build an engine. Never built an engine. In for the education.
 
FYI ksuspension fab has been heavily criticized especially ripping people off with poor quality fuel injectors. I’ve also read countless forums where people “upgrade” their fuel injectors and then their Jeep runs like shit with CEL on. I don’t know a lot about fuel injectors other than my OEM injectors from 92 are still going great :D


Sent from my iPhone using Tapatalk
 
NickMaul said:
FYI ksuspension fab has been heavily criticized especially ripping people off with poor quality fuel injectors. I’ve also read countless forums where people “upgrade” their fuel injectors and then their Jeep runs like shit with CEL on. I don’t know a lot about fuel injectors other than my OEM injectors from 92 are still going great :D


Sent from my iPhone using Tapatalk
Click to expand...


if you buy injectors from anybody, be sure to google the numbers for true ratings. I was going to purchase from ebay, and the rating was not what was advertised. I ended ordering 27lb from Russ per his recommendation on my stroker parts.
 
I did a low buck stroker on mine back in 2003. 4.2 crank and rods, 4.0 pistons. Stock cam/injectors/airbox/head/everything else. Been running smooth and strong for 16 years now. Power is great from idle to 4000rpm, but falls off a bit from 4500 on. Runs fine on 89 octane, pings a little on 87.

Without a doubt, best mod I ever made to the Jeep.
 
With regard to injectors, I have run 12 hole injectors in my XJ for a couple of weeks now (probably have 500 miles on them). I also ran 4 hole LS1 (24lbs?) injectors in my old 91 YJ. Neither jeep threw a code or CEL. The YJ probably had 20k miles on the new injectors and lots of wheeling on them when it was sold.
Both Jeeps were AX15 / 4.0l. I can say that both Jeeps had 240k+ miles on what looked like factory injectors, and that the XJ (12 hole) showed what I would consider significant improvements in driveability and off idle torque, the YJ (4 hole) had much less 'bog' when you mashed the gas on the highway without downshifting and idle was slightly improved.

There are a couple of good videos that demonstrate the differences between 1 / 4 / 12 hole injectors....it is very "impressive".....does it matter???? Shooting high pressure gasoline at that back of a hot intake valve probably does a pretty good job of atomizing the fuel too.

I suspect 90% of the improvement is a result of clean injectors.....I suspect the change from the factory revolved around better emissions and has less to do with power or fuel economy. All things being equal, I would still toss a new set of multi-hole injectors into a new build, just be sure to buy brand name injectors.....lots of junk copy-cats out there.
 
84jimmy said:
So Its finally time to rebuild the 4.0 in my zj. Already started tearing it down. I had a couple questions I needed help with. Was originally thinking about doing a stroker but for longevity and price I decided against it.

first- Camshaft upgrade is a must. The problem is everything I keep finding wont work. Mostly looked on summit and jegs. Most everything I found said doesn't work with fuel injection even though I clearly typed in my vehicle and that is what it pulled up. I did look on 505 performance. They are a little expensive for the stage 2 and 3 cam kits but does come with everything. Does anyone have any experience with them or other recommendations?

second- fuel injector upgrade will also be needed. So I found 4 hole and 12 hole injectors that say they will work for my 4.0zj. I know that the 4 hole is better for atomization compared to the stock 1 hole. With that theoretically the 12 hole should be better then the four hole, but is this really true? ksuspensionfab.com has a 12 hole injectors for a good price. Any opinions on 12 over 4?

And third- any ideas on bottom end parts like new pistons (brand, bore, compression)? And does anyone know what the stock compression is on the 98 4.0?

Thanks
Click to expand...

If you're not gonna stroke it, no need to church it up IMO.
Like @shawn said, the 231 series camshafts from Comp work just fine with EFI. No need for any tuning or additional fuel either since you're not changing displacement (even if you bore it a bit). I say this from multiple stock to 0.030" rebuilds I have done and used their cams. Plus, being a 98 model engine, you can reuse the timing cover and camshaft bolt/spring/pin combo. In 99, they changed the design and you have to retrofit.
As far as injectors go, just order some name brand, OEM replacements from a reputable source. You won't need "bigger" injectors since you aren't adding much displacement.
Installing a larger throttle body and a 99 and up intake manifold will help it breathe a bit, but not a night and day difference.
For bottom end parts, quality OEM type pistons will be just fine. Many of them are just repackged anyway, just like lower end ring and pinions.

Keep it simple. It's a tractor motor. Lowish RPM and lots of torque in stock form. No need to re-engineer a proven combo IMO.
 
Last edited:
Jeff B said:
505 performance, specifically Zach the owner. is a douche bag that will sell you shit parts for big coin. Then wont stand by said parts.. Stay away as far as you can.

A big cam may hurt you more then help, unless you are changing the displacement. A stroker will last as long as any other engine as long as you keep it well maintained.

contact Russ Bishop-Buehl Racing Engines a very nice, well rounded in the stroker engine building dept. Sells quality parts and will make sure the parts you buy will fit. Will even work directly with your machinist if you wish.
Click to expand...

Thanks man. Did a little google search and heard a lot of horror stories so you just saved me some money and heart ache.
 
Mac5005 said:
As far as other concerns, I would never rebuild a 4.0, and not do a stroker. It’s just too easy and cost is pretty much the same.

4.2 crank & rods, 4.0 pistons and done.

Port the crap out of the head and be happy.

If I did it again, I would use 4.2 crank, 4.0 rods, and go for custom pistons.

I like the lighter weight late 4.0 (89/90) crank as it is quicker to rev and is plenty strong.

Just would do forged pistons so I could add n2o or boost later without changing anything internally.

There are some tricks to reduce squish so you can run pump gas and keep the CR up some.

Jody can elaborate on that.

I’ve broken nearly everything behind my stroker being abusive, except for the 14 bolt. It can roast 39” stickies and pull 3rd gear clutch dumps all day in low range. Never really had an issue with power, but a lot of that is with the heavy porting done by my dad.

If I had to rebuild a 4.0 and not stroke it, I’d still without a doubt do a comparable cam to what I have above, and again port the crap out of the head and polish the chambers.
Click to expand...


The 4.2 crank is the same as the AMC 258 Correct?
 
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