After reading around for a bit, I've stumbled on some information regarding the non-HO 4.0L motors, that I previously hadn't seen. I had automaticaly assumed that the HO was a better choice for my intentions, but as it turns out, maybe not.

First off, I will need a quick replacemet for my current engine. Blow-by is bad, and I think I can hear the mains rattling at anything above 2 grand... I was looking for a HO to swap in, as I hear that it is a fairly easy transition from Renix to HO. I also intended to have the replacement motor's shortblock built turbo-ready stroker (although funds may not permit this quite yet)

Now comes the delima, I'm hearing that the pre-HO (Renix) 4.0 block is a better choice for strokers, and the only real advantage of the HO is the head/intake/exhaust/cam combo, which is interchangable with any 4.0 or 4.2 anyways. This is supposedly because the Renix system utilizes a knock sensor (and since strokers like to ping...) My question now becomes: are there any issues/concerns that I should consider if I chose to use a Renix block for my turbo/stroker build? I would still have a variety of head castings/intakes/etc. to choose from, have the added insurance of a KS, and have one sitting in the garage ready to go... what to do!?

If the knock sensor is tied into the ecm to pull timing - yes. You will need a scantool to monitor knock retard to get your tune correct.

What are the things you dont like about the HO block other than the fact that it has a KS? I am just curious because all the positives to me would out weigh just a knock sensor. There are alot of very high output stuff out there that would not dream of using a knock sensor. Just tune it right and you dont need to worry about knock. Run good fuel be easy with the timing and you will be far better off with better flowing components. IMO

Sorry i meant to say that the HO block doesnt have the KS. Just to clarify.

I am just curious because all the positives to me would out weigh just a knock sensor.


You obviously have no clue about keeping a turbo motor together. Knock - detonation - lifting a headgasket.

What are the things you dont like about the HO block other than the fact that it doesn't have a KS?
I'm not sure... that's partially what I'm asking.
I am just curious because all the positives to me would out weigh just a knock sensor.
What are these "positives" you speak of? Are there any other advantages to an HO besides the topend? Because as far as I'm seeing, I can put that head/cam/intake on a Renix block and get the best of both worlds.

And what's this I hear about a Renix block being stronger??

You don't tune the motor, it's all electronic. You can't set the timing.

I would definitely use the Renix motor. That knock sensor is good to have, especially on a budget stroker, but could be invaluable if you plan to boost it. You won't be able to build a budget stroker in yours, since you'll need custom pistons to get the compression ratio down and to help you get the quench height where you need it. Because quench height will be real important if you add a turbo, you'll also need to get the deck blocked. The 4.0L motor was not designed quench compliant, and doing a stroker with stock pistons makes it worse, which is why a Renix block and premium fuel are the standard for budget stroker builds.........but with 10.5 to 1 compression and a good cam they run really well. That's what I have in mine.

So, assuming you already have a Renix equiped rig, so the electronincs are Renix, I'd definitely stick with the Renix motor. It's good insurance.

So, assuming you already have a Renix equiped rig, so the electronincs are Renix, I'd definitely stick with the Renix motor. It's good insurance.
That's what I was thinking, I've already got the electronics for the Renix system, so why not go with it :D

I would definitely use the Renix motor. That knock sensor is good to have, especially on a budget stroker, but could be invaluable if you plan to boost it. You won't be able to build a budget stroker in yours, since you'll need custom pistons to get the compression ratio down and to help you get the quench height where you need it. Because quench height will be real important if you add a turbo, you'll also need to get the deck blocked. The 4.0L motor was not designed quench compliant, and doing a stroker with stock pistons makes it worse, which is why a Renix block and premium fuel are the standard for budget stroker builds.........but with 10.5 to 1 compression and a good cam they run really well. That's what I have in mine.

Question 1) Ok, so now can someone please spell out exactly why a "Renix" block makes a better stroker engine? All early 4.0L blocks were the same, until the NVH blocks were introduced in 1997, and then they changed very little - the Renix blocks just had a boss machined for the knock sensor.

Question 2) 4.0L not designed quench compliant? WTF is the flat machined portion on the top circumference of a 4.0L piston used for then? For looks?

Question 3) I run a Jeep I6 turbo engine. I don't use a knock sensor. Why should he? If you need a knock sensor to hold your turbo motor together, you are probably not qualified to be building one.
BTW the Renix fuel system is shite - please don't tell people it has redeeming features - it doesn't.

The knock sensor is not insurance, it's gonna be a pain in the ass.

It's nice to be able to pull codes if necessary when you are tuning for forced aspiration. Even God cannot pull codes from a Renix system - without the increasingly rare MOPAR dealership only scan tools.

Question 4) Why does he have to deck the block if he is going to run a turbo on his stroker? This makes no sense.

First off, I have built many, many forced induction engines and never I say never would trade a good flowing head and intake for a KS. A KS is for some one who cant tune or has no idea what you are doing. I have built 1400 HP on 93 octane with carbs and guess what no KS. If you are basing all of what you want on a KS then you will be shorted from an engine that can breath better. So once again I say what are your reasons for thinking the non HO block. So before you go running your mouth about things you think you know about get your facts straight. Just my .02:flipoff2:

Budd,first off if the KS pulls timing you have already done some damage with forced induction obviously you have a thing or two to learn my friend. Reason being is that unlike NA with forced induction when a knock or ping occurs little pieces of piston are already coming off even if just a super small amount you have already done some damage. I believe there is no difference between the 2 blocks I dont think there is any extra webbing or thicker walls so unless I am wrong there, really it would not matter to me which one you used. That is what I was getting to was what is the difference in the block.

Wow, my engine is in the exact same condition as A-man's.



BTW the Renix fuel system is shite - please don't tell people it has redeeming features - it doesn't.


So which engine would you recommend? I've been watching your build and am seriously considering a similar setup for mine.

Goatman did his and it seems to be working well. Although it's not turbod.

Budd,first off if the KS pulls timing you have already done some damage with forced induction obviously you have a thing or two to learn my friend.

Correct to an extent - and yes I have more learning to do on my turbo motor. The KS can pull timing before catostrophic failure occurs. Sure - you may have had some self clearancing occur - but with a scan tool you can tune to eliminate knock. Tuning in regards to adjusting the fuel curve, fuel pressure, boost level, where (if) to start adding your methanol injection, etc. I am going to be running 15 psi initially without methanol injection. Will probably eventually run it up to 18-19psi and start adding methanol with a progressive kit at 10psi.
BTW - this is a 87 Buick GN motor - it can handle the boost.

You don't tune the motor, it's all electronic. You can't set the timing.


Tuning in a boosted motor is programming fuel curve, programming timing, fuel pressure line off, adjustable fuel pressure regulator, injector size, boost level, etc. You do tune a boosted motor.

So which engine would you recommend? I've been watching your build and am seriously considering a similar setup for mine.

Goatman did his and it seems to be working well. Although it's not turbod.

It's not the engine I'm grouching about - It's evil Renix ECU that I have no time for - especially in boosted applications.

If you have no option, then sure, run your Renix - just be aware that it has some inherent flaws; the dreaded intermittent high idle problem, the timing retarding (lose power) knock sensor, the lack of a check engine light, the inability for the home mechanic to pull codes, ect.

In my opinion, and people may disagree, ODB1 4.0L engine management is king for boosted applications.

So other than there being a boss for a KS already machined into the block, there are no significant differences between any 4.0L block casting? When it comes time to actually do this, I'll probably go with a standalone system (painless, megasquirt, etc...) instead of trying to rig any factory system to do what I need. I just want my build to have a solid foundation, and it sounds as if using my non-HO block casting will be plenty good. Come to think of it, I recall hearing that blocks with alot of miles (heating and cooling cycles) are better suited for high stress situations... is this the same theory behind cryogenic treatment?

Once the block has been through many heat cycles it is considered seasoned. Race engines are seasoned before being built, everyone has a different way of seasoning and yes heat cycles is one of them. Cryo just aligns the atoms thus making the block stronger, I have never cryoed a block but have had good luck on hard parts cranks rods and pistons, so I cant see where it wouldnt do the same with these. I agree completely with a stand alone system FAST is the system I have used and it is a super easy to use system and great customer service. The original guy I think was trying to do a budget build so I didnt even bring that up, but now that it has been I lean towards fast. All you have to do is make a run let it ping and turn off the ignition pull the plugs and look at all the bright silver on the plug, no maybe not fatal but over time very bad.

My understanding is that ideal quench height is in the 50 thousands range, and a stock 4.0L is a little over 70, and in a normal stroker that uses 4.2 rods and 4.0 pistons the piston doesn't quite come to the top of the deck at TDC, so the quench height is increased slightly more. The standard build recommendation is to use a Mopar Performance head gasket that is .043 thick rather than the standard .053 and deck the block .010-.020 to get the quench height in a better range. That allows running reg gas rather than premium if the comp ratio is kept higher. But, if you are going to use custom pistons, you have more options.

Since I know nothing about building a turbo'd motor, I will back out of this conversation and leave it to you who know what you're talking about. :D

Well I do believe you stated that you cant tune that motor because you cant set the timing, whats that about I can still adjust pull or add so you tell me how cant I tune that motor????????

Well I do believe you stated that you cant tune that motor because you cant set the timing, whats that about I can still adjust pull or add so you tell me how cant I tune that motor????????
If this is the same as any other ignition system with a distributor, then you are limited as to how far you can adjust the timing due to the fact that there's a physical contact on the rotor moving from point to point. Does the 4.0 distributor system utilize a vaccum or mechanical advance? or is it computer controlled? Are there igintion boxes for this system? Now if you were to go DIS (distributorless AKA coil on plug, which was used on late 4.0s), then you have unlimited flexibility of the ignition timing.

Btw, I am the original poster, I was initially shooting for a budget-ish build, but it doesn't look as if it will go that way, lol.

Hey they never do!!!! HAHAHA But hey its just money.

If this is the same as any other ignition system with a distributor, then you are limited as to how far you can adjust the timing due to the fact that there's a physical contact on the rotor moving from point to point. Does the 4.0 distributor system utilize a vaccum or mechanical advance? or is it computer controlled? Are there igintion boxes for this system? Now if you were to go DIS (distributorless AKA coil on plug, which was used on late 4.0s), then you have unlimited flexibility of the ignition timing.

Btw, I am the original poster, I was initially shooting for a budget-ish build, but it doesn't look as if it will go that way, lol.

You cannot alter base timing, unless you jury-rig your distributor or CPS.

Painless wiring is developing an after-market 4.0L computer for ODB1 systems, which will have a base timing alter feature, and can be boost referenced.

As has been said, having a knock sensor isn't exactly a plus...

For a turbocharged fuelie, you should go with megasquirt&spark or other standalone ecm anyway if you're that serious about it. Though I can't imagine any 4.0 being a great candidate for forced induction, they have enough hg, block, and header problems naturally aspirated...

Though I can't imagine any 4.0 being a great candidate for forced induction, they have enough hg, block, and header problems naturally aspirated...

So I guess you don't know much then do you?

Though I can't imagine any 4.0 being a great candidate for forced induction, they have enough hg, block, and header problems naturally aspirated...

What are you talking about??!!

These motors are super reliable, tough little bastards. I've ran mine pointing straight up, straight down, on its side, and not once did it ever hiccup, or sputter, my oil pressure never went below 15 psi in all extreme conditions. A Turbo is the best thing to put on these things. As long as the turbo is properly matched to the engine, the power gains can be great starting at low rpm's.

Im never gettin rid of my motor. IF my YJ is destroyed beyond repair and the motor is still good, its coming with me!!

Wow lot of chunks floating around in this thread.

First off knock is not tiny pieces of piston breaking off! Good god man where did you hear that? It's the sound of the air/fuel charge igniting before it is supposed to usually moments before spark. The flame front from the spark and the flame front from pre-ignition slam into each other making a noise that we call ping or knock or dieseling. This can happen (usually happens) with no actual physical damage to anything, but of course it can cause damage, from holes in pistons to bent broken or burnt valve train parts.

The knock sensor is often talked about for budget strokers to make up for deficiencies inherent in trying to stroke a 4.0 for super cheap (bad quench, high compression). In other words a bandaid for a sucking chest wound.

The KS function of the renix ECU has been observed (on the Yahoo strokers group) to not have enough range to provide useful function on boosted strokers, where timing retard was needed. In other words it couldn't retard enough to dynamically control ping. Take this for what it's worth, there's no proof but it makes sense to me. If you end up with aftermarket boost retard ANYWAY then the renix KS, isn't doing you much good is it?

From what I can tell the Renix KS function opperates by the ECU advancing timing until the KS reads knock, at which point the ECU backs off a small amount... To achieve the best N/A power and fuel efficiency. Do you REALLY want a Renix ECU throwing timing at your turbo motor when you aren't expecting it? The pre programmed OBD1 timing curve can be lowered or raised with a mod to allow adjustment of the CPS.

The Renix block is said to be heavier and of higher nickel content than Chrysler blocks. It May be; I've never seen this proven and "heavier" doesn't necessarilly mean better... It may move less with heat cycling but STIFFER is certainly better... The later blocks that were supposedly improved for NVH (noise vibration and harshness) are stiffer by implication. If they VIBRATE LESS then they are stiffer. That said I have seen no proof that one is stronger than another.

How many cracked 4.0 blocks of any casting have you seen? Me either... A couple with holes in them, but rods tend to make holes in just about any block.

The 4.0 is an EXCELLENT candidate for Forced induction. It has low compression from the factory (mid 8's CR I don't memorize numbers so someone else will correct with the actual number I'm sure)... It is as durable as any American made gasoline motor ever was. It is often mated to the AW4 which is widely regarded as over strength for the 4.0 N/A application. The 4.0's main weakness is breathing and lack of cross flow, so a blower with a charge cooler is a natural. Couple that with many low buck fuel/air tweaks (adjustable MAP, 24-30lb mustang injectors, adjustable CPS mods, etc.). And you have a pretty good set of "criteria" for a boostable stock engine.

Wow lot of chunks floating around in this thread.

First off knock is not tiny pieces of piston breaking off! Good god man where did you hear that? It's the sound of the air/fuel charge igniting before it is supposed to usually moments before spark. The flame front from the spark and the flame front from pre-ignition slam into each other making a noise that we call ping or knock or dieseling. This can happen (usually happens) with no actual physical damage to anything, but of course it can cause damage, from holes in pistons to bent broken or burnt valve train parts.

The knock sensor is often talked about for budget strokers to make up for deficiencies inherent in trying to stroke a 4.0 for super cheap (bad quench, high compression). In other words a bandaid for a sucking chest wound.

The KS function of the renix ECU has been observed (on the Yahoo strokers group) to not have enough range to provide useful function on boosted strokers, where timing retard was needed. In other words it couldn't retard enough to dynamically control ping. Take this for what it's worth, there's no proof but it makes sense to me. If you end up with aftermarket boost retard ANYWAY then the renix KS, isn't doing you much good is it?

From what I can tell the Renix KS function opperates by the ECU advancing timing until the KS reads knock, at which point the ECU backs off a small amount... To achieve the best N/A power and fuel efficiency. Do you REALLY want a Renix ECU throwing timing at your turbo motor when you aren't expecting it? The pre programmed OBD1 timing curve can be lowered or raised with a mod to allow adjustment of the CPS.

The Renix block is said to be heavier and of higher nickel content than Chrysler blocks. It May be; I've never seen this proven and "heavier" doesn't necessarilly mean better... It may move less with heat cycling but STIFFER is certainly better... The later blocks that were supposedly improved for NVH (noise vibration and harshness) are stiffer by implication. If they VIBRATE LESS then they are stiffer. That said I have seen no proof that one is stronger than another.

How many cracked 4.0 blocks of any casting have you seen? Me either... A couple with holes in them, but rods tend to make holes in just about any block.

The 4.0 is an EXCELLENT candidate for Forced induction. It has low compression from the factory (mid 8's CR I don't memorize numbers so someone else will correct with the actual number I'm sure)... It is as durable as any American made gasoline motor ever was. It is often mated to the AW4 which is widely regarded as over strength for the 4.0 N/A application. The 4.0's main weakness is breathing and lack of cross flow, so a blower with a charge cooler is a natural. Couple that with many low buck fuel/air tweaks (adjustable MAP, 24-30lb mustang injectors, adjustable CPS mods, etc.). And you have a pretty good set of "criteria" for a boostable stock engine.

Truer words were never spoken. Now can we consider the original question answered?

By the way, I have Chrysler documentation that states that the nickel content of the blocks stayed the same from inception until 1999. Have to dig that up if anyone really wants to argue.

So I guess you don't know much then do you?

Yeah, I know you jeep guys are loyal and nothing is better than the almighty jeep. I also know how many of these I've helped pull and repair. Maybe it's just coincidence that everyone around me has problems. Maybe if you were to o-ring the heads, use head studs and a fabricated header you could solve a lot of these problems.

Yeah, I know you jeep guys are loyal and nothing is better than the almighty jeep. I also know how many of these I've helped pull and repair. Maybe it's just coincidence that everyone around me has problems. Maybe if you were to o-ring the heads, use head studs and a fabricated header you could solve a lot of these problems.

The 4.0 has no documented chronic head gasket or head bolt issues, the HG is rarely brought up on forums. If you want to talk about known weakness' of the 4.0, then the 0331 early head castings had a tendency to crack, but it's the poorest flowing HO head so no one into Jeeps cares too much about it. The stock cooling system tends to get problematic when mods start going in and the gears and tires get taller..

Tube header cracks are certainly nothing specific to Jeep's 4.0's but they certainly are a chronic problem.

Maybe if you were to o-ring the heads, use head studs and a fabricated header you could solve a lot of these problems.
To answer your question, I plan on fabricating a split-entry header. While we're talking about blocks, did the 4.0 ever come with a stud girdle?

To answer your question, I plan on fabricating a split-entry header. While we're talking about blocks, did the 4.0 ever come with a stud girdle?

Yes 96 and later and they are easy to retrofit onto earlier blocks

Yeah, I know you jeep guys are loyal and nothing is better than the almighty jeep. I also know how many of these I've helped pull and repair. Maybe it's just coincidence that everyone around me has problems. Maybe if you were to o-ring the heads, use head studs and a fabricated header you could solve a lot of these problems.

Jeeps suck. Broncos are the shit.

Yes 96 and later and they are easy to retrofit onto earlier blocks
Are they worth the trouble?

about the NVH-reduction in '96, was it just the addition of a stud girdle? or was there extra webbing?

Yeah, I know you jeep guys are loyal and nothing is better than the almighty jeep. I also know how many of these I've helped pull and repair. Maybe it's just coincidence that everyone around me has problems. Maybe if you were to o-ring the heads, use head studs and a fabricated header you could solve a lot of these problems.


Its not coincidence, its common sense.

Thats like saying all sbc's are junk because we've all seen so many of them blown up. Well no shit, they are among the most common motor out there.

The jeep 4.0 is one of the longest lived, most abundent domestic motors out there. They are also probably in the top 2 or 3 for motors used in the offroading, close behind the sbc.

So of course you see a shit ton of them with problems. From the way you talk you either work on junk for a living, or on the side.

I dont know about you, but every guy that runs a 4.0 doesnt stop by my shop to tell me "she's running great". Pretty much all see is the busted shit. :shaking::shaking:

Are they worth the trouble?

Yeah, doesn't make much sense to design it and manufacture it (or have it manufactured) and then add it to the engine build process, if it didn't do anything.

Inline engines have longer cranks that flex more, which obviously increases bearing wear rates among other things. If say the girdle increased the life of your main bearings by 10 or 20%, over typical life span of 150-200k miles you would be looking at 15,000 to 40,000 additional miles of bearing performance.

Now obviously I pulled 10-20% out of my ass, but whatever the real number is, it's probably high enough for Chrysler to think that piece of hardened 3/16th steel was worth investing in. Maybe it was just enough to get a profitable percentage of 4.0's out of warranty coverage.

What matters is it's an improvement (and a low buck one at that) and considering most of us are probably driving ours harder than a warranty covered 4.0 it's probably well worth it.