CJ7 stroker build...questions?..KB944...quench??

[LetchcoreCJ7]

Here are my specs so far. I am looking to run on 89 or lower gas. I am not going for huge hp/torque rather a smooth running engine that is a decent upgrade over the 4.0L. Anything is an upgrade from the 90hp AMC 258

1991 4.0L HO engine
86' 258 crank
Comp Cam 68-232
Possibly long 4.0L rods w/ the KB944's 0.040 over.

What needs to be done to run the KB944's? Is the best way to go now that they are on the shelf?
Why do people lower the quench height when it was 0.080 or so from the factory?
Do I have to mill the deck with the KB944's?
Can I use my stock piston pins?
Do I need to change the valve springs with this cam?

Thanks...there is so much info out their that its hard to narrow down the choices.

[YJ_and_Corey]

Here are my specs so far. I am looking to run on 89 or lower gas. I am not going for huge hp/torque rather a smooth running engine that is a decent upgrade over the 4.0L. Anything is an upgrade from the 90hp AMC 258

1991 4.0L HO engine
86' 258 crank
Comp Cam 68-232
Possibly long 4.0L rods w/ the KB944's 0.040 over.

What needs to be done to run the KB944's? Is the best way to go now that they are on the shelf?
Why do people lower the quench height when it was 0.080 or so from the factory?
Do I have to mill the deck with the KB944's?
Can I use my stock piston pins?
Do I need to change the valve springs with this cam?

Thanks...there is so much info out their that its hard to narrow down the choices.

It's easy to build mucho power these days.

The crank is a good choice, as the 4 CW version is the best way to go hands down.

To answer your questions:

The KB944 pistons accept 4.0L rods. They were made for it. They are forged, have a centered pin and a short skirt. The KB 944 is THE only way to go unless you
want to spend big cash on custom slugs.

People make too much of a deal about the fawkin' quench. I have a stroker with NO quench surface on the pistons, it makes 440 HP on the dyno.
The KB 944s will leave you about 10 thou down the bore if your block is uncut - run a standard VR head gasket and you are golden.

NO - do not mill the deck. If the block is that twisted, go get a different block. The 4.0L has been around since 1986.

Yes, 4.0L pins work.

YES YES YES you must run different springs (just like the literature that cam comes with states). If you don't feel like
milling the valve seats use MOPAR performance springs (PN 5249464) and retainers (PN 4452032).

[gradon]

Welcome Corey--I enjoyed reading your builds on Pirate. KB gives you specs that the 944/945s are down .010" in the hole, but that is after you have taken .020" off the block(it's an ok off the shelf piston, but far from ideal in the dimensions they chose). Granted the 4.0 and stroked variants can get by on sloppy quench, but when you are bumping up the compression and are using cams with short overlap, cylinder pressures can get high and then you have to fight pre-ignition. Having a good quench--.040-.060"--will help keep the pre-ignition down. So yes, do use the .043/.044" VR head gasket and try to get a 0-.010" deck height, which means you'll have to take ..020-.030" off the block depending on what piston/rod combo you go with.

[YJ_and_Corey]

Welcome Corey--I enjoyed reading your builds on Pirate. KB gives you specs that the 944/945s are down .010" in the hole, but that is after you have taken .020" off the block(it's an ok off the shelf piston, but far from ideal in the dimensions they chose). Granted the 4.0 and stroked variants can get by on sloppy quench, but when you are bumping up the compression and are using cams with short overlap, cylinder pressures can get high and then you have to fight pre-ignition. Having a good quench--.040-.060"--will help keep the pre-ignition down. So yes, do use the .043/.044" VR head gasket and try to get a 0-.010" deck height, which means you'll have to take ..020-.030" off the block depending on what piston/rod combo you go with.

AHHH snap! I remember now (been awhile) that I did have a decked block on MY last build! Thats why I got a measured 0.010 down at TDC.

I'm pretty sure they will work without cutting the block however.

The last 6 motors I built all used KB 944/945 without any block cutting. They are working very well on mid-grade fuel according to my feedback.

[LetchcoreCJ7]

Welcome Corey--I enjoyed reading your builds on Pirate. KB gives you specs that the 944/945s are down .010" in the hole, but that is after you have taken .020" off the block(it's an ok off the shelf piston, but far from ideal in the dimensions they chose). Granted the 4.0 and stroked variants can get by on sloppy quench, but when you are bumping up the compression and are using cams with short overlap, cylinder pressures can get high and then you have to fight pre-ignition. Having a good quench--.040-.060"--will help keep the pre-ignition down. So yes, do use the .043/.044" VR head gasket and try to get a 0-.010" deck height, which means you'll have to take ..020-.030" off the block depending on what piston/rod combo you go with.

AHHH snap! I remember now (been awhile) that I did have a decked block on MY last build! Thats why I got a measured 0.010 down at TDC.

I'm pretty sure they will work without cutting the block however.

The last 6 motors I built all used KB 944/945 without any block cutting. They are working very well on mid-grade fuel according to my feedback.

Well I ordered the KB 944's today!! Now you guys have me really confused. Why would KB make the pistons where you have to shave the block? Why not just make them .010 in the hole without any machine work? I might give them a call. I suspect they engineered them to work with the block shaved or not.

Also if you dont shave the deck you give up optimal quench. If you do shave the deck you add compression and put you further away from running mid grade fuel.

How much does it cost to have the block shaved .020??

Am I thinking right here?

[YJ_and_Corey]

Ok,

For the record DO NOT SHAVE the block.

The KB944 works fine without shaving the block.

And quit worrying about quench - it's a 4.0L not a V8 for Pete's sake.

[lafrad]

I am confident they put them where they did so people with high mileage engines COULD shave the block on rebuild.

I know my 4.0L block NEEDED a cut (at least 0.010) to be brought back to "flat". it was warped, just pitted and rough from years of mis-treatment from previous owners. Starting with a fresh surface on both the block AND the head is ALWAYS preferable, and gives you the best chance for success on the increased CR/HP engines.

Quench is always GOOD. unless you have the option to remove quench and gain better airflow (open chamber head vs closed chamber...), it ALWAYS helps to have better quench. The amount of compression ratio increase is FULLY offset and MORE if you are "within" good quench range.... (That is, if you are at 10:1 and 0.070" quench, you would *ALMOST ALWAYS* be better to mill the block to get 0.040" quench, even though your CR will increase)

[YJ_and_Corey]

I am confident they put them where they did so people with high mileage engines COULD shave the block on rebuild.

I know my 4.0L block NEEDED a cut (at least 0.010) to be brought back to "flat". it was warped, just pitted and rough from years of mis-treatment from previous owners. Starting with a fresh surface on both the block AND the head is ALWAYS preferable, and gives you the best chance for success on the increased CR/HP engines.

Quench is always GOOD. unless you have the option to remove quench and gain better airflow (open chamber head vs closed chamber...), it ALWAYS helps to have better quench. The amount of compression ratio increase is FULLY offset and MORE if you are "within" good quench range.... (That is, if you are at 10:1 and 0.070" quench, you would *ALMOST ALWAYS* be better to mill the block to get 0.040" quench, even though your CR will increase)

With all due respect, quit hawkin' the quench! Stroker engines should never have been built with 4.2L rods to start with.

This is my turbo motor. It has less quench surface than 99% of the stroker engines out there. It is an angry potent engine from idle on up. It has never detonated.
And when the boost starts, it gets downright scary.

[yuppiexj]

Here's the infamous YJ_and_Corey boosted stroker build.

http://www.pirate4x4.com/forum/showthread.php?t=614289

aptly titled "400HP pump gas friendly 4.5L stroker"

[LetchcoreCJ7]

Can anyone recommend a cam that I can use stock valve springs but still be better then stock? I am going to run fuel injection too. Most comp cams say you cant run with fuel injection.

[YJ_and_Corey]

Can anyone recommend a cam that I can use stock valve springs but still be better then stock? I am going to run fuel injection too. Most comp cams say you cant run with fuel injection.

If you are going to run the Comp Cams, you need upgraded springs.

I know 4 of those cams DO work with fuel injection, despite what they say.

[LetchcoreCJ7]

Can anyone reccomend a camshaft that is mild/medium and will either work with stock springs or simple "drop in" springs? Im not going for maximum power here. THX

[dwg86]

Can anyone reccomend a camshaft that is mild/medium and will either work with stock springs or simple "drop in" springs? Im not going for maximum power here. THX

The comp cams part number 68-200-4 or 68-201-4 will work with stock springs.

[Muad'Dib]

YJ_and_Corey...

Just because you have had good luck building engines without the slightest though about quench, doesnt mean that quench is a bad thing. And with engine building (which is what we do here), i dont think its a good idea to spread false information .. ESPECIALLY about quench. Quench is not bad and should never be overlooked!

Alot of us have grown to learn that having a tight quench has been one of the single most important things to have in our engines when trying to prevent ping, preignition, detonation and running high octane fuel.

Its again of my opinion that telling people to ignore quench is setting them up for failure... However your entitled to think, and work the way you do. If it works for you thats great, but its not what most people have learned to be the case.

[YJ_and_Corey]

YJ_and_Corey...

Just because you have had good luck building engines without the slightest though about quench, doesnt mean that quench is a bad thing. And with engine building (which is what we do here), i dont think its a good idea to spread false information .. ESPECIALLY about quench. Quench is not bad and should never be overlooked!

Alot of us have grown to learn that having a tight quench has been one of the single most important things to have in our engines when trying to prevent ping, preignition, detonation and running high octane fuel.

Its again of my opinion that telling people to ignore quench is setting them up for failure... However your entitled to think, and work the way you do. If it works for you thats great, but its not what most people have learned to be the case.

It's not me who is telling people to obsess over quench in a non-quench engine.

All you guys with budget strokers that ping, turn the pistons around in the bores. Problem solved.

False information? Give me a break.