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

[Cheromaniac]

Stroker engines should never have been built with 4.2L rods to start with.

That's a pretty strong statement to make. Then I guess all the budget strokers that have been racking up thousands of trouble-free miles (including mine) since the first one was built more than a decade ago must have been big mistakes.

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

No problem here. I'm running my budget stroker on 87 octane with a 9.25:1 SCR, stock '92 cam, 0.088" quench, and stock Champion RC12LYC plugs so it must be a fluke.

[YJ_and_Corey]

Stroker engines should never have been built with 4.2L rods to start with.

That's a pretty strong statement to make. Then I guess all the budget strokers that have been racking up thousands of trouble-free miles (including mine) since the first one was built more than a decade ago must have been big mistakes.

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

No problem here. I'm running my budget stroker on 87 octane with a 9.25:1 SCR, stock '92 cam, 0.088" quench, and stock Champion RC12LYC plugs so it must be a fluke.

Stock cam huh?

And yes, 4.2 rodded strokers do not hold a candle to 4.0L rodded ones. -Rude Comment Removed-

[Cheromaniac]

Stock cam huh?

Yes indeed. I did originally run my stroker with the Crane 753905 cam until two lifters and one cam lobe decided to bite the dust after 34,000 miles, so I just threw my old stock cam in with new lifters. I've been running it like that for the last 23,000 miles and it's with the stock cam that I got my dyno numbers.

And yes, 4.2 rodded strokers do not hold a candle to 4.0L rodded ones.

Those of us who've built sub-$2000 budget strokers that are still running strong with more than 50,000 miles on them won't even care.

[lafrad]

I do find it odd that the I6 would be an engine that does NOT benefit from quench.

Do you have an explanation for that? or is it just "we tried it once and WOAH!!!"?

One explanation I can come up with for that, is the new combustion chamber shape (no longer a hockey-puck shape with on end lopped off...) encourages more/better/something of turbulence... OR, the fact that the spark plug is now closer to the "center" of the compressed volume, encouraging a more even combustion...

The only other thing I can think of is that builds that did try it usually gave up on going for a high SCR with quench, just stuck with a lower SCR and then didn't NEED the quenching effect. (or went with a real late intake closing event...)

[YJ_and_Corey]

I do find it odd that the I6 would be an engine that does NOT benefit from quench.

Do you have an explanation for that? or is it just "we tried it once and WOAH!!!"?

One explanation I can come up with for that, is the new combustion chamber shape (no longer a hockey-puck shape with on end lopped off...) encourages more/better/something of turbulence... OR, the fact that the spark plug is now closer to the "center" of the compressed volume, encouraging a more even combustion...

The only other thing I can think of is that builds that did try it usually gave up on going for a high SCR with quench, just stuck with a lower SCR and then didn't NEED the quenching effect. (or went with a real late intake closing event...)

I don't know "why" exactly, but take that same engine and turn the pistons around in the bores - and viola! no more detonation. And it is good for another 30-40 ft/lbs on the ol' dyno.

Look at the KB 945 piston, it has next to zero quench surface.
My dished 8:1 turbo pistons have no either, and that engine is abused hard and often (no detonation).
Back in the day when we wanted to lower the SCR on a budget stroker, we would mill the quench surface completely off the piston.

[lafrad]

I do find it odd that the I6 would be an engine that does NOT benefit from quench.

Do you have an explanation for that? or is it just "we tried it once and WOAH!!!"?

One explanation I can come up with for that, is the new combustion chamber shape (no longer a hockey-puck shape with on end lopped off...) encourages more/better/something of turbulence... OR, the fact that the spark plug is now closer to the "center" of the compressed volume, encouraging a more even combustion...

The only other thing I can think of is that builds that did try it usually gave up on going for a high SCR with quench, just stuck with a lower SCR and then didn't NEED the quenching effect. (or went with a real late intake closing event...)

I don't know "why" exactly, but take that same engine and turn the pistons around in the bores - and viola! no more detonation. And it is good for another 30-40 ft/lbs on the ol' dyno.

Look at the KB 945 piston, it has next to zero quench surface.
My dished 8:1 turbo pistons have no either, and that engine is abused hard and often (no detonation).
Back in the day when we wanted to lower the SCR on a budget stroker, we would mill the quench surface completely off the piston.

Hmm... from KB's site...


They did *try* to get some sort of quenching in there, otherwise it would be cheaper to just make a round dish... or just drop the compression height for a flat-top. Hard to believe a company would do something in a more expensive manner if it didn't matter. Bean counters are too efficient at their jobs.

Even as-is, there is SOME quench area when flipping those around. just definitely not maximized.

None of the pistons I have seen have had a design that would allow for much to be taken off the top, without having a negative impact on how the ring-pack works. Milling the quench surface completely off the piston would pretty much fully expose the first ring on the 2 sets of "stock replacement' pistons I have seen... and from the KB 944/945 piston pictures and published measurements, looks like it would do a number on them too. now, you might be talking about a different engine build/rotating assembly... I just can't see it in the parts available on the AMC/Mopar/Jeep stuff.


30-40 ft/lbs on the dyno is 10-20%... PERCENT... just by flipping pistons around? no way I guess thats one I'm going to have to see with my own eyes. Thats easy/free power (and efficiency) that AMC/Mopar could have done from the factory. would have sold more, might have bumped efficiency (MPG!!!), and costs NOTHING to do. 10-20 ft-lbs? sure. I could buy into that.

Your 8:1 trubo motor is in a 100% different ballpark. not relevant to "budget level stroker rebuilds". 8:1 is a very conservative compression ratio to start with (no need for quench N/A), and the amount of Water/Meth you run under boost (with intercooler!) removes ANY need for octane help. its a purpose built, nearly exclusive off-road vehicle that sees little time in the engine load/rpm areas that this conversation is talking about. NOTHING in that build applies to a higher-compression N/A build.

I had the block decked for my build... "short rod" and "dished" hyper-eutectic pistons. Quench is ~0.045. The block NEEDED it... 150K+ miles on it had a rather ugly deck surface and I didn't trust an MLS gasket to seal well on. I would imagine there are MANY blocks in that condition. Why NOT go for a good quench height, eh? It didn't cost any more...

I'm all for sharing information, helping others out, trying to take in information from others so I don't HAVE to learn all the lessons on my own... but these other comments just seem so *different* than what my current experience has shown, that it really is tough to buy into it... do you have any write-ups where a build is documented to ping one way, then rebuilt exactly the same way and ping goes away? some sheets showing the 10-20% torque gain? That would go along way to buying into some of this...

[Cheromaniac]

Well, here's the answer from an expert, Lee of Hesco:

When I did the testing on the boosted piston I used the "V" mark on the piston. The boosted piston is the end results of all that testing.

Maybe the reason the VERY SMALL quench area in the boosted piston worked as it did was boosted engines have a history of turbulent flow to the chamber that quench is not needed. My idea came from diesel knowledge and design.

I have tested NA engines and changed the quench and had data to confirm the results. Tight is best!!!!!!

[YJ_and_Corey]

I do find it odd that the I6 would be an engine that does NOT benefit from quench.

Do you have an explanation for that? or is it just "we tried it once and WOAH!!!"?

One explanation I can come up with for that, is the new combustion chamber shape (no longer a hockey-puck shape with on end lopped off...) encourages more/better/something of turbulence... OR, the fact that the spark plug is now closer to the "center" of the compressed volume, encouraging a more even combustion...

The only other thing I can think of is that builds that did try it usually gave up on going for a high SCR with quench, just stuck with a lower SCR and then didn't NEED the quenching effect. (or went with a real late intake closing event...)

I don't know "why" exactly, but take that same engine and turn the pistons around in the bores - and viola! no more detonation. And it is good for another 30-40 ft/lbs on the ol' dyno.

Look at the KB 945 piston, it has next to zero quench surface.
My dished 8:1 turbo pistons have no either, and that engine is abused hard and often (no detonation).
Back in the day when we wanted to lower the SCR on a budget stroker, we would mill the quench surface completely off the piston.

Hmm... from KB's site...


They did *try* to get some sort of quenching in there, otherwise it would be cheaper to just make a round dish... or just drop the compression height for a flat-top. Hard to believe a company would do something in a more expensive manner if it didn't matter. Bean counters are too efficient at their jobs.

Even as-is, there is SOME quench area when flipping those around. just definitely not maximized.

None of the pistons I have seen have had a design that would allow for much to be taken off the top, without having a negative impact on how the ring-pack works. Milling the quench surface completely off the piston would pretty much fully expose the first ring on the 2 sets of "stock replacement' pistons I have seen... and from the KB 944/945 piston pictures and published measurements, looks like it would do a number on them too. now, you might be talking about a different engine build/rotating assembly... I just can't see it in the parts available on the AMC/Mopar/Jeep stuff.


30-40 ft/lbs on the dyno is 10-20%... PERCENT... just by flipping pistons around? no way I guess thats one I'm going to have to see with my own eyes. Thats easy/free power (and efficiency) that AMC/Mopar could have done from the factory. would have sold more, might have bumped efficiency (MPG!!!), and costs NOTHING to do. 10-20 ft-lbs? sure. I could buy into that.

Your 8:1 trubo motor is in a 100% different ballpark. not relevant to "budget level stroker rebuilds". 8:1 is a very conservative compression ratio to start with (no need for quench N/A), and the amount of Water/Meth you run under boost (with intercooler!) removes ANY need for octane help. its a purpose built, nearly exclusive off-road vehicle that sees little time in the engine load/rpm areas that this conversation is talking about. NOTHING in that build applies to a higher-compression N/A build.

I had the block decked for my build... "short rod" and "dished" hyper-eutectic pistons. Quench is ~0.045. The block NEEDED it... 150K+ miles on it had a rather ugly deck surface and I didn't trust an MLS gasket to seal well on. I would imagine there are MANY blocks in that condition. Why NOT go for a good quench height, eh? It didn't cost any more...

I'm all for sharing information, helping others out, trying to take in information from others so I don't HAVE to learn all the lessons on my own... but these other comments just seem so *different* than what my current experience has shown, that it really is tough to buy into it... do you have any write-ups where a build is documented to ping one way, then rebuilt exactly the same way and ping goes away? some sheets showing the 10-20% torque gain? That would go along way to buying into some of this...

When I say milling the quench surface off, I am referring to the taking the flat spots off - so all that remains is perfectly round dish. NOT removing the concentric ring land ring!
Sorry if that was not clear. YES I am talking about 4.0L stuff. KB are not experts on EVERY engine they sell pistons for.

YES, flipping the pistons around gains you 10-20% more torque. The factory knew this well, but they chose not to sell engines in that configuration.
Why was that? Loud piston slap on start-up, and I mean loud. Not soccer mom friendly. By MOPARs own admission it is not an issue for engine longevity and it is their documentation
that states the increase is as high as 20%. All their racing teams did this, as did AMC teams before they bought the farm. If you simply cannot believe this, you
need to consider that I have quite a few engines out there now running this way on regular gas at 10.5:1 compression. That was not <<< a typo. Every engine we build now gets
reversed pistons.

The reason so many budget stroker motors detonate is the short 4.2 rods combined with OEM replacement 4.0L pistons. Everyone (I thought) knew this. It's the short piston dwell time at TDC coupled with the large cylinder wall exposure (too much "quench surface") and high compression, creating a hot spot just below the deck. This is why in that case the block needs to be decked to get the quench height under control OR (I much prefer) flip the pistons around in the bores and save your cash on decking a block.

As far as Lee Hurly wanting a tight quench - well YEAH! (I thought we all knew close to zero deck is best) - my point here has been that if you run 4.0L rods and KB or custom pistons it becomes a non-issue. I further that by stating that stroker engines should never be built with 4.2 rods, too many issues. The technology and knowledge has progressed to where we know better and cheaper ways to do it now and get better results. My kits, soon to released, will cost about $1000.00 - that includes a NEW replica 4 CW 258 crank, 6 custom YJ_and_Corey forged pistons, and moly rings. It is a 325 HP engine. No decking required. Factory head. Off-the-shelf cam. Runs on regular fuel.

BTW most blocks are not twisted to the point of needed a milled surface. I have no problem with a few thou to clean up the mating surface but that is all I would want.

[Bodo]

By MOPARs own admission it is not an issue for engine longevity and it is their documentation
that states the increase is as high as 20%.

This whole thing is easy to clear up. Where is this documentation? Post is here and let us see it.

[YJ_and_Corey]

By MOPARs own admission it is not an issue for engine longevity and it is their documentation
that states the increase is as high as 20%.

This whole thing is easy to clear up. Where is this documentation? Post is here and let us see it.

Here is a better idea. YOU guys go and do the digging in the REAL WORLD.

Put down the keyboard, go to your local used bookstores/flea markets/dealership archives/speed shops etc etc etc and find
the old AMC racing literature.

I'm not going to spoon feed you everything I found out the hard way over the years. I'm serious.
If you don't take my word for it, go find the literature yourself.

BTW, Google does not = research

[Bodo]

Why would anyone just take your word for it? What literature are you referring to? Do you have titles? Authors? Anything besides your word?

With a response like that, it dodges the question. Facts talk and BS walks.

It's pretty obvious that you have no intention of actually helping increase the body of knowledge here. It's a shame too. I was hoping we could benefit from your alleged expertise.

[YJ_and_Corey]

Why would anyone just take your word for it? What literature are you referring to? Do you have titles? Authors? Anything besides your word?

With a response like that, it dodges the question. Facts talk and BS walks.

It's pretty obvious that you have no intention of actually helping increase the body of knowledge here. It's a shame too. I was hoping we could benefit from your alleged expertise.

I had every intention of helping you guys! I laid out the facts.
I'm not dodging anything - but I am also not going to spoon feed you my sources.

One of you will eventually have the balls to try it, then you'll realize I know exactly what I am talking about.

The real bullshit here is people who not only want the how but the why as well. Go build a few engines, and learn the "why".

[Plechtan]

I emailed Rick Mudge, he worked at Chrysler JTE (Jeep-Truck engineering)for 20 years in the flow lab. He worked on the 0331 head design. Here is a copy of the Email:

Rick:

Have you ever heard of installing the pistons in a 4.0 180 deg out? A guy on one of the boards claims that this increases torque 10% and that Chrysler (jeep) knew about it, but did not do it because of piston slap noise when cold. he also claims that all of the race motors were built this way.


Is this guy full of crap or is he on to something?

Thanks

Peter Lechtanski

Rick Mudge Wrote:

The answer is YES and NO! The stock JEEP pistons had a pin offset about .060" so the piston slap noise (when cold) is reduced. TRUE!
Turning the pistons around will reduce friction and gain some power BUT, the dish is moved off the chamber and the squish area is reduced. We had pistons having the dish in the stock location but using ZERO offset pins. This produced the best power by keeping the dish orientation correct and eliminating the friction of the offset pins. But, turning a stock piston 180 will increase power, YES! NOW, the biggest noise problem wasn't piston slap but cylinder miss fires. Inconsistent spark light off at low engine speeds, like idle. We tried pin offsets as high as .125" and saw NO improvement in noise, it was miss fires causing the noise. Low charge motion (swirl/tumble) at idle and just off idle, bad spark plugs, cylinder to cylinder distribution all contributed to the miss fires.

So it looks ike the increase in power is related to the pin offset and not the dish. Do Replacment pistons have offset pin bores?

[YJ_and_Corey]

I emailed Rick Mudge, he worked at Chrysler JTE (Jeep-Truck engineering)for 20 years in the flow lab. He worked on the 0331 head design. Here is a copy of the Email:

Rick:

Have you ever heard of installing the pistons in a 4.0 180 deg out? A guy on one of the boards claims that this increases torque 10% and that Chrysler (jeep) knew about it, but did not do it because of piston slap noise when cold. he also claims that all of the race motors were built this way.


Is this guy full of crap or is he on to something?

Thanks

Peter Lechtanski

Rick Mudge Wrote:

The answer is YES and NO! The stock JEEP pistons had a pin offset about .060" so the piston slap noise (when cold) is reduced. TRUE!
Turning the pistons around will reduce friction and gain some power BUT, the dish is moved off the chamber and the squish area is reduced. We had pistons having the dish in the stock location but using ZERO offset pins. This produced the best power by keeping the dish orientation correct and eliminating the friction of the offset pins. But, turning a stock piston 180 will increase power, YES! NOW, the biggest noise problem wasn't piston slap but cylinder miss fires. Inconsistent spark light off at low engine speeds, like idle. We tried pin offsets as high as .125" and saw NO improvement in noise, it was miss fires causing the noise. Low charge motion (swirl/tumble) at idle and just off idle, bad spark plugs, cylinder to cylinder distribution all contributed to the miss fires.

So it looks ike the increase in power is related to the pin offset and not the dish. Do Replacment pistons have offset pin bores?

Most of them are centered, my pistons will have them centered as well.

Remember that Rick (above) most likely was working within the restraints of stock 4.0L stroke and OEM ignition (weak).

[lafrad]

Only thing that changes for most of us is the stroke...

CR bump does help light off in idle and just off idle situations, but it hurts ignition in high load/high rpm areas.