4.6, low compression daily driver build questions

Performance mods and Advanced Stroker discussion.
Jacob8822
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4.6, low compression daily driver build questions

Post by Jacob8822 »

Hello everyone, I am admittingly lost. This build has turned into a giant, confusing debacle and I need some sound advice. I'm

a new member, so please forgive me if I end up posting this in the wrong place. I decided to just join the forum after

realizing the plethora of information and knowledgeable folks on this site




Here are the calculator results for a -.005" block decking, KB421 hypereutectic circular dished pistons (new, just released

by UEM) and mopar -28 cam




Cylinders: 6 Cylinders
Bore: 3.905 inches
Stroke: 3.895 inches
Combustion Chamber: 58 cc
Deck Clearance: 0.165 inches (Block resurface .0215" - .005" = .0165")
Gasket Thickness: .043 inches
Gasket Bore: 4.00 inches
Dome/Dish/Valve Relief: 27.5 cc
Piston to Bore Clearance: .002 inches
Connecting Rod Length: 6.125 inches
Cam Intake Duration: 240 degrees
Cam Lobe Separation Angle: 108 degrees
Advance or Retard: 0 degrees


Your Cam Selection:
Manufacturer: Mopar
Model Number: P4529228AD


Your Calculated Results:
Cubic Inches: 279.89
Liters: 4.59
Static Compression Ratio: 8.83:1
Dynamic Compression Ratio: 7.89:1
Quench: .059499"



There are some new pistons that UEM just came out with, that I decided to give a try. From what I understand, I dont think

anyone is even running these as of yet because of how recently they came out with them. They are Keith Black P/N KB421.



What I'm thinking is that these new KB421 pistons are, for the most part identical to the Icon IC-668's except for their

composition. Being that I will be operating this in northern IL climate, I searched and waited for UEM to produce a

hypereutectic version of the IC-668. After a few weeks, I decided to check back with UEM for the status of these new KB

421 pistons. They told me they have several on their shelf, ready to ship, so I sent my new set of IC-668's back in exchange

for the new KB421's. The KB421's have a full circular dish, just like the IC-668's. These will enable me to run a tighter

piston-to-wall clearance for reduced piston slap in cold weather.



Some questions I have.....


1) With the combination of selected parts and the numbers shown, should I be safe running 87 pump gas with these numbers

without decking too much off my block? (I would like to keep as much meat on the block as possible to facilitate the

valvetrain components I already have and stock-ish valvetrain geometry)



2) The pistons have roughly a 1/2" wide circular piston quench area, which isn't much when compared to a "D" dished piston.

Will zero-decking my block and increasing compression, just to increase this possibly not needed quench be necessary for my

application? (I'm getting mixed answers on this, even from some well-seasoned engine builders/machinists).



I am building this engine for best possible longevity and reliability and need to get this right the first time.

It's difficult to form any sound answers when "trusted sources" of information seemingly produce different results for the

questions that I have, and kinda making my head spin. Your knowledge and help with this is greatly appreciated!!
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Re: 4.6, low compression daily driver build questions

Post by Cheromaniac »

If you're intent on building a low compression stroker that'll run on cat pee, I suggest you revise the specs a bit to something like this:

4.6L Low-buck, low CR "rockcrawler"

Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Custom forged +0.030" bore pistons, compression height 1.380", dish volume 32cc
8.8:1 CR
CompCams 68-115-4 192/200 degree camshaft
DIY ported HO 1.91"/1.50" 57cc cylinder head
Mopar/Victor 0.043" head gasket
0.043" quench height
Ford 24lb/hr injectors for '87-'95 engines, Accel 24lb/hr injectors for '96-'04 engines, '98 Chevy LS1 25.2lb/hr injectors for '05-'06 engines
242hp @ 4600rpm, 317lbft @ 3000rpm
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Re: 4.6, low compression daily driver build questions

Post by Jacob8822 »

It took some time to type this all up and was honestly looking for some sound advice. Did you happen to review the similarities between the two builds?
There is a newer piston out now that will be better suited for my intended purposes being that I deal with -20 degree climate in the winter months. I'm not personally convinced that forged pistons are the way to go with a ~ .0045" ptw clearance.
That thing would rattle itself apart after a month of cold soaked -20 degree startups. Hypereutectic pistons will run around a .0015" - .002" ptw clearance. The question I had was about the necessity for quench with low compression, full circular dished pistons on these motors. Given that folks on here seem to have experience building these things, I thought I'd post my question. :huh:
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Re: 4.6, low compression daily driver build questions

Post by Cheromaniac »

Since you're concerned about the PTB clearance of forged pistons, I suggest you get in contact with Russ Pottenger and ask him to put together a set of custom hypereutectic pistons to suit your needs. They'll have the proper D-shaped dish to provide the quench action that's necessary to fight off detonation.
The only other change I suggested is the cam. The Mopar 28 cam has much too little duration for a stroker and you'd find the engine's performance petering out by 4000rpm.
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Re: 4.6, low compression daily driver build questions

Post by Jacob8822 »

My thoughts were to get a cam with a little less duration and overlap so that the cylinder pressure builds better at the lower rpm range. I really don't want to spin it up past 4K anyway. It's an iron head, flat tappet stump pulling tractor engine for crying out loud. Straight outta the industrial revolution era. I can get the KB 421 pistons for around $400. USD. The -28 cam and new lifters cost me around $200. shipped, and has a factory fit with the proper factory lobe width. I didn't want to run a cam that had lobes which were 3/16" narrower than a stock cam. To me, that just doesn't make sense. Distributed load vs area type thing. There is a reason that the stock cam/valvetrain will last a ridiculous amount of miles on these engines. With the -28 cam and a SCR of 8.83:1, I show a DCR of 7.89:1. That cam produces power down in the lower rpm range. Unless I missed something, it seems to be the best cam choice for what I'm shooting for. Correct me if I'm wrong.
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Re: 4.6, low compression daily driver build questions

Post by Russ Pottenger »

Jacob,
In a normally aspirated engine I would advise you to stay away from a full circular dish.
With a full circular dish you've lost the efficiency and benefits of any kind of quench area.
A properly designed piston with a reverse mirror dome along with a tight piston to cylinder head
will allow you to run more static compression for a givin octane grade of gasoline due to its combustion efficiency.

I wouldn't be too concerned about running a forged piston in cold climate conditions.
My custom forged pistons are made from a 4032 alloy. It has a higher percentage silicone that has a much lower expansion rate.
Therefore allowing tighter piston to cylinder wall clearances.
The other benefits from the 4032 alloy is that it has much the same scuff resistance as a cast piston, but is substantially stronger.

Feel free to shoot me a call or email.

Russ Pottenger
Bishop-Buehl Racing Engines
531 N. Lyall Avenue
West Covina, California 91790
Work (626) 967-1000
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Re: 4.6, low compression daily driver build questions

Post by SilverXJ »

Russ Pottenger wrote: I wouldn't be too concerned about running a forged piston in cold climate conditions.
My custom forged pistons are made from a 4032 alloy. It has a higher percentage silicone that has a much lower expansion rate.
Therefore allowing tighter piston to cylinder wall clearances.
The other benefits from the 4032 alloy is that it has much the same scuff resistance as a cast piston, but is substantially stronger.
I run the Icon pistons in 4032 in my stroker. On the coldest days (-10*) the rattle may last all of 1.5 minutes. But you still have to deal with the thick cold oil before you get on it, which is on any engine in cold weather. If you can run a block heater.
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Re: 4.6, low compression daily driver build questions

Post by Jacob8822 »

Russ.....
my e mail: [email protected]
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Re: 4.6, low compression daily driver build questions

Post by ronazon »

Jacob,

I am in the same boat. I have a 2004 WJ and am looking to build a stroker primarily for the torque...for towing. In researching this I found lots of information but it seems the big sticking point is the cam choice. Seems there are issues with the newer engines possibly due to fuel injection and or the computer, and they require a lobe separation angle of around 113. Comp Cams recommends the 68-232-4 cam for this application but I read where there were some issues so Comp Cams came up with a new custom grind...'It has a duration @ 0.050" of 206/212, with valve lift being .435/.448, and a lobe separation angle of 113° (110-degree intake centerline). The cam price is $186.15.' Here is the link about it: http://forums.4wdmechanix.com/topic/645 ... -wrangler/

I also like these KB421 pistons. They seem to fit the bill as far as my needs. I am looking to make a very reliable daily driver that runs on 87/89 octane that will pull a heavy trailer through the mountains. I would prefer to retain stock valve springs as well.

A couple years ago the water pump went out and the engine overheated. They resurfaced the head at that time but I don't know how much. It had a complete valve job at that time so I want to retain that work done on the head. I plan to do a FIPK and cat back 2.5" exhaust with a Flowmaster 70 series muffler. I need to keep the cost down as much as is reasonably possible because I have been unemployed for 1.5 years.

I'm sorry if this is bad form. No intention of hijacking your thread, but since your post includes all the same specs except the cam, I wanted to see if Dino or someone else might be able to lend some guidance.

Best Regards,

Ron
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Re: 4.6, low compression daily driver build questions

Post by Cheromaniac »

ronazon wrote:Comp Cams recommends the 68-232-4 cam for this application but I read where there were some issues so Comp Cams came up with a new custom grind...'It has a duration @ 0.050" of 206/212, with valve lift being .435/.448, and a lobe separation angle of 113° (110-degree intake centerline). The cam price is $186.15.' Here is the link about it: http://forums.4wdmechanix.com/topic/645 ... -wrangler/
Those custom cam specs seem to be similar to the 68-232-4 except for the 110* ICA (107* on the 68-232-4) and the lower valve lift, which allows the use of stock valve springs. It's recommended by none other than Moses Ludel himself and looks good to me.

http://forums.4wdmechanix.com/topic/493 ... #entry2747
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Re: 4.6, low compression daily driver build questions

Post by ronazon »

Thanks for the quick response! Looks like this is the right cam.

I am curious as to your thoughts about piston options. These KB421's seem like the best one available now as far as I can find using the 258 crank and 4.0 rods. I am building this strictly for towing and fuel economy. I don't need forged pistons. This engine will almost never go over 3000-3500 rpm. What is the best value piston option for this scenario. I like the coated skirts if available.

Couple more questions...

My reading of the adjustable map sensor is that it is only effective at 80-100% WOT. Is this true? If so, my application would not require it. I was hoping it would be effective to dial in a/f ratio to maximize economy while towing long distance and in the mountains.

Ok, last one....lol

Injectors...I have a 2004 WJ. I have not found a consistent answer about whether I would need them and if I do, which ones. The 24lb ford ones are commonly recommended but seems that's foe the older 4.0. Also found the 2003 Dodge 5.9 injectors listed as an option and I believe for my 2004. Are these the right ones? I like the 4 hole design for best optimal atomization too. Do they have that?

I know, lots of questions...but I don't want to struggle. I prefer to be educated first and then finalize a plan. Then execution of that plan is easy.

Thanks again for your guidance!

Best regards,

Ron
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Re: 4.6, low compression daily driver build questions

Post by Cheromaniac »

1. I suggest you talk to Russ about getting a set of custom pistons.
2. The MAP adjuster only works at >70% throttle acceleration. Under lighter throttle acceleration the O2 sensor commands a 14.7:1 air/fuel ratio.
3. You could use the Dodge Neon 24lb injectors.
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Re: 4.6, low compression daily driver build questions

Post by ronazon »

Ok, who is Russ? I understand this KB421 is a good fit but that it has a circular dish design with no quench. My understanding is the D shaped dish is the best for quench...which should be optimal. Please correct me if this is not correct.

No point in doing the adjustable map sensor...got it.

Are the dodge neon injectors rated at 24lbs at 49psi rail? Also, are those the 4 hole injectors? Are they Bosch? Sorry, this injector thing has me confused a bit.
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Re: 4.6, low compression daily driver build questions

Post by Russ Pottenger »

I'd advise you to stay away from a full circular dish piston. Maintaining a tight quench area will be a big help with low RPM torque that your looking for.

Dino has lots of good information on his site you'll have to check out. It covers a lot of the fundamentals

Feel free to shoot me an email or call and will happy to go over costs and options on my Pistons, Rods, Cylinder Heads, and custom Stroker kits.

Thanks,
Russ Pottenger
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West Covina, California 91790
(626) 673-2203
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Re: 4.6, low compression daily driver build questions

Post by ronazon »

Hi Russ,

I have been reading for several days...Dino's site included. I like the idea of the stroker with the longer 4.0 rods. I believe the lesser rod angle will increase life expectancy due to less sideways torque on the piston skirts. However, the only pistons off the shelf that I know of are forged which are way too expensive and severe duty for my application. I need basically a HD stock type piston. It would be nice if I didn't have to deck the block to achieve perfect quench too, but not sure that's possible.

I have found that the best cam is the Comp Cams custom grind for my later model 4.0. My only questions now are what pistons to go with and which injectors. I will shoot you an email and we can go from there.

Thanks,

Ron
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