Just Picked Up A 4.2...

[Cheromaniac]

If I went with these:

http://www.summitracing.com/parts/slp-h ... /overview/

What would the 1.592 compression distance do compared to the stock pistons?

If I were to leave my deck height alone and go with the .073 quench, what would the negative effects be other than definitely requiring premium fuel? Is there a thinner head gasket available than .043?

Stock pistons have a compression height of 1.601". Unfortunately all the aftermarket pistons are shorter and the Speed Pro H802CP's are the tallest of them with a compression height of 1.592". Those pistons have a 15.2cc dish so if you left the block undecked, the quench height would be 0.073" and the SCR would be 9.9:1 (assuming 57cc head). You could gain some volume and lower the SCR by polishing the combustion chambers and piston dishes to a near mirror-like finish.
Alternatively you could use the 4.0L rods with IC944 pistons (21cc dish). With the block undecked the quench height would be 0.070" and the SCR would be lower at 9.4:1. This rod/piston combo would allow you to set the SCR at your desired level but with a lower quench height.

[Jr. Mechanic]

If I went with these:

http://www.summitracing.com/parts/slp-h ... /overview/

What would the 1.592 compression distance do compared to the stock pistons?

If I were to leave my deck height alone and go with the .073 quench, what would the negative effects be other than definitely requiring premium fuel? Is there a thinner head gasket available than .043?

Stock pistons have a compression height of 1.601". Unfortunately all the aftermarket pistons are shorter and the Speed Pro H802CP's are the tallest of them with a compression height of 1.592". Those pistons have a 15.2cc dish so if you left the block undecked, the quench height would be 0.073" and the SCR would be 9.9:1 (assuming 57cc head). You could gain some volume and lower the SCR by polishing the combustion chambers and piston dishes to a near mirror-like finish.
Alternatively you could use the 4.0L rods with IC944 pistons (21cc dish). With the block undecked the quench height would be 0.070" and the SCR would be lower at 9.4:1. This rod/piston combo would allow you to set the SCR at your desired level but with a lower quench height.

The IC944's just plain aren't in the budget or else that's the route I would take.

Is there a thinner head gasket than .043" available? Would I be able to get away with running the stock deck height with a quench of .073" and 9.9:1 compression? What would the negative effects be? I'm aware a tighter quench generally equates to more power and less chance of predetonation. If I run strictly premium fuel could I get away with it or am I just asking for trouble?

Alternatively, if I were to deck the block .020" for a .053" quench and end up with a 10.3:1 CR, what would the negatives be, especially without a forged bottom end? I know I can't expect it to last another 200,000 with that high of a CR, however as I stated before I am looking short term reliability. This rig has another 50,000 miles in it at the very most.

Basically my question is this: Am I better off with a .073" quench with a 9.9:1 CR, or a .053" quench with a 10.3:1 CR? Or even a .063" quench with a 10.1:1 CR?

[Cheromaniac]

Is there a thinner head gasket than .043" available? Would I be able to get away with running the stock deck height with a quench of .073" and 9.9:1 compression?

That's the thinnest HG you can get. If you can live with using premium fuel on a daily basis, just run a 9.9:1 CR with the stock deck height and use a bigger CompCams 68-235-4 instead of the 68-231-4 that I mentioned earlier. The bigger cam will lower the DCR just enough to keep detonation at bay.

[Jr. Mechanic]

Is there a thinner head gasket than .043" available? Would I be able to get away with running the stock deck height with a quench of .073" and 9.9:1 compression?

That's the thinnest HG you can get. If you can live with using premium fuel on a daily basis, just run a 9.9:1 CR with the stock deck height and use a bigger CompCams 68-235-4 instead of the 68-231-4 that I mentioned earlier. The bigger cam will lower the DCR just enough to keep detonation at bay.

I like those cam specs, a lot actually.

Can you confidently tell me I will be okay, or am I asking for trouble leaving my quench that high?

On another note, I'm definitely going with the Comp 235 cam. Instead of the MP springs, I plan on ordering a set of Hughes 1110 springs (same specs as the MP's at half the cost), along with the matching 1278 retainers and new valve locks.

[Cheromaniac]

Can you confidently tell me I will be okay, or am I asking for trouble leaving my quench that high?

I wouldn't sweat too much over the quench. Matching the cam duration and valve opening events to the SCR is far more important in order to keep cylinder pressure and DCR at a level where you can run pump gas without detonation.
Polishing the combustion chambers/piston dishes and feathering out the sharp edges will also help some.

[Jr. Mechanic]

Can you confidently tell me I will be okay, or am I asking for trouble leaving my quench that high?

I wouldn't sweat too much over the quench. Matching the cam duration and valve opening events to the SCR is far more important in order to keep cylinder pressure and DCR at a level where you can run pump gas without detonation.
Polishing the combustion chambers/piston dishes and feathering out the sharp edges will also help some.

Thank you very much for the advice, I appreciate it. Are there any issues with using the Hughes springs and retainers over the Mopar Performance? Ive used them in several Magnum engines with no issues and they all seemed to be high quality pieces. I'll be able to get the springs, retainers, and locks for less than $150 whereas the Mopar Performance springs, retainers, and locks would be closer to $300.

Is the timing set that comes with the Comp kit any good? It doesn't specify what type it is. I figure for another $40 over just the cam and lifter kit it would be worth it instead of a stock replacement though.

Here's my current parts list:

Have/Ordered

4.2L Crank/Rods
ARP Rod Bolts
APN Stainless Header
99+ Intake Manifold
703 Neon Injectors
Sealed Power Cam Bearings
Dorman Harmonic Balancer
Brass Freeze Plug Kit
Sealed Power Rocker Pivots
New water pump, hoses, thermostat, severe duty fan clutch

Need To Order:

Speed Pro ZH802CP60 Pistons
Sealed Power ZE234K60 Moly Ring Set
Main and Rod Bearings (will probably have the machine shop source these)
Hughes 1110 Springs, 1278 Retainers, and Locks
Mopar Performance Head Gasket
Comp Cams SK68-235-4 Cam, Lifter, and Timing Set
Gasket Set

Any suggestions/Changes?

[SilverXJ]

Are there any issues with using the Hughes springs and retainers over the Mopar Performance? Ive used them in several Magnum engines with no issues and they all seemed to be high quality pieces.

If they have the same dimensions and similar loads they should work fine. Keep an eye on the closed seat load and open load. Since you used the in a Magnum, which is a roller cam iirc, so they may be a bit on the stiff side. If you do use they let us know how it works out.
Make sure to get your balancer balanced. They frequently aren't. Personally I try to avoid Dorman parts as much as possible.

[Jr. Mechanic]

Are there any issues with using the Hughes springs and retainers over the Mopar Performance? Ive used them in several Magnum engines with no issues and they all seemed to be high quality pieces.

If they have the same dimensions and similar loads they should work fine. Keep an eye on the closed seat load and open load. Since you used the in a Magnum, which is a roller cam iirc, so they may be a bit on the stiff side. If you do use they let us know how it works out.
Make sure to get your balancer balanced. They frequently aren't. Personally I try to avoid Dorman parts as much as possible.

You're right, roller cams are *supposed* to have stiffer springs... But as we figured out in my other thread the stock Magnum springs are the same as the stock 4.0 springs. The MP P5249464 and Hughes 1110 are the two big springs used in Magnum build ups, so I figure if they're interchangeable for that application they should be for the 4.0 as well. Here's the 1110's:

http://www.hughesengines.com/Index/prod ... rtid=10280

[Cheromaniac]

The MP P5249464 and Hughes 1110 are the two big springs used in Magnum build ups, so I figure if they're interchangeable for that application they should be for the 4.0 as well. Here's the 1110's:

http://www.hughesengines.com/Index/prod ... rtid=10280

Those Hughes springs should work but since their installed height is 1.660" compared to the installed height of 1.640" of the stock springs, it looks like the spring seats will need to be cut 0.020" deeper. Find out how much that'll cost 'cause that'll eat into any savings you'd make over using the Mopar springs.

[Jr. Mechanic]

The MP P5249464 and Hughes 1110 are the two big springs used in Magnum build ups, so I figure if they're interchangeable for that application they should be for the 4.0 as well. Here's the 1110's:

http://www.hughesengines.com/Index/prod ... rtid=10280

Those Hughes springs should work but since their installed height is 1.660" compared to the installed height of 1.640" of the stock springs, it looks like the spring seats will need to be cut 0.020" deeper. Find out how much that'll cost 'cause that'll eat into any savings you'd make over using the Mopar springs.

I've always been told that .020" difference in install height is 4 pounds either way, so I'm not going to concern myself too much with that.

[SilverXJ]

I don't see how that generalization can hold up for all springs with different spring rates. Anyhow, the 120+ lb is a bit much so it is an option to increase stack up heigth and get the seat load that the cam manufacture recommends (usually around 110 lbs). Or it may just not matter that much.

[Cheromaniac]

I've always been told that .020" difference in install height is 4 pounds either way, so I'm not going to concern myself too much with that.

Those Hughes springs have a spring rate of 360lb/in. so a 0.020" increase in installed height would reduce the spring pressure by 7lb. If you kept the installed height at the stock 1.64", the spring pressure would be 127lb and that'll be too high. If the cam manufacturer recommends 110lb at the seat, you'll need to machine 0.050" from the spring seat and set the installed height at 1.69".

[Jr. Mechanic]

I'm going to put the valve springs on the back burner for now and concentrate on the bottom end.

I made it over to the machine shop last night after work. Pretty reasonable pricing and he said we should be able to work on the price a little, plus I can use my shop's tax exempt status. Here's what him and I came up with at a bare minimum:

Mag block: $30
Hot tank: $40
Bore/hone .060: $180
Install cam bearings: $40
Resize rods: $90
Remove/install pistons: $70
Polish Crank: $40

Total: $490.00

Here's worst case scenario:


Mag block: $30
Hot tank: $40
Bore/hone .060: $180
Install cam bearings: $40
Resize rods: $90
Remove/install pistons: $70
Grind crank: $170
Deck block: $65

Total: $685.00

He also said they can assemble the short block for an additional $250.00 which is tempting.