4.6L "Poor Mans" Questions

[SilverXJ]

KB944s are semi custom forged pistons. They are made to work with the 4.0L rods on the 258 crank. However they still sit about .020" down int he hole and you still need to deck the block to get a decent quench.

[woodjeep]

Thanks...just wanted to make sure he didn't have the wrong pistons for those rods

[go4lo]

KB944s are semi custom forged pistons. They are made to work with the 4.0L rods on the 258 crank. However they still sit about .020" down int he hole and you still need to deck the block to get a decent quench.

That was my main question, should I still have the block decked with the KB944s. Thanks for the response.

[gradon]

The KBs will still be about .030" below deck, so your block could still use some decking to get a good quench(it'll be slightly better quench than stock with the .043/4" hg or slightly worse w/ the .051" hg). Is it necessary? No. Play around with the calculator and see what a difference .030" will make on the SCR&DCRs.

[go4lo]

The KBs will still be about .030" below deck, so your block could still use some decking to get a good quench(it'll be slightly better quench than stock with the .043/4" hg or slightly worse w/ the .051" hg). Is it necessary? No. Play around with the calculator and see what a difference .030" will make on the SCR&DCRs.

Regarding the quench height. When I use the calculator with a stock deck height of .0215" with the .044" HG it gives me a quench height of .0655". I assume this is not an ideal height? A lot of people seem to be successfully running the "poor man's" quench height of .081" which is .016" more than my recipe? Since I'm considering running the 4.0L rods and KB944s does quech height become even more of a factor?

[go4lo]

Ok, I ran the numbers again on the calculator with milling the deck to 0.00 and milling to 0.010.

At 0.010 my quench drops to .054 and SCR up to 9.55:1
At 0.000 my quench drops to .044 and SCR up to 9.75:1

My fear is with a SCR of 9.75:1 will I only be able to run 91+Octane?

[gradon]

Your deck clearance will change from .0215" to about .0295" due to the compression height of the KBs(1.353"). The long rod w/ kb combo should be less prone to pinging(bigger dish and longer dwell at tdc). My build is a 10:1 scr and 8.57 dcr. I'm in the red with the high dcr. Shoot for a 8-8.25 dcr and you'll be fine. Some people want to use 87 and others want to use 93 and max out the compression(more power). I would always shoot for a .010" or less deck clearance. I just ran numbers and if you took .020" off, you'd be in the 9.7:1 scr range and 9.9:1 if you took off .029"(based on a 57cc CC).

[go4lo]

Your deck clearance will change from .0215" to about .0295" due to the compression height of the KBs(1.353"). The long rod w/ kb combo should be less prone to pinging(bigger dish and longer dwell at tdc). My build is a 10:1 scr and 8.57 dcr. I'm in the red with the high dcr. Shoot for a 8-8.25 dcr and you'll be fine. Some people want to use 87 and others want to use 93 and max out the compression(more power). I would always shoot for a .010" deck clearance. I just ran numbers and if you took .020" off, you'd be in the 9.7:1 scr range and 9.9:1 if you took off .029"(based on a 57cc CC).

ok, so now i'm confused even more. how are you calculating the .0295" deck clearance with KBs? If this is case then wouldn't the calculator be off since the formula is based off a stock .0215?

I noticed this on Dino's site:
If the stock Jeep 4.0L 6.125" rods are used, expensive custom forged pistons with a shorter pin height than stock (1.380") are required to achieve zero deck clearance, but these allow you to avoid milling the block deck and you can select the head gasket thickness required to achieve the desired 0.040"-0.050" quench height.

[gradon]

Even though you're using the same rods(which are 6.123" btw), you're using a different crank with more stroke and a different piston with a shorter comp height, so throw that .0215" deck clearance out. When you are using the calculator, are you using KB's 1.353" comp height? An ideal custom piston would have the additional .0295" comp height over the KB's. 1.353+.0295=1.378"(which is why dino said 1.38" is the dimension to choose when ordering a custom piston). IMO KB blew it when choosing their comp height. It should be at least 1.373" and they even give wrong SCR specs on their site and assume you've taken .020" off(the .020" they should've added).

I see that they are no longer kb944/945s, but have a new name: THE ICON FORGED & FINISHED IC944/945:
http://www.kb-silvolite.com/icon/icon.p ... s&P_id=543

As you'll note, they assume you have a 60cc combustion chamber and the deck height is 9.433(.020"-.023" less than stock).
As a side note, I still prefer using the old calculator in the general board discussion.

[go4lo]

ok, i'm with you now. thanks for all the help.....i feel like an idiot asking all the questions but i'm still new to engine building.

what do you think about this combo?

4.7L +.060
Bore: 3.935"
Stroke: 3.895"
Combustion Chamber: 57cc
Deck Clearance: .0095"(.020 milled off deck w/KB944s)
Gasket Thickness: .044"
Gasket Bore: 4"
Dome/Dish/Valve: 21.7cc (KB944s)
Connecting Rod Length: 6.123" (stock 4.0L)
Cam Intake Dur: 250* (Comp Cams 68-241-4)
Cam Lobe Separation Ang: 111*(Comp Cams 68-241-4)
Advance or Retard: 4* Advance (Comp Cams 68-241-4)

[gradon]

Looks like a good recipe to me. I was where you're at--keep asking away.

[go4lo]

Looks like a good recipe to me. I was where you're at--keep asking away.

I forgot to include these:

9.66:1 SCR
8.43:1 DCR
0.0535 Quench

Basically a copy of Dino's "Medium Buck" build

A few more questions:
Do you think I can run 89 on this combo?
What springs, locks, retainers need to be used on my 0630 head with the Comp Cam?
What should I expect to pay to have the block milled?
I have a 12wt crank on the way with matching rod and main bearings, can the rod bearings be used with the 4.0L rods or do I need to order 4.0L rod bearings?

[billy_bob]

ok, i'm with you now. thanks for all the help.....i feel like an idiot asking all the questions but i'm still new to engine building.

what do you think about this combo?

4.7L +.060
Bore: 3.935"
Stroke: 3.895"
Combustion Chamber: 57cc
Deck Clearance: .0095"(.020 milled off deck w/KB944s)
Gasket Thickness: .044"
Gasket Bore: 4"
Dome/Dish/Valve: 21.7cc (KB944s)
Connecting Rod Length: 6.123" (stock 4.0L)
Cam Intake Dur: 250* (Comp Cams 68-241-4)
Cam Lobe Separation Ang: 111*(Comp Cams 68-241-4)
Advance or Retard: 4* Advance (Comp Cams 68-241-4)

This is pretty much the set up im going with, but Im going with the comp 68-239-4 and a 1990 block which has a shorter deck height. Ive been having trouble finding a 4.00 bore head gasket, around .044 compression thickness. anyone know a good web site? everyone i found is 3.875 bore

[billy_bob]

im wanting to put a shot of nitrous in it too...

[MapleDitch]

This is pretty much the set up im going with, but Im going with the comp 68-239-4 and a 1990 block which has a shorter deck height. Ive been having trouble finding a 4.00 bore head gasket, around .044 compression thickness. anyone know a good web site? everyone i found is 3.875 bore

I have the Mopar 4529242 sitting on my bench, and it measures a 3.98 bore with .044 compression thickness.

I got it here for dirt cheap: http://chucker54.stores.yahoo.net/jecyhega.html