another n00b, another build

[tomcat]

my 4.0 died recently, with only 140k on the clock . drained out a gallon or two of coolant from the pan. radiator drain didn't let out a single drop....

it is coming out of (and going back into a '99 XJ, aw4 (lifted, 31's, locked, blah blah blah)

instead of fixing, why not upgrade?

here is the build idea so far:
4.2 crank and rods (that is obvious)

~ Keith-Black Silvolite UEM-2229 +0.030" bore pistons
~ Piston dish volume -> 22cc
~ CompCams #68-231-4 206/214 degree camshaft
~ Mill block deck 0.035"
~ Mopar Performance 0.043" head gasket
~ Ford 24lb/hr injectors with stock 49psi FPR

I plan on doing a bored out throttle body too, and because it is a 99, it already has the good intake.

the recipe that i am using says this will be a 0.058" quench, my question is when playing with the compression ratio calculator, i am not sure what to put down for the deck clearance to get this number to come out for the quench, or how i could determine that from the parts selected. or should i just tell the machine shop 0.035 and call it good? i am reluctant to buy any parts until the block comes back from machining, or is this just stupid?

also, the current block is an NVH block. my cousin did a stroker kit years ago, and give me his old short block. it is a 1991-95 53008405 block. if i threw a rod into the water jacket, is there any reason to NOT use the 91-95 block for the build? is the extra webbing on the NVH block worth it? i have access to a 98 wrangler shortblock if this is the case, it just means pulling it (framerails are on the ground at the present moment) so it isn't as convenient as the 94 in my garage.

so, does the build make sense, and am i on the right track?

awesome forum, learning a lot so far. all the accessories are off of the motor, just need to take off the exhaust, fuel line, and trans, and the motor should be out this coming weekend.

[gremlinsteve]

right away i would say you might need a custom pushrod for that much decking of the block. all else to me looks like a good combo.
should have alot of cyl pressure with the short duration cam and might need better fuel for that reason that say..87 octane.

i am sure others will chime in...

i just got my new long block in...going to start my build one day...


steve

[tomcat]

i am willing to change the recipe, i am just going from what others have written:
(low buck 4.6 rockcrawler option 2)
http://www.jeep4.0performance.4mg.com/stroker.html

i guess the 4.6 low buck option 1 gives a very similar result, the cam i specified in my modified recipe, with no decking, but a higher quench height. from everything i have read, a lower quench height the better, so maybe use that recipe, and deck the block a bit? torque value is that same at the same RPM, so i can be pretty happy with that, and no added expense of piston dishing. i think quench is my only question for this build in this case. it looks like the SP 667 piston is also a decent option in this case, add more combustion volume, and reduce the compression ratio. ugh, this is confusing

would love to hear if anyone has run the 4.6 option 2 in an ODBII truk, and if they have had any problems etc.

[oletshot]

From what I see, he needs to shorten the rods by .043" (.035" from decking and .008" from the thinner head gasket). That would mean, he should need 9.598" long push rods (9.641-.043=9.598). He should be able to get away with Sealed Power RP3171 push rods from a 1980 4.2L, as they are 9.594. Of course that assumes the cams are the same diameters, not across the lobes of course.

[rradford9]

the recipe that i am using says this will be a 0.058" quench, my question is when playing with the compression ratio calculator, i am not sure what to put down for the deck clearance to get this number to come out for the quench, or how i could determine that from the parts selected. or should i just tell the machine shop 0.035 and call it good? i am reluctant to buy any parts until the block comes back from machining, or is this just stupid?

I kinda went through the same thing in my build. I was confused for a week or so until I finally figured it out. The absolute best way (and only way to measure your true deck clearance) is to install one of the pistons on the rods and mock up the crank and piston assembly. Make sure to include the rod bearing when mocking it up. Someone on here forgot it, I won't mention names

You can also calculate the theoretical deck clearance using this formula.
Deck height = Rod length + stroke/2 + piston pin height + deck clearance
According to Dino's website the stock deck height for all 4.0's is 9.453". Also, the 4.2 rod length is 5.875" and the stroke of the 4.2 crank is 3.895". You will need to find out the piston pin height for the KB pistons and then just solve for X. When I did this I got within .003-.008 of my actual deck clearance.

9.453" = 5.875" + (3.895"/2) + Pin height of piston + X


Then to determine how much you need to deck, quench = deck clearance + head gasket height.
So, .058= deck clearance + .043 (If you use the VR MLS headgasket the height is actually closer to .038")


Hopefully that makes sense...

[tomcat]

awesome, this tells me pretty much what i needed to hear, and have been using the CR calculator all night.

this is where i am now:
(3.895/2)+5.875+1.585=9.4075" (Speed Pro 677CP pistons with 4.2 crank and rods) 0.0446 from stock block height,
theoretically removing .030 from the block to bring the deck clearance down to 0.0146, and use the .043 head gasket for speculation purposes. plugging this into the CR calculator, i get this:



i think that is pretty damn good, and don't have to pay for piston dishing.

[RAPTORFAN85]

You might have to run premium with that setup. 8.54 DCR is kinda high

[Exos]

Problem I see here is piston dish a little low. I'm using forged pistons, so I don't know alot about cast pistons for that recipe. But I would choose a bigger dish to get DCR down a bit.

I'd say aim for a quench of 0.040-0.045. Have the block zero-decked. No need for calculations, give your pistons, rods and bearings to your machinist and tell him you want zero deck. Your quench will be whatever gasket thickness you choose.

Man did I learned some things since I'm here..!!

[tomcat]

that is the deepest dish i could find from the factory...

Stock 4.0 cast aluminium '87-'93 #83500251, '94-'95 #4773157, '96-'04 #4798329----1.601" 13.1cc
Keith-Black Silvolite hypereutectic 2229----1.581" 11.5cc
Speed Pro hypereutectic H825CP----1.592" 15.8cc
Speed Pro cast aluminium 677P/677CP----1.585" 17.5cc
Speed ProH802CP/18.8cc

any recomendations on dishing pistons? it sounds like the "factory" pistons don't have enough

thanks for all the help, i really appreciate it. zero deck with the SPH802cp/18.8cc actually gives me 8.68DCR (higher) and a 0.043 quench (lower, but better) .22cc dish puts it right at 8.4DCR.

anyone know a good piston to dish? i know i started this whole thing off with the KB's but i have been hearing mixed things about them.

[Exos]

Why not use the 242 rods, and KB (or other) forged pistons? My KB944 have 21.7 dish volume. Sure, it costs more, but you have forged pistons and don't have to dish 'em.