Need some math help here

[SSC-XJ]

Hello board,

I'm new to this board but not in the Jeep world. I have a race XJ stroked originally with a AP Stroker kit 4.6L with Eagle 4.2L forged rods with flotating pin and the kit came with Venolia pistons in 0.030"

After many many races and seevre punishment, the engine gave up with the recently N20 added and shot of 50 HP with some over heat while trying to climb a big dune.

Anyways, I need a set of forged pistons to repalce my worn pistons. The block was in .030" (hence 4.6L) the crank it's the 4 counterweight model with the know 3.895" stroke. The CR was 9.5:1 told by the kit. The quench it's unknown at the moment of the build in that time as well the cc's piston and head combustion chamber.

My machinist said my block support fine .040" super. SO this is the route I want to go. Also, I want to yield 9.0:1 CR this time, in favor of prevent knock-ping during race with soe little over heat of the engine as well the pump stations vary it's fuel quality alot down here and can knock sometimes even with noral temp engine.

I'm undiceded what brand of piston to go:

Diamond
JE
Ross
Wiseco
CP

So far I took messures of the head and got 57cc on each combustion chamber for the head. What would I need to get optimal power with reliable against ping using 90octane fuel (90, 95, 98 available ove rhere, but 98 it's in real life about 93 US octane grade so don't get fooled). What would be the optimal quench? CC's for the dished piston?

These are some numbers I got from the block today in the machinist with the old Venolia pistons:

- Piston deck clearance : 0.009" (stickin over the block-deck) But this was with recently fresh machined-milled crank journal seats of the block to get them stright, machinist told they milled down about 0.003", so that would be equal in the past like 0.006" sticking above the deck (I even got knock with this quench sometimes)

-Piston compression height : 34.79mm

-Engine block deck height : 239.71mm

-Stroker crank : 3.895"

-Rod Lenght C-C Eagle : 6.150"

-Chamber volume : 57cc

What else I'm missing to order the correct pistons?

Thanks for any tip-feedback.

-Diego

[SSC-XJ]

I forgot to mention, I'm installing the MOPAR HG multilayered steel P/N: 53010587AA wich has 1.5mm of height.

[Flash]

Are you saying that your present piston, set above the block buy .006"???????? that would be extremely good quench.....maybe to good.........

I thing the new forged KB-944 piston would be perfect with your Eagle rods (6.150") Don't know for sure, you would have to do some math to make sure that rod wouldn't make the piston stick up to far....................but they would be cheaper then custom.....and maybe just as good!?

Something tells me you were a long ways a way from a good Quench (.040) the better you quench the better chance that 9.0:1+ compression will run on a lower octane.

What failed in you motor?


Flash

[SSC-XJ]

Two rod bearings rolled-seized and the psitons of those bad bearing got sided wall , scuffed.

I'm not good in maths, and worse in " inches messures, I prefer use mm wich it's a lot easier. I will have to check the deck o piston clearance again as that number, 0.006" to be extremely good, maybe it's 0.06", but I will have to double check that by tomorrow in the machining shopp.

Now, the quench stuff, how do you actually messure it? by the piston-deck clearance? Or it's another thing?

ABout that piston, I will have to ask Sil-o-lite, you refer they are forged? That would be cool.

[RAPTORFAN85]

Correct me if I am wrong Diego but you were running a supercharger on this engine right?

[Mgardiner1]

Also, what cam are you running? Don't get tooooo crazy about static compression ratio as dynamic compression ratio has more of an effect on pump gas

[Exos]

Your 0.006 must have been below deck... I'm pretty sure.

I don't think that the KB944 will work with the Eagle rods. They are made to work with stock rods, at 6.123".


And : Quench height = Deck clearance + compressed head gasket thickness

[Alex22]

If you are looking for a forged piston and want to keep the Eagle connecting rod you are going to need some custom pistons made up.
From the list of manufacturers I would say (quality) JE, Diamond then Ross. The only weisco pistons I have used were for snowmobiles and quads.
The CP brand sounds familiar but I can't remember much about them.

[Flash]

Your 0.006 must have been below deck... I'm pretty sure.

I don't think that the KB944 will work with the Eagle rods. They are made to work with stock rods, at 6.123".


And : Quench height = Deck clearance + compressed head gasket thickness

I could be wrong, but it seam to me that when the Kb944 came out that they still set in the hole (below deck)
and the Eagle rods would put then flush with the deck.


Quench is the distance between the top of the piston and the top of the head,(flat surface) With the head gasket installed.


Flash

[Exos]

I could be wrong, but it seam to me that when the Kb944 came out that they still set in the hole (below deck)
and the Eagle rods would put then flush with the deck.

You may be right. But what about pin diameter? KB's have a .931 pin, and Eagle rods have a .912 pin... unless I don't have the correct info.

[gradon]

We discussed this when we first found out about the KBs, right? The 6.150" eagles are for full floating pistons--the KBs are not. How awesome would it be to be able to use them 6150s and the KBs w/ a 1.353" pin height. With the first calc we had here, the KBs would stick .003" or so above deck(which is fine for those who don't know--imagine using the .043"hg and having a .040" quench). However, there are deck height tolerances, so you really have to measure to be exact cause it'll be +/- thousandths). As said, you have to go with custom forged floating pistons to use the eagles and so the custom combo can cost $800-1000 easy(but is worth it for the $3K-5K builds, and esp. with the forced induction builds).

[Flash]

Yah forgot about the pressed to floating pin issue

Flash

[SSC-XJ]

I'm having a hard time to order my pistons, none of the pistons company are replying my emails. I guess the economic situation for all them are fine and it's not affected by the rest of the world because seems they don't want to make business.