Another 4.0L rebuild question :)

[Old XJ]

Hello all and thanks in advance for any input that can be added!
I'm a new guy and have been lurking here for a while.
I apologize in advance for the long winded first post.

I have a 93 Cherokee sport 4x4 that has given up the ghost and will be rebuilding a 4.0 out of a 94 donor parts car I have.
The jeep currently runs fine with no cooling issues as all those parts are new.
It just has something in the bottom end coming apart loudly and is toast with 318,000 showing on the odometer.
I'd like to stroke it, but that's not in the cards right now.
I want to finish up with a strong stock engine.

It will be a daily driven car and a vacation car in the future.
I literally could see duty from Key West FL to the Rocky Mountains.
It will have 4.10 gears and 31 inch tires.
Cruise rpms should run 1800-1850 at 55MPH and 2300-2350 at 70MPH

Should this combo run reliably on pump gas with no issues?
I entered this info into the calculator and came up with.

.0165 Deck clearance
.051 Head Gasket
Pistons 11cc dish
Cam intake duration 242
Lobe separation 108

Calculated Results:
Cubic Inches: 245.26
Liters: 4.02
Static Compression Ratio: 9.1 :1
Dynamic Compression Ratio: 8.03 :1
Quench: 0.0675
Intake Valve Closing Angle: 49


This is the parts list I have come up with so far
.030 over bore with 2229C Silv-o-lite pistons.
Comp Cams 68-501-5 Advertised Duration 242/246, Lift .450/.450 lobe separation 108
Comp Cams Lifters
The rest of it will be stock components
Clevite bearings
Felpro gaskets
Cloyes timing setup
Melling standard oil pump and pickup tube.
Melling Rocker kits and Melling pushrods.
New replacement stock injectors.
I will have the head worked with new stock valves and springs.
Thanks again and sorry for the long post!

Jeff

[Randy Bobandi]

I have a 93 Cherokee sport 4x4 that has given up the ghost and will be rebuilding a 4.0 out of a 94 donor parts car I have.

I'd like to stroke it, but that's not in the cards right now.

Should this combo run reliably on pump gas with no issues?

Cam intake duration 242
Static Compression Ratio: 9.1 :1
Dynamic Compression Ratio: 8.03 :1

You can run whatever compression ratio you want on pump gas as long as the fuel and ignition maps oblige.

Why not just run the stock engine from the 94'? Why let the magic out? With the stock ecu and fuel system, it won't make any more power regardless of modifications anyway.

You noted intake duration at 242'. That must be advertised duration which is irrelevant and for marketing only. Duration at .050" tappet lift is standard.
Dynamic compression is also mostly irrelevant.

[Old XJ]

I have a 93 Cherokee sport 4x4 that has given up the ghost and will be rebuilding a 4.0 out of a 94 donor parts car I have.

I'd like to stroke it, but that's not in the cards right now.

Should this combo run reliably on pump gas with no issues?

Cam intake duration 242
Static Compression Ratio: 9.1 :1
Dynamic Compression Ratio: 8.03 :1

You can run whatever compression ratio you want on pump gas as long as the fuel and ignition maps oblige.

Why not just run the stock engine from the 94'? Why let the magic out? With the stock ecu and fuel system, it won't make any more power regardless of modifications anyway.

You noted intake duration at 242'. That must be advertised duration which is irrelevant and for marketing only. Duration at .050" tappet lift is standard.
Dynamic compression is also mostly irrelevant.

That’s good to know.
I was just imputing numbers into the caculator here and those are what is ask for.
I thought (and you know what that leads to) that stock numbers are lower from the factory.
I was under the impression that if the dynamic compression went too high that it could cause issues and I really don’t know what the stock numbers would be.

The 94 is high mileage and is due an overhaul.
I want to do this once and the knowledge here seems to be first rate.

Thanks for your thoughts on it!

Jeff

[Randy Bobandi]

[/quote]

I was under the impression that if the dynamic compression went too high that it could cause issues and I really don’t know what the stock numbers would be.

[/quote]

4' advance, the stock 91'-95' intake valve closes 27' after bottom dead center. 8.5:1 Dynamic Compression. 14' advance at WOT, 8.7:1. Insignificant...

Of course. If cylinder pressure exceeds the limits of a given octane, the mixture will pre-ignite. Compression is far too often over-emphasized however. Ignition timing is easily modified to allow for proper combustion for any fuel type and any compression ratio.

You kinda mentioned that you want to do this once, and only once. Get the proper ECU and never look back. FuelTech FT550. You didn't mention a power goal though, so if you would rather keep the stock setup, keep the stock engine.