Engine rebuild questions

[Maurice66]

1978 Cherokee Chief. 185,000 miles,4 speed with lock outs. 360 in the shop and needs a new cam, over sized pistons (.10),guides and a couple valves. Not to bad. Question: This is going to be a cruising rig, trail riding(?), highway and towing my military jeep. So is there any improvements I can make while its being rebuilt to improve fuel mileage, reliability and maybe add a little HP? Also is there any inheritance issues with the engine,transmission,transfer case and diffs that I can take care of while the engine is out of the vehicle? Its mostly original. The ignition is Motorcraft and the carb is also Motorcraft. The inside is totally gutted. OK I am rambling, you get the idea. Thanks for your help!

[440sixpack]

For all practical purposes higher compression pistons are where it all starts. how much fuel economy are you willing to sacrifice and how much money do you want to spend? that is what you need to decide and then you can make a plan..

I rebuilt my 360 with a mild cam upgrade and pistons to put me in the 8.5 to 1 range and kept it pretty much stock. I'm not headed to the drag strip so this works for me.

As far as the rest of it goes you say it has 188 k on it . that in itself means you should be planning to rebuild everything in the not too distant future upgrades or not. Your TH400 has no inherent issues, your axles don't either. but they wear out.

[Ristow]

put cam bearings in it. the performer grind is the best cam for a stock block,it'll make the most usable power in the transmissions shifting range.

dual exhaust,and long tube headers as well are a big help.

[Maurice66]

Thank you for your replies. Good stuff. Another question: What about all that emissions tubing? Can I eliminate all that without affecting the engine performance? I mean will it idle and accelerate OK without it? I want to just get to the bare necessities. Is the Motorcraft carb OK to rebuild or do you suggest another? What about the ignition system? I heard it is suspect? Thank you for replying and helping a noob out!!

[BA_051]

Personally, If i was to build a mostly stock 360, I would put amc 343 flat tops in it with a melling MTA-1 cam, or the performer cam, both are very similar grinds if not the same... anyway, back to the specs...

4.08 bore plus 0.010 overbore
3.44" stroke
5.875" rod length
with the performer or melling cam, intake closes 27 degrees ABDC...
compression ratio:
343 4 barrel pistons are 4.0cc flat top
343 2 barrel pistons are 12cc flat tops (so it seems)
stock, low comp 360 pistons are 28cc
Heads (Im assuming 1974+ are 58cc heads)

static compression ratios are 10.82:1 with the 4 barrel 343 pistons and 9.87:1 with the 343 2 barrel pistons...

Dynamic compression is where its at... With the melling/performer cam, the dynamic ratios are 10.42:1 with the 4 barrel 343 pistons, and 9.46:1 with the 2 barrel pistons.

9.46:1 can run on regular pump gas just fine, the 10.42 may need mid grade... My stroker was 11.6:1 static, 10.2:1 dynamic and i could run it on regular, but I lived at 5000-7000 ft... For just a daily driver, I would recommend the 4 barrel 343 pistons.

As for other upgrades... Run some nice long tube headers... the Motorcraft distributor is ok but do the TFI upgrade or run an HEI... And put on a performer intake and 4 barrel carb. Get rid of all the emissions, your motor will thank you. The motorcraft 2b is decent, but an edelbrock or holly 4 barrel, 500-600 cfm will really wake it up especially with headers and higher compression.

[J20 project]

Built a couple....my thoughts are:

Interior: 9.0-9.5:1 compression. I agree on the performer cam grind...pretty much the Melling Mt 1A grind(used it before)...Headers if a highway rig...manifolds if trail only and say 65-70 mph short run miles.\
Melling double roller timing chain and gears. Cam bearings, triple check the rockers/bridges/pushrods. three angle grind on the valve seats. I had an engine fail and starve #7 and 8 rod bearings so.....oil galley bypass.

Exterior: HEI ignition. HEI type 8mm wires, better plugs,,,lastly...and I could not justify it yet...fuel injection. I am running Edelbrock manifold and carb w/ Hedman headers....works but I wish...hope for injection

Oh, and fuel mileage....phttt. .good luck w/ that.


J20

[440sixpack]

You're pushing the limit of premium pump gas at 9.5 to 1 and will probably have to retard timing a bit. 10.5 to 1 you're on performance fuel . I'm talking actual compression and practical cams . decide if it's worth it to you.

My 10.5 engines need a blend of super and race fuel or LL100 to run decent at all.

There are issues according to competent builders with 343 pistons you need to be clear on if you go that route. nothing that can't be overcome but must be considered.

[babywag]

Honestly the octane/compression deal gets exaggerated IMHO.
No reason w/ proper tuning you shouldn't be able to run 87 octane even @ 9.5:1.
These aren't high reving race engines @ the track.
Just need to dial in the timing curve properly.

Plenty of engines on the road that do just fine on 87 octane.

[440sixpack]

To run TRUE 9.5 compression on 87 octane you'll have to retard the timing to a point you're gaining nothing over 8.5 compression.

[68glad]

ok whats true 9.5 compression mean in layman terms? My calculations on my engine says 9.5cr & i run 87 octane.

[440sixpack]

Your calculations based on what information ? did you do the measurements or use the advertising specs?

I can make a 10.5 engine run on 87, just not for crap. lets not make crap our goal.

9.5 compression needs a minimum of 91 to function at even a reduced level.

http://www.carbibles.com/fuel_engine_bible_pg3.html

[babywag]

Again these aren't race cars revving to 6k+
OP is asking about a 78 360/4spd equipped Cherokee.

Believe whatever you want/read...
A mild 360 @ 9.5cr will likely be just fine on pump gas 87 octane even.

You are comparing apples vs. oranges with your 10.5cr engine, that requires 100 octane race fuel.

[440sixpack]

not really. I have a 1970 AMX with a 390 built to 9.6 to 1. no way in hell will it run decent on 87. no way. even with premium it's marginal unless I keep the advance backed off a bit. add 25% LL100 and it purrs like a kitten with the timing where it belongs.



It's simple physics it's not a matter of opinion. you can retard the timing to get away with it but as I said why build it if you're not going to feed it what it needs? if you want to pay for 91 go for it. in a Jeep it made no sense for me and I suspect the OP may feel the same.

[babywag]

There are many on here that have no issue(s) running there modified JEEPS on 87 octane. It's all in the tune/timing, you will never notice any minor hp loss unless you're on a chassis dyno with the thing.

Mine runs the same on 87, 93, or 110. I've made passes back to back with 87 vs 110 it runs nearly identical times either way.

my 401 is 9.5+ and burns 87 octane fine.

An AMX isn't a Jeep, and again comparing it to one is pointless. Totally different animals.

You do realize how many cars came outta the factory with 9.5cr or higher these days? That run fine on 87...

[Ristow]

i ran 15 degrees initial timing on that 401,and no egr. it would burn 87,but i ran 91 for the no alky.

AMC combustion chambers are pretty tolerant of compression.

but as BA051 said,dynamic is what's important. and these motors will tolerate 9.5 static with a mild cam.