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  #1  
Old 08-12-2017, 09:01 AM
Maurice66 Maurice66 is offline
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Engine rebuild questions

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!
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Old 08-12-2017, 09:29 PM
440sixpack 440sixpack is offline
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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.
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  #3  
Old 08-13-2017, 01:51 PM
Ristow Ristow is offline
 
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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.
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  #4  
Old 08-14-2017, 06:43 PM
Maurice66 Maurice66 is offline
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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!!
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  #5  
Old 08-17-2017, 06:29 PM
BA_051 BA_051 is offline
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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.
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Last edited by BA_051 : 08-17-2017 at 06:35 PM.
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  #6  
Old 08-22-2017, 08:15 PM
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J20 project J20 project is offline
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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
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  #7  
Old 08-27-2017, 11:16 PM
440sixpack 440sixpack is offline
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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.
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  #8  
Old 08-28-2017, 09:30 AM
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babywag babywag is offline
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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.
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Old 08-29-2017, 10:45 PM
440sixpack 440sixpack is offline
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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.
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  #10  
Old 08-30-2017, 06:53 PM
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68glad 68glad is offline
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ok whats true 9.5 compression mean in layman terms? My calculations on my engine says 9.5cr & i run 87 octane.
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  #11  
Old 08-31-2017, 08:28 AM
440sixpack 440sixpack is offline
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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
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  #12  
Old 08-31-2017, 03:02 PM
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babywag babywag is offline
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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.
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  #13  
Old 08-31-2017, 08:40 PM
440sixpack 440sixpack is offline
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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.
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  #14  
Old 08-31-2017, 11:38 PM
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babywag babywag is offline
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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.

Quote:
Originally Posted by Ghinmi
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.
Quote:
Originally Posted by Ristow
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...
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  #15  
Old 09-01-2017, 01:54 PM
Ristow Ristow is offline
 
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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.
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Originally Posted by Hankrod
Ristows right.................again,


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  #16  
Old 09-01-2017, 07:14 PM
440sixpack 440sixpack is offline
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I think this has been beat to death. I'll leave it with this everyone can make up their own mind .


http://www.huntsmachine.com/383ss01p3.html
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  #17  
Old 09-01-2017, 11:02 PM
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72jeeperjoe 72jeeperjoe is offline
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I agree with 440sixpack. If you are running 9.5 or higher compression on a street motor with iron heads you should run 92 or higher octane (or the equivalent in your area). Modern cars do run up to 12:1 compression and they are fine due to knock sensors and other sensor that can adjust timing on the go even per cylinder. If you run 87 you may not have any issues I agree, however you will need to retard timing which makes the higher compression somewhat a mute point to a degree (pun intended haha). It does not hurt anything to run higher octane but it will hurt things if you have too far advanced timing and not enough ignition on 87 octane (remember you also need a stronger spark with higher compression), not worth the risk. Higher compression helps torque and power with the right combo (camshaft, intake etc) only if you build it right.
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Old 09-01-2017, 11:11 PM
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72jeeperjoe 72jeeperjoe is offline
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Different engines do tolerate more or less compression in stock form than other's. For example I run 9.8:1 compression on my 302 with heavily worked over factory 351 iron heads on 93 octane, mainly due to the way the combustion chamber is designed. I also have a pretty advanced timing curve, however I also run good aftermarket ignition components and have it tuned well, I am still careful of detonation though. There is no absolute rule for what all engines can run, it is dependent on design, tuning, building and etc.
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