Discussion in 'Early CJ5 and CJ6 Tech' started by mwinks-jeep, Jul 9, 2013.
JEEP - Just Everyone Else's Parts
I strongly disagree that an AMC engine in a preAMC Jeep is anymore pure than any other swap. In 1958, AMC was still shaking off the Nash/Hudson stuff and had NO relationship to Kaiser that I know of.
And as far as Tim's comment on economy, the 360 was the MOST INEFFICIENT ENGINE I have ever owned. In my J20, I was feeling very good when it managed 12 mpg on a couple of occassions. That wasn't even up to the 13 to 14 mpg (loaded or empty, made little difference) I got from the 75 Chevy K30 with a 454 or the mid teens I have gotten with multiple carbed W series Chevy big blocks (348-409's) of decades past.
That, and I really hated working on them. Who else would design a front cover seal that installs from the back side? Or how to make a simple 2 hour job into a 2 day job.
Guess I'm just spoiled rotten working on sbc's.
I thought I was pointing to the economy of the inline sixes ...
I'd guess the main problem with the Jeeps is aerodynamics, not the engines. It would be interesting to compare the economy of equivalent AMC and Chevy/Ford/Chrysler passenger cars with similar engines. The AMC passenger cars got styling upgrades every couple of years (the market required it), so I'd expect their aerodynamics to be comparable to their peers. The FSJs design was outdated by 1970.
IIRC my 304 CJ-5 got about 13-14 mpg when new, and I was a young and enthusiastic driver, so that does not seem too terrible. My 258-powered CJ-6 did not do a lot better, and I am sure cars like the American and Gremlin were as good or better than their peers.
You could put the best and most efficient engine in the chassis, and it would not change the amount of energy needed to push it around. You can't squeeze blood from a stone...
I have to assume that an AMC 360 would get similar gas mileage to a GM 350 and Ford 351.
I would think it’s more about engine displacement and RPM’s than who made the engine.
Having said that, my 327 actually gets pretty good gas mileage, at least I was pleased to see 15-17 MPG around town. It think it has to do with the light weight of it and the gearing, 4.27’s with 33” tires, because gas mileage actually goes down with highway miles.
It should indeed be about vehicle weight and aerodynamics, but that isn't the case when it comes to AMC V8's which seem to get consistently less mileage than similar displacements from Ford of GM. And it doesn't seem to matter whose aftermarket manifolds or carbs are used, that deficit is still there. My personal opinion is it is that weird porting in the heads but obviously gears and cams come into play here also.
The weight/aerodynamics thing seems to hold true for my two CJ's (CJ 5 with 225 and the 3B with the 381 sbc) which both get around 18 mpg. That said, one of them is a lot more fun to drive than the other.
There were some Olds that did the same. Not sure about Pontiac.
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Yes indeed , very indepth and a very interesting topic.
The techniques for directly comparing various engines is quite complex.
One should start with basic comparisons before an indepth analysis can be performed with any confidence.
So I'll provide the basic data listed for the two main engines in question here plus two additional engines.
These particular engine examples are of similar discplacement which greatly simplifies the comparison.
I will use 1970 factory specifications for this comparison.
Note: that many factors including the vintage can effect these results.
GM vs AMC
ENGINE AMC 304 HP 210 RPM 4400 TORQUE 305 RPM 2800
ENGINE GMC 307 HP 200 RPM 4600 TORQUE 300 RPM 2400
Note here that the standard 304 puts out more torque than the standard 307.
Also note that it does so at higher RPM.
Note that higher RPM generally indicates a shortened service life.
ENGINE AMC 360 2 barrel HP 245 RPM 4400 TORQUE 365 RPM 2400
ENGINE AMC 360 4 barrel HP 290 RPM 4800 TORQUE 395 RPM 3200
ENGINE GMC 350 2 barrel HP 250 RPM 4800 TORQUE 345 RPM 2800
ENGINE GMC 350 4 barrel HP 300 RPM 4800 TORQUE 380 RPM 3200
Note here that the standard 360's puts out more torque than the standard 350's.
(both 2 and 4 barrel versions)
Note the lower RPM for the AMC 360 two barrel torque rating.
Also note that 4 barrel versions supply greater output than 2 barrel versions.
The 4 barrel versions generally increase the crankshaft RPM required to attain the improved results.
Crankshaft RPM is a main factor effecting both vehicle efficiency and engine service life.
Optimum crankshaft RPM is always relative to the vehicles gearing.
So here it cetainly appears that AMC engines rule concerning torque output.
And they generally appear rule concerning lowered crankshaft RPM (service life).
But let's not get over excited just yet !
This was only a basic comparison for similar discplacement engines.
It does not include costs comparisons, design deficiencies, nor the effects from numberous possible modifications.
Modified intakes, carburetion, port polishing, camshafts, exhaust, etc.
Comparing engines of dissimilar configurations and discplacement becomes increasingly complex .............
Separate names with a comma.