Tweaking a 360 for towing duties

[Flowers]

I've been to ifsja.org only to find controversy. Any advice on building a 360 to gain torque for towing and a bit more HP?

Ed Stevens, are you familiar with the 360?

This is on an 86 GW.

 

[Georgia Mike]

Mine's got a mild "towing" cam and 3.73 gears (on 31X10.50's) and it pulls quite nicely. I will say,however,that the electric fuel pump is a good upgrade (Holley "red" pump) that will eliminate the all-too-common vapor lock on the SJ's with the mechanical pump(you can use a BB Chevy fuel pump block-off plate on the 360). I would also recommend a good four barrel intake (Edelbrock makes excellent intakes!) and a good 600 or 750 CFM carb. Holley or Edelbrock are excellent choices. Right now mine will pull an equipment trailer with a car on it with ease,I can only imagine what it would be like with a four barrel carb and intake! What gear ratio are you currently running? I know quite a few of the later SJ's came with 2.73 gears uke: so that's the first thing I'd change

 

[Flowers]

Not sure on the gearing. I just picked up the SJ on Mon. I want to get a few upgrades (mostly performance) completed before I sell my XJ, just in case I have to have the engine tore down for a week or two.

I "think" it may have a cam in it now. It's been more than 10 years since I have owned a rig with a carb. Originally, I thought it needed some carb work, but a few people have told me it sounds like a mild cam.

How about exhaust? Would headers and dual exhaust enhance the lower end performance or hurt it?

thanks,

Tim Flowers

 

[Eagle]

The 360 at one time was available with either a 2-barrel or a 4-barrel. I had a '78 with the 2-bbl and my brother had a '78 with the 4-bbl. There was a significant difference. You can buy an aftermarket intake manifold for big bucks, or you can look in the bone yards for an older 360 or 401 that has the factory 4-hole intake. Doesn't have to be in a Jeep -- the same engine was used from 1970 and up in AMC Matadors, Ambassadors, Javelins, AMXs, Hornets (SC/360), and perhaps a few Eagles.

In an '86 you won't have the "wide wheel" option, since it wasn't offered then. That means you most likely have 3.07 gears. Mine did. The wide wheel versions had 3.55s.

If you decode to change the cam, be sure you get an RV or towing cam. Most cams won't enhance low-end torque. Actually, unless you plan to tow a 747 across the country, once you put on a 4-bbl intake and a decent carb (Carter AFB or Edelbrock clone thereof) I doubt very much you'll need a cam. I'd put money into gears before I messed with the cam.

 

[LRRH]

contraversy on ifsja...that's rare =)

vapor lock is not that bad...or common in FSJs. People just weren't prepared to take their rigs to 9000ft plus on a hot day. Make sure the fuel line is routed well (and insulated) and you should not have problems. An electric fuel pump will help to though.

I took my manual fuel pump to 12000+ ft. in the Rockies and had no problems with vapor lock.....but that's in my 70 that has a Buick350 and a two year old mech fuel pump.


now...back to the 360. 4bbl intakes are somewhat rare on a FSJ. I believe 78 was the last year they were offered....same as the 401. Try a new intake/carb/exhaust before you throw a cam in it. You'll be surprised by the power. As for a dual exhaust...you will need to make it exit the rear to avoid loosing ground clearance....but this is can be a pain with the stock coffin style gas tank.

good luck!

 

[Flowers]

Aftermarket intake and 4 bbl. are in the plans. Will I NEED an elctric fuel pump for a 4 bbl. or is just recommended? Exhaust ground clearance is not an issue since this machine will only see DD and towing duties. And now gas prices have to shoot up!!!

Another question: Is the little idle control thingy (idle stepper?) on the carb controled by the computer? Mine will stick in the high idle mode unless you shut off and re-start or unplug it.


Thanks for the advice,

Flowers

 

[Georgia Mike]

As for exhaust,I'm running a single 2 1/2" pipe all the way to the rear. I'm running a Hooker Aero Chamber muffler and the sound is awesome! Nice low rumble without a lot of decibels. I've always been told that single exhaust is better for torque,but I'm no expert.

As far as the vapor lock thing goes,I've heard it was a very common thing when I was searching for answers to my dilemma. Mine would run fine,as long as you never stopped. If you stopped at a red light for extended lengths of time,or stopped to fill the tank with it shut off,you could bank money on it that when you got going down the road again it would vapor lock every time! The electric fuel pump cured the ills of that! Then again,I'm no *expert* at it,I'm just telling my experiences Maybe it is an altitude thing? :dunno: We're not all that high around my area :smoker:

 

[Eagle]

All the vehicles (Jeeps, Matadors, Javelins, AMXs, etc) that came from the factory with the 4-bbl came with mechanical fuel pumps. You won't need an electric pump just because you're switching to a 4-barrel carb. The thing is that the mechanical pump, being mounted on the front of the engine, is a "sucker" -- it has to pull fuel from the tank to the front of the engine before it can push it up to the carb. The closer you can mount a remote pump to the tank, the less you have under suction and the more you have under pressure. And we're not talking a lot of pressure, not like the 40 psi for electronic fuel injection. Carburetors only require 7 psi.

As I already commented, the stock Autolite carbs were trash. AMC changed over from Carter AFBs to Autolite beginning in 1970. The previous versions of the same engine (290/343/390) used a 550 CFM Carter AFB and were much easier to tune, more reliable, and delivered far better gas mileage. Don't get suckered into thinking you need a huge carb for this thing. Regardless of how much you towm and engine is basically an air pump and at low to moderate RPM you just won't flow that much CFM. A larger carb than you need will actually cost you torque, gas mileage, and throttle response. My autocross/hillclimb car was a 343 Javelin (at least, the last engine was) and I ran that with a mild cam and the stock carburetor. I rejetted slightly, but I was good for 6000 RPM on that setup, and in a tow rig you're never going to see 6000 RPM (I hope). Look for a carb in the 500 to 600 CFM range, no more (IMHO).

 

[Flowers]

Damn!!!!!!!!!!!!

I checked prices on a few parts tonight and was blown away by the cost in comparison to a 350 Chevy.

Edelbrock intake for a 350: $159
Edelbrock intake for a AMC: $299

Thanks for all the advice.

Flowers

 

[Georgia Mike]

Damn!!!!!!!!!!!!



Edelbrock intake for a 350: $159
Edelbrock intake for a AMC: $299

Shows how much Chebbies are worth,eh? Now,who was it that said "You get what you pay for"?

 

[Eagle]

Damn!!!!!!!!!!!!

I checked prices on a few parts tonight and was blown away by the cost in comparison to a 350 Chevy.

Edelbrock intake for a 350: $159
Edelbrock intake for a AMC: $299

Thanks for all the advice.

Flowers

Start checking junk yards. The 304 never came with a 4-barrel but the 360 and 401 both did. If you have a choice, the 401 version will be very slightly taller and provides a smidgen more ram effect, but either will work fine.

You could also use an intake off a 343 or 390 (again, the 390 version is taller), but the deck height was increased in 1970 which meant the intake manifold had to be wider. To use a 343 or 390 intake you would have to run a thick gasket to make it mate up. Better to look for a 1970 or newer.

[EDIT] Just searched on www.car-parts.com for an intake for a 1971 AMX 401. Found a half dozen or so for prices ranging from $35 to $50. Check it out. You'' have to run separate searches for the different vehicles and years, but a couple will probably get you cross-references anyway.

Happy hunting.

 

[Flowers]

I'd prefer Al but at that price diff., cast it is!


Thanks Eagle,


Flowers

 

[REDXJ4FUN]

I have a bit of time tweeking AMC V8s and have tried a few diffrent set ups. bang for the buck i used a edlebrock AFB that i got used on top of a stock 4bbl intake and 2.5in duals and it worked very well. If you can find a used aftermarket intake like a performer or an offy work great for tourqe. even cms like the performer aren't much more than what most stock 360 cams were. the stock exaust manifolds flow pretty well so leave them for now. As was said above mid 80s FSJ cam with pitiful gearing si I'd spend the money on gears.