'75 360 tune

[The Other Ross]

I recently installed a dual plane Edelbrock and 750 AFB on my Camper Special.Also did the timing chain and gears,pickup coil,vacumn advance and coil.Runs great,cold weather starts the way it should overall made a whole new truck out of it.The problem is it went from 10mpg to less than 8.The carb has a fresh rebuild on it with the fat rods in the primaries.I know I changed a lot of things at once but I thought improvements would also help the milage.It ran really bad before with the typical accelerater pump problem in the stock two barrel Holley,a completly shot vacumn advance and about 5 degrees +/- slack in the timing chain.The vacumn pulls about 14 inches steady and I've backed the timing up till there is no ping and hot starts are fairly quick.D200,360,727 Loadflight,4.10's,dual stainless 2" exhaust about a 4700 pound truck.

[712edf]

I gonna guess and say the carb may be a little bigger than what you need.

bucky

[The Other Ross]

I'll give you that,but it's not running like it's overfueled.If you cut back the fuel delivery with the fat metering rods what's the difference?

[OLD DODGE]

.If you cut back the fuel delivery with the fat metering rods what's the difference?

Smaller venturies on a smaller carb. Might be more efficient?

[greed]

YES, i would say 625 to 650 would work better.

[Deathdeelr]

I don't know about going with a smaller carb. I've got a 600 4150 on the Edelbrock manifold on my 318 and I get less than 10mpg (full rebuild in 1999) then flip that over and I had a 750 Q-jet on a 350 Chevy and that Camaro got over 20mpg. I think you actually solved the problem in your post. You said it pulls 14" and you have dual 2" exhaust. That's where you lost the mpg and actually I think you might not be making as much power as you could if you go back to the y-pipe and single outlet. You're scavanging too much; basically you're blowing fuel right out of the motor before it gets a chance to burn it. The 2" exhaust coupled with the larger intake is making the airflow too fast. My suggestion is to either go back to a 2 into 1 y-pipe or upgrade the cam. With the setup you have I think you'll get some vacuum back with the Edelbrock Torker cam. The wide separation angle on the Torker cam will shorten the time the intake and exhaust valves are open at the same time and slow down the airflow.

If you go with a smaller carb you might get a little more low end grunt than with the 750 but that also means you're going to be into the throttle more while you're cruising which is where you're blowing the fuel away already. Where right now you thinned out the 750 to try to get that fuel back you're going to have to fatten up the 600 to get it to the same place but like I said, you're still going to be into the throttle more.

[The Other Ross]

Now that's interesting.The Edelbrock intake is a small port type.And the 318 setup you describe is the same as in my D 500 dump(with single exhaust and 31" Walker) and it makes 10 mph in a 8000 pound truck.The D 200 is a beater farm truck and I really don't want to recam it.This whole venture is a kind of parts is parts thing.If I'm really not burning all my fuel couldn't an ignition upgrade(plugs,wires, Mopar perf ignition) be the answer?

[Deathdeelr]

The small port manifold actually increases the speed of the airflow. It acts like the squeeze point in a venturi. The ignition upgrade wouldn't hurt. I ran the MSD 6AL system in my cars and trucks for years with great results and reliable as any stock system. IMO, the problem is not on the transfer from compression to power strokes (at the ignition point). The problem in the transfer from the exhaust to intake strokes. The valves are staying open too long at the same time causing the flow of exhaust out exhaust valve to draw too much intake charge right past the cylinder and out the exhaust valve.

We're really bench racing here. If it was me I'd just leave it alone if it was my beater or something to play around with in the mud. I'm just kicking around ideas to generate power in the rig. My own setup is the 318 with the Performer plus cam, performer intake, 600cfm 4150, stock exhaust manifolds with stock exhaust system. I set that up when I rebuilt the motor in '99 but it was easy with the engine out of the truck. I wasn't looking to make too much power and that setup gives me a lot more than stock for under $700 to do the entire motor (rings, bearings, gaskets, etc.).

Try that 6AL ignition. I think you'll like it.

[The Other Ross]

I guess what I'm looking for is the silver bullet.Usually you do a bunch of things to an engine and finally find the missing piece if you don't quit to soon.I just don't have the last digit to the combination.Since this was a fairly common upgrade to 360's back in the day I figured someone had the answer.

[The Other Ross]

More of the same.I have a set of AC plugs one heat range hotter than stock to stick in.Recommended by some serious Mopar nuts.Who makes a good set of 8mm wires?I used to run Jacobs wires on everything but they are pretty much done.

[Deathdeelr]

MSD Street Fire or Accel 8.8. Very good wires with little or no noise that affects the radio. Advance Auto and Autozone both carry them for about $50. You can order a custom set for the Mopar or buy a universal set and make your own lengths if you run wire separators.