Maybe when it's done and tuned to perfection you can save up for some good headers. I would bet there would be an increase as long as you have it 'scienced out' with the correct tube size/length and enough back pressure.

I guess the quiet thing is tough to get around.

From what you have so far, I think to get that last couple mpg better you are going to have to resort to some expensive measures. NV3500 swap, 2xx gear swap, lowering it, coating pistons, swapping rods/bearings, and shedding weight.

But even then, the factory injection won't pinch anymore fuel off at minimal throttle position: I've tried it with my 360 Magnum with heavy tail-wind and throttle goes to a "light-switch", on-off mode and max mpg I see is about where you are at right now. I have all the mileage tricks on my truck too. One thing is for sure on my 360: 1500 rpm gets the best mileage.


I guess on a side-note, If it was me I'd leave the 360 idea and either get a 3.9 V6 or the 2.5 and run a T3 turbo on either one. Less pistons to feed means better mileage (works for the 5.7 MDS).

I don't have many tricks done to it yet, just real sensible driving and like you said under 1500 RPM unless I am on the highway. I can not find any higher gears for the front diff or I would do it. Don't want to make it complicated under the hood so no turbo. I sold my V6 truck a year ago because it was too underpowered for pulling my trailer so V8 it is, besides getting good MPG out of a V8 is 1/2 the challenge.

On a nother note I may try the teflon coating on the piston skirts, hadn't thought of that one. I think the ceramic coating would increase detonation by not transfering the heat away fast enough.

I do have an NV3500 in it already. Maybe there is a higher OD ratio in a chevy trans I could swap in...

Like you I felt that headers were not a key item in an "economy" build engine.

But then i read a paper by Mazda describing their "SkyActiv" series of engines that have 13 to 1 static compression but can run on 87 AKI gasoline.
(Mazda runs 14 to 1 overseas where 91 Motor Octane gas is a bit better)

Mazda claimed that a specially determined
23.6 inch first section length in a
4-2-1 Tri-Y type header was necessary
to evacuate the last of the hot "residual gas"
that would otherwise overheat the fresh intake charge
if left in the clearance space of the chamber.
Mazda claimed this was a key step to raise the compression ratio the last point.

They can retard the intake timing on that thing a bunch plus it is direct injected-you can wait till it is too late to detonate before you inject the fuel.

I think in order to get a proper header for it at the low RPM range I use most it would need abnormally long and small tubes.

In one of the Mopar Performance small block books Larry Shepard wrote that 4 into 1 header tube length needed to be a slightly longer than normal 38 to 42 inches to get best all around performance.

My memory is foggy but i think long ago one of the car magazines fitted 48 inch long 4 into 1 headers onto an economy build V8 small block and claimed some success?

I thought it was interesting that Mazda emphasized that the first segment of their 4-2-1 header had to be longer than 600 mm/ 23.6 inches to get the mix of fresh charge and residual gas down to a temperature that would not detonate at 13 to 1 static compression.

There is a warning though. Sometimes those tech papers to impress customers deliberately contain "misinformation" to confuse their competition automakers engineers.

I believe that with
62 cc combustion chambers,
0.026 quench,
flat top pistons with no valve reliefs or soap dish bowl,
the static compression of a 4.00 bore Magnum 5.9V8 is just shy of
13 to 1

I wonder if anyone has already built such a Magnum V8
And run it either on
race gasoline
Or E85?

It would be interesting to then fit such an 12.7 to 1 Magnum V8 engine
with a 23.6 inch first segment 4-2-1 header
and see if there was an Octane tolerance improvement before knocking.

An alternative test would be to fit that Magnum V8 with water injection and see how the water spray requirement changed when the 4-2-1 header was on.

That comes out around 12 to 1.

The way mine is gonna come out is a hair under 11 to 1, I think it will be fine on premium. I may try takeing one or two CC out of the chamber to unshroud the valve and take a smidge of compression out.

Try building a set of spray bars to squirt oil on the bottom of the pistons. That will help draw the heat out of them and reduce detonation.

Something like that should be easy for your to put together.

What you need is a combustion chamber that works with 20 deg of total advance +/-.

Kevin

In the past didn't a machine shop in Florida have a jig that drilled holes in small block mopar oil mains to create oil squirters?

The original Viper V10 combustion chamber was similar to the Magnum V8.
Since then several Viper shops have created CNC programs that recontour the chamber,
Especially near the sparkplug threads.

My take on the Magnum chamber is that it was created for the 5.2V8,
and that the 5.9 V8 deserved its own chamber
Perhaps with more cc's on the exhaust valve side.
The 5.9 V8 piston should be flat top like the 5.2 design.

I wonder what the maximum ignition advance programmed into the 1995 Mopar Performance PCM for the 5.2 is, say around 4400 rpm, full throttle?

If it is less ignition advance than Mopar Performance programmed into the 5.9V8 (like I own) then that would indicate a better chamber/piston crown combination, that is faster burn.

The 5.2 cam is slightly different than the lower duration 5.9 cam. That is a wrinkle.

The 318 cam has more lift and less duration, very slightly on both counts.

My 99 at 4400 WOT only gives about 25 degrees, my experience slapping carbs on stock magnums they seem to run way better around 35 total but with the air in the beer barrel being baked will not allow more advance. With a tight quench and fast burn from good injectors the 25 degrees becomes not so bad. When I built a tigh quench 5.9 magnum it was happy around 30 toatal advance.

Slotting and advancing the crank sensor only nets a 2-3 degrees but is noticably snappier.

My guess is the flat top in a 5.9 created too high combustion temp for to keep the NOX under control so they just dished the piston instead of redeisghning the intake to keep the IAT down.

I agree the magnum head is perfect for the 5.2 but think it is still very good on a 5.9, just open around the valve to match the bore size and call it good.

I'm following this topic with interest as I'm currently putting together a 360 with a focus on engine-efficiency.

Using KB107 pistons, polished 302-heads and valves and balanced crank assembly I'm shooting for around 10.5:1 cr.
I've got a cam on the shelf for the engine but I'm not 100% sure yet if I'll use it; it's a CompCams XE256H

I wonder what cam specs you'll end up with.

On the 302 heads on a 360 the TQ peak is so low you just about need a manual to use it. Also if you do stick with em make sure to grind the point in the middle of the chamber out and smoothe the left overs. At 10 to one it gets real hot and starts detonating. If you are useing a dual plane intake then your cam should be good.

Will be running an Edelbrock RPM intake for the time being. Engine will be run on LPG propane only, but propane sometimes likes a single plane intake better.

Maybe will be LPG injected later on in time with Megasquirt to see if better MPG's can be achieved.
(A518 transmission in '73 Dart. 3.55 gears). The transmission alone eats away some MPG's. Would like to exchange it for a A500 if I can find one overhere.

I've polished the chambers to a shine and blended and polished the in/ex ports.
In the chambers I've pretty much ground away the pointy nubs and unshrouded the valves a bit with smooth curves just about everywhere.

I'm hoping the high CR and degreed cam keeps the torque of the small port heads high and help with 'low rpm' daily economy.
Will be using shorty headers into 2.5" X-pipe exhaust a Dynomax mufflers, maybe with resonators on the rear.

LPG would love at least 11.5 compression, 12.5 would make it really happy also. It is pretty high octane and cold both of those help it be very happy with a lot of compression. Without the compression to speed up the burn it will still be burning as the exhaust opens and it will burn your ex seats so it is important to get the compresison up for that also.

The KB-pistons should supposedly be able to create a 11:1cr, but since I've smoothed the sharp edges on the piston and the chamber along with valve unshrouding, I'm not sure it will still reach that number without a few more cuts on the heads.

I have however ordered thinner headgaskets (0.028")
http://www.summitracing.com/int/parts/mrg-1121g/
to gain back some cr.

Any ideas of using 1.6 rockers with the XE256 cam?

Wouldn't hurt. Also you can try advancing the cam a couple degrees to get a little more cylinder pressure but that also advances the ex opening. If you can get the head cut more it should only help.

LPG and methane are very high Octane rating fuels, and adding a test port to a cylinder and then squirting in a little propane or methane is a way to find out which of your eight is the knocking cylinder.

Cylinder # 1 on Magnum V8s already has a "test port" in the runner - the IAT threaded hole.

I wonder how this could be used to find the maximum allowable static compression ratio for cylinder #1 alone?

Spray something into the IAT port before tearing down the engine.
Spray LPG/propane or methane in, starting from a large amount, then gradually reduce it until the knock comes back.
Or....
Spray Hexane/diesel fuel in, starting from a small amount, increasing until a slight knock is detected.

An alternative involving far more work,
Would be to acquire multiple fuel injectors
27, 28, 29, 30, 31, 32, 33, 34, 35, 36 lbs per hour
Then swap them in and out.

A second alternative involving even more wrenching
Would be to gradually grind out the combustion chamber of cylinder #1 to more and more CC's.

A very easy way to quickly add a few CC's to #1
would be to remove the sparkplug
and add in a "fires in oil" extender sleeve,
but this also slows combustion speed like a severe timing retard.

Another quick method would be to slowly screw in a bolt of the right thread deeper and deeper into the IAT hole. As the bolt pinched off more of the airflow, the air- fuel ratio would grow richer and the volumetric filling percent of that cylinder would decline.... both of which would decrease the tendency to detonate.

A chain is only as strong as its weakest link.
A safe and smooth V8 is limited by its most knock prone cylinder(s).

On a Magnum V8
What is the limiting compression ratio of the most knock prone cylinder?
What is the quickest-cheapest-but dependable method to find the needed info prior to building a Magnum V8 to SuperDuper Fuel Economy nirvana?