1978 4x4 supercab F250 NP205/435 4:10 Dana’s. It’s a DD work truck.

Fresh big money 410M stroker that gets 7 MPG and only runs on premium. It’s gotta go.

Love the 300 I6. I know they work and last forever.

I don’t mind gearing down to get the most out of it. I don’t expect it to make 350hp and 450tq, I just need it to reliably haul and dump a ton of firewood, plow a bunch of snow and go on a few road trips while getting better than 10 MPG on 87 octane.

Is this reasonable expectations from a 300 6? Where do I start?

thanks

 

I cant really answer your question but I think I would relook over the stroker and see where it went off the tracks for the MPG.
You have to remember that the motor is a package and if 1 part does not work with the package the whole thing will be bad.
Maybe also ask over in the 400 area how to get more MPG of what you got. list the motor build from the compression ratio, cam, heads, intake & exhaust, carb, distributor / timing, etc. as something has to be off.
Dave ----

 

The 351M/400M iron open chamber heads are terrible for detonation.
What heads did you use?

The 351M/400M does not have the same bell housing pattern as the 300 six and 302, 351W, 351C small block V8s

A stock 300 six with a Clifford intake manifold and small 4 barrel carb along with the EFI exhaust manifolds has been a good reliable workhorse.
The newer Clifford intake manifolds have a built-in water jacket that is used to regulate the manifold temperature in both winter and summer which will provide you with the best fuel economy.
The best carburetor is the Holley 390 which has really gone up in price.
The second and less expensive choice is the Quick Fuel 450 cfm SL-450-VS carb which will give you the extra cfm needed if you decide to change to a different camshaft.

If you are looking for more torque and power beyond the above combination, then one of the high torque roller cams from Straub Technologies would be in order.
Any new flat tappet aftermarket camshaft is no longer an option due to their high failure rate.
Most of the aftermarket suppliers no longer offer flat tappet camshafts because of that.

The key to tuning any carburetor is to install an Air/Fuel ratio meter and a vacuum gauge.
The AEM 30-0300 has been a very good unit.
AEM Electronics 30-0300 AEM Electronics X-Series Wideband UEGO Air/Fuel Sensor Controller Gauges | Summit Racing

 

Do you know what heads, pistons and camshaft your machinist used on your 410M engine?
That engine will go a long way if built correctly.

 

Yes. Early 400 heads, resurfaced, lightly pocket ported with the EGR bumps knocked down. Balanced rotating assembly, Hyper flat tops that were still slightly down in the hole a bit after zero decking. Comp 270H, scorpion roller rockers, edelbrock dual plane, 800 avs carb. guessing compression ratio is in the high 9s, higher than stock for sure Runs STRONG.

I understand a 335 series will run forever. I’ve owned enough of them to know that single digit fuel economy is the norm, and I’m looking at options.

Are the six cylinder guys getting any better fuel mileage?

 

The early 400M heads had a chamber volume around 78cc.
If the pistons are flat top with 6.5cc valve reliefs and are .005" in the hole, the static compression ratio is right at 9.9 and the dynamic compression ratio is 8:1 using the Comp 270 camshaft.
That is very high for pump gas and the open chamber heads do not help with detonation as there is no quench.
You would need to drop the compression ratio under 9:1 to use 87 octane pump gas.

The Edelbrock carburetors always run rich out of the box and require the calibration kit to jet then properly.
This is where the Air/Fuel ratio meter comes into play.
A Holley 650 vacuum secondary would be a much better carb to work with.

A 300 six that is properly tuned will give you much better fuel mileage, but you will miss the torque of your 410M.

A set of closed chamber aluminum heads with custom dish pistons from DSS along with a Holley 650 carb would solve the problem and allow you to use 87 octane pump gas.

 

If you still want to go the 300 six route and the budget is not a problem, the following is a high torque 300 six with good fuel mileage and longevity.

The Straub Tech version of the Promaxx CNC ported head.
The "The Bowtie Buster" Hydraulic Roller Camshaft.
DSS 25cc pistons.
Clifford intake manifold.
Quick fuel Slayer Series Carburetor 600CFM VS

Ultimate Master ProMaxx Head & Cam Kit – Ford 300 I6