I don't think you could go wrong with the Comp 255DEH grind for a mild, low compression build.

As far as keeping the 351M - totally up to you. I'm keeping my 400, even when a lot of people would suggest swapping in a 460. Ditch the 351W idea IMO, they just aren't that great of a performer unless you swap heads. Not a bad truck engine mind you, but keeping the 351M makes more sense to me, especially if you want to maintain some originality.

 

. New full size trucks get up to 25 MPG and are heavy, we should be able to get close to that by getting our compression heights up, compression ratios up, quench size down, cam size sensible, carb.s properly tuned...

. A 351M will blow away a 351W if can get the pistons somewhere's near the heads...

. A bigger cam doesn't help a stock 351M because even the stock cam is too big... a bigger cam can add upper RPMs, but loses torque and MPG without the proper compression ratio...

. The new trucks run 11:1 compression ratio... or use twin turbos to stuff the cylinders to the same extent...

. I have some 35 x 14.5's to play with on my truck sometimes...
.

 

Sad part is the 351m will never be noticed in the performance world because its so easy to make a 400 outta them, and if its a 351 ya want, the C and W are also available. M's are dime a dozen and could be turned into real revvers (probably a decent neck snapper) but since theres no aftermarket it kinda blows.

New trucks can get 25mpg, but theyre also running boosted v6's that our motors dwarf and 4 valves per cylinder, VCT, EFI, variable displacement, multiple overdrive gears, gasoline direct injection, etc. They seem a little more sophisticated haha.

I always had this idea that if you were good enough at engine tuning that you could get at least 20 outta one of these rigs. Hell, my 96 bronco with a 351 got 18-19 hwy with 259k on the clock. Seemed everything on it was set up just right. I guess it all has to do with that "sweet spot" for mpg, and if a 9:1 351 could get 18-19 at 57 mph only, then there must be a sweet spot. Did a compression test on it, all cyl were within 10 psi of 185psi. Leakdown showed 15% loss through rings and valves (hissed out exhaust, intake, and dipstick).

 

Yeah i figured the same thing. The m has decent torque, its a basic design, and the only thing thats tough to do with em besides find decent pistons is pass a car!

I'd definitely take workin on and driving my 77 over my 99 f150 5.4.

 

.
. My '86 Chevy Monte Carlo with carb.'d 305" V8 rated 17 MPG City and 25 MPG Hiway... 2006 Mustang with EFI'd 286" V8 also rated 17/25... so much for EFI and 20 more years of 'sophistication' as far as MPG goes...

 

Justforkicks,

I hear you - ask me which I'd rather work on, my 78 Bronco or my 2000 F150 5.4.....

 

To that point, I was getting 15mpg with the stock cam in my 400. My friend gets 16 out of his modded 2010 6.7 Cummins. I'd rather have 15mpg at $3.70 a gallon than 16mpg at $4.05 a gallon. Not to mention he has at least twice the torque and power but that Cummins costed about 20x what my truck did...

 

.
. Yeah, regular gas only $3.09 around here today... but the diesel hasn't come down...

. And HP on the gas 400" can be bumped way up fairly easily and cheaply... with little or no loss on MPG... or even better MPG if the stock 400 was a 1972 or newer...

 

Regular unleaded here is ranging from $3.75-$4.00 a gallon.

 

.
. $3.08 today... $2.96 briefly a week ago... received the Summit K5201 218/228 cam/lifters for my 351M/400 today...

 

I rarely even see it drop below $3.20 a gallon in the winter time

 

the best mpg's I have ever got was pure highway 65 miles each way one mile of town driving at each end of the commute with 72 Torino 351C 2barrel heads stock four barrel intake 735 cfm holly (of a 68 390GT) with two stage power valve installed, C6 trans 3.55 gears, after market cruse control 60 mph, worked this job for over a year, checked mileage many times, 19.5-20.5 80,000 on stock engine, 8* BTDC timing, the two stage power valve, limits fuel on light throttle application, and opens fully when WOT is desired, a must for getting mpg's from a holly IMO you will never see 26mpg even with EFI in a truck using this engine family....