Fuel Efficient Build---352 or 351W

[410bruce]

Okay guys, another fuel economy question for you regarding a couple engines.
If you had your choice, which engine would be a better candidate for a fuel-efficient build, a 352 or 351 Windsor?
Given the current situation around us now has me thinking more about MPG than HP.
Would still like to have good torque and a throttle responsive engine, only focus more on efficiency.
Factory cylinder heads, pump gas, backed by a C6 in a 4000lb truck. Will be using an aftermarket throttle body EFI system.
I do have one of those overdrive Top Loaders that came in late '70s trucks I could install, if it would be worth the trouble.

As always, any input greatly appreciated.

[MRadke]

How about a straight six? 

[My427stang]

Okay guys, another fuel economy question for you regarding a couple engines.
If you had your choice, which engine would be a better candidate for a fuel-efficient build, a 352 or 351 Windsor?
Given the current situation around us now has me thinking more about MPG than HP.
Would still like to have good torque and a throttle responsive engine, only focus more on efficiency.
Factory cylinder heads, pump gas, backed by a C6 in a 4000lb truck. Will be using an aftermarket throttle body EFI system.
I do have one of those overdrive Top Loaders that came in late '70s trucks I could install, if it would be worth the trouble.

As always, any input greatly appreciated.

Here is my input.....if that's the goal, the one you can build the cheapest, to include all ancillary parts for the whole  project

Why?  Put the extra money in the bank for gas. 

Neither was known as a gas sipper in their day, both need good parts to be more efficient, and depending on transmissions, headers,  intakes, heads, etc...the one that saves you cash on the build will likely give you more gas money than the difference in mileage.  That being said...the 351 would also have a weight advantage depending on configuration

Another sorta wise guy comment...with inflation at 5% and climbing in some markets, you are also increasing potential cost by thinking too much

[TJ]

For what my two cents is worth...I believe how you build either engine will make the real difference.  Modern ring packs for less friction and better sealing, custom pistons to dial in your compression, EFI will help and even better would be port injection for better balance, and believe it or not a roller cam to allow use of modern oils.

My fuel economy jumped 0.5 to 1 mpg switching from a high zinc oil to a modern synthetic (10W30 for both)...that's after several thousands of miles and always calculating my mpg using each oil with my roller cammed FE.

IMO, the trick to building fuel economy into any vehicle is sizing the engine to the job.  For instance, I had a 390 in my truck that got the same mpg as new F150's with the 3.5 ecoboost when pulling a 10K lb camper.  Running empty the 3.5 beat my 390 easily for mpg.  The 390 wasted gas when my truck was running empty (no trailer attached)...it was the wrong size for that job. 

My427stang has a good point...you're loosing buying power by hemming and hawing :-)

[410bruce]

How about a straight six?

The truck has an EFI 300 6 in it now. The fuel economy is nothing to write home about. I've heard how great these engines are as far as low RPM torque and towing capacity, I don't tow, but so far have not experienced the awesome torque. In fact, it's relatively flaccid as far as I'm concerned.
I'm just a V8 guy.

[TJ]

How about a straight six?

The truck has an EFI 300 6 in it now. The fuel economy is nothing to write home about. I've heard how great these engines are as far as low RPM torque and towing capacity, I don't tow, but so far have not experienced the awesome torque. In fact, it's relatively flaccid as far as I'm concerned.
I'm just a V8 guy.

They do have good low end torque...for their size.  Around 3000 rpms is the end of their world.  They can't keep up towing with a bigger V8, especially at highway speed.

  I expect around 16 mpg with them in a pickup.  A very carefully custom built 351 or 352 should get real close to that.   

[410bruce]

Okay guys, another fuel economy question for you regarding a couple engines.
If you had your choice, which engine would be a better candidate for a fuel-efficient build, a 352 or 351 Windsor?
Given the current situation around us now has me thinking more about MPG than HP.
Would still like to have good torque and a throttle responsive engine, only focus more on efficiency.
Factory cylinder heads, pump gas, backed by a C6 in a 4000lb truck. Will be using an aftermarket throttle body EFI system.
I do have one of those overdrive Top Loaders that came in late '70s trucks I could install, if it would be worth the trouble.

As always, any input greatly appreciated.

Here is my input.....if that's the goal, the one you can build the cheapest, to include all ancillary parts for the whole  project

Why?  Put the extra money in the bank for gas. 

Neither was known as a gas sipper in their day, both need good parts to be more efficient, and depending on transmissions, headers,  intakes, heads, etc...the one that saves you cash on the build will likely give you more gas money than the difference in mileage.  That being said...the 351 would also have a weight advantage depending on configuration

Another sorta wise guy comment...with inflation at 5% and climbing in some markets, you are also increasing potential cost by thinking too much

Ross, why do you always have to be such a downer? lol.
As far as your last statement, I'm kind of in a predicament. My family has all passed and I have no friends who are motorheads to bounce ideas off of. So unfortunately, I have lots of time to think too much and post up seemingly inane threads in front of thousands of strangers. Yay me. 

[GerryP]

Your weight and aero are all wrong for MPG.  You can try to get better fuel economy out of a truck, but if you are really concerned about fuel economy, you'd have yourself a driver for when you don't need the truck.  But you will have to drive some incredible miles to make up the money on what you put in the tank.

As has been pointed out, when it comes to vehicles, spending money to save money almost never works out.  We went through this in the middle '70s with the Arab oil embargo and gas shortages.  Back then was a little different in that fuel was being rationed, so it wasn't so much the price, but more if you could even get gas.  There were some parts out there to increase fuel economy.  The Edelbrock SP2P comes to mind.  And, yes, they did work but only for fuel economy.  The engine sucked otherwise.  A lot of people dumped Cobra Jet Torinos to get a Corolla.

You would do better with a 351W as far as the most up to date technology, price, and weight.

[JimNolan]

On an FE engine the base RPM that you can run is 1700 rpm (rpm in which you can mash the gas down in any gear without having to go to a lower gear). If you can keep your rpm between 1700 and 1850 rpm when cruising you'll get all kinds of gas mileage out of a FE. My 1957 Fairlane 500 with 390ci-315hp/5 speed Tremec TKO 600/3.50 True Trac and 27" rear tires gets over 21 mpg at 65-70mph. Around town in stop and go traffic is where nothing is going to shine. The transmission is where you get gas mileage.

[shady]

maybe just keep what you have and do a rear swap. More than once have I put a steeper rear in that resulted in better performance and better MPG. Keeps the truck in its torque range.

[e philpott]

as far as day dreaming no cost out of pocket , the 352 is what I would build with tiny roller cam , modern piston and ring package as high of compression you can get away with, TFS heads , port fuel injection , headers and some kind of OD 6 speed manual or automatic transmission and functional Lock up Converter if it an automatic

[FrozenMerc]

I have done both.  In fact, they were very similar builds.  Both engines have a +0.030 over bore, similar cams, 600 cfm Holley's, approx 9:1 compression, etc.  The only real difference is the 352 got aluminum Edelbrock heads, and the 351W used the stock '78 LTD smog heads.  The 352 is in my '62 Merc Monterey wagon, backed by a non-lock-up AOD and 3.6 rear axle.  The 351W is in a '51 F-1, backed by a M5R2 5 spd, and 3.08 rear axle.  Tire size is real similar between the two.

The '62 will pull down 15 mpg cruising at 65 mph.  The '51 will also pull 15 mpg on the highway.  You could argue 352 is the more efficient motor of the two since the wagon weighs a good 1000 lbs more than the little pickup.  I think the wagon probably has better aerodynamics, but it probably isn't all that great of a difference. 

That said, I also built a decent 300 6.  Full length split header, Comp 270-H cam, Offy Dual-Port Intake and Holley 600 cfm carb, flat top slugs that brought the compression up to about 9:1.  Backed by an AOD in a '83 Bullnose, it would pull a consistent 18 mpg down on the highway at that magic 65 mph mark.

If I was concerned about mileage, I sure as heck wouldn't build something around a C6.  Great, durable transmission, but terribly inefficient.  Manual transmission with overdrive would be the best way to go.

As JimNolan said, target a 1800 to 2000 rpm cruising range.  Build as much compression into it as you can get away with, and cam it to have the torque peak in the 2200-2500 rpm range and be prepared for the thing to be out of wind around 4500 rpms.  Optimize the build so you can maximize the area under the entire torque curve, and dial in you AFR's across the cruising range.

[cjshaker]

If I was concerned about mileage, I sure as heck wouldn't build something around a C6.  Great, durable transmission, but terribly inefficient.  Manual transmission with overdrive would be the best way to go.

Agree 100% with that statement. Unless you spend big bucks to adapt a newer automatic trans, manual is the way to fuel efficiency.

If you're going to stick with factory heads, I'd go with the 352. All factory heads on the 351 platform suck, bad.

A couple things that people typically ignore when it comes to fuel efficiency.
 1: Rolling resistance. Wheel bearings that don't freewheel extremely easily, or ANY brake drag will pull efficiency down quickly. A front end alignment that minimizes resistance is mandatory.

 2: Driving style/throttle opening. Driving style has as much to do with efficiency as anything. A vacuum gauge can teach someone how to drive more efficiently. Any time you see the gauge needle drop, that's efficiency going away. Slow on the pedal, slow off, neutral coasting to lights and stop signs, etc etc. I watch how most people drive and can instantly see why their fuel economy sucks. Not saying the OP is that way, just people in general.

I managed to regularly get 16+ mpg out of a '68 F250 Highboy with factory iron heads and iron 4bbl intake with a mild Crane cam. The truck had no rolling resistance, and coupled with a light foot and driving style, it would get that every time. It probably would have pushed 20 in a much lighter F150, given the same engine and freewheeling resistance.

[frnkeore]

For your criteria, I would definitely stick with the 300-6.

If the bottom end is still good, I'd pull the head, install 1.6 Ex valves and smooth the bowl, do the best In valve job, that you can do or get, mill the head about .020. Put a small cam in, with LSA of 114 - 116 and then top it with a turbocharger, for the extra pulling power you want and of course put that alum TL 4 spd OD trans in it.

All that said, your still going to have to keep your foot out of it, for mileage but, the FI will also help you with town mileage.

[Tommy-T]

FE in a full size truck and good gas mileage. That's a good one! Keep 'em coming!

351W is a pig too.

I had an '82 F100 Stepside with a 300-6 and an overdrive stick transmission. Down hill with a good back wind it might have gotten 15mpg. The power was nothing to shout about although those "in the know" touted the torque of the truck six. I am convinced a 302 V8 would do everything better.

Thinking a 4000lb brick can do better than 15mpg is a bit "optimistic". Those that say they've done better than that are putting their credibility on the line.

Case in point. I have a Jeep Wrangler with an automatic, 4.0-6, and 3.50 gears with 33" tall tires. On flat ground on the highway we may get 15-16mpg. Another example of moving a nearly 4000lb brick with a six cylinder motor.