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turfclubroad 01-12-2010 07:55 AM

how to improve fuel efficiency of Chevy 350?
I am interested in purchasing a MH with a 350 chevy engine. I'd like to improve the fuel efficiency as much as is economically sensible but have no idea where to start. I have found a lot of posts with suggestions for 454's but non for 350's and even if they would apply equally I have no idea what brand/type etc to go for. For instance: most of the time if I look up headers in the internet I see products from high performance co's focused on more HP, not really stating if they also increase mpg....

Can the Forum help me with making a list of goodies, biggest fuel economy gain for the buck ranked, for a 350?



overlander63 01-12-2010 08:06 AM

Drive under 60 mph.
Inflate tires to maximum pressure marked on the sidewalls.
Headers and a free-flowing exhaust.
Gear Vendors overdrive unit.
Remove gasoline engine and install a diesel powerplant.
In that order.

ROBERT CROSS 01-12-2010 08:39 AM

I did some up-grades on our 454 Burb, Banks, computer, ignition etc etc.

:blush: It did improve mpg but took over 150k miles to start recouping the investment. Keep this in mind.:)

Cold air intake system and a good set of headers is a good place to start. Check out what Gale Banks has available, first rate stuff all the way.

slowmover 01-12-2010 08:43 AM

Intake and exhaust efficiency. Power centers around making the cylinder heads generate great bsfc numbers in the desired rpm range (where camshaft, torque converter, and rear axle gears are matched), as fuel efficiency is about doing the same work with less fuel.

Biggest bang-for-the-buck is the driver. In the big truck industry the difference between the best and worst drivers -- all other conditions controlled -- is 30%. Granted, driving a Class 8 truck demands skill an RV'er doesn't need, but I'd be willing to be the 30% number can be fairly applied.

Start with a dash-mounted vacuum gauge, a quality one such as AUTOMETER, and place it in your line-of-sight. Nothing, IMO, will do more to "train" a driver. A fuel flow meter next to it would also be good (but they're not cheap).

Search out the many uses of a vacuum gauge, be diligent. It is little short of awesome what knowing how to read one can tell you about a gasoline motor.

After that, highway rib tires properly sized to intended rpm/cruise speed. A front air dam. AIRTABs. All kinds of stuff to catch your attention.

Probably the place where you can spend some money is in the exhaust system. David Vizard is by far the best writer if you can access his articles on this subject (racing consultant). A note: anyone can bend up an exhaust system (lots of info and mis-info about pipe diameter), but remember this:

A press-bent exhaust pipe -- where the bend is compressed to, say, 1-3/4" -- gives you a 1-3/4" exhaust system REGARDLESS of main pipe diameter. MANDREL-BENT is key.

As to exhaust headers:

14-ga or thicker
3/8" or 1/2" mounting flange
STAGE 8 Locking Fasteners
Copper or COMETIC exhaust gasket.
A flexible/swivel union at the exit/entrance to exhaust piping.

Standard iron manifolds are good to about 1,500 - 1,800 rpm. Headers, properly-sized and designed (1-5/8" maybe; TR-Y design [see DOUG THORLEY]) can offer better exhaust scavenging at cruise rpm IF

the system is designed as a whole.

As a motorhome has no need of a dual system (velocity/pressure falls off as temperatures drop internally), the need for good, low-restriction piping from both banks to a single pipe is crucial. As to muffler, any good low internal restriction piece is adequate (where HD use is specified). Muffler placement (distance from engine) is the type of subject Vizard tackles.

GALE BANKS ENGINEERING is probably the best source for an aftermarket kit that is designed to work together.

I wouldn't spend any money on big ticket items until engine compression is verfied; that there are no vacuum leaks; that ignition and fuel delivery is as-new, etc. Underhood heat has a way of cooking wiring covers, connectors and terminations.

Synthetic lubricating fluids are an obvious step in the right direction as is an extra strong primary and secondary ignition system. A firm shifting transmission is great to have, and no slop in the torque converter.

Frankly, there are no magic fixes, but EVERYTHING that allows the driver to make fewer -- and finer -- inputs is to the good. It's all about working margins.

Understand, too, that the Chev 350 was designed as a throwaway motor (Chrysler had far better engines by design geometry), but the post-1987 design changes helped, and, especially, port fuel injection. The sheer number of them, and parts for various uses, has led people to believe that it is some super motor from the past. It wasn't, it simply gained by being produced in impressive numbers and the amount of development for racing by both the factory and aftermarket make it a brain-dead choice for most applications.

Find out what the specs are for your motor (camshaft & compression ratio [actual, not advertised]), the rear axle ratio, tire height (measured, not published) and torque converter efficiency, and install a high quality tachometer (again, AUTOMETER or other, where the top number is 6,000 rpm; dash mount [probably a diesel tach can be adapted]), and use it to determine from calculators online to make informed decisions about any other modifications.

As to what I've seen around AIRFORUMS I like Andy/Inland RV's idea of mounting an airspeed indicator.

The trio of vac/tach/air would be a great set to work off of for driver fuel input decisions. And cheap, in comparison to most other "solutions" offered (where electrical & mechanical & airflow problems are mediated).

slowmover 01-12-2010 09:11 AM

Assuming one is serious about fuel economy, then travel speeds will be 55-60 mph.

CUMMINS and other manufacturers publish information about fuel economy, and the rule of thumb is:

1. Rolling resistance to 50 mph
2. Aerodynamic resistance after 60 mph

(Now you know why the 55-mph speed limit wasn't a random choice)

Besides tires, and engine internals (plus fuel/air/electric), one should be going over the entire drivetrain: bearings, bushings, brakes, and ESPCEIALLY, steering/suspension. How is the brake adjustment (rear drums); does it lock early on gravel on the RR tire? (Etc). Test and verify.

Does tire air pressure rise 5-psi after 1.5-hrs steady-state driving? Should only be 3-psi. Etc.

If all sources of adjustment have been checked -- that there is no "play" outside of spec -- then perfecting the steering pays the biggest dividend, as, IMO,


(One may substitute "safety" for "economy" in the above).

Anything I can do to improve steering feel and response pays dividends in economy.

With a given speed for all travel one can make comparisons. And, the biggest change from one road type to another generally affects steering control. In a mile, how many steering corrections are being made? At the end of the trip, how much "farther" did the rig have to travel due to constant steering input. This is truly small, but truly significant.

As motorhomes are notorious for poor control, shock absorbers, anti-roll bars, poly bushings, STEER SAFE, kingpins, etc, are all worth examining and improving. Above and beyond any aftermarket "power making, mpg increasing" kits.


Anything that improves steering control lessens driver fatigue. An alert driver makes better decisions, faster. And that 30% number can be reduced. The feedback from dash gauges can be integrated and the rig's "margins" can be elbowed outwards as experience is gained.

So, as you maintain, as you plan repairs (be systematic, NOT component focused; treat systems as a whole), have in mind the plan to make improvements as you go along.

The driver is the alpha and omega of fuel economy.

slowmover 01-12-2010 10:15 AM

Start by weighing it. Driver, full fuel, full fresh water/propane, NOTHING else. Try to get each side as well, individual wheel weights best. Do NOT inflate tires to maximum, first, as sidewall numbers are generally meaningless; second, as "over" inflated tires lead to lesser handling and changes in brake balance. With the individual wheel weight, contact the tire manufacturer with your scale readings, and ask for a recommendation. Know the GVWR -- state it -- and indicate you will respect this number in all instances.

Second, use a GPS to ascertain speedometer error. Most are off by a percentage. This means that 35 true [37 indicated] can be 60 true (64 indicated). Have it corrected, or note actual speeds vs indicated and post it on dash after measurements at speed.

Third, look to improve visibility. Most of driving is about same, so dial in the mirrors (and correct driver posture), and use optical quality eyeglasses. Clean the RV glass with a mild acid solution and 000 steel wool. Etc. (And clean every morning, and at every fuel stop; or more often; inside and out).

Fourth, look to reduce fatigue. Loose trousers over "tight" blue jeans. Empty pockets, etc.

Fifth, trip plan. Nothing, and I mean NOTHING kills fuel economy more than having to come to a full stop. I plan fuel stops on time, miles and INGRESS/EGRESS from the fuel station. I'll take one in my direction of travel over one on the other side of the highway (use GOOGLE Maps, satellite view; or other for a "real" look at the station). Plan breaks every 2-hours. Know in advance your stops. Do all, in other words. to remove distractions ("should I stop here, or . . . ") as these all have an effect on fuel mileage. (These are pro driver practices).

Sixth, eliminate idle time. There is no advantage at any time, in idling. Take advantage of city traffic's mean speed of 15-mph. Do NOT accelerate to the posted limit, but only into top gear. Glide, imperceptibly, upwards. NEVER stop at stop lights, learn how to glide back down. Even a slow roll helps. (And it is a measurable difference AND easy to learn to do). Always know where you are going (mental map) and avoid lane-changing at the last moment. Get in the correct lane early, a mile or more if you can.

All of these seem incremental, and changing the drivers mind from the usual American hurry, hurry, pays off. Better than 95% of all drivers are really lousy. The ones who have made a couple of changes think themselves better than average (that's a real laugh); so practice in any vehicle you drive.

How will you measure? Easy. Higher fuel mileage is not the only way. I need only glance at someones tires, or watch them brake to a full stop one time to tell you how good they actually are. On an ordinary car anything less than 70,000 miles on a set of brakes is room for improvement. Same with tires (but that is more vehicle dependent as well as initial tire quality).

How to measure fuel gains? It will take a minimum of 30-miles driving for the vehicle to warm up completely, so fuel at that point. And fuel again -- several hundred miles down the road before stopping for the day -- prior to entering big city or off onto secondary roads. The best test is a round trip to account for terrain, winds, etc. Consistency, over many tanks, is the only way.

slowmover 01-12-2010 10:32 AM

Aerodynamics is the last thing I can think of. I was recently reading a thread where the rig was:

diesel pickup
enclosed trailer weighing 7,500-lbs
mpg was 8

My rig was

diesel pickup
TT weighing 7,500-lbs
mpg was just short of 16

"Aero", means all corners rounded (sides as well as front/rear), and an enclosed underside. All else is compromise. Lower height over weight. Etc.

Best motorhomes were the FMC and CORTEZ from years past, with gasoline engines. Fully independent suspension gave them the handling edge that squared corners lost in fuel economy. A GMC was about good enough to carry the family from Joisy City to Flawrida down I-95 with reasonable economy due to a decent front rounding (but still a square back, an equally worse sin), but not made so well. Motorhomes are always a compromise. VIXEN may have been the best for fuel economy (but durabiity was an issue).

If they were still being made, this is the motorhome I'd look for that used a smallblock V8:

Go for basic design first, aero second, and

Perfect mechanical operation
Reduce driver fatigue
Monitor engine vacuum (etc)
Trip plan
Maintain perfect sight visibility
Alter habits for all driving of all vehicles

This may seem like a lot, but I have barely touched on it.

slowmover 01-12-2010 11:11 AM

Here's another view:

1970 ? Balboa Dodge Motorhome RV Ad:eBay Motors (item 370158264896 end time Feb-06-10 11:58:44 PST)

Personally, I'd rather have this:

Tin Can Classifieds - 1978 Silver Streak motor home - Powered by PhotoPost Classifieds

None of them are going to -- in size Class C [correction?] -- get very good mileage.

Maybe a low-roof TREK or other van based job.

Lumatic 01-12-2010 12:49 PM


Originally Posted by REDNAX (Post 793109)

Start with a dash-mounted vacuum gauge, a quality one such as AUTOMETER, and place it in your line-of-sight. Nothing, IMO, will do more to "train" a driver.

Search out the many uses of a vacuum gauge, be diligent. It is little short of awesome what knowing how to read one can tell you about a gasoline motor.

Can anyone give me the skinny on Vacuum Gauges for Idiots, or, links to more info.

ROBERT CROSS 01-12-2010 02:40 PM

Vacuum Gauge Theory

;) Enjoy...

choctawmel 01-12-2010 05:16 PM

I put GM TFI on my 454 and increased fuel mileage about 30% (4mpg to 6mpg) I installed the O2 too far back (they say) on the headers. Been told I needed a heated O2 and before we left for New Orleans I put one in. Thought I'd hit gold on the first fill up-7mpg!!! Then the next was 5.9mpg. So still getting 6-6.5mpg.
Be going home in April without the car. Then I'll see if I can get that 10-11mpg some say they get.

Lumatic 01-12-2010 05:38 PM


Originally Posted by choctawmel (Post 793277)
I put GM TFI on my 454 and increased fuel mileage about 30% (4mpg to 6mpg) I installed the O2 too far back (they say) on the headers. Been told I needed a heated O2 and before we left for New Orleans I put one in. Thought I'd hit gold on the first fill up-7mpg!!! Then the next was 5.9mpg. So still getting 6-6.5mpg.
Be going home in April without the car. Then I'll see if I can get that 10-11mpg some say they get.

What is "TFI"?

DanN 01-12-2010 06:04 PM

Throttle body Fuel Injection...similar to what the GM installed from '88 to '96. Simple, reliable setup.


ROBERT CROSS 01-12-2010 06:51 PM

TFI= Throttlebody fuel injection
TBI= Throttle body injection

EFI=everybodies fuel injection :rolleyes:

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