The Stovebolt Site Forums The Shop Area The HiPo Shop tricks for better mpg

ok i know i had a thread a while back about easy power but i think that id rather spend less on gas money so just wonderin if theres any tricks to using up less gas. i know a 2 bbl card uses less gas so ill probably go with that, but thats about all i know. thanks.

2bl does NOT mean less gas.
In fact if you have 2bl and 4bl same cfm, the 4bl will get better milage because during cruseing it is running only on the primarys
a few more tricks to get better milage are
1. Dont accelrate hard
2. Keep your truck tuned up and clean filters
3. Check your tire pressure
4. Using A tachometer and watching your rpms can also help you keep track of how hard you push your engine

Overdrive and fuel injection. Neither of which will probably ever pay for themselves unles you drive several hundred thousand miles.
Scott

4 more ideas:

1) buy everything mail order!
2) draft trucks where possible !
3) use Mobil One (I did notice a difference)
4) if state laws allow, drive with tailgate open..... less drag. Or buy a cover.

keep fat dawgs out the bed...........

Draft trucks???A very stupid thing to do.

The tailgate down wont see much difference. I read somewhere that, if I recall correctly, drag/resistance does not have an affect on a vehicle until you reach 120km/h. Do you seriously draft trucks often Johnnny?

there has been reports of a 2 mpg increase with a cover over the bed or the tailgate down. i think it was a thread on here a while back...

4bbl carb with small primary jetting run the most advance you can on the timing no hole shots from stop lights.leaving the gate down DOES make a differnce(checked it my self)keep the tries inflated to recommended pressures.clean air filter.put it in neytral and coast on long down hills. And the #1 way to save gas dont start the engine

hey guys ,,, the thread here awhile back should have included at least one link to professional studies that have shown leaving the tailgate down does nothing for your mileage, tho all the bed cover folks claim the covers help

check this and also the link from there to this

as I commented the last time this idea came up, I've noted on several occassions that I can drive the truck in pouring rain w/ cardboard boxes in the bed and they don't get wet till I stop - always was evidence to me that the wind over the truck does not swoop down and hit the tailgate to create drag

Bill

JOKER, not nice to talk about a fellows significant others when you don't even know them. ron

Not really at all, was just kiddin!

You found it before I did Red! I don't draft trucks, but I wonder if you would notice a difference?

hahahah yea that sounds really dangerous thats funny to think about though. so should i go w/ a 2 or 4 bbl to get better mileage?

I used to draft big rigs with my old 72 VW camper. It worked great, but the scenery sucked and the truck drivers really didn't care much for it. I could totally lift off the gas and have to ride the brake to keep from getting into the back of the truck. Oh, those good ole college days...

Leaving the gate down does make a difference all the air that passes over the cab hits the tail gate and at 60 mph its kinda like draggin a parachute.i have checked milage both ways and it does make a difference.not an extreme difference maybe 1 mpg but if you figure that to a tank of gas it adds up.

V6Jimmy - yer not payin attention! - it does not create a drag, as the air coming over the cab clears the gate, regardeless of what some think

Bill

it probably depends on the truck for if the air would hit the gate or not. and we could just stop arguing about this and buy a friggin tonneau cover. thats probably what im going to do. but IMO i think it could make a difference on some trucks.

The small primary throttle theory is an engineer's pipe dream . In all cases,adding a second carb on a Chevy 6 gave better fuel mileage if driven normally.This is well known by those who actually worked on these engines.We are takin old Chevy 6's here.
Several years ago wrote an article for Inliners on the various carbs I had tested out on a 261 engine,Holly 350 and 500 2bbls,old Carter WCFB and small AFB's and the butt ugly Pinto carbs, and even 2 Rochester B's.
In all cases,one the carbs were jetted properly,fuel mileage was all about the same,of course there was performance differences.
For better fuel mileage,work on the areodynamics.

Tony hit on a good one there.... aerodynamics! It's usually helpful if you lower (not slam) the truck. Also maybe use smaller mirrors? Some mirrors are pretty huge on trucks. If you have a visor, maybe adjust it so air escapes the top edge instead of collecting there. Probably just easier to save money elsewhere in life and feed the truck what it needs!

yea i was thinkin about lowering it but definetly not gona slam it or anything that drastic.

My own experience has proven this to be the case. I run a 625 CFM Carter 4-barrel on my 64 Ugly Truck. If I stay outta the throttle in town, I get about the same mileage I got with the Monojet. On the highway I get 15 mph, same as before. In my case, the low gearing and the aero effect of pushing a barn door down the highway seems to have more to do with mileage (as does a heavy foot) than the carb.

Again, in my own experience, the only thing a 2-barrel carb has ever given me is less performance than a 4-barrel. I suppose you could say that it increases mileage by keeping me from opening up the secondaries (of which there ain't any) but I'd rather have the power on hand if I need or want it (and it DOES sound ossum when the secondaries open up thru the cherry bombs) and then take the blame for the lousy mileage myself.

doesnt an overdrive transmission help w/ mileage too?

1964, you're right about the OD transmission, but it's a hard transfer (most of the time) and won't pay for itself for a long time. But if you've got nothing, that's the way to go.

ArticCat, you're right about the 120 km/h thing, the wind resistance doesn't play a factor until then, so if you're just going around town, it won't matter.

And personally, I was part of the tailgate post, so I did my own experiment, and found that when it was DOWN i got 15 mpg, and when it was UP i got 12 mpg, so there ya go folks, my 2 cents.

I setup the 350 in my '72 Cheyenne/20 with TBI for inside of $400 (now over 400 but only cause I bought an emulator, chip burners etc). Netted me 2 MPG better. Local Upull yard sells transmissions for under $100, go pick up a used 700r4 at that price it'll justify its own cost real fast, especially for the older trucks that made up for lack of displacement/torque in ungodly high gearing.

kris, thats a really good idea ill definetly think about doing that. will that tranny bolt right in?

Yes and no. Unlike the TH350/400, it has a more complex cable for controlling pressure (as opposed to just kickdown/detent) so you need brackets for that and its not a bad idea to have a shop setup the pressure with a gauge for longevity of the transmission. It also needs a small wiring clip for the automatic TCC lockup, I think summit sells a kit for $39. Otherwise, its the same bolt pattern as SB/BBC but I think that the flexplate pattern is different for the 700r4 TC than the TH350 TC. Length is different too, might need to have your driveshaft shortened (or take the opportunity to move to a 1-piece)

It's true that in a driving rain storm going down the highway, hardly any rain hits the bed. I've noticed that myself.

I have a theory that when a vehicle has to work extremely hard to "get out of its own way" because of having too small an engine, it runs much less efficiently. An engine with a surplus of power and good gearing can loaf along and actually potentially be much more economical (per horsepower).

For example, the too small 235 in my truck is at its very edge of its capabilities and I'm barely keeping up with highway traffic. The 1-bbl Rochester strikes me as more of an inefficient fuel dumping system rather than a precise fuel metering system.
In contrast, the huge and massively powerful 465 cubic inch big block Pontiac in my '68 Firebird gets 1 mpg BETTER gas mileage than my truck, and it doesn't even have an overdrive.

That's one point that hasn't been touched on. I feel that inadequate power in a heavy truck is half the reason these inline sixes are so horrific on gas.

We have posted a few ideas on fuel economy on our website. Here is the link:

http://www.thecarburetorshop.com/Troubleshooting.htm#Fueleconomy

Jon.

Here is a proven theory on tailgates up and down or covered:

Tailgate up = the air flows over the top of the cab, hits the tailgate and starts to "roll"... as the air "rolls" it forces the air coming over the cab up and away from the tailgate, this is proven by driving in the rain.

Tailgate down = the air flows over the top of the cab, and out the back of the truck, where it creates the draft, that the daft like to linger in... the draft actually pulls on the back of the truck, slowing it down or making you use more gas pedal to overcome the suction.

Bed Cover = You can gain some fuel economy by covering the bed, as the air flows over the cab, starts rolling right behind the cab, which forces the airflow to go up, rather than down, which eliminates (somewhat) the suction of the draft.

I validated my theory today using a couple handfulls of straw.

I observed the straw "rolling" in the bed while driving at highway speeds.... which further supports my theory.

Tomorrow, I will drive with the tailgate down and see what happens.

Gearing-gearing;Don't trade away that set of 16's!!Swapping from 235/75R-15's to 235/85R-16's will improve your gearing noticeably.
Driving with my tailgate down CONSISTENTLY gives me 2 to 3 miles per gallon improvement.
A small 4 barrel,properly jetted,is worth some more savings.
Make sure you don't have a wheel brake or your e. brake dragging.
Keep your trucks alignment correct.

Keep your u-joints properly lubed.
A cruise control will help your mileage on the highway.
Synthetic lube in the transmission and rear end is a good thing.
I guess,if you wanted to really get into this,a lighter flywheel and smaller diameter clutch would take less horsepower to spin,but that's getting deep into the nit-picky details.
Speed

I've read on other threads on this site that the following things help with gas milage:

1. Two progressive two barrel carbs rather than one 4 bbl, one two barrel or the original 1 bbl.

2. HEI ignition

3. PCV Valve

4. Dual exhuast

5. Lower gearing in the rear differential

6. Transmission with better gearing.

In my truck I'm doing all that and the cost isn't gonna be much more than a pure stock rebuild because the parts all need replaced or rebuilt anyhow.

If your truck is already running, some of that stuff you can do fairly cheaply with patience and putting in some free time at the boneyard. For example, I got my T-5 for under a hundred bucks, including the clutch disc that'll work on the original fly wheel. The rear differential was $100 (a 3.42 10 bolt posi with good brakes) Throw in a gasket, shim kit and saturday making adjustments. Driveshaft was $15 plus u-joints. The HEI gets pulled out of a later v-6 and ground to work in the straight six. Carbs, manifold and dual exhaust are pricey though!

I meant 'higher gearing' in the rear end, not lower...

how does a pvc valve help?

NM51, lower gearing is okay if you mean lower numerically. Most people today use the term that way, but when older guys say higher geared they mean higher speed gears, which is the same as lower numerical gearing.

One problem with the argument concerning the tailgate is that different trucks have different aerodynamics. One may do tests on one's own truck and then come to a general conclusion, which may or may not prove to be erroneous.

I have personally tested the "lower the tailgate" theory on two pickup trucks; both picked up mileage in the realm of 5 to 8 percent. Not a lot, but certainly measurable. When a cab-high shell was placed on top of the bed, another 12-15 percent was realized.

However, on one specific truck I have kept good records and done before and after testing on a number of modifications. The best modification on this truck was to REMOVE the bug shield.

I started with a 1968 Ford 360 A/T with a bug shield. As things wore, replaced the bias ply tires with radials, replaced the dogmatic trans with a 4-speed, replaced the 360 2 barrel with a 390 4 barrel, removed the bug shield, added dual exhausts (tried headers for awhile, huge mistake), and now drive with the tailgate down (I had a shell on the truck but have now removed it). Mileage at 70 MPH has increased from 9 MPG to a little over 17 MPG with these modifications. Others may find different results. The two best individual gains were by removing the bug shield (about 2 MPG) and junking the dogmatic in favor of a 4 speed (about 2 MPG). Truck has highway gears (I don't know the exact ratio).

I have built a set of dual 4 barrels to put on the engine if I ever get reasonably caught up in the shop.

As mentioned earlier, these changes may or may not help others, depending on the aerodynamics of the truck.

Jon.

Carbking,
I built up a 235 many moons ago. It had the old standby Offy manifold with three, somebodies, BXVD carbs on it. I was told it would not get any WORSE mileage because the engine still would pull in only a specific cubic measure of air, and now that measure was divided by three! Do you think I should have had my manure shovel with me when I was told this?


Stuart.

Here is the expensive way to reduce MPG and save the environment. I've talked to this company on occasion to see when they will be mass producing their rotary valve heads for Chevy V8's and 6's. They have done Ford 302 V8's and Mercedese 6's with remarkable horsepower gains, lower emissions and higher MPG. I wish I had the $14,000 for a tricked out injected 350! Check it out: http://www.coatesengine.com/engine_of_the_future.html and http://www.coatesengine.com/photo_gallery.html