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Challenge for all the gear heads, The quest for gas mileage
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Knarley Darley
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PostPosted: Thu Mar 14, 2013 12:36 am    Post subject: Challenge for all the gear heads, The quest for gas mileage Reply with quote

Lets put our heads together and see if we can get this gas pig to mileage numbers not thought possible. The candidate is a bone stock 1976 Chevy 3/4 ton camper special pick up truck with a 454/ T-400 3 speed automatic. It came with factory dual exhaust (no cats) although the tail pipes are small, and the mufflers are very quiet, and probably restrictive. It has the stock Qudrajet, and single snorkel air cleaner, although the snorkel is fairly good size, and ducted to cold air. It has a EGR valve, and a air injection pump. Has the stock HEI ignition large distributor cap with the coil mounted in the cap. The engine is new but built to stock specs, and will run on 87 octane without the slightest hint of a ping. It does run good, and will spin its non posi one leg rear tire for about 100 feet if you stab it from a dead stop, but it sucks fuel like nobody's business. 8MPG city, and 10 MPG highway is about it. So lets see what everyone comes up with. This is my own personal truck, so anything goes within financial reason, in fact lets do this as inexpensively as possible.
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Knarley Darley
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PostPosted: Thu Mar 14, 2013 9:47 am    Post subject: Reply with quote

What do you think unplugging the EGR will do? How about a hotter ignition/ MSD?
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Thu Mar 14, 2013 11:54 am    Post subject: Reply with quote

The ignition is a good start.
My list of stuff that might yield a little.

1. You have to put the truck on a diet too heavy.
2. Free up the exhaust (headers,free flowing mufflers and pipes)
3. Cold air is always good which I think you said you have already
4. Synthetic oils everywhere
5. Make sure there are no brakes dragging for obvious reasons
6. Good alignment
7. Tire pressures can be increased for least rolling resistance
8. Keep the tailgate up the bubble forms and you will get better mileage with it up.
9. Slowly roll into the throttle to keep the revs down from a standing start to speed. This where you lose all the mpg
10. Carb adjustments for leanest idle possible might help slightly.

If you take it apart there is more in some minor port work, cam ect.

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2001 Focus 2.0 Zetec
15.63@87 MPH 1/4mi
1971 - Chevelle 408 SBC N.A.
6.95@98.6 MPH 1/8mi
10.97@121 MPH 1/4mi
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Thu Mar 14, 2013 12:53 pm    Post subject: Reply with quote

Everything Paul said is a great start. However not sure I buy leaving the tail gate up.

Get a wideband O2 sensor with datalogger. Use this to determine the air fuel ratio and where the engine spends most of its time. Then try to optimize the BSFC for those rpms. Or possibly change gears to get the engine where the BSFC is optimum.

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Big Dave
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PostPosted: Thu Mar 14, 2013 1:12 pm    Post subject: Reply with quote

an old used Hone-O-Drive or a brand new or used Gear Vendors over-drive unit bolted to the back of your TH400.

Big Dave
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Knarley Darley
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PostPosted: Thu Mar 14, 2013 3:17 pm    Post subject: Reply with quote

I will start with the least expensive stuff first, and report back. It has a 18 gallon tank, and I have to fill it about every 6 days so it will take some time after each change to see the results. The gear vendor would do more than anything, but that is not in the budget. Paul the only thing that you suggested that I can't do is the diet because I still want to be able to haul/tow with it. I guess I could take the tail gate off. That would satisfy Smokes argument that open is better, and paul's diet, although only a slight weight reduction, but every little bit helps, right? I do drive it like grandpa already, but almost all are short trips. I have the choke backed off as far as I can get away with so it isn't sucking any more than it has to on cold start ups, and the fast idle is barely above normal idle when cold. I think I have a MSD laying around that I can bolt on first, and see what that does. Then maybe I will cut off the tail pipes, and put turn downs on for starters. I did just change the engine oil to synthetic, and lightened the weight to 5-30 because it has a lot of oil pressure, and that takes power to turn that pump. Maybe I will also remove the air pump belt to save a little there.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Thu Mar 14, 2013 7:06 pm    Post subject: Reply with quote

at risk of being offensive.... why dont you just get rid of the gas hog and get a F250 with the old 7.3L powerstroke ? they average more than double what youre getting with the BBC and can tow just about anything.

i know, you didnt ask what to trade it in on. i just dont see getting any significant fuel mileage improvements out of a BBC.

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Knarley Darley
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PostPosted: Thu Mar 14, 2013 9:41 pm    Post subject: Reply with quote

Man 10sec you sure can be a wet blanket on a project. Why did you have to come along and RUIN EVERYTHING!!! LOL Actually the only reason I am driving this thing is because we are in the process of moving, and our other 2 daily drivers sold sooner than we thought. When I get to Idaho I am going to buy a newer truck. This chevy is something I already had so I started driving it. It is actually a pretty cool truck in really good original condition. The engine, and all the related are new plus I restored the AC which blows out freezing cold. I have not advertised it yet, but it is technically for sale. So I just figured it would be fun to see what could be done to improve the mileage until I sell it. BTW you could never offend me.
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89Gmcsierra
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PostPosted: Fri Mar 15, 2013 10:14 am    Post subject: Reply with quote

instead of O/D unit for TH400 which is 2-3K go find a 4L80E and manual valve body. 1000-1500 total.
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af2
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1933 Willys Coupe

PostPosted: Fri Mar 15, 2013 5:10 pm    Post subject: Re: Challenge for all the gear heads, The quest for gas mileage Reply with quote

Knarley Darley wrote:
Lets put our heads together and see if we can get this gas pig to mileage numbers not thought possible. The candidate is a bone stock 1976 Chevy 3/4 ton camper special pick up truck with a 454/ T-400 3 speed automatic. It came with factory dual exhaust (no cats) although the tail pipes are small, and the mufflers are very quiet, and probably restrictive. It has the stock Qudrajet, and single snorkel air cleaner, although the snorkel is fairly good size, and ducted to cold air. It has a EGR valve, and a air injection pump. Has the stock HEI ignition large distributor cap with the coil mounted in the cap. The engine is new but built to stock specs, and will run on 87 octane without the slightest hint of a ping. It does run good, and will spin its non posi one leg rear tire for about 100 feet if you stab it from a dead stop, but it sucks fuel like nobody's business. 8MPG city, and 10 MPG highway is about it. So lets see what everyone comes up with. This is my own personal truck, so anything goes within financial reason, in fact lets do this as inexpensively as possible.


Advance the cam 4+ degrees. The smog cams and timing gears were pretty lame.... All the egr does is allow the 87 octane fuel IMO.
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Knarley Darley
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PostPosted: Fri Mar 15, 2013 8:03 pm    Post subject: Reply with quote

It seems to run worse with the EGR un plugged. It acts too lean, and has a noticeable flat spot. I would have thought it would have a little more power because of no exhaust gas being diluted into the intake charge, and less throttle to get the thing moving? We shall see at the next fill up.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Fri Mar 15, 2013 10:37 pm    Post subject: Reply with quote

it needs the EGR because it most likely is lean and the temps in the cylinders are HOT. the smog crap is whats killing you. its horribly inefficient. might try getting a used air gap intake and a Holley carb. i know that has a tremendous effect on the old 305 "H" motor that was in the mid 80s pickups. a better cam would help too. of course, now were getting deeper into the engine and you didnt want to do that. i also agree that you need some sort of OD trans.

ive never heard of using a 4L80 with a manual valve body. i like the sound of that if it actually works. looks like i need to do some research. i could benefit from one of those in the Impala.

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Knarley Darley
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PostPosted: Sat Mar 16, 2013 2:19 am    Post subject: Reply with quote

One thing that helps is it has 3.73s instead of 4.11s in the rear, and the tire is pretty tall so it is turning a reasonable RPM on the freeway. I still have to deal with smog every 2 years here, but if I end up taking it to Idaho, I will strip everything off, and do a manifold cam and headers.
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clay
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1972 Chevrolet Nova

PostPosted: Sat Mar 16, 2013 9:08 am    Post subject: Reply with quote

I believe Transgo has a kit that will allow you to run a 4L80E full manual. Forget the GearVendors - you can never recoup the cost in fuel savings and it's beyond the scope anyway. I put a MSD on my S-10 years ago because I had one laying around like you and never saw any mileage improvement. How fast do you drive? With the aerodynamics you are working with absolutely the slower the better. I don't know what temp thermostat you have but run it hot as possible. Do you have the intake exhaust crossover blocked? If so I would open it up to heat up and vaporize the fuel as much as possible. Also do you still have the factory heated air system on the air cleaner? What sucks for you is even with a 10% improvement (which is resonable) you're still only talking about 1 mpg. Trying to get economy and power is a different tuneup and can be a problem on conventional engines - non computer controlled. Sort of like setting up a race car to run great on motor and nitrous - almost impossible - too many things need to be different. On economy it amazes me how many people don't know how to drive. All of us that have bought Saturns have asked the previous owners what it got for mileage and it is usually in the high 20 to low 30 range. With no changes we ususally get high 30's to low 40's so driver can be 20% difference. I know you know what you're doing in that department though. A BBC pushing a sheet of plywood down the highway is going to be a challenge for sure. Clay
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89Gmcsierra
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PostPosted: Sat Mar 16, 2013 9:49 am    Post subject: Reply with quote

Guy i bought my MSD setup from told me in Truck series that he builds engines for they had to get rid of MSD and go to HEI and they gained 2 mpg on a race car from MSD but lost 10 horse.

also go to any junk yard u can find a 4L80E for early 90's truck so u dont need an adapter plate from LS bell housing and u can take that electric transmission and put a Full Manual valvebody in for 3-400 dollars and have a overdrive transmission that will hold the power, only down fall is Full manual u have to shift it everytime.

700R4 is good if u dont beat it. but yeah i've broke the sunshell in 5 transmissions in a very mild 355 nothing more depressing than banging gears and go for 3rd gear and just watch ur tach hit 6k instantly.
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