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Discussion Starter · #1 · (Edited)
I recently had quite a few modifications done to my 56 and everything is working out well. Except for the gear in the rear. My 56 is now a GAS SUCKING PIG. Not to be irreverant but.

If you were to change the gear in the rear what would you change the gear to? and why?

From what I understand the previous owner changed the gear in the rear end to a "Highway Gear" and that is why she now needs a fuel truck towed behind me when I drive in the city.
I am thinking that it might be cheaper to change the gear in the rear end rather than keep towing a fuel truck behind me.

Any information appreciated thanks.:shakehands:

PS I do more city driving than highway. I drive her to work every day and around town might do a tour once in a while.
 

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You didn't say whether you have a stick or an automatic, but sticks tend to have a little lower ratio than automatics. For standard duty cars, I think I'd go with something around 3-00 to 3-10 for an automatic, and probably 3-31 to 3-55 for a stick.
 

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I run a 309 and love it, but would also like a 335 too....Both are good for hiway crusing...:anim_25:
:gba:
bowtie-trifive
 

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if you have a highway gear in your ride already,sounds like the modifications you did is whats messed up.Need to know if anything was done to the engine or transmission and if its a stick or automatic.A high road gear in town shouldn't be as big of a gas hog as a low geared rear end.Any engine up grades and if so what
 

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Upgrade?

Have you given thought to upgrading to a more modern axle? Could you use positrac or disc brakes? There are many feature and ratio choices to be had.
 

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My 3:55 with a muncie 4 speed pushes 3000 rpm at 60 to 65 mph. Sucks gas. A drive to a local car show runs me about 15.00 in gasoline.
 

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I recently had quite a few modifications done to my 56 and everything is working out well. Except for the gear in the rear. My 56 is now a GAS SUCKING PIG. Not to be irreverant but.

If you were to change the gear in the rear what would you change the gear to? and why?

From what I understand the previous owner changed the gear in the rear end to a "Highway Gear" and that is why she now needs a fuel truck towed behind me when I drive in the city.
I am thinking that it might be cheaper to change the gear in the rear end rather than keep towing a fuel truck behind me.

Any information appreciated thanks.:shakehands:

PS I do more city driving than highway. I drive her to work every day and around town might do a tour once in a while.
I'm confused. :D (my normal state)

You say that the previous owner changed the gear to a "highway gear".

To me, that means that the PO put a lower numerical gear in the rear for highway cruising, something in the 3.08, 3.36 area.

That low numerical ratio should decrease your RPM for cruising and thus increase gas mileage.

What ratio is in the car now?

A high numerical rear, something like a 4.11 or even 4.56 will increase engine RPM at cruising speed, thus using more gas.

What other modifications were performed?

Chuck
 

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Alleycat, we really need to know what you began with and what was done to your car that has resulted in the recent poor mileage. There are too many variables to speculate. Can you tell us what was done?

For instance, if something in your engine combo is now mismatched to the remainder of your engine components......

Or if you installed a cam with a lot of duration and/or one which moved the powerband up in the RPM range, making the engine less efficient with present gearing and use......

Then there is carburetion...... Some types of carburettors are more efficient than others with certain engine combos and run better/get better mileage.

If you changed over from a manual transmission to an automatic, that will generally drop your mileage, as it takes a certain amount of power just to run an automatic in addition to the 5% - 8% slippage you will have unless in high gear with a locking converter engaged out on the highway.

High stall converter (even more slippage)...... Forget about mileage.

So what was done that resulted in the mileage dropping?

Happy Motoring,

Harry
 

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Discussion Starter · #10 · (Edited)
Ride Gas Woes

My 3:55 with a muncie 4 speed pushes 3000 rpm at 60 to 65 mph. Sucks gas. A drive to a local car show runs me about 15.00 in gasoline.
Exactly I think now don't quote me on this I have a 342 if that makes any sense. I have been trying to find this out for a while.
Hurst Competitin shifter 4 speed. Headers mild cam 4 barrel edelbrock and intake. 14 inch wheels.
 

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Discussion Starter · #11 ·
Alleycat, we really need to know what you began with and what was done to your car that has resulted in the recent poor mileage. There are too many variables to speculate. Can you tell us what was done?

For instance, if something in your engine combo is now mismatched to the remainder of your engine components......

Or if you installed a cam with a lot of duration and/or one which moved the powerband up in the RPM range, making the engine less efficient with present gearing and use......

Then there is carburetion...... Some types of carburettors are more efficient than others with certain engine combos and run better/get better mileage.

If you changed over from a manual transmission to an automatic, that will generally drop your mileage, as it takes a certain amount of power just to run an automatic in addition to the 5% - 8% slippage you will have unless in high gear with a locking converter engaged out on the highway.

High stall converter (even more slippage)...... Forget about mileage.

So what was done that resulted in the mileage dropping?

Happy Motoring,

Harry
I went from a two barrel to a 4 barrel carb and Edelbrock intake. Part of the problem is I cannot get actual information from the previous owner as to gear in rear end etc. All I know is the gears were changed to a highway gear before I got her. She has headers and I recently changed my cheap ass exhaust to a couple of Magnaflow 50s as well.(She was very loud). The Police are starting to crack down on noise and $100 fine per offence. What I need to do is talk to the actual person who did the gear change. I am going to contact him shortly. I might get him to change the gear back if I can figure out what to get. My mechanic says if you go high you can pull a house down the street and low you won't. She is fairly slow off the line so I believe she is somewhere int eh 350 range. My mechanic recommended something in the range of low 300s.:shakehands:
 

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Discussion Starter · #12 ·
No I had not thought of that YET

Have you given thought to upgrading to a more modern axle? Could you use positrac or disc brakes? There are many feature and ratio choices to be had.
One of my problems is I do not know enough about my rear end and gear etc. hence all of the questions. I have disc brakes in the front now. Changed this winter.:shakehands:
 

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Discussion Starter · #13 ·
PS I do more city driving than highway. I drive her to work every day and around town

More:shakehands: city than highway
 

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Cocke County, TN. 55 Bel Air Sport Coupe
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Exactly I think now don't quote me on this I have a 342 if that makes any sense. I have been trying to find this out for a while.
Hurst Competitin shifter 4 speed. Headers mild cam 4 barrel edelbrock and intake. 14 inch wheels.
Is the new 4 barrel carb a "spread bore" (or a qaudrejet clone)? (remove air filter and look to see if the front 2 barrels are significantly smaller than the rear 2 barrels). If it isn't I doubt you will ever get good fuel mileage with it.
 

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My two cents, 3:08, 3:20's are the common highway gears, 3:55 nice all around gear, 3:73 little more aggressive, 4:11, something we all would like to have for off the line but not so good for highway cruising. If I am remembering correctly, 3:55 is stock for 6 cylinder 56-57, 3:73 stock for 55 6 cyl, 4:11 for overdrive, all optional for any car. V-8 cars came usually with less aggressive gearing, no?
 

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:) Alleycat, the gear ratios are important (both transmission and rear gearing). This will give you your torque multiplication factor in each gear. Along with rear tire height, you can use these to predetermine actual RPMs in each gear at various roadspeeds.

The original 3-speed transmission installed in '55 - '57 cars (with the exception of the rare close ratio gearset) had a first gear in the 2.92 -2.94 range if I remember correctly. In '55 and '56, a standard shift car (without OD) came with 3.70 rear gearing. The OD cars had 4.11 rear gearing and with 0.70 overdrive factored in, that equates to an effective rear gearing of 2.87:1 in high gear overdrive out on the road.

In '57, standard shift cars were fitted with 3.55 rear gearing to allow for the new, shorter 14" tires and wheels. Cars with overdrive retained the previous year's 4.11 rear gearing in '57.

Anyway, the point of all this is that for maximum efficiency (equating to best mileage), the engine RPMs must be matched to its powerband at whatever roadspeed the car is moving at any given time.

A dash mounted vacuum gauge can be helpful in determining this when driving and a tachometer is nice to have as well. Its a balancing act...... From a mechanical standpoint over the long term, its worse to lug an engine than to over-rev it (so long as it isn't damaged mechanically from turning excessive RPMs if over-revved).

As for the cam...... It will be designed to produce its powerband within a certain RPM range and hopefully is matched to the other engine components, as well. So the goal is to keep revs within this RPM range. (A notable mismatching of cam to engine is the '290 HP' GM crate engine...... In actual practice, these engines do not check out at the advertised static compression ratio and even the advertised comp ratio is too low for the installed cam.)

When I first began driving big trucks in the '60s, the driver trainer jumped in the cab with me and told me to read the operating manual.

Shortly after, he quizzed me on certain things (operating temps, engine warmup, double clutching, etc.). Primary amongst them was the engine's designed operating range (RPMs). In the case of that old late '50s rig, its operating range was between 2,200 and 4,600 RPMs. The driver trainer was a tough old bird and made it very clear than if he looked over at the tach and saw me lugging the engine (or less likely, over-revving it)...... He'd haul off and knock fire from me.

Having just mustered out of the service (Marine Corps) at the time, I could relate to that and learned quickly. The only time I really screwed up was when I used the (separate) trailer air brake to slow us before going into a tight left hand turn on a rain slick asphalt road beneath an overpass. We did that a lot on dry paving to save the brakes on our tractors when hauling a heavily loaded 40 ft. trailer (moving van).

I learned not to do that on slick paving the hard way that morning. When you use the trailer brake by itself on slick paving, it can break loose the trailer wheels and the weight and mass of the trailer pushes the tractor...... And even if you don't use the tractor brakes, this can jacknife a tractor-trailer rig, especially when going into a turn.

Fortunately, I had been in quite a few high speed turns in cars where the rearend broke loose and was able to let off the accelerator pedal, stay off the brake and steer into the skid, then through the turn and recover control just as our outside wheels (his side of the truck) 'kissed the curb' (it was a tee intersection with a train track paralleling the road closeby and if we hadn't recovered, we would have crashed into the freight train that was going by). Kinda like a Grand Prix drift in a moving van.

A ways down the road, the driver trainer broke his silence and told me to pull over and stop the truck on the side of the road. There was no colour in his face. We got out and I fully expected him to punch me out. Instead, he lit a cigarette and after smoking it down to a butt, he looked me square in the eye and quietly said...... 'If you ever do that again, I'll kill you.' Then we got back in the truck and not another word was said about it.

Thanks for the memories,

Harry
 
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