Easiest way to get my truck up to like 65 or so on the highway

[ahshoe]

I have a finished 1956 F100 with a very nice running 2 barrel 292 Y block. Been driving it for about 5 years now off and on during the spring, summer, and fall. It is a factory 3 speed that I converted to the floor. It has a 60’s mustang 8 “ rear end with a 3:25 traction lock rear gears. It pretty much maxes out at 55 or so mph with quite a lot of rpm’s…….Question: Is there any options to get this to cruise at say 65-70 on the highway without converting over to an AOD automatic transmission? I am open to doing most anything to make this more of a highway cruiser.

[1930artdeco]

With that diff. you should fly down the hwy. So unless you have something that is off like carb being a bit lean, valves, clogged single exh., not sure what is going on.

Mike

[oldave57]

I have a 57 Skyliner with 312 engine and Fordomatic. It originally had a 3:56:1 rear end ratio and I changed to a 3.25:1 really to correct a 5 MPH speedometer error that I could not correct with speedometer drive gear change. The original differential also had a front seal leak and so the new differential corrected two issues.

My original setup resulted in an engine speed of around 3200 RPM at 70 MPH (calculated based on tire rolling radius of 13" (800 X 14" tires). The change from 3.56 to 3.25 reduced that engine speed to around 2940 and the car seems to run fine and not make much noise. With that said, 2940 RPM is still on the upper end of "comfy" for the Y-Block and your 292 could handle the torque of a lower engine speed at 70 MPH.

Probably your best "fix" would be a 3-speed manual transmission with overdrive. They are getting hard to find, I imagine, but would reduce your highway (70 MPH) engine speed to around 20-100 RPM. According to an article I found (Google) the Y-Block is happiest between 2200-2800 RPM. The 3-speed with OD would let you keep the same "around town" ratio (overdrive usually kicks in around 30 MPH or so but with a 3.25 it might be a bit higher, since most overdrive cars had a 4.11 rear end back in the day). The overall ratio would be reduced from 3.25 to 2.28 at highway speeds.

Good Luck,
Dave

[Bleach]

It doesn’t make sense that RPMs would be that high in 3rd gear at 55 mph with that rear end. I had a truck with 4:11 gears that would be revving a little higher at freeway.
Are you sure you really know the rear end gearing? Is there a tag on the differential cover? You can also check by turning the rear wheels off the ground and comparing it with how many times the driveshaft turns.

[ahshoe]

I installed the whole rear end housing and new rebuilt carrier…that is what I did for a living some time ago. I really do not want to run very high rpm’s.Carb is not a problem It runs great just don’t want to cruise at as high of rpm that I am now for a long highway trip…I do not want overdrive for my 3 speed. Parts are hard to find and just went through the complete rear end .Had overdrive on my 55 tbird and not the way I want to go.

[miker98038]

Sponsored Links (Register now to hide all advertisements)

Change the rear gears. Bigger tires probably won’t give you the decrease in rpm you want.

Find one of those odd 4 speeds Ford used, where 3rd was converted to an overdrive. Due to the deep bellhousing a transmission swap isn’t as easy as a car Yblock.

[51504bat]

2.80 ratio third members were used in many mid '60's Fords with 8 inch rear ends. It would be a simple swap to change 3rd members. But I am surprised about the speeds you are referring to. In HS I had a '65 Falcon with an 8 inch. It had an automatic with 2.80's. I then converted to a full syncro 3 speed with 3.25's. Never had an issue with top end speeds. Routinely cruised at 70 on the freeway with G70x14 tires.

[oldave57]

A good way to get exact engine RPM's (at any speed) would be to add a tachometer. The electronic tachs are easy to install and relatively inexpensive. That would be a good baseline to have to determine exactly what is going on.

Reducing engine speed really comes down to reducing the overall engine to wheel drive ratio and that can only be done in one (or both) of two ways. Overdrive trans (which you don't want) or lower differential ratio.

[ahshoe]

Got a sun tach already on tje steering column….and don’t have a real problem with a overdrive automatic transmission. Just want to see if there is a way I haven’t thought of.

[miker98038]

There had to be a lot of 56 ford trucks (and related years and makes) in Iowa. Most 3 speeds would have been 3.5’s to 4.11’s. Since nobody ever drove fast, there’s probably 1,00,000 miles on all those old trucks. It’s just that today we’re used to low rpm cruising. Not then. You can run a Yblock in good shape for fairly long distances at 3000 rpm. I doubt you’re that high. My bird runs 2900 rpm at 70 (3.73, 25.5” tires, .8 o/d in T5)

[oldave57]

Just curious, what is your engine speed on the tach when you are running 55 MPH?

[ahshoe]

Tucked away for the winter but probably was 2300 to 2700 range at 55-65 ish,again not much memory left at my age ….I just would like to get the rpm’s down to cruise a 3-5 hour trip.

[Gene F]

If you hold that engine wide open for 3 -5 hours it will have a major failure. Y-blocks had a bulleting come out about oil flow at sustained high RPMs. The oil level in the sump would "hunt" a bit. That means it would tend to starve a bit, and when that happens it will pump a bit of foam (oil). Foam means lack of oil.

The story I have always heard is never put a y-block on a dyno, and make a pull it will lock up. It is your engine, but if it truly is turning RMPs flat-out, it will be cheaper to get another transmission/overdrive, and deal with this, that try for more RPM.

Anyone else ever heard this?

[miker98038]

Never heard that. Certainly Ted Eaton hasn’t, lord knows how many dyno pulls on his test mule 312. Karol Miller sure didn’t know about it when he drove to Bonneville and set new records.

The really heavy duty trucks used a bigger oil pan, more like 6-7 quarts. And you know fully loaded in the hills (like the Rockies) those boys driving them had them flat out and wound up for miles at a time.

But 3-5 hours firewalled is marine usage, and my recollection of gas engines was about 70% power and rarely over 3000 rpm. Serious diesel marine engines (cat, Cummins, gmc) came with charts for power setting and limitations. If I recall correctly the 370VT8’s (been a long time) would take something like 900 degrees on the egt’s for 6 hours, dropping to 6-700 for the fishing boats headed to Alaska and running for days like that.

But Iowa doesn’t go on forever, and his rpm range isn’t into a danger zone for a good engine.

[ms fowler]

What tires are you running? Can you fit larger diameter tires?
It seems as if you are running pretty close to where peak torque is generated. Is that a problem with Y blocks? I thought running near peak torque RPM would be a good idea.

[trulyvintage]

What have you done with the factory brakes ?
You have to be able to stop safely
at higher speeds.

Jim