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Trying to determine what would be my best setup in my '66 build. I have 2 engines, a 390 and a 300. I've driven it with the 390, 3.50 gears, 4 speed, 4wd. And I was planning to go with a higher rear end. Now I'm thinking I want to do the 300L6 instead , I've haven't owned a 300L6 truck in 40 years so I have no idea what they were running for gears and how they were to drive.
I'd like to know what your 300L6 is running for gears and how you like it.
I found that my 2.73 diff was a bit lethargic and limited its tow ability, but when I added a 600cfm carb, Offy intake, EFI manifolds, and a larger exhaust the truck accelerates better as well as getting better highway mileage. I generally only use it for light hardware or dirt loads anyway (kinda how a light truck was intended to be used!) For someone looking to smoke the tires or tow 10,000 pounds it would be totally wrong. 300s were even used for UPS trucks, so the engine has more than enough grunt...
My 81 F100 Flare Side has 2.75 rear gear and a NP435, came with a T18, both have a granny first gear and guessing that is what your truck has?
I a, running the factory carb & intake but EFI exh manifolds in to the stock size pipes & muffler out pass the rear tire like factory.
You also did not post what size tires you are running? I have 235 / 75 / R15 that is close to the factor size.
As HD said it is a little slow off the line and if I want to load it or pull my car trailer I have the granny first.
I am also running Advance Adaptor over drive unit so I can split all the gears if need be when pulling a load.
I can cruise at 70 / 75 MPH under / at 2000 RPM unloaded.
There is a post on another forum were someone did MPG on long trips and different things he did to help get it better.
He was running the SROD trany, 3sp with 4th a over drive and think he had a 3.25 rear gear and was in the 20's.
The gear change to the 3.25 was what got him more MPG don't remember what the had but it was a higher ratio (lower number like my 2.75) as it put the motor in the peak power area.
Thing is you don't have over drive other wise I would say keep the 3.50 gear.
Thing is if you go changing gears, yes front & rear on a 4x4 get into $$$$, you will need to slip the clutch more to get going from a stop and more so with a load.
The AA over drive would be a nice add on even with the 390 motor to get the RPM down and less wear on the motors.
Dave ----
ps my MPG did not change but the RPM did come down so less wear on the motor.
My 81 F100 Flare Side has 2.75 rear gear and a NP435, came with a T18, both have a granny first gear and guessing that is what your truck has?
I a, running the factory carb & intake but EFI exh manifolds in to the stock size pipes & muffler out pass the rear tire like factory.
You also did not post what size tires you are running? I have 235 / 75 / R15 that is close to the factor size.
As HD said it is a little slow off the line and if I want to load it or pull my car trailer I have the granny first.
I am also running Advance Adaptor over drive unit so I can split all the gears if need be when pulling a load.
I can cruise at 70 / 75 MPH under / at 2000 RPM unloaded.
There is a post on another forum were someone did MPG on long trips and different things he did to help get it better.
He was running the SROD trany, 3sp with 4th a over drive and think he had a 3.25 rear gear and was in the 20's.
The gear change to the 3.25 was what got him more MPG don't remember what the had but it was a higher ratio (lower number like my 2.75) as it put the motor in the peak power area.
Thing is you don't have over drive other wise I would say keep the 3.50 gear.
Thing is if you go changing gears, yes front & rear on a 4x4 get into $$$$, you will need to slip the clutch more to get going from a stop and more so with a load.
The AA over drive would be a nice add on even with the 390 motor to get the RPM down and less wear on the motors.
Dave ----
ps my MPG did not change but the RPM did come down so less wear on the motor.
TY Fuzz, I never remembered any remorse over my 300 trucks, and I tend to abuse everything I own, but my old brain doesn't always co-operate with reality. But you seem pretty down to earth, and if you are getting away with the 2:73, I think I'll start with the 3:50's that are in it now and order the AA splitter. I already received the twin stick for the 205, so the splitter is the only thing missing. i finished the front air bag alterations yesterday, and did about 90% of the rear mods today, so I'll be ready to strip the frame and sand blast in a few days. I'm hoping to get the rolling chassis done before I have to go back to work.
I found that my 2.73 diff was a bit lethargic and limited its tow ability, but when I added a 600cfm carb, Offy intake, EFI manifolds, and a larger exhaust the truck accelerates better as well as getting better highway mileage. I generally only use it for light hardware or dirt loads anyway (kinda how a light truck was intended to be used!) For someone looking to smoke the tires or tow 10,000 pounds it would be totally wrong. 300s were even used for UPS trucks, so the engine has more than enough grunt...
Ya, when I decided to go with the 300, I figured I'd screw with it a bit, just because we can. And if you guys are getting away with 2:73's I should be happy with the 3:50's that are in it for a starter, with the addition of the AA splitter of course.
That 2.75 gear is factory in my 81 F100 flare side with a T18
A 2.47 that was in my parts truck was also factory but it ran a SROD trans that had over drive.
I don't know how that was as I never drove it.
Both trucks were 300 power & 9" rears.
Even with out the AA OD the RPM was not really that bad but after driving a truck all day that has a max RPM of 1500 anything more than that was screaming
Dave ----
I found that my 2.73 diff was a bit lethargic and limited its tow ability, but when I added a 600cfm carb, Offy intake, EFI manifolds, and a larger exhaust the truck accelerates better as well as getting better highway mileage. I generally only use it for light hardware or dirt loads anyway (kinda how a light truck was intended to be used!)
Eric
HoustonDave gave you a good direction to go.
The stock intake and carb along with the stock log exhaust manifold is very restrictive.
Changing those for the combination he suggested will give you much more power to run the 3.50 rear.
The following video shows the power gains as each component is replaced.
AFAIK no one has recently used or at least reported on the Clifford dual Webber setup yet.
The alternative is to use the lower half of the EFI intake with a fabricated plenum for two carburetors.
The equal length longer runners should give a better low rpm response as well as better distribution than the Clifford.
You can interchange tops for different configurations.
When the pinion gear broke on my '66 with a 240 and 3.5 gears, I threw in a rear with 3.00 gears. It's a dog starting out but great at higher speeds. I i'm rebuilding a 300 to put in it, and am anxious to see the difference it makes with the 3.00 gears
I have an older truck, a 1975 f250. I originally had 374 gears. For the trucks made to haul/tow, Ford used 374's. They were great for towing/hauling over the passes from Cal to Oregon, but top end—without OD—was 65mph. I changed to 331 gears and got a bit more top end, but towing over those passes about killed me. 350 gears for a truck, regardless of engine, is the perfect combo gear set, imo. You'll be right in the sweet spot with the 350 gears.
I have an older truck, a 1975 f250. I originally had 374 gears. For the trucks made to haul/tow, Ford used 374's. They were great for towing/hauling over the passes from Cal to Oregon, but top end—without OD—was 65mph. I changed to 331 gears and got a bit more top end, but towing over those passes about killed me. 350 gears for a truck, regardless of engine, is the perfect combo gear set, imo. You'll be right in the sweet spot with the 350 gears.
I'm hoping so, plus I'll have the splitter for an OD, and if I need to I can split shift the transfer case as well. I put the twin stick in my '76 CJ last year and used low range to start off with my trailer loaded with concrete, and she shifted to high range fine double clutching. I'm assuming I can do the same with the ford. We will see.
A few questions. Do you have 4x4 or no? If you have 4x4, you're MUCH more limited in your gear selection as the front end has to match. 3.00, 3.50, 3.73, 4.11, 4.56, etc. You don't get the full selection of the 9" options.
Secondly is what size tires do you have? That'll change things too.
Lastly, what's the intended usage? Towing? Cruising? Gas mileage? Combination?
I've had a few combinations over the years.
My initial setup was a 3.00 rear with a 4 speed overdrive manual transmission. The tires were 235 75R15s (about 29" diameter). It was alright overall but could pretty sluggish going up hills.
I upgraded to a 4bbl carb, EFI exhaust, etc. and it did a lot better with power. I also tried pulling a few things like a car trailer, and a u-haul full of stuff. It was okay around town, but it'd smoke the clutch.
Next, I changed to 31" tires.
It still handled this well, but overdrive became pretty useless. Just way too low RPMs to be of any use.
I swapped out the transmission for an NP-435 with a granny gear and no overdrive. This was much better as I could use the granny low if I ever needed the better low end grunt to get moving.
The 3.00 kept the RPMs low on the interstate as well, which was nice for gas mileage.
I then got a second truck with a 3.55 rear (8.8"), the NP-435, 31" tires, and a 300. This also had the full 4bbl EFI exhaust upgrade and it was a very fun, zippy combination. Lots of low end grunt, pulling power, and cruising power. I loved the combination. Interstate was a bit high on the RPMs, but nothing crazy. It hit around 3000 RPMs at 75.
Next was 32" tires with the 3.55" and the NP435. It didn't really seem to make much difference.
Next was 32" tires, 3.55", and swapping out the NP-435 for a ZF5 5 speed. The ZF5 has less aggressive gearing than the NP-435. 1st, 2nd, and 3rd with the 3.55s are almost mathematically equivalent to the 1st, 2nd, and 3rd of the NP-435 with 3.00 gears.
To counter this, I now have 4.11s in the rear and it's a great combination with the ZF5.
Gearing is a compromise, and really depends on your drivetrain and the intended use of the truck. Different transmissions require different gears. Different tire sizes do too.
There is a post on another forum were someone did MPG on long trips and different things he did to help get it better.
He was running the SROD trany, 3sp with 4th a over drive and think he had a 3.25 rear gear and was in the 20's.
The gear change to the 3.25 was what got him more MPG don't remember what the had but it was a higher ratio (lower number like my 2.75) as it put the motor in the peak power area.
A few questions. Do you have 4x4 or no? If you have 4x4, you're MUCH more limited in your gear selection as the front end has to match. 3.00, 3.50, 3.73, 4.11, 4.56, etc. You don't get the full selection of the 9" options.
Secondly is what size tires do you have? That'll change things too.
Lastly, what's the intended usage? Towing? Cruising? Gas mileage? Combination?
I've had a few combinations over the years.
My initial setup was a 3.00 rear with a 4 speed overdrive manual transmission. The tires were 235 75R15s (about 29" diameter). It was alright overall but could pretty sluggish going up hills.
I upgraded to a 4bbl carb, EFI exhaust, etc. and it did a lot better with power. I also tried pulling a few things like a car trailer, and a u-haul full of stuff. It was okay around town, but it'd smoke the clutch.
Next, I changed to 31" tires.
It still handled this well, but overdrive became pretty useless. Just way too low RPMs to be of any use.
I swapped out the transmission for an NP-435 with a granny gear and no overdrive. This was much better as I could use the granny low if I ever needed the better low end grunt to get moving.
The 3.00 kept the RPMs low on the interstate as well, which was nice for gas mileage.
I then got a second truck with a 3.55 rear (8.8"), the NP-435, 31" tires, and a 300. This also had the full 4bbl EFI exhaust upgrade and it was a very fun, zippy combination. Lots of low end grunt, pulling power, and cruising power. I loved the combination. Interstate was a bit high on the RPMs, but nothing crazy. It hit around 3000 RPMs at 75.
Next was 32" tires with the 3.55" and the NP435. It didn't really seem to make much difference.
Next was 32" tires, 3.55", and swapping out the NP-435 for a ZF5 5 speed. The ZF5 has less aggressive gearing than the NP-435. 1st, 2nd, and 3rd with the 3.55s are almost mathematically equivalent to the 1st, 2nd, and 3rd of the NP-435 with 3.00 gears.
To counter this, I now have 4.11s in the rear and it's a great combination with the ZF5.
Gearing is a compromise, and really depends on your drivetrain and the intended use of the truck. Different transmissions require different gears. Different tire sizes do too.
This build is strictly a toy, it will be my daily driver til I die, but I'll change whatever I don't like after I start driving it. I do run the beach, so It'll more than likely get 32-33" rubber on 15x8 rims. From what I got from you guys it will start with the 3:50's that were in it when it was a 390. It is 4wd and will get a twin stick so I can shift from low to high on the fly, and I tryed to order the AA splitter last night, but it's not showing up on the Advance Adapters web site. I'm hoping it's a glitch with the website. I emailed them yesterday but haven't heard back yet. So if that falls threw I'll have to change my plans. I found it listed at Summit, so I emailed them as well to make sure I can order it.
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