Gas mileage feedback...

[Danny G]

215/75 X 15 "road" tires.

Interesting! They are the same size tire that was on my 1984 when it was new. The cool part for me is that the much larger (wider, actually) tires that I'm running now (275/60-15) are actually the same OD as the original 215's. So, while they are much heavier by comparison, they actually kept my speedometer correct to within 1%.

I know they will hurt my fuel efficiency, but I like them enough they're worth the "cost" to me.

This is one of the reasons I like that link above it shows a good break down of the tire differences.

[Danny G]

215/75 X 15 "road" tires.

Interesting! They are the same size tire that was on my 1984 when it was new. The cool part for me is that the much larger (wider, actually) tires that I'm running now (275/60-15) are actually the same OD as the original 215's. So, while they are much heavier by comparison, they actually kept my speedometer correct to within 1%.

I know they will hurt my fuel efficiency, but I like them enough they're worth the "cost" to me.

This is one of the reasons I like that link above it shows a good break down of the tire differences.

The PO had 235/70/R15 on mine, the door sticker actually reads 195/75 R15 from the factory. But personally I feel like those look very small and out of place on the trucks.

[Whisler]

The PO had 235/70/R15 on mine, the door sticker actually reads 195/75 R15 from the factory. But personally I feel like those look very small and out of place on the trucks.

Anyone have an idea where to find the "torque peak RPM" for my '84 351w (originally 2 barrel not HO)?Then I could use the calculator to see what speed that relates to (or just watch the tach).

[Gary Lewis]

Anyone have an idea where to find the "torque peak RPM" for my '84 351w (originally 2 barrel not HO)?Then I could use the calculator to see what speed that relates to (or just watch the tach).

Yep, sure do. Probably only one place on the interweb - here!

Go to Documentation/Engines/Windsor and then the 351W tab and then the Specifications tab. And then scroll down to the 1984 spec's.

[Gary Lewis]

215/75 X 15 "road" tires.

Interesting! They are the same size tire that was on my 1984 when it was new. The cool part for me is that the much larger (wider, actually) tires that I'm running now (275/60-15) are actually the same OD as the original 215's. So, while they are much heavier by comparison, they actually kept my speedometer correct to within 1%.I know they will hurt my fuel efficiency, but I like them enough they're worth the "cost" to me.

This is one of the reasons I like that link above it shows a good break down of the tire differences.

That's an interesting calculator. And I was excited when I saw the "embed" info thinking we could embed it here. But, it really isn't embed code and is instead a link.

 

We have the calculator shown below on the Documentation/Driveline/Calculators tab. And I'm wondering if we should incorporate a tire size calculation in it. Tire size calc's are pretty close, but each manufacturer's tires vary a bit in size, as you can see on the Tire Rack site. But, I think it would be pretty easy to add the tire size calculations to the spreadsheet to allow us to play what-if games.

 

So, what do y'all think? Would it help?

 

[Whisler]

That's an interesting calculator. And I was excited when I saw the "embed" info thinking we could embed it here. But, it really isn't embed code and is instead a link.

 

We have the calculator shown below on the Documentation/Driveline/Calculators tab. And I'm wondering if we should incorporate a tire size calculation in it. Tire size calc's are pretty close, but each manufacturer's tires vary a bit in size, as you can see on the Tire Rack site. But, I think it would be pretty easy to add the tire size calculations to the spreadsheet to allow us to play what-if games.

 

So, what do y'all think? Would it help?

 

The documentation and the calculator are awesome.What surprised me, when I looked up my 351W 2V, is the 1800 RPM torque peak. With 3.55:1 gear ratio I am not likely to cruise in that range much. Then I looked at the 351W 4V and saw that the torque peak was at 2800 RPM. If I am correct in believing that the difference between the 2V and 4V (HO) is carb. and cam, then the cam used in the HO version moved the torque peak 1000 RPM, because I don't see how the carb. change could move the torque peak RPM. So now, with my C6 transmission, I need an HO cam to move the torque peak so I can cruise at 65 and be in the 2800 RPM torque peak range. Oh DARN!!! (Should have changed the cam while I had the engine out.)Or I could switch to an AOD transmission with its deep overdrive and cruise at 1800. But that option would be a lot more expensive and troublesome. "What-if" is sure fun even if you know you will never do it.Thanks for all your work , Gary.

[Gary Lewis]

The documentation and the calculator are awesome.

What surprised me, when I looked up my 351W 2V, is the 1800 RPM torque peak. With 3.55:1 gear ratio I am not likely to cruise in that range much.

Then I looked at the 351W 4V and saw that the torque peak was at 2800 RPM. If I am correct in believing that the difference between the 2V and 4V (HO) is carb. and cam, then the cam used in the HO version moved the torque peak 1000 RPM, because I don't see how the carb. change could move the torque peak RPM.

So now, with my C6 transmission, I need an HO cam to move the torque peak so I can cruise at 65 and be in the 2800 RPM torque peak range. Oh DARN!!! (Should have changed the cam while I had the engine out.)

Or I could switch to an AOD transmission with its deep overdrive and cruise at 1800. But that option would be a lot more expensive and troublesome.

"What-if" is sure fun even if you know you will never do it.

Thanks for all your work , Gary.

There are LOTS of variables in play when trying to achieve max efficiency. One is the engine RPM, but not only is the max torque important, but so is the friction loss w/in the engine. MIT has an interesting paper entitled Engine Friction And Lubrication, and in it is this chart on engine friction. As you can see, the engine friction goes up dramatically as the RPM increases. So while you may gain efficiency by the engine operating at max torque, raising the RPM by 55% will certainly increase the friction, and that might negate the gain.

So it is best to get RPM down to a reasonable value AND to get the max torque to coincide with the lowered RPM. But with a C6 you are also battling inefficiencies in it as well. The torque converter doesn't have a clutch so is always slipping, and depending on the load that's usually between 200 and 300 RPM. Not only does that raise the RPM and, therefore, the friction, all of that slippage is turned into heat and is lost energy. Plus the C6 is notoriously inefficient in and of itself. And, it has no OD.

The AOD is a more efficient design as it is based on the C4. Plus, it does have a mechanical lock that bypasses the torque converter, and it has overdrive. And I'm told that it is possible to build one of those to stand up to a strong 351W. But it is expensive to do and you'd have to drive a lot of miles to make it pay off.

 

[85lebaront2]

There are LOTS of variables in play when trying to achieve max efficiency. One is the engine RPM, but not only is the max torque important, but so is the friction loss w/in the engine. MIT has an interesting paper entitled Engine Friction And Lubrication, and in it is this chart on engine friction. As you can see, the engine friction goes up dramatically as the RPM increases. So while you may gain efficiency by the engine operating at max torque, raising the RPM by 55% will certainly increase the friction, and that might negate the gain.

So it is best to get RPM down to a reasonable value AND to get the max torque to coincide with the lowered RPM. But with a C6 you are also battling inefficiencies in it as well. The torque converter doesn't have a clutch so is always slipping, and depending on the load that's usually between 200 and 300 RPM. Not only does that raise the RPM and, therefore, the friction, all of that slippage is turned into heat and is lost energy. Plus the C6 is notoriously inefficient in and of itself. And, it has no OD.

The AOD is a more efficient design as it is based on the C4. Plus, it does have a mechanical lock that bypasses the torque converter, and it has overdrive. And I'm told that it is possible to build one of those to stand up to a strong 351W. But it is expensive to do and you'd have to drive a lot of miles to make it pay off.

Gary, that was the secret to the old Mercury Turnpike Cruisers, big engine (368 ci in 1957, 430 in 1958-59), 2.69:1 rear. Engine was only turning around 1700 rpm with the Merc-O Matic or Cruise-O-Matic transmissions. Another item to consider, stroke length, longer stroke = more friction losses, which is why a 302 vs a 300 in a truck, highway usage, the 302 has it all over the 300 with the same drivetrain. Granted the total linear travel is the essentially same 8 pistons at 6" per revolution or 6 pistons at 7.96" per revolution is 48" vs 47.76". Due to the angularity of the 300 connecting rod to the piston at mid stroke (it's bad enough that performance builds sometimes use 240 rods and special pistons) creates a lot of side load compared to a 302.

[Danny G]

There are LOTS of variables in play when trying to achieve max efficiency. One is the engine RPM, but not only is the max torque important, but so is the friction loss w/in the engine. MIT has an interesting paper entitled Engine Friction And Lubrication, and in it is this chart on engine friction. As you can see, the engine friction goes up dramatically as the RPM increases. So while you may gain efficiency by the engine operating at max torque, raising the RPM by 55% will certainly increase the friction, and that might negate the gain.

So it is best to get RPM down to a reasonable value AND to get the max torque to coincide with the lowered RPM. But with a C6 you are also battling inefficiencies in it as well. The torque converter doesn't have a clutch so is always slipping, and depending on the load that's usually between 200 and 300 RPM. Not only does that raise the RPM and, therefore, the friction, all of that slippage is turned into heat and is lost energy. Plus the C6 is notoriously inefficient in and of itself. And, it has no OD.

The AOD is a more efficient design as it is based on the C4. Plus, it does have a mechanical lock that bypasses the torque converter, and it has overdrive. And I'm told that it is possible to build one of those to stand up to a strong 351W. But it is expensive to do and you'd have to drive a lot of miles to make it pay off.

Checked out that spec page... Got to love that low end torque on the 300 six. 1986 numbers showing 250ftlbs at 2000 rpms, 245 at 1800 and still... 240 at 1200 rpms. That means if you got your gear/tireset up and transmission in OD to where you were running at 1200 rpms you are still getting 240ftlbs of torque while sipping fuel. With the EFI donor engine I have and I would expect a bit more.

Couple that with a E4OD, my 3.08 rear and some 30 inch tires and at 55mph your supposedly cruising at 1350rpms. If you use an AOD it would be a bit different as the AOD is a 0.67 OD vs the E4OD's 0.71.

If you wanted to get silly, same set up with a gear vendors unit (double OD of 0.55) at 65mph drops the rpms to 1233, or change the rear to 3.55's and be pushing about 1450rpms at 65mph with that double over which is about what the E4OD would do at 55mph on its own.

[1986F150Six]

Checked out that spec page... Got to love that low end torque on the 300 six. 1986 numbers showing 250ftlbs at 2000 rpms, 245 at 1800 and still... 240 at 1200 rpms. That means if you got your gear/tireset up and transmission in OD to where you were running at 1200 rpms you are still getting 240ftlbs of torque while sipping fuel. With the EFI donor engine I have and I would expect a bit more.

Couple that with a E4OD, my 3.08 rear and some 30 inch tires and at 55mph your supposedly cruising at 1350rpms. If you use an AOD it would be a bit different as the AOD is a 0.67 OD vs the E4OD's 0.71.

If you wanted to get silly, same set up with a gear vendors unit (double OD of 0.55) at 65mph drops the rpms to 1233, or change the rear to 3.55's and be pushing about 1450rpms at 65mph with that double over which is about what the E4OD would do at 55mph on its own.

Or, do as Ford did for stellar gas mileage... put a 2.47 rear end with manual OD!!!