20 mpg hijack thread

[68 TT]

Getting the TBI tuned properly and the fuel pressure pushed to the top end of the factory range will make a big difference in efficiency. The higher pressure atomizes the fuel better. A throttle body spacer is a proven power and efficiency gain for TBI motors too. The stock ignition system is quite weak. A good cap & rotor, plug wires and stronger coil will make a nice improvement.

Lifting the truck will lower MPG because it increased the drag due to increased frontal area. Keep it as low as you can if MPG is what you are after.

Gearing and tire size have a huge impact on MPG. Rotating mass eats up efficiency very easily. Every inch in tire diameter dropped my MPG by two full points. With 31's I got 14, 32's I got 12 and with 33's I got 10. With a gearing change this might not have been so bad but it gives you an idea of what it can do to your MPG.

[bojak]

68TT thanks for the info. I've read about getting the TBI pressures correct for better effectiveness but that is past my level of mechanical ability, at least for now. I do have a question though. My assumption is that going to an after market unit like a Holley or an edelbrock would address the pressure needing to be adjusted. Is that a correct assumption or would the new unit need adjustment as well? In terms of dollars spent with a goal of fuel efficiency being more important than track performance is the better solution to tune the TBI I got or go replacement? Any input on this would be great.

[bojak]

Picture of the new lighter wheels. That should fix everything, right?

[bammax]

Those wheels look good on that truck. Now I'm thinking of keeping my eye out for some of them for when my truck build gets going.

[bojak]

I know the answers to this question will be all over the place but what tire pressure would be the right balance between fuel economy and tire wear? I know the harder the better for economy but over inflation can ruin tires too quickly. What psi do you guys run? I'm at 55 psi today but not sure if that's too much.

[school boy]

Just run right below max psi rating for the tire, it should be on the side wall

[meatwagon83]

i run what it says on the sidewall

[Skunksmash]

Originally Posted by bammax

I assume you're joking about the helium in the tires. Some folks run nitrogen in the tires but it's never been proven that it has any advantage over regular air. The idea is the molecules are a different density so it helps to maintain a more constant pressure and in turn a more consistent heat pattern. Helium would just escape right through the rubber even if you could find someone to put it in the tire. Rubber is porous so anything made up of super small molecules will pass through it. I may be oversimplifying this thing though, so ask someone who spent the night at a holiday in

Perhaps a coating on the inside of the tires, so that the helium couldn't escape? Probably a dumb idea I'm sure. But I'm always trying to think of stuff like this. Say you could get the helium to stay in the tire. Even then, would it make much difference? Is it actually going to to make the rim and tire "lighter" on the truck?

[mrhino]

Originally Posted by Skunksmash

Perhaps a coating on the inside of the tires, so that the helium couldn't escape? Probably a dumb idea I'm sure. But I'm always trying to think of stuff like this. Say you could get the helium to stay in the tire. Even then, would it make much difference? Is it actually going to to make the rim and tire "lighter" on the truck?

[Keith Seymore]

Originally Posted by Skunksmash

Perhaps a coating on the inside of the tires, so that the helium couldn't escape? Probably a dumb idea I'm sure. But I'm always trying to think of stuff like this. Say you could get the helium to stay in the tire. Even then, would it make much difference? Is it actually going to to make the rim and tire "lighter" on the truck?

No.

F=ma, where m = mass.

Putting helium in the tire does not change the mass of the tire/wheel assembly.

K

[Jabes1]

Ideally you want a nice even contact patch across the whole tire for best wear and mileage. If you overinflate the tire, the center wears out faster than the shoulder. Underinflation results in wearing out the shoulder with more tread left in the center. Experiment with your pressures... as a baseline go with what the manufacturer states, then adjust from there. For example, my Impreza states around 35psi for factory settings. The wheels and tires I have aren't factory on it anymore. The tires I have on it state that 55psi is max. After experimenting with pressures, I got the best contact patch and pressure at 38psi. Sometimes you can see the contact patch when the tires are on a dusty CONCRETE surface. My car is AWD so I experimented with pressures based on wear characteristics. For my truck especially the rear, Ill do a burn out and measure the width of rubber laid. Next adjust your pressures to the point of the biggest contact patch with the most pressure.

[bammax]

Somewhat removed but still on topic.....

To get good mileage leave you're tailgate on and latched closed. Tests showed that removing the tailgate, leaving it down, or replacing it with a net all reduced performance. Turns out a cushion of turbulent air builds up in the bed and acts like a cap to improve aerodynamics at speed. You could also just go with a full cap for the same effect, but the one nature provides doesn't cost anything and weighs less.

Another thing that helps is to put skid plates under the truck. Any time you can cover a rough surface like a transfer case or a transmission with a smooth plate it helps. The more the air can slide along the surface the less resistance it will impart on the vehicle. Some people in the racing world will actually put sheet metal across the entire underside of their vehicles to provide the least wind resistance. From underneath it looks like someone unrolled a 20' roll of aluminum and screwed it to the bottom of the framerails.

[Keith Seymore]

Originally Posted by bammax

Somewhat removed but still on topic.....

To get good mileage leave you're tailgate on and latched closed. Tests showed that removing the tailgate, leaving it down, or replacing it with a net all reduced performance. Turns out a cushion of turbulent air builds up in the bed and acts like a cap to improve aerodynamics at speed. You could also just go with a full cap for the same effect, but the one nature provides doesn't cost anything and weighs less.

Agree. The truck was consciously designed for it to perform in that manner.

When we built the Don Stringfellow Bonneville speed truck (S truck) we found that even a "1/2 cover" (enclosing just the back half of the pickup box) was sufficient.

K

[Skunksmash]

Originally Posted by Keith Seymore

No.

F=ma, where m = mass.

Putting helium in the tire does not change the mass of the tire/wheel assembly.

K

Well no, but it is lighter than air. So you'd gain the difference in weight of 44psi of helium, vs 44 psi of air. Whatever that number is.

[Keith Seymore]

Originally Posted by Skunksmash

Well no, but it is lighter than air. So you'd gain the difference in weight of 44psi of helium, vs 44 psi of air. Whatever that number is.

Right. But the mass of the tire/wheel assembly would so overwhelm the difference in mass between helium and air as to make it not worth mentioning. So I didn't mention it.

We call this "directionally correct but not measureable".

Additionally, the polar moment of inertia of the tire/wheel assembly would be unaffected. Polar moment of intertia of the tire/wheel assembly is probably even more important than static mass.


K

[Keith Seymore]

Originally Posted by bammax

Another thing that helps is to put skid plates under the truck. Any time you can cover a rough surface like a transfer case or a transmission with a smooth plate it helps. The more the air can slide along the surface the less resistance it will impart on the vehicle. Some people in the racing world will actually put sheet metal across the entire underside of their vehicles to provide the least wind resistance. From underneath it looks like someone unrolled a 20' roll of aluminum and screwed it to the bottom of the framerails.

The 2011/2012 Chevy Volt has aeropanels to smooth the underside of the vehicle.

Cd = .284

K

[bojak]

In regards to the airopanels, what amount of mpg gain are we talking? Just thinking that could be a fairly cheap DIY project unless the gains would be minimal? As a manufacterer you have resources that may make even a minimal gain worth it but would it be a realistic application for retro fitting? Or is it a great idea but just not sexy to us truck guys?
Posted via Mobile Device

[Keith Seymore]

Originally Posted by bojak

In regards to the airopanels, what amount of mpg gain are we talking? Just thinking that could be a fairly cheap DIY project unless the gains would be minimal? As a manufacterer you have resources that may make even a minimal gain worth it but would it be a realistic application for retro fitting? Or is it a great idea but just not sexy to us truck guys?

I suspect, for a full size truck, not worth the effort.

You would likely experience more gain from lowering the vehicle, adding a front air dam and (perhaps) chopping the top. These would combine to reduce the frontal area and push air around rather than going underneath the vehicle.

That - and SLOW DOWN! The drag increases with the square of the velocity, so the increase is exponential, not linear.

K

[Keith Seymore]

Leaving this here, just for fun:



I'm in the back, just to the right of the guy holding the Car of the Year award.

Standing inside the tunnel is a surreal experience. It's so huge, and there are no "corners" so it tends to make one a bit woozey...like being in the belly of a big ship.

K

[Skunksmash]

Are you on the engineering team of the volt?

[Keith Seymore]

On the patio, behind the GM Design Dome:

[Keith Seymore]

Originally Posted by Skunksmash

Are you on the engineering team of the volt?

For 4 years. I was the Program Engineering Manager, reporting to the Vehicle Chief Engineer. The folks in the picture are the Program Execution Team and represent Engineering, Program Planning, Marketing, Service, Purchasing, Program Quality and Assembly/Manufacturing. The guy holding the award has retired from GM and is now the CEO of Fisker.

I'm back with Truck Engineering now, as of last Monday.

You must have missed this discussion:

http://67-72chevytrucks.com/vboard/s...d.php?t=570263

You might also be interested in my build/intro thread, linked below, if you have not already seen it.

K

[bojak]

Keith- thanks so much for your input and advice. I for one like I am getting to pick the brain of someone who knows what he's talking about versus a guy who thinks he knows. Your background with these trucks we all love so much makes the info you share a very appreciated resource. If I never say it again at least let me say it now, thank you very much. Keep it square.
Posted via Mobile Device

[68 TT]

Originally Posted by bojak

68TT thanks for the info. I've read about getting the TBI pressures correct for better effectiveness but that is past my level of mechanical ability, at least for now. I do have a question though. My assumption is that going to an after market unit like a Holley or an edelbrock would address the pressure needing to be adjusted. Is that a correct assumption or would the new unit need adjustment as well? In terms of dollars spent with a goal of fuel efficiency being more important than track performance is the better solution to tune the TBI I got or go replacement? Any input on this would be great.

Don't waste your money on the aftermarket TBI unit if you are after MPG. The only reason for one is to increase air flow into the engine. Their higher CFM rating will make gas mileage worse.

An adjustable fuel pressure regulator is an easy install but you will also need a fuel pressue gauge adapter to know where you are at as the stock TBI system has no test port. Put the adapter on first and see what your stock fuel pressure is at as a baseline. After you know your starting pressure you can install the AFPR and not be completely lost as to where you are pressure wise. It is always good to limit the variables when making changes like this so finding a problem is as easy as possible.
Posted via Mobile Device
Posted via Mobile Device

[Keith Seymore]

Originally Posted by bojak

Keith- thanks so much for your input and advice. I for one like I am getting to pick the brain of someone who knows what he's talking about versus a guy who thinks he knows. Your background with these trucks we all love so much makes the info you share a very appreciated resource. If I never say it again at least let me say it now, thank you very much. Keep it square.

Thank you, and you are welcome.

I guess now I don't feel so bad about hi-jacking your thread - lol!

K