so question...Has anyone played with this?
Here's a formula you can plug data in. The 5th gear ratio is .729 to 1, tire diameter is 27.03. If you know a specific RPM at a specific speed then you can calculate the effective rear end ratio. Guessed at some rpm/speed values and when plugged in it showed a fairly high rear end ratio which would coincide with mpg.
MOTOR - A Rear Axle Calculator
Here's a formula you can plug data in. The 5th gear ratio is .729 to 1, tire diameter is 27.03. If you know a specific RPM at a specific speed then you can calculate the effective rear end ratio. Guessed at some rpm/speed values and when plugged in it showed a fairly high rear end ratio which would coincide with mpg.MOTOR - A Rear Axle Calculator
LOL 
Way over my head. I was meaning more along the lines of, has anyone played with the gearing in their Sling to achieve different numbers. Not the mathematical mumbo jumbo. That shit lost me right away, lol
I remember having an F150 that I had to change out the rear end in because it was geared way too low for power, and not for the highway and my mileage sucked. Now, I can't remember which I changed, but the numbers were 3.55 and 4.10. One of those being the power and the other being the mileage. My Mechanic friend is the one who did it all for me. The theory made sense when he explained it and I just remember the numbers is all. Basically letting the RPM's fall while maintaining speed and using less fuel.
I don't remember at all which was which.
But my thought process is, can this be done to the Sling? Would that be a change in the transmission, or the angle drive?
Display MoreLOL
Way over my head. I was meaning more along the lines of, has anyone played with the gearing in their Sling to achieve different numbers. Not the mathematical mumbo jumbo. That shit lost me right away, lol
I remember having an F150 that I had to change out the rear end in because it was geared way too low for power, and not for the highway and my mileage sucked. Now, I can't remember which I changed, but the numbers were 3.55 and 4.10. One of those being the power and the other being the mileage. My Mechanic friend is the one who did it all for me. The theory made sense when he explained it and I just remember the numbers is all. Basically letting the RPM's fall while maintaining speed and using less fuel.
I don't remember at all which was which.
But my thought process is, can this be done to the Sling? Would that be a change in the transmission, or the angle drive?
OK, understood...the 4:10 is a high performance gear ratio. More acceleration, more tow capacity and higher RPM. Higher rpm=more HP and more responsive. Lower rear end ratios can dramatically increase gas mileage but at the expense of performance. Changing rear pulley size would probably be the easiest method although tire diameter can affect this also (smaller diameter will increase effective rear end ratio while larger diameter tires will lower it. Using the formula it appears we have (stock) a fairly high rear end ratio. I would tend to think that is what most of us would opt for if given a choice. Performance and responsiveness over MPG.
With my HP being around 320 I changed the rear tire from a 285 35 18 to a 295 45 18 which increased the tire circumference almost 8 inches. This has made 1 st gear more usable and increased traction in 2 nd gear tremendously.
The revolutions per mile went from 804 down go 730.
I changed to this tire size to increase grip, so I have not checked the MPG with it. I'll check it soon and post it up.
I'm really disappointed with the efficiency of the GM motor in the Sling. Drove to Laredo (about 300 miles) and reset the calculator. I avg about 18 mpg when driving at the speed I'd like to 90-100mph in 5th. But it freaking struggles to cruise at that speed...
Had to drop to 75-80mph to get to 20-21mpg...
I don't care in the city when I'm launching and driving hard, but highway cruising? Come on man!!!
Have you used the cat delete pipe? That will also increase the mileage and the HP.
I haven't read all of this thread, so I apologise if someone has already pointed the following maths out.
Drag force is increased by the square of speed, but as P=Fv, (P= power F = force v = velocity) the power you need to overcome that force increases with the cube of the speed.
That's why 90mph can cause such a increase in consumption over 70mph.. You may be running the engine a little more efficiently, but you need 2.1 times the power to do it!
(It all becomes a little more complicated than that, as you must account for the forward motion velocity and this will in turn reduce the ratio a little).
But let's keep it simple, so in simple terms:
(A) "If you go a JUST little faster at slow speed: You increase fuel consumption JUST a little."
(B) "If you go a JUST little faster at high speeds: You increase fuel consumption by VERY BIG amounts."
I hope that helps explain things, without it getting too complicated
Display MoreI haven't read all of this thread, so I apologise if someone has already pointed the following maths out.
Aerodynamic drag force is increased by the square of speed, but as P=Fv, (P= power F = force v = velocity) the power you need to overcome that force increases with the cube of the speed.
That's why 90mph can cause such a increase in cinsumption over 70mph.. You may be running the engine a little more efficiently, but you need 2.1 times the power to do it!
(It all becomes a little more complicated than that, as you must account for the forward motion velocity and this will in turn reduce the ratio a little).
But let's keep it simple, so in simple terms:
(A) "If you go a JUST little faster at slow speed: You increase fuel consumption JUST a little."
(B) "If you go a JUST little faster at high speeds: You increase fuel consumption by VERY BIG amounts."
I hope that helps explain things, without it getting too complicated.
ETA - Bear in mind, however, that as Talksteer points out, this doesn't mean you need 2.1 times the fuel, as despite using it faster, you're travelling faster too - you would in fact need 1.65 times the output from your fuel. Energy requirement per mile, then, varies more or less with the square of speed at motorway speeds
so, what you're saying is .... lay your foot heavy on the peddle until grinning from ear to ear and have the credit card ready for refueling?
so, what you're saying is .... lay your foot heavy on the peddle until grinning from ear to ear and have the credit card ready for refueling?
Certainly does.
There is a lot more to it than just that, but as the energy required goes up by "the cube", so the fuel consumption to supply that energy also goes through the roof, at high speeds.
The fact that the ratio goes up by the cube, is what kills the fuel consumption.
ie. To increase power by 2X you will increase fuel consumption by 2X2X2 that works out at 8 times the consumption for twice the power.
27 times the fuel @ 3 times the power.
64 fuel @ 4 power
125 fuel @ 5 power
216 fuel @ 6 power
343 fuel @ 7 power
... and so it goes
You can see above why the consumption goes up so quickly at high speed.
It's all relative.
Skinny pedal on the right makes the gas drain out.
It's all relative.
Skinny pedal on the right makes the gas drain out.
Well done Sir!! I have always been a fan of the KISS theory .....
Keep It Simple Stupid 
