Originally Posted by kickflipjr

Someone tested a saturn stock and a saturn with no crank pully at all and said they only gained 3 hp. They implied that underdrive pullies would provide little if any hp gains.

https://www.teamscr.com/pulleys.htm

I belive this test is totally wrong because the crank pully acts as a blancer for the engine. and a engine with no crank pully would be out of balance.

Originally Posted by MetroMPG (Post 3626)

i still think it's going to be much lower than 8%.

ooo! surfing around, just found this... some serious underdrive debunking:



so the argument there is the only gains to be had in underdriving are the water pump and the reduced air drag from the alt pulley "fan".

water pumps... the quote above is talking about racing engines (v8's i gather). obviously the size of the gains to be had depend on engine size.

let's do some rough math for my car:

on the teamswift site, one guy replaced his water pump with an electric one that is rated at 1/2 hp, and is stronger than stock. so let's say the stock one costs 1/3 hp. underdriving it by 25% would save me 1/12th of one hp. let's be generous and round it to 1/10th to accound for reduced aero drag on the alt.

1/10th of 1 hp = 75 watts. that won't even power my headlights. yes, it will save fuel, but looks like the savings will be negligible.

continuing further down my very rough calculation road, another figure you see quoted often is road horsepower at highway speed. i.e. i've read several estimates that it takes a modern car between 10-15 hp to cruise at highway speeds on level ground.

assume my car gets 50 mpg (US) at 60 mph and needs 12 hp. if i save 0.1 hp with the underdrive calculations, my highway load drops by 0.83% (0.1 / 12 hp). if the fuel consumption drop is linear, i have just gained 0.42 MPG (50 mpg * 0.83).

suddenly the investment "risk" doesn't look so good (from a strictly fuel saving perspective)...

Originally Posted by kickflipjr (Post 3627)

Someone tested a saturn stock and a saturn with no crank pully at all and said they only gained 3 hp. They implied that underdrive pullies would provide little if any hp gains.

https://www.teamscr.com/pulleys.htm

I belive this test is totally wrong because the crank pully acts as a blancer for the engine. and a engine with no crank pully would be out of balance.

Originally Posted by Ryland (Post 41120)

I would think you could be better off finding a more efficent battery, making sure all of your electrical connections are clean, and reducing your electrical loads.
gold electroplated electric contacts? (gold is not a great concuctor in wire form, but doesn't correde to cause resistance)

Originally Posted by MetroMPG (Post 3646)

you often hear that statement made about cars in general (if they could make them more efficient, they would have already). seems reasonable. but it's not always true.

cooling systems in particular are designed for "worst case" conditions (e.g. idling in traffic for extended periods in 110 degree heat trying to escape an approaching hurricane). they're not even designed for "average" conditions. the result is that average and "best-case" owners experience lost efficiency through "worst-case" designs that they rarely or never need.

[edit - removed my off-topic rant about aerodynamics being another area where car companies aren't offering efficient choices. will save that for another day.]