The real benefits of lightweight pulleys (quantified)

[Spuds]

I'mma just gonna leave this here for y'all to consider...

[86TOYO2k17]

Originally Posted by nikitopo

@86TOYO2k17 You don't have a 1000lbs atlas stone and you shave 4lbs. Your engine revs much faster in 1st and 2nd gears with the same car weight, meaning that the crankshaft drives much less weight in these gears. Have you ever ride a bicycle? Do you understand the basic mechanism of gearing and the effect it has on your foot pedal?

And by the way Toda underdrives only the alternator and the gain is in the range of 1 hp max. The dyno shows more gains and it is not a 0 hp gain for the crank pulley.

Perfect analogy. If a car is a bike lightening the crank pulley is like removing the bell from your handle bars.

Toda is undersized crank pulley, so it underdrives everything.
Fensport is oversized alt and water pulley, so it underdrives alt/water

[86TOYO2k17]

Originally Posted by gtengr

I'm not convinced the alternator (at least on the +2017) is consuming engine power under load. My voltage spikes to +14 when I let off the throttle. Other manufacturers run schemes to eliminate alternator load under throttle, so it's not unheard of.

I think the AC pulley is made to lock up the inside of pulley, and free spin outside when not activated to not leach power when off.

Pretty sure alternator doesn’t have that feature, so not sure how it would stop leaching power. It may not be charging the battery or powering the system under certain engine loads but it would probably still be spinning and “functioning” leaching power. But you may be correct not sure.

[FRS Justin]

I got tired of reading this so if this has been addressed sorry, but underdrive pulleys and lightweight pulleys are 2 different things. That's like apples to oranges and can not be compared

[mrg666]

Originally Posted by FRS Justin

I got tired of reading this so if this has been addressed sorry, but underdrive pulleys and lightweight pulleys are 2 different things. That's like apples to oranges and can not be compared

It came up when somebody posted a link to Toda kit to support his claim that lightweight pulleys add so much power.
http://www.toda-racing.co.jp/en/prod...lley-fa20.html

I would call them like snake oil and holy water though. Apples and oranges are both useful things.

[gtengr]

Originally Posted by 86TOYO2k17

Pretty sure alternator doesn’t have that feature, so not sure how it would stop leaching power. It may not be charging the battery or powering the system under certain engine loads but it would probably still be spinning and “functioning” leaching power. But you may be correct not sure.

It's different from the AC compressor because the rotor in an alternator is a spinning electromagnet, so resistance can be altered by changing the current flowing through it.

Found a relevant passage in the 2017 Updates pdf, pg. 89 of 120:

Battery Condition Sensor
The previous current sensor always maintained control to keep the battery fully charged. The battery condition sensor calculates the charge status, level of deterioration and internal resistance of the battery from data such as its voltage, current and temperature, and controls charging so that there is always spare capacity available. This allows the recharging rate to be increased when decelerating, which improves fuel efficiency.

If fuel efficiency is being improved, then resistance of the alternator under load is being reduced. I'm not sure how much, but I think it's safe to say the already small number being thrown about for power consumed by the alternator can be chopped in half or more for the +2017's. I think the E92 M3's alternator disengages completely and that was 2007.

[Ultramaroon]

@Subsonic, your units for inertial moment are incorrect. Should be in kg*m^2. It's only in notation, though. The numbers converting from imperial to SI are good so it must've been a typo.

I appreciate your statement to the effect of neglecting the contribution from the other rotating masses. I did the same in my calcs which I never finished.

[86TOYO2k17]

Originally Posted by gtengr

It's different from the AC compressor because the rotor in an alternator is a spinning electromagnet, so resistance can be altered by changing the current flowing through it.

Found a relevant passage in the 2017 Updates pdf, pg. 89 of 120:

Battery Condition Sensor
The previous current sensor always maintained control to keep the battery fully charged. The battery condition sensor calculates the charge status, level of deterioration and internal resistance of the battery from data such as its voltage, current and temperature, and controls charging so that there is always spare capacity available. This allows the recharging rate to be increased when decelerating, which improves fuel efficiency.

If fuel efficiency is being improved, then resistance of the alternator under load is being reduced. I'm not sure how much, but I think it's safe to say the already small number being thrown about for power consumed by the alternator can be chopped in half or more for the +2017's. I think the E92 M3's alternator disengages completely and that was 2007.

Interesting.
I think it was 4hp is what someone calculated for when in use. Making the alt 3.4hp to spin with pulley. I wonder how much of that resistance goes away when not charging. If it’s half then still leaching 2hp / 1.7hp with pulley. Either way it was semi cheap after already getting water pulley and belt. Kind of a why not mod at that point. And besides going FI im pulling at straws to get any small gains at this point.

[Tcoat]

Originally Posted by Ultramaroon

@Subsonic, your units for inertial moment are incorrect. Should be in kg*m^2. It's only in notation, though. The numbers converting from imperial to SI are good so it must've been a typo.

I appreciate your statement to the effect of neglecting the contribution from the other rotating masses. I did the same in my calcs which I never finished.

Too bad Stu isn't still around. Pretty sure had done many of the calculations for all the rotating mass. Sombody may be able to find them if they wanted to wade through a hundred or so light weight pulley threads.

[Ultramaroon]

Originally Posted by Tcoat

Too bad Stu isn't still around. Pretty sure had done many of the calculations for all the rotating mass. Sombody may be able to find them if they wanted to wade through a hundred or so light weight pulley threads.

Nah. People either get it or they don't want to because they're emotionally attached to justifying their purchases. I got far enough to confirm my suspicion but got bored with my little paper. I should finish it.

[Sapphireho]

So, how many HP?








Sorry, couldn't resist.

[Tcoat]

Originally Posted by Sapphireho

So, how many HP?








Sorry, couldn't resist.

None but that .58% improvement in acceleration makes the car come alive. Ditch that junker Lotus and invest all the cash in anodized aluminum rotating parts and you can probably bring that acceleration increase up to 1% and hit the pro race circuit.

[Sapphireho]

Originally Posted by Tcoat

None but that .58% improvement in acceleration makes the car come alive. Ditch that junker Lotus and invest all the cash in anodized aluminum rotating parts and you can probably bring that acceleration increase up to 1% and hit the pro race circuit.

Worth it!

[humfrz]

I remember back-in-the-day, when I was a child, I tried to convince my grandpa that if he let me drill holes in the arms of that drive pully on the steam engine, it would be lighter and spin faster, thus allow the thrashing machine to run faster and we could get done thrashing sooner.

He told me to go back up to the farmhouse and bring back another jug of iced tea -


humfrz