Improve throttle response

[Baldeagle]

Originally Posted by Ernest72

Over 80k on my 04WRX (143k) with lightweight pulley. Boxer engine is in great shape based on last used oil analysis at about 125k. I think abuse from other things will get the engine before the pulley. But either way the light weight pulley on the BRZ was not an earth shattering improvement, maybe a little faster rev. So do it if you feel like or don’t.

A. Just saying the rubber ring is there for a reason.

B. Not surprised you said the effect of your lightweight pulley is minimal. The math will tell you it is near zero. Acceleration gains that result from decreasing rotational inertia (lightweight wheels, flywheels and in this case drive pulleys) are derived from decreasing the car’s effective weight to power ratio. In effect you are making the car lighter, not making the engine more powerful. Physics will tell you that the effect of reducing one pound of spinning weight (any spinning weight) can be no more than reducing two pounds of static weight from the car, like off the frame of the car. The maximum ratio cannot exceed 1:2.

If you replace a 4-pound pulley with a 1-pound pulley, you eliminated 3 pounds of spinning weight. That effect on acceleration cannot be more than removing 6 pounds of weight from the frame of car. In terms of changing the car’s weight to HP ratio, that is less than a ½ hp.

If a twin weighs 2,700 lbs and you just reduced its “effective” weight by 6 pounds, it now weighs 2,694 pounds. If it has a 205.00 HP engine, the weight to HP ratio is 2,694/205 or 13.14146:1. For a stock twin that weighs 2,700 pounds to have the same weight to HP ratio, it must have 205.46 HP.

If viewed in terms of a weight to power ratio, going from a four-pound pulley to a one-pound pulley is the equivalent of adding .46 HP to a stock twin. While the engine may rev faster when the transmission is in neutral, or blip faster for downshifts, I doubt anyone can feel what the equivalent of an extra .5 hp does to acceleration. Of course that supports your observation.

[Tcoat]

Originally Posted by Baldeagle

A. Just saying the rubber ring is there for a reason.

B. Not surprised you said the effect of your lightweight pulley is minimal. The math will tell you it is near zero. Acceleration gains that result from decreasing rotational inertia (lightweight wheels, flywheels and in this case drive pulleys) are derived from decreasing the car’s effective weight to power ratio. In effect you are making the car lighter, not making the engine more powerful. Physics will tell you that the effect of reducing one pound of spinning weight (any spinning weight) can be no more than reducing two pounds of static weight from the car, like off the frame of the car. The maximum ratio cannot exceed 1:2.

If you replace a 4-pound pulley with a 1-pound pulley, you eliminated 3 pounds of spinning weight. That effect on acceleration cannot be more than removing 6 pounds of weight from the frame of car. In terms of changing the car’s weight to HP ratio, that is less than a ½ hp.

If a twin weighs 2,700 lbs and you just reduced its “effective” weight by 6 pounds, it now weighs 2,694 pounds. If it has a 205.00 HP engine, the weight to HP ratio is 2,694/205 or 13.14146:1. For a stock twin that weighs 2,700 pounds to have the same weight to HP ratio, it must have 205.46 HP.

If viewed in terms of a weight to power ratio, going from a four-pound pulley to a one-pound pulley is the equivalent of adding .46 HP to a stock twin. While the engine may rev faster when the transmission is in neutral, or blip faster for downshifts, I doubt anyone can feel what the equivalent of an extra .5 hp does to acceleration. Of course that supports your observation.

Finally a voice of reason and rationality!
By the time an engine is spinning everything up to and including the wheels there is zero measurable effect beyond the math. Makes no difference at all when the whole system is considered. Not like the engine is just spinning that one pulley.
Even out of gear the reduction of spinning mass is pretty much just noise compared to the flywheel, crank and everything else moving in the engine.

[new2subaru]

Originally Posted by Baldeagle

A. Just saying the rubber ring is there for a reason.

B. Not surprised you said the effect of your lightweight pulley is minimal. The math will tell you it is near zero. Acceleration gains that result from decreasing rotational inertia (lightweight wheels, flywheels and in this case drive pulleys) are derived from decreasing the car’s effective weight to power ratio. In effect you are making the car lighter, not making the engine more powerful. Physics will tell you that the effect of reducing one pound of spinning weight (any spinning weight) can be no more than reducing two pounds of static weight from the car, like off the frame of the car. The maximum ratio cannot exceed 1:2.

If you replace a 4-pound pulley with a 1-pound pulley, you eliminated 3 pounds of spinning weight. That effect on acceleration cannot be more than removing 6 pounds of weight from the frame of car. In terms of changing the car’s weight to HP ratio, that is less than a ½ hp.

If a twin weighs 2,700 lbs and you just reduced its “effective” weight by 6 pounds, it now weighs 2,694 pounds. If it has a 205.00 HP engine, the weight to HP ratio is 2,694/205 or 13.14146:1. For a stock twin that weighs 2,700 pounds to have the same weight to HP ratio, it must have 205.46 HP.

If viewed in terms of a weight to power ratio, going from a four-pound pulley to a one-pound pulley is the equivalent of adding .46 HP to a stock twin. While the engine may rev faster when the transmission is in neutral, or blip faster for downshifts, I doubt anyone can feel what the equivalent of an extra .5 hp does to acceleration. Of course that supports your observation.

I'll take it!



Seriously, very well written.

[Tcoat]

Originally Posted by new2subaru

I'll take it!



Seriously, very well written.

Go on a diet and reduce weight by even more!

[StraightOuttaCanadaEh]

How do we know the weight is halved when the pulley starts spinning? Isn't it also dependent on the engine speed? We have centrifuges that spin down blood samples in the lab and if you don't balance the tube of blood, at 10000 rpm the centrifuge will literally blow up, which tells me that a spinning tube weighs a lot more than the 10 g or so that it weighs when it is static. When it starts spinning, the weight must be in the pounds to pull a heavy centrifuge off the table top. It's also why the effect is felt the most in neutral and 1st gear. It must be rpm dependent, and further affected by the gear the car is in. Just my hunch, I haven't plugged any numbers into a formula

[Ernest72]

Originally Posted by Baldeagle

A. Just saying the rubber ring is there for a reason.

B. Not surprised you said the effect of your lightweight pulley is minimal. The math will tell you it is near zero. Acceleration gains that result from decreasing rotational inertia (lightweight wheels, flywheels and in this case drive pulleys) are derived from decreasing the car’s effective weight to power ratio. In effect you are making the car lighter, not making the engine more powerful. Physics will tell you that the effect of reducing one pound of spinning weight (any spinning weight) can be no more than reducing two pounds of static weight from the car, like off the frame of the car. The maximum ratio cannot exceed 1:2.

If you replace a 4-pound pulley with a 1-pound pulley, you eliminated 3 pounds of spinning weight. That effect on acceleration cannot be more than removing 6 pounds of weight from the frame of car. In terms of changing the car’s weight to HP ratio, that is less than a ½ hp.

If a twin weighs 2,700 lbs and you just reduced its “effective” weight by 6 pounds, it now weighs 2,694 pounds. If it has a 205.00 HP engine, the weight to HP ratio is 2,694/205 or 13.14146:1. For a stock twin that weighs 2,700 pounds to have the same weight to HP ratio, it must have 205.46 HP.

If viewed in terms of a weight to power ratio, going from a four-pound pulley to a one-pound pulley is the equivalent of adding .46 HP to a stock twin. While the engine may rev faster when the transmission is in neutral, or blip faster for downshifts, I doubt anyone can feel what the equivalent of an extra .5 hp does to acceleration. Of course that supports your observation.

On the EJ205 in my WRX I noticed a good rev response. The BRZ not so much. But it’s on there and I am too lazy to take it off. Personally, I think the BRZ needs every bit of help it can get, even placebo butt dyno can help.

[Baldeagle]

Originally Posted by StraightOuttaCanadaEh

How do we know the weight is halved when the pulley starts spinning? Isn't it also dependent on the engine speed? We have centrifuges that spin down blood samples in the lab and if you don't balance the tube of blood, at 10000 rpm the centrifuge will literally blow up, which tells me that a spinning tube weighs a lot more than the 10 g or so that it weighs when it is static. When it starts spinning, the weight must be in the pounds to pull a heavy centrifuge off the table top. It's also why the effect is felt the most in neutral and 1st gear. It must be rpm dependent, and further affected by the gear the car is in. Just my hunch, I haven't plugged any numbers into a formula

Your hunch is absolutely correct. The gear ratio has a direct effect on the rate in which the engine revs. Gear ratios multiply torque. Because of this multiplier effect, with flywheels and pulleys the “static mass equivalence” can be much more than 2X in lower gears, but much less than 2X in higher gears. The average however will not exceed 2X.

I have provided a link that does an excellent job in crunching numbers and providing explanations- most certainly better than I can:

https://bndtechsource.wixsite.com/ho...tia-calculator

I hope this can address any of your questions.

[Ultramaroon]

Damping unwanted, potentially harmful modes of resonant vibration is helping the engine. Even at cruising levels, the engine operates more efficiently.

If anything, even with stock everything else, I might consider replacing it with something like





or

[new2subaru]

Originally Posted by Tcoat

Go on a diet and reduce weight by even more!

If I went on a diet I would become invisible...

[Spuds]

Do I need to dig out my rotating mass calculator again?

Edit... Nevermind, the one above looks better.

[albert]

Good write up, BaldEagle.

I got a 2013 BRZ about 2 months ago and noticed the throttle response was very lazy/sluggish.

A friend suggested to clean the MAF sensor, did that. Googled a way to 'reset' the throttle map, found it here by 'start' button to 'on', but not start the engine, then step on/off the throttle 10-15 times at varying speed. That actually helped a lot!

Fast forward to now... using the DashCommand app, I can see that the initial 10-20% throttle travel is vague/delayed/imprecise, but gets better after that, and a lot more responsive passing 4K RPM and up.

Conclusion... not much I can do for the initial vague throttle feel. And when I want to 'play', I keep it up at the higher RPM. Reminds me of a 90s manual hot hatch.