Perrin light wieght pulley

[justatroll]

Originally Posted by nikitopo

You get approximately 2-3whp from the underdriven alternator and 5-6whp from the light pulleys. Overall +8whp.

There is absolutely NO physical reason for the LWCP to provide ANY extra HP just because it is lighter.
Just saying it, does not make it "evidence".


Please explain WHY a lighter pulley should give extra HP.
I have never heard a single explanation (using physics) why a lighter rotating assembly should provide extra HP - Since HP can be measured at constant RPM.


There is "evidence" in the other post that the LWCP gives LESS HP:


http://www.motoiq.com/MagazineArticl...velopment.aspx

Do you just dismiss THAT evidence and believe your own?

[nikitopo]

Originally Posted by G-awesome

I'm gonna enjoy this thread.

Got a perrin lightweight crank pulley last fall but never rushed to install it and it's sitting gather dust. It suuure looks pretty in red though!

Tried to install it once but it was a PITA getting the oem off an auto since you have to hold it in place while taking off the crank bolt. Debating whether I should just sell it or attempt it again in the near future...

Yes auto transmissions need a special tool.

Originally Posted by justatroll

Please explain WHY a lighter pulley should give extra HP.
I have never heard a single explanation (using physics) why a lighter rotating assembly should provide extra HP - Since HP can be measured at constant RPM.

Hey again

It doesn't make extra HP, you just have less rotational inertia and thus less HP loss. Not in constant RPM, but as you accelerate. This is the most important thing. How much power you have under acceleration at full throttle. This is also what dyno's are measuring.

Maybe you heard about Subaru's attempt to break their own record in the Isle of Man. They used a specially tuned 550-hp WRX STI with many changes from Prodrive and STI. They transported the car in the island and made many test laps and attempts for several weeks. I was checking some screenshots and I found they were also using a lightweight pulley. It is the lowest pulley in the screenshot:



I believe it is clear that it is not the solid pulley with the rubber. Do you thing they would change it if there was a risk to broke the engine or if there were no gains?

[Cole]

Originally Posted by nikitopo

Yes auto transmissions need a special tool.



Hey again

It doesn't make extra HP, you just have less rotational inertia and thus less HP loss. Not in constant RPM, but as you accelerate. This is the most important thing. How much power you have under acceleration at full throttle. This is also what dyno's are measuring.

Maybe you heard about Subaru's attempt to break their own record in the Isle of Man. They used a specially tuned 550-hp WRX STI with many changes from Prodrive and STI. They transported the car in the island and made many test laps and attempts for several weeks. I was checking some screenshots and I found they were also using a lightweight pulley. It is the lowest pulley in the screenshot:



I believe it is clear that it is not the solid pulley with the rubber. Do you thing they would change it if there was a risk to broke the engine or if there were no gains?

Using an example from Motorsport is not applicable here though. Show us concrete proof of gains, rather than anecdotes.

If you can show me a bunch of dyno runs showing consistent gains (outside the margin of error of dynos, of course) then I'll take a sip of the Kool-aid

[justatroll]

Originally Posted by nikitopo

Hey again

It doesn't make extra HP, you just have less rotational inertia and thus less HP loss. Not in constant RPM, but as you accelerate. This is the most important thing. How much power you have under acceleration at full throttle. This is also what dyno's are measuring. ?

What you just said is gibberish. You cannot have LESS HP loss, but not MAKE more HP. That statement negates itself.


And "what a dyno is measuring" is Horsepower.
The definition of HP is Torque (at a specific RPM) Times the RPM.
A plot of HP is a series of discrete measurements made at a discrete points in time.
HP in no way cares about how long it took to get from one RPM to a different RPM.


P(hp) = (Torque (ftxlb) X N (RPM))/5252


Please point out where in that equation is Time, or seconds.
Even the RPM term 'N' is a STATIC RPM.
On dyno run sheets does it say anywhere how long the pull took?
No? that is because it does not matter.

Originally Posted by nikitopo

Maybe you heard about Subaru's attempt to break their own record in the Isle of Man. They used a specially tuned 550-hp WRX STI with many changes from Prodrive and STI. They transported the car in the island and made many test laps and attempts for several weeks. I was checking some screenshots and I found they were also using a lightweight pulley. It is the lowest pulley in the screenshot:



I believe it is clear that it is not the solid pulley with the rubber. Do you thing they would change it if there was a risk to broke the engine or if there were no gains?

This has also been addressed many times.
If you are building a race car from the ground up, and have already reduced mass in other more relevant areas like Flywheel, Crank, Rods, Pistons, wheels, tires, etc, then by all means continue the weight reduction trend and reduce weight wherever you can as it does all add up and make a difference.


But - On an otherwise stock vehicle reducing the weight of the crank pulley by a couple of pounds will result in no noticeable difference in the acceleration of the vehicle.


And when building an engine with a likely unlimited budget while attempting to set a world record, I am certain that they care absolutely ZERO about the longevity of the main bearings.

[humfrz]

Originally Posted by G-awesome

I'm gonna enjoy this thread.

Got a perrin lightweight crank pulley last fall but never rushed to install it and it's sitting gather dust. It suuure looks pretty in red though!

Tried to install it once but it was a PITA getting the oem off an auto since you have to hold it in place while taking off the crank bolt. Debating whether I should just sell it or attempt it again in the near future...

I'd suggest you use it as a centerpiece for your coffee table ..... as a conversation piece .......


humfrz

[G-awesome]

Originally Posted by humfrz

I'd suggest you use it as a centerpiece for your coffee table ..... as a conversation piece .......


humfrz

Brilliant idea again humfrz!

[nikitopo]

Sorry guys, I won't continue this. Have a nice day!

[justatroll]

Originally Posted by nikitopo

Sorry guys, I won't continue this. Have a nice day!

So one of my statements above offended you in some way?

[cdrazic93]

this gave me a fantastic laugh before work.

[ysu]

Hey justatroll. I am not a scientist but i have found your missing seconds fairly easily. The measurement of rpm is 1/s. ( or 1/m)

[nikitopo]

You don't even need time, but he is a justatroll and he'll not stop arguing. I just don't want to explain him anymore.

Whoever wants he can install a light pulley and check for himself if he likes it or not. Oil analysis, which is also a good thing to do in a non-factory car, can provide signs of any bearing wear. He won't find anything, but if this makes someone to feel better then it is an option. Otherwise, just keep the car stock and enjoy the life. This is my last advice guys and have fun!

[steve99]

[justatroll]

Originally Posted by ysu

Hey justatroll. I am not a scientist but i have found your missing seconds fairly easily. The measurement of rpm is 1/s. ( or 1/m)

True but to perform the calculation for HP, you use a static value for RPM.
The calculations for HP do not care how long it takes to transition from one RPM value to another.
You can do a very fast dyno pull, or a very slow one, the data will be nearly the same.
The slower the pull the more accurate the data.

I asked above, but never received an answer to: "On dyno run sheets does it say anywhere how long the pull took?"

On a pure Inertia Dyno (old school) you DO use the time rate of change of RPM to determine HP.
This was because all you needed was a known inertial mass flywheel and a stopwatch.

Newer technology uses high speed data gathering and controlled sweep loads to perform the measurements at a series of discrete points in time.

People that want to exaggerate their dyno values will try to run the sweep test as quickly as possible to maximize the rotating mass error and give inflated HP values.

Using Steady State testing eliminates the rotating inertial mass error of a sweep test, as there is no acceleration during this type of test.

Originally Posted by nikitopo

You don't even need time, but he is a justatroll and he'll not stop arguing. I just don't want to explain him anymore

First: You have not "explained" anything.
You "make statements" with no real world data to back them up.

So now presenting facts (backed up with MATH and PHYSICS) is arguing?

People post things like "you just have less rotational inertia and thus less HP loss" but present no facts to back up the statement.

Just explain where my statements are incorrect using facts.
I am all ears.

Start with this one:
Axiom 1 "HP can be measured at constant angular velocity"
Axiom 2 "rotational inertia is not a factor in systems rotating at constant angular velocity"

Inference "Rotational inertia is not a factor in HP measurements at constant angular velocity."

Where am I wrong?

I DO know the answer to "how does inertia of the rotating assembly in a car's drivetrain affect acceleration of a vehicle?"

But that is a different question from "Does a lightweight crank pulley make more horsepower?".
The answer to the second question is 'no'.


One thing I have learned is that many people just repeat things they have heard as facts.
When confronted with challenges to assertions like "Why?" people who dont have an answer interpret the question as an attack and get defensive.
MOST people are incapable of saying "I dont know".
Professional engineers have learned to say "I dont know, but I will go and try to get that answer" or they will not last long as an engineer.
I dont know everything, but there are very few concepts that I cannot understand after doing some research.

I am also perfectly capable of admitting I am wrong when someone presents me with answers that prove I am wrong.

[nova.86]

I'm excited for Mechanics in the Fall, it's gonna be fun when we take everything we learn halfway in the semester and then rotate it lol. Centripetal forces, torque, all that good stuff.