Home
What's new
Latest activity
Authors
Store
Latest reviews
Search products
Forums
New posts
Search forums
What's new
New posts
New listings
New products
New profile posts
Latest activity
Members
Current visitors
New profile posts
Search profile posts
Log in
Register
Cart
Cart
Loading…
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Search titles only
By:
Menu
Log in
Register
Navigation
Install the app
Install
More options
Change style
Contact us
Close Menu
Forums
Cobra Forums
2013-14 Shelby GT500
Why more torque with lower pulley?
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="Bad Company" data-source="post: 13685051" data-attributes="member: 141815"><p>You're welcome</p><p></p><p>I was surprised that nobody had done the math to see the differences in the use of different upper pulleys versus lower pulleys. So I took a few minutes to run the numbers to verify my thoughts using a stock 2013 GT500 for the baseline and posted my results for everybody else to see.</p><p></p><p>Now the next part of this question is, why doesn't the Hp increase as much at high RPM with the larger lower with a stock upper on the 2.3L TVS?</p><p></p><p>Again this has to do with the fact you are turning the blower extremely fast.</p><p></p><p>8" divided by 2.71" = 2.952</p><p></p><p>2.952 ratio x 7000 engine RPM = 20,664 blower RPM</p><p></p><p>Now we are getting to the point of the parasitic Hp loss to turn the blower this fast is getting as high as the the extra Hp generated by the higher boost. So the net Hp gain at the flywheel isn't as high as one would think for the boost being introduced into the engine.</p><p></p><p>2.3L of air per revolution of the Supercharger x 20,664 RPM = 47,527.2L of air per minute is being ingested by the engine. </p><p></p><p>Now lets look at a 3.6L SC and the number of RPMs needed for this blower to generate the same amount of air flow entering the engine.</p><p></p><p>47,527.2L divided by 3.6L = 13,202 RPM for the blower speed. </p><p></p><p>The 3.6L SC closest pulley combo to match this RPM would need to be a stock 7.1 lower with a 3.75 upper.</p><p></p><p>7.1 divided by 3.75 = 1.8933 drive ratio</p><p></p><p>1.8933 x 7000 engine RPM = 13,253.1 Blower RPM. </p><p></p><p>We are close, but not a perfect match. Unfortunately there isn't a upper/lower combo that would be a perfect match. But in doing this math we see how close we can get to the same air flow from both blowers and the RPM each is turning to achieve it.</p><p></p><p>Now for the real math I'll use our original RPM numbers to calculate the differences in blower speeds </p><p></p><p>20,664(2.3L blower RPM) - 13,202(3.6L blower RPM) = 7,462 RPM </p><p></p><p>This is the difference between these two Superchargers for the same exact amount of air flow entering into the engine. I'm not a mechanical engineer, but it would be easy to see how much more energy(Hp) is required to turn the smaller blower(2.3L) for the same air flow entering the engine at peak Hp with this big of a difference in blower speed. The 3.6L SC is turning 36% slower in RPM for the same air flow when compared to the 2.3L</p><p></p><p>Again we can also do calculations for the Peak Torque RPM of the engine, to see if the air flow is still close at these lower RPM for a solid torque gain with the larger blower.</p><p></p><p>3.6L blower math is</p><p></p><p>1.8933 drive ratio x 4500 Engine RPM = 8,519.85 blower RPM</p><p></p><p>3.6L of air per revolution x 8,519.85 blower RPM = 30,671.46L of air per minute at peak torque</p><p></p><p>2.3L blower math is</p><p></p><p></p><p>8" divided by 2.71" = 2.952 ratio</p><p></p><p>2.952 ratio x 4500 engine RPM = 13,284 blower RPM</p><p></p><p>2.3L of air per revolution x 13,284 blower RPM = 30,553.2L of air per minute at peak torque.</p><p></p><p>Both of these blowers again are very close at the peak torque in air flow. But the RPM difference is still high. </p><p></p><p>13,284 - 8,519.85 = 4,764.15 difference in blower speeds. </p><p></p><p>Now the question is, are both of these blowers working in there perspective efficiency range as far as RPM and air flow being produced? Because it will be a matter of which SC is doing the job more efficiently then the other for the highest net Hp and torque result at this engine RPM. Again there is a big RPM difference in blower speeds, but it also will be about which SC is more efficient at this target RPM for the air being moved. I'd be willing to bet the 3.6L is starting to lose some efficiency turning this slow, so the peak torque and Hp numbers are going to be closer to each other between these two SC at this RPM. But then that again there is a large difference in blower RPM, so on paper the 3.6L should be ahead by a considerable amount and a slight drop in efficiency shouldn't hurt its final dyno numbers.</p><p></p><p>Now we could also do this math again for 2500 engine RPM to see how slow we are turning the 3.6. But you've seen how it works and can do it now. The math will be very close to each other again. The difference will be in whether or not the 3.6L SC can be efficient at moving air at this slow of a blower RPM</p><p></p><p>Yes, I was bored and spent waaaaaaaayyyyyyyyyyyy too much time on this LOL</p></blockquote><p></p>
[QUOTE="Bad Company, post: 13685051, member: 141815"] You're welcome I was surprised that nobody had done the math to see the differences in the use of different upper pulleys versus lower pulleys. So I took a few minutes to run the numbers to verify my thoughts using a stock 2013 GT500 for the baseline and posted my results for everybody else to see. Now the next part of this question is, why doesn't the Hp increase as much at high RPM with the larger lower with a stock upper on the 2.3L TVS? Again this has to do with the fact you are turning the blower extremely fast. 8" divided by 2.71" = 2.952 2.952 ratio x 7000 engine RPM = 20,664 blower RPM Now we are getting to the point of the parasitic Hp loss to turn the blower this fast is getting as high as the the extra Hp generated by the higher boost. So the net Hp gain at the flywheel isn't as high as one would think for the boost being introduced into the engine. 2.3L of air per revolution of the Supercharger x 20,664 RPM = 47,527.2L of air per minute is being ingested by the engine. Now lets look at a 3.6L SC and the number of RPMs needed for this blower to generate the same amount of air flow entering the engine. 47,527.2L divided by 3.6L = 13,202 RPM for the blower speed. The 3.6L SC closest pulley combo to match this RPM would need to be a stock 7.1 lower with a 3.75 upper. 7.1 divided by 3.75 = 1.8933 drive ratio 1.8933 x 7000 engine RPM = 13,253.1 Blower RPM. We are close, but not a perfect match. Unfortunately there isn't a upper/lower combo that would be a perfect match. But in doing this math we see how close we can get to the same air flow from both blowers and the RPM each is turning to achieve it. Now for the real math I'll use our original RPM numbers to calculate the differences in blower speeds 20,664(2.3L blower RPM) - 13,202(3.6L blower RPM) = 7,462 RPM This is the difference between these two Superchargers for the same exact amount of air flow entering into the engine. I'm not a mechanical engineer, but it would be easy to see how much more energy(Hp) is required to turn the smaller blower(2.3L) for the same air flow entering the engine at peak Hp with this big of a difference in blower speed. The 3.6L SC is turning 36% slower in RPM for the same air flow when compared to the 2.3L Again we can also do calculations for the Peak Torque RPM of the engine, to see if the air flow is still close at these lower RPM for a solid torque gain with the larger blower. 3.6L blower math is 1.8933 drive ratio x 4500 Engine RPM = 8,519.85 blower RPM 3.6L of air per revolution x 8,519.85 blower RPM = 30,671.46L of air per minute at peak torque 2.3L blower math is 8" divided by 2.71" = 2.952 ratio 2.952 ratio x 4500 engine RPM = 13,284 blower RPM 2.3L of air per revolution x 13,284 blower RPM = 30,553.2L of air per minute at peak torque. Both of these blowers again are very close at the peak torque in air flow. But the RPM difference is still high. 13,284 - 8,519.85 = 4,764.15 difference in blower speeds. Now the question is, are both of these blowers working in there perspective efficiency range as far as RPM and air flow being produced? Because it will be a matter of which SC is doing the job more efficiently then the other for the highest net Hp and torque result at this engine RPM. Again there is a big RPM difference in blower speeds, but it also will be about which SC is more efficient at this target RPM for the air being moved. I'd be willing to bet the 3.6L is starting to lose some efficiency turning this slow, so the peak torque and Hp numbers are going to be closer to each other between these two SC at this RPM. But then that again there is a large difference in blower RPM, so on paper the 3.6L should be ahead by a considerable amount and a slight drop in efficiency shouldn't hurt its final dyno numbers. Now we could also do this math again for 2500 engine RPM to see how slow we are turning the 3.6. But you've seen how it works and can do it now. The math will be very close to each other again. The difference will be in whether or not the 3.6L SC can be efficient at moving air at this slow of a blower RPM Yes, I was bored and spent waaaaaaaayyyyyyyyyyyy too much time on this LOL [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Cobra Forums
2013-14 Shelby GT500
Why more torque with lower pulley?
Top