Something about Pully sizes I don't understand - Page 3

Harley#356 · 06-10-2009, 01:16 AM

if you've already got the belt and installed and it seems too loose, probably best bet is just get one 1/2" shorter.

glassman · 10-08-2009, 04:01 PM

Quote:

Originally Posted by Ryan@RhynoTune

People need to reference their pullies in terms of diameter, not gains in PSI. Bottom line is a 8.5'' pulley will not gain the same on both engines.

This is a simple calculation, the hardest part is figuring out why people can't grasp this simple concept.

7.5/2.93= 2.55 blower ratio for a Lightning @ 8 PSI
7.5/3.25= 2.30 blower ratio for a HD @ 6 PSI
8/2.93= 2.73 blower ratio w/ 8'' lower (2#) for a Lightning
8/3.25= 2.46 blower ratio w/ 8'' lower (2#) for a HD
- Time out, so with a 8'' lower, you still aren't even at the same blower speed as a stock Lightning. So how do you gain two pounds? Do I really need to go on? I guess I must.
8.5/2.93= 2.90 blower ratio w/ 8.5'' lower (4#) for a Lighting
8.5/3.25= 2.60 blower ratio w/ 8.5'' lower (4#) for a HD
- Another time out, so with a 8.5'' lower on your HD, your not even at the same rate as a Lightning with a 2lber. So you start w/ 6PSI, buy a so called 4lber, slap it on with your stock upper, and bam your at 10PSI!!! But the odd thing is, your still spinning your blower slower to get that same 10PSI than a Lightning does. It's magic

I assume after reading that, someone is saying that isn't much of a difference. These numbers are small and meaningless. This is the part where I multiply the given ratio times 5250 RPM.
5250x2.73 (L blower ratio for a 8'' lower aka 10 PSI)=14332.5
5250x2.60 (HD blower ratio for a 8.5'' lower aka 10 PSI)= 13650

So you have a difference of 900 RPM for the supposed same amount of boost. Bottom line, you do not get the same amount of increase on the two engines with the different uppers.

Never one to accept things at face value
8.5/3.25 = 2.615
5250 x 2.615 = 13723
Difference is more like 600 rpm. Fair bit less than 900.

Ryan@RhynoTune · 10-08-2009, 08:06 PM

Not sure what you're saying, the difference between your calculation and mine is 78 RPM, and in the favor of my point.

glassman · 10-09-2009, 11:22 AM

5250x2.73 (L blower ratio for a 8'' lower aka 10 PSI)=14332.5
5250x2.60 (HD blower ratio for a 8.5'' lower aka 10 PSI)= 13650

So you have a difference of 900 RPM for the supposed same amount of boost. Bottom line, you do not get the same amount of increase on the two engines with the different uppers.[/QUOTE]

You wrote this not me.

10-08-2009, 08:06 PM	#33 (permalink)
Ryan@RhynoTune Drivetrain Calibration Join Date: Feb 2004 Posts: 758 View this user's gallery iTrader: 0 / 0%	Not sure what you're saying, the difference between your calculation and mine is 78 RPM, and in the favor of my point. __________________ 2002 HD - 631 RWHP - 757 RWTQ Currently fabbing twin-turbos

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06-10-2009, 01:16 AM	#31 (permalink)
Harley#356 Worlds Fastest HD F150!!! Join Date: Jan 2003 Location: Week-Philly; Weekend-Souf Jerz Posts: 31,622 View this user's gallery iTrader: 0 / 0%	if you've already got the belt and installed and it seems too loose, probably best bet is just get one 1/2" shorter.

10-09-2009, 11:22 AM	#34 (permalink)
glassman Registered User Join Date: Jul 2003 Location: Edmonton, Canada Posts: 15 View this user's gallery iTrader: 0 / 0%	5250x2.73 (L blower ratio for a 8'' lower aka 10 PSI)=14332.5 5250x2.60 (HD blower ratio for a 8.5'' lower aka 10 PSI)= 13650 So you have a difference of 900 RPM for the supposed same amount of boost. Bottom line, you do not get the same amount of increase on the two engines with the different uppers.[/QUOTE] You wrote this not me.