#1  
Old 09-25-2019, 10:37 AM
Tom Vaught's Avatar
Tom Vaught Tom Vaught is offline
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Default Supercharger RPM Calculator

Most People have Excel on their computers.

Here is how to create a "Calculator" to figure out your Supercharger RPM
with a very few clicks on the computer.

Open a Excel File (It typically has alphabetic letters for the columns and numbers for the rows)

Step #1:

a) Type "Crank" in Column C and Row 5 DO NOT TYPE THE QUOTES IN ANY INSTRUCTIONS

b) Type "Pulley" in Column C and Row 6
c) Type a value, say 9.5 in Column C and Row 8
(Put a "Border" around Column C and Row 8)

Step #2:

a) Type "Blower" in Column E and Row 5
b) Type "Pulley" in Column E and Row 6
c) Type a value, say 3.65 in Column E and Row 8
(Put a "Border" around Column E and Row 8)

Step #3:

Type the formula "= C8/E8" in Column D and Row 10
(Put a "Border" around Column D and Row 10)

The calculation should show the value of 2.60274

Step #4:

a) Type "Engine" in Column C and Row 13
b) Type "RPM" in Column C and Row 14
c) Type a value, say 6000 in Column C and Row 16
(Put a "Border" around Column C and Row 16)

Step #5:

a) Type "Blower" in Column E and Row 13
b) Type "RPM" in Column E and Row 14

Type the formula "= C16 * D10" in Column E and Row 16
(Put a "Border" around Column E and Row 16)

The answer in Column E and Row 16 should be 15616.44 Blower RPM

There are safe limits for each of the Supercharger types out there.

A Roots style supercharger might have a RPM limit of 12,000 rpm
A Screw Supercharger might have a 18,000 rpm limit
A Vortech Supercharger might have a safe limit of 55,000 rpm
(same deal for the Vortech/Paxton and the Torqstorm units)

A Turbo Charger RPM is typically based on the impeller diameter.
Smaller diameter Impeller Turbochargers might be capable of 120,000
rpm and the large Turbochargers like a 118 millimeter wheel unit might
be limited to 85,000 rpm.

The calculator above is for Belt Driven Superchargers.

There are some Electric Superchargers out there made for the OEM
Companies but are not readily available and very expensive.

Tom V.

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"Engineers do stuff for reasons" Tom Vaught

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  #2  
Old 09-25-2019, 11:11 AM
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Scott65 Scott65 is offline
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Excellent information. No pun intended...

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  #3  
Old 09-25-2019, 09:14 PM
Scott Roberts Scott Roberts is offline
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Why does a vortec need to spin so high compared to a roots or screw? Not as efficient at moving air or just a smaller overall surface area to move it? That's a big leap from 18krpm to 55k...

  #4  
Old 09-26-2019, 10:14 AM
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The reason why is a Vortech Supercharger uses a Turbocharger Compressor Wheel, Scott.

The Vortech Compressor in no way operated the same as the Roots style supercharger.
(Except that they are both Belt Driven in some cases on the Vortech units.) Vortech can be gear driven too.

With Turbochargers as you increase the Impeller RPM the mass flow thru the unit goes up much higher and sooner (due to the higher gear multiplication in the Vortech unit) vs the fixed belt drive ratio on the Roots style system.

Roots has one pulley on the supercharger and one pulley on the crankshaft.
The ratio is either under-driven, over-driven, or the same speed vs the engine rpm.

The Vortech Unit has the Belt system, same design as the Roots, (crank pulley drives the supercharger pulley), but the Vortech supercharger also has a 2nd set of gears inside the front of the supercharger case that has a 3.60 to 1 set-up there.

So the Vortech unit has the abiility to have a 3.6 to 1 step up ratio (crank and supercharger pulley the same size (but never used except in a flow bench application) or a large crank pulley, typically a 6" or 7" pulley and sometimes a 7.5 or 8" pulley on the crank depending on package space near the pulley. The supercharger pulley can be a 3.6" diameter or a 3.25 diameter or even a 2.7" diameter but could have belt slip there. The max speed of the Vortech unit sets the belt pulley ratio. The race stuff uses cog pulleys on the Vortech unit and the pulley sizes are more limited.

So 55K is a normal speed, the Keens used to run 62K or 64K speeds but got free superchargers. But they won a lot too.

The New Vortech Race units are sometimes crank driven with a transmission driven by the crank but no belt, that drives the supercharger. Transmission ratio vs a belt/pulley ratio. Again max supercharger rpm vs engine rpm sets the ratio for the system.

You need to get the ratios right there as fewer ratios are available. The superchargers are larger and you can package bigger and stronger gears inside the newest race units too so higher step up ratios there also.

Tom V.

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"Engineers do stuff for reasons" Tom Vaught

Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward.

Last edited by Tom Vaught; 09-26-2019 at 10:20 AM.
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