Sc14 5k Pully Dimentions

[neil]

i need some help with some maths lads.

i have EVERYTHING but a bottom pully for a wolf 3d EFI sc14 intercooled 5K. my previous pullys were sold some time ago and i never got the measurements for the 16psi it was creating. this time I'm wanting to run the standard magnetic clutch instead of a throttle body to controll the boost via throttle position and various other WOLF3D capabilities. the blower pully size is 115mm. ive managed to find a couple of formulas but I'm not much of a maths wizz. ive looked everywhere for this info and the only thing i havent done is called some performance shops. making a bottom pully is a one off thing and has to be done right the first time.

 

here is what i have found so far. it doesnt really give me the answers and I'm not sure i can trust it.

 

When fitting a supercharger, you should match the swept volume of the supercharger to the size of the engine. If the choice is made carefully, problems from overboosting and the required paraphenalia to solve these problems will be minimised.

The supercharger will also be kept in its safe operating speed with correct selection.

 

To choose a setup you need to know :-

1. Engine capacity

2. Maximum engine speed you will be using.

3. Boost level desired

 

I am setting out the calcs needed for a 1200cc engine in the steps below.

 

FIRST CALCULATION (Engine Litres/min @ 0 Psi )

Multiply engine capacity (in litres) times maximum engine Rpm. E.g. 1.2 litres x 6000 rpm = 7200 litres/minute. Divide this figure by two as engine only fills every second stroke. (7200/2 = 3600 litres/min.

This is the engines air requirements in litres/minute at 0 Psi boost.

 

SECOND CALCULATION (boost ratio)

Add the boost pressure desired (7 Psi) for the engine to 14.7 Psi (atmospheric pressure).

(7 psi boost desired +14.7 =21.7 psi)

Divide this answer by 14.7 and this gives the boost pressure ratio. (21.7/14.7=1.476) This is the boost pressure ratio above atmospheric pressure.

 

THIRD CALCULATION (Actual air requirements @ desired boost)

 

Multiply the boost ratio by the litres/minute obtained for 0 Psi and you get the actual air requirements in Litres/min for the engine at that boost. In our example this is 3600 litres/min X 1.476 = 5313.6 litres/min for 7Psi boost.

 

To decide on the correct size of supercharger you need to know :-

1. The swept volume per revolution of the supercharger. (Eaton M62 1 litre/rev, SC14 from a 1G-GZE 1.5 litres/rev, SC12- 1.2 L/rev)

2. The maximum continuous safe operating speed for the supercharger. (Eaton M62 14000 rpm continuous, Toyota SC14 12000 rpm??)

3. The maximum pressure that can be safely produced by the supercharger continuously. (Eaton M62 12 psi, SC14 10-12Psi??? teflon on rotors melts??)

 

CALCULATION (Supercharger rotor speed)

Divide the desired air flow (5313.6 L/min) by the swept volume of the supercharger (SC14 from the 1G-GZE is 1.5 litres per revolution). This will tell you the maximum speed the supercharger rotors must be run at to produce the volume required.

5313.6/1.5 litres = 3542.4 rpm for the SC14.

5313.6/1 litre = 5313.6 rpm Eaton M62

 

CALCULATION (Pulley size ratio)

Divide the rotor Rpm by maximum desired engine rpm to get the drive ratio of the pulleys. For an SC14 on a 1200 @ 7psi boost the desired supercharger pulley ratio is

3542.4 /6000 rpm = 0.5904.

 

EXAMPLE OF CHANGE OF DRIVE RATIO

If the 1200 cc engines supercharger pulley ratio is increased to 0.75 using the 1.5 ltr/rev SC14 charger, the volume of air produced when running to 6000 would be 6000 x 0.75 x 1.5 litres =6750 litres/min

 

Boost produced would be 6750 litres/3600 litres (at 0 boost) =1.875 boost ratio For Psi boost ((1.875 x 14.7) - 14.7)=12.86 Psi.

 

if you want to get even more technical the sc14 is actually 1.42litres/min!

 

thanks

[KEI069]

Gday mate,

I'm actually doing something similar at the moment, using a sc14 on a 5k.

iHave a 145mm crank shaft pulley/balancer and using the same eqaution

worked out that i need a pulley for the supercharger to be about 180mm

to get the desired boost of 8psi at 6000rpm. this means the supercharger is under-driven

don't know if this helps you at all but good luck with it

cheers

Justin

[neil]

ive done the calculations and my (pully size ratio) = 1.124 for 15psi at 6500rpm

does that mean that my top pully which is 115mm needs to be timesed by 1.124 to get the size of my bottom pully??

it seems that there is a little maths missing to that formular???

 

 

CALCULATION (Pulley size ratio)

Divide the rotor Rpm by maximum desired engine rpm to get the drive ratio of the pulleys. For an SC14 on a 1200 @ 7psi boost the desired supercharger pulley ratio is

3542.4 /6000 rpm = 0.5904.

 

EXAMPLE OF CHANGE OF DRIVE RATIO

If the 1200 cc engines supercharger pulley ratio is increased to 0.75 using the 1.5 ltr/rev SC14 charger, the volume of air produced when running to 6000 would be 6000 x 0.75 x 1.5 litres =6750 litres/min

 

Boost produced would be 6750 litres/3600 litres (at 0 boost) =1.875 boost ratio For Psi boost ((1.875 x 14.7) - 14.7)=12.86 Psi.

 

 

cheers