pulley install questions

[JPJP]

This is great info (above).

I suppose the HO impeller "should" have made even more boost. Any numbers available?

[89LX]

I just went to my 10 rib setup with the stock 4.25" charger pulley and a 7" crank pulley
the 10 rib belt was so tight I figured I would have to go to the next belt up which is 2-1/2"
longer which would be too long by my estimation. I had to put the belt on while sliding the
4.25" charger pulley onto the shaft and with the belt tentioned, it just misses the stock water pump pulley bell edge. I have run it now for a couple of weeks and it is stretching
a little and is fine nothing to worry about and no belt slip at all. The 7" crank pulley came with the accessories belt underdriven, I use all the others stock diameter and use an 89"
Outside Circumfrence belt number K060883/6PK2246. I had to try several different belts
to get the correct length with this setup.

[hey its me]

The stock 4.25 s/c pully and 6 inch crank is what i have on my mustang kit and it was suppose to make 6 psi???? now i have a 4" and its suppose to be around 7.5 psi??

Im even more confused now.

Im gonna post all the numbers and model and what not and can somebody tell me if they have the same and what it is making??

Gernetalli can you help by teling me what these numbers mean? I will post them soon. Thanks for all help

[89LX]

There is a specific formula which tells you what RPM's the supercharger will be spinning. It all depends on what your Max Engine Rpm's are going to be. When you change your pulley diameters on either end all it does is make the charger spin higher RPM's and the boost comes on much sooner than it did before. Example, if when you first got your charger and at 5500 engine RPM's you were seeing 5 PSI. Now you make a pulley change, at the same 5500 engine RPM's you now get 7PSI. The rotational torque reading inside of the charger has not been changed at all, this is what determines how much it will
put out for boost as the balls inside are tight in the races. If the balls slip or are set too loose the boost will be less. Get them too tight it will make tons of boost but major heat as well and the charger will not last. I have a VR4 which is fully capable of making 15 PSI, I'm looking for around 10-12 and I'm also going to run the largest cooler I can shove in front of my AC condenser. I currently run an SN-2000 on it's best day saw maybe 5 PSI. My VR4 came with 10 rib pulleys and the crank was 7" the charger is a stock 4.25. I now see 7-8 PSI just by changing the crank pulley on the SN-2000 setup. Take 7" divide it by 4.25" gives you 1.6470588 now multiply that by 6,000 engine RPM's and multiply by 4.44 = 43,877.646 supercharger RPM's. This is safe rpm's for my Paxtons to be in. To look up your reduction ratio aspracing.com has a chart to show your specific charger reduction ratio if you don't know or are not sure.
My paxton centrificals happen to be 4.44:1 .

[89LX]

The other things to remember are every cars a little different with the add on configurations. I have a BBK-SSI intake which has extra large intake ports and runners
that eats up some of the air PSI because it has to fill the empty air space as the motor cycles. I also have larger Aluminum heads I 'm putting on a brand new motor configuration
which will also eat up some of the PSI but remember the booster is still boosting at the same CFM flow rate what ever your is going to be. I guess it's like this, I could in theory
change back to stock and raise the PSI but it would restrict the motors ability to cycle more air. The general theory is more air and fuel in and more air and exhaust out let the motor breath and you will see an increase in horsepower even if the PSI drops a little.

[hey its me]

Yea i understand how the pulley's and RPM's work together. Im just trying to figure out what the unit should be making if it were brand new. what it SHOULD be making, if all my internals are good.


[quote=Granatelli;63622]When this kit was sold new Model number 18001 for 88-93 Mustangs it came with 4.25 blower pulley and 6 inch crank. Required belt was Gates KO60500. it made 5psi at 6k

Next came 4.00 blower pulley and used KO60495 belt and should have made 6.5 to 7 psi.

According to this i should be making 6psi at least.. which im not. this is why im confused.

where do you guys have your boost gauge vac line hoked up to? Maybe mines not in the right spot

[Granatelli]

There is a specific formula which tells you what RPM's the supercharger will be spinning. It all depends on what your Max Engine Rpm's are going to be. When you change your pulley diameters on either end all it does is make the charger spin higher RPM's and the boost comes on much sooner than it did before. Example, if when you first got your charger and at 5500 engine RPM's you were seeing 5 PSI. Now you make a pulley change, at the same 5500 engine RPM's you now get 7PSI. The rotational torque reading inside of the charger has not been changed at all, this is what determines how much it will
put out for boost as the balls inside are tight in the races. If the balls slip or are set too loose the boost will be less. Get them too tight it will make tons of boost but major heat as well and the charger will not last. I have a VR4 which is fully capable of making 15 PSI, I'm looking for around 10-12 and I'm also going to run the largest cooler I can shove in front of my AC condenser. I currently run an SN-2000 on it's best day saw maybe 5 PSI. My VR4 came with 10 rib pulleys and the crank was 7" the charger is a stock 4.25. I now see 7-8 PSI just by changing the crank pulley on the SN-2000 setup. Take 7" divide it by 4.25" gives you 1.6470588 now multiply that by 6,000 engine RPM's and multiply by 4.44 = 43,877.646 supercharger RPM's. This is safe rpm's for my Paxtons to be in. To look up your reduction ratio aspracing.com has a chart to show your specific charger reduction ratio if you don't know or are not sure.
My paxton centrificals happen to be 4.44:1 .

We offer a book for $20.00 that tells every impeller speed for every centrifugal blower on the market - in 100 rpm increments

http://www.granatellimotorsports.com...lay.php?gid=95

For you guys 12.00 shipped

[Granatelli]

The VR4 kits did have a 7" crank - becuase we wanted more belt wrap

7 / 4.25 = 1.647 x internal step up 4.44 = 7.31 x eng RPM on the Mustang that was 6200 factory) = 45,322

[JPJP]

http://www.superchargerhelp.com/showthread.php?t=4907

Above link is spread sheet from this superchargerhelp website for easy viewing of impeller speeds.

[Granatelli]

ya - that works too