Rotrex pulley change
 

Searched and found nothing, has anyone with a GTM SC changed the pulley on their rotrex supercharger? My stage 1.5 is running great but I found out they sent me a 92mm pulley when I had ordered an 88mm. They sent me the 88 and I'm ready to swap it, but after taking the 6 pulley bolts off it's still on there really tight.

Don't you need some sort of press tool?

No idea. I did on my Cobalt ss sc, but this pulley looks alot different. And it says "Changing pulleys is a 20 minute job", I don't think I should have to remove the sc or anything

88 pulley produces how much boost on the stage sc 1.5 ?

Check out page 13 in the guide below.

http://www.rotrex.com/media/e859c20d...let%20V5_5_pdf

Thanks, the GTM one is different though like there's no center screw. Figured it out this morning though, I looked at the inside of the new pulley and there's a little intention for the shaft to fit in, so I just had to pry a little bit with a flat head and it popped off. Slapped the 88 on there and I'm hitting 11 pounds!

Very nice!

Um retune! Or did you already?

So changing the pulley is not a 20 minute deal unless the unit is not on the car.

I have a 1.5 kit for my HR and I had this same question when I swapped pullies. I asked Mike@GTM for the method of removal and what he said to do was take two screw drivers, wrap them with painters tape (so they dont scratch anything). Put one screw driver under the pulley from one side and then use the other screw driver in the same manner from the other side.

You then push down on the screw drivers and essentially pry up the pulley.

Of course the screws that keep the pulley mounted need to be out but if you work the screw drivers gently you'll pup the pulley off.

This assumes the SC itself is sitting in front of you and again not on the car. If you are clever enough this might be doable with the unit in the engine bay but it's probably a real PITA to do.

I was actually able to do it while it was on the car. I took the undertray off and moved the tensioner from below, took the screws out and I ended up just taking a screwdriver and prying it off. It probably only does take 20 minutes, I just waited to see if anyone knew cause I didnt wanna bend the shaft or anything crazy.

Not sure exactly what it's supposed to make, but my prosport gauge is reading 11 pounds. I think that's about right but it's not a super high end gauge or anything. Getting a dyno tune on Wednesday and then I should know the true psi.

and then some day go down to the 84mm pulley:stirthepot:

Dude what's up with the 84 anyways, Sam refused to sell it to anyone??

I unno maybe it blows chargers up?

Sent from my HTCONE using Tapatalk

Supercharger kits are usually listed with different sizes of pulley and alot of times the really small sizes are for when you are running smaller crank pullies(especially on murican cars because there are many different options for crank pullies) some of the small sizes when run with a larger crank pulley can overspeed chargers. you would want to look at the redline on the charger and then figure crank pulley diameter/blower pulley diameter x crank rpm to figure out how fast the charger will be spun. sometimes this means you need to also calculate the step up n the chargers gearing when it's max rpm is listed at the impeller not input pulley

http://www.the370z.com/members/pokey...6-sc-speed.jpg

Red is over design speed with the stock crank pulley. Both the 88 an 84 are over

I have a 84mm pulley and ran it on a 1.0 install with no issues. Just waiting to put it on my 1.5 setup.

Interesting, so even the 88 is techically smaller than this setup should allow? I think it's the most popular pulley size though and I've never heard of a blower go out from over spinning. Thanks for that info though, cool to know how fast I'm actually spinning it

from rotrex's website the c38 has a 1:7.5 gear ratio with a max impeller speed of 90,000 now we need an accurate measurement of the O.E. pulley.

Edit: also due to the high speed nature of centrifugal superchargers the manufacturers redline is usually set a little lower than it's designed redline to CTA for warranty reasons.

the factory crank pulley is 146mm

SO an 88mm pulley would be 146/88 x 7500 x 7.5 = 93324rpm

^ So I (and everyone who runs an 88mm) am over spinning the blower by about 3k rpms? Doesn't seem to be a big deal though, you're right it can probably take a little more with no problems they just want you to stay conservative

I have found Rotrex compressor maps the show data to 120K, so someone (Rotrex) has spun the -81 that fast. I think we all be safe with some overspeed. I ran the 84mm for 10K miles and my blower did not pop.

You are only overspeed when you are turning the engine near redline. If you want to be safe, reset your max RPM to 7K with Up-Rev.