Is a VR4 dimensionally different from an SN-89?

[pianoprodigy]

The way I understand it, the VR4 is an internal upgrade of the SN series. Is this correct? I'm in the process of getting my SN-89 installed on my 90 Rx-7. It is being a PITA with regard to fitment. I don't mind so much so long as it works well in the long run. Eventually, I'd like to get the blower rebuilt to a VR4 and have a neat 300+ whp sleeper.

This is the same supercharger kit I have on another car.


If I want to have the SN rebuilt to a VR4 down the road, will it be the same from the outside?

Thanks

[speedytang]

It is about 1/4-1/2" thicker. The VR4 unit is done by increasing ball pressure on the race and a 4" impeller of course and a difffernt rear housing to allow the increase of impeller size and depth.

[pianoprodigy]

It is about 1/4-1/2" thicker. The VR4 unit is done by increasing ball pressure on the race and a 4" impeller of course and a difffernt rear housing to allow the increase of impeller size and depth.

Speedy,

Just to confirm...If you look at the picture I posted, the supercharger would just extend about 1/2 an inch further back, right?

My mechanic finally got my car running today. My SN-89 is only producing 6 psi (measured at the manifold) being spun right up to 39k RPMs at 7k engine RPMs. The supercharger is quite old, so I think in a month or two (depending on how well the current setup dynos) I'll be sending my unit off to Craig @ PW to be rebuilt to a VR4.

[speedytang]

Correct you need 1/2" more clearance at the rear of the unit.