So I blew my engine over the weekend

[PercentSevenC]

My experience with the 5" has been rather underwhelming. Jeff's setup with the -7 pulley (and I think he'll agree) wasn't all that powerful, especially at the low end. My friend's 5" with the -10 pulley was better, but honestly I think my car has at least as much power now with the 7" and -7, and my throttle response actually seems better (granted, my flywheel is a couple of pounds lighter). The only reason I would use a 5" is if I was limited by the space in the engine bay.

[Rotarydave]

Originally Posted by PercentSevenC

My experience with the 5" has been rather underwhelming. Jeff's setup with the -7 pulley (and I think he'll agree) wasn't all that powerful, especially at the low end. My friend's 5" with the -10 pulley was better, but honestly I think my car has at least as much power now with the 7" and -7, and my throttle response actually seems better (granted, my flywheel is a couple of pounds lighter). The only reason I would use a 5" is if I was limited by the space in the engine bay.

I understand what you are saying, Jeff knows who I am we have talked this a bunch elsewhere.

IMHO I used both the 5 inch and the 7 inch on the same motor same carb on both setups, I used the 5 inch with a -10 pulley and the 7 inch with the -7 pulley they pulled nearly the same boost but on the track I was a full 0.5 seconds faster with the 5 inch at the 1/4 mile. Now I also drove several other Rx7s with blowers 5 inch and 7 inch, different setups FI/carbed 12a/13b different engines. I like the 5 inch better it has always given me faster throttle response.

I guess I can equate it this way, it seems to me that using the 7 inch blower with the -7 pulley the engine was having a hard load to turn it over. It was as if the -7 pulley on the 7 inch acted like changing the ft sproket on an bike to the larger gear (yea it dosen't spin as many times to go as fast but takes a much larger energy load to do it)

Regardless of the outcome I am very pleased with the supercharger vs the turbo for street use and you will be also once you start hitting the gas station. If you call Dave Atkins and ask him on some of this he will probably agree with me as my car was the one he did a bunch of testing with while I was stationed there. I know that he has continued testing since I left but last I knew he was recommending the 5 inch exclusively for most rotaries esp if it was a street application. If you have time try to sit down with him and explain everything you have done and what you are trying to do I can't see him not wanting to help you and share info to the same, regardless of what you may have heard.

Again my results may not be typical but I tried to keep them within a controlled standard so I could identify the parts improving or not.