How long will SN89 last at 42,624 max RPM?

[Polecat_Racing]

I currently spin my SN89 to 39,960 max rpm with a 4" pulley. Thanks to a fluid cooler and frequent fluid changes, it seems to be holding up.

I'm considering trying a 3.75" pulley which will put it at 42,264 max rpm. Is this too much?

I've searched many past posts and read conflicting reports on what the maximum "safe" rpm is for an SN.

Any input is appreciated. thanks

[speedytang]

If your Ball Drive pressure is tight enough(on the edge) so the the balls don't skip across the impeller you can. I ran a 7" crank and 3.75" on the street for 15 years with no problems and would take the engine up to 6800 rpm. I was way over 42k rpm at WOT. I would change to a 3.5" for racing and since I was only at over 45k rpm when reaching 5k+ rpm and not in it long I had no problems. I did use a huge cooler about the size of a condenser on the front of the car to give more fluid area.

[Polecat_Racing]

Thanks for the reply.

I guess my next question would be what is the normal ball drive pressure in an SN, and what kind of pressure would be required to keep it from slipping at upwards of 42K rpm?

[speedytang]

It seem the daily 'SN' is between 35-38inlbs. VR4 with a good ball drive(balls are matched in size) 48-52inlbs.