Sparks ... stay away from the 50 wt for the street . I used it all the time in my race engines , but down here , our summer temps reach 100 degrees + in July and August .
I use Brad Penn multi viscosity
oil . Unless the have large clearances or are racing for more than a 1/4 mile ... 50 wt is too much . For what it`s worth , a friend of mine used to build engines for the Penske team and is still involved with NASCAR . He told me that most of the teams run a multi viscosity
oil . To really get picky , they use a light
oil in the engine , rear end and tranny for qualifying and then go to a heavier oil for the race ... but it`s still a multi viscosity oil .