Motor oil weight

[Craig 94 TA GT]

I'm ready for my 4th oil change on the new motor and was wondering what weight I should get. The engine builder recommends 20/50, but he said 10/40 will work too. He said the thickness is due to the "race" bearing clearances. Do you think it's ok if I get 10/40 for the winter? It gets in the 30s at night in the dead of winter, and maybe mid 50s for the high on the cooler days. Or is this a question only the builder would know?

The car is a daily driver and hasn't seen the track yet. Thanks in advance.

[Injuneer]

I'd say use the 10W-40 in the winter. My engine is about as "race" as you can get, and the builder's recommendation was to run a 25W-50 Pennzoil racing oil for any nitrous use. But they also recommended 10W-30 for winter use, to prevent cold start wear. Obviously, I'm not going to be spraying in the dead of winter.

[Craig 94 TA GT]

Thanks Fred. Looks like I can even get away with 10W-30 in the winter then.

[Injuneer]

If your builder said 10W-40, I would use 10W-40.

[Craig 94 TA GT]

Thanks again, Fred...I bought some "Durablend" oil to transition from conventional to break it in, to full synthetic. The next change will probably be full synthetic. I hope the "blend" theory is a valid one when transitioning.