I'm running M1 10W-30 this winter. Oil pressure comes up just as quiclkly on a cold start at 10 degrees as it did at 70 degrees. It was in the 20's today, but I ran half a bottle through the motor @ 125 shot today with no noticeable ill effects(good pressure). I would say 10 or 5W-30 should be just fine for the winter as long as you're not running the engine at 7K all day long. Oh yeah, cold tires are lots of fun when you hit the button!

 

Fred, out of curiosity, why did the builders recommend 20w50 in your stroker? I've been thinking about this as I'm breaking my motor in currently that was built by a reputable builder and am using 10w30 and plan to use 10w30 or possibly 5w30 after breakin. I have 70psi idle pressure when cold, and 45psi when idling hot w/ the 10w30. I'm also running a HV pump and Canton pan.

I've heard of others using the thicker oils and I was wondering on what the theory is behind it? Does it have to do with the fact that the clearances are set soo loose that it is needed to maintain adequate pressure? What kind of pressures are you seeing w/ engine warm/cold idle? Thanks.

 

The know how they put the engine together, how they set the bearing clearances, what they did to accomodate the solid roller camshaft and the required oil distribution for a daily driver, and what they needed to do to keep the engine together with a 300-shot on top of a 500HP build. The oil needs to maintain a given film thickness, and how well it maintains the film thickness is related to viscosity. With nitrous, they feel the 50-weight is necessary. Without nitrous, they feel the loads are reduced to the point where 30-weight will hold the required film thickness. And, of course in the winter, you don't want a "20W" in there... that's why they recommended the 10W-30.

Everything I have seen and heard has said DO NOT use a HV pump (I have a blueprinted stock pump, 80psi spring and tack-welded pickup). I have also seen more negatives on the Canton pan than on the stock pan (I run a stock pan - George Baxter had the exact same oil setup in his 1,125HP LT1. My engine is good to mid 7,000's, George's routinely exceeded 8,000rpm).

I'd say the engine starts at about 60psi cold, drops to 40-45psi at 800rpm hot idle, and pushes right up to the top of the gauge at 7,000rpm, although at that point I'm focused on things other than the oil pressure gauge. I have had a passenger confirm .

The GM factory recommendation for the LT1 is 5W-30 year round, with 10W-30 allowed when ambient temperatures are not below 0degF. That's right out of the owner's manual, and the shop manual.

I wouldn't use how fast your oil pressure rises on cold start as a measure of the correct selection of "winter" viscosity. The thicker the oil, the harder it is to force it through a cold engine, and the less flow there is to protect the bearings. Rising pressure is a sign of poor circulation, at low rpm.

 

Fred, if you don't mind, could you let me know what you are running for bearing clearances on the rods and mains? Thanks.