After seeing an online discussion a little while back I decided to change the weight of oil I was using in my bracket car. I have always run Mobil 1 15W-50 with a Motorcraft FL-1A filter. I had originally picked the 15W-50 as I run wide side clearances on my rods per Eagle (.022 side clearance). The rod and main bearing clearances are right in the middle of stock tolerances. The oil pump is a blueprinted Melling HV. With the 15W-50 it would idle cold at 65 psi, hot at 45, on a pass the pressure would be ~70 psi. This is a 383W stroker with an offset ground stock crank (3.70" stroke) that sees 6800 on shifts. It will go higher, but is more consistent at 6800.

I recently changed to Mobil 1 10W-30. New FL-1A at the same time. Saw a pressure drop to 40 psi cold idle, 20 hot idle, 50-52 on a pass. Scared me. Only ran it one night at the track like that. No faster, but I did go some rounds. I just changed back to 15W-50 and a new filter. Pressure was back to normal.

I would normally say the oil was just too thin, but there shouldn't be *that* much difference form 15W-50 to 10W-30. This seems a bit much for it to be only oil. The filter perhaps? A buddy of mine has a 460 crate motor on a dragster. He recently changed the oil in it. Same oil as before, new FL-1A. Fired it up. Oil pressure was zero. Shut off, fired again. Still zero pressure. Changed the filter and pressure went back to normal.

Comments?

Later,

If you numbers didn't pick up at the track going down to the 30W and the pressure numbers bother you change back. Your pressure numbers don't scare me, in my 390 I run straight 30W and get about 65 at cold idle, 20 at hot idle in Texas heat, and not quite the 10 lbs per 1000rpm that everyone seems to want.

Personally I prefer straight weight oils over multi's, there are far fewer additives in them. Why not ask Alex for a suggestion on trying some Royal Purple in your engine? RedLine also makes a top quality product.

Most of those out there who run those watery thin oils DO indeed see lower pressures, but insist that the QUALITY of the oil allows their engines to live.

That lower oil pressure is what is increasing the horsepower. The engine is using less power to circulate the oil, plus the thinner oil reduces windage.

Personally, since I'm not a wealthy guy, and am not into 'heads up' class racing... I plan on sticking with my $17.88/5 quart container (at Wal-Mart) Mobil 1 15w50. It's not too thick, not too thin, and has delivered great reliability. It's always worked plenty well for me.

To reduce windage, I use an 8 quart pan filled with only 7 quarts of oil... and use a windage tray.

Good Luck!

jkilroy, the cold idle pressure I was talking about was anywhere from 50-80?F, with an engine that hadn't been started that day. I wasn't worried about the idle pressure so much as only having 50 psi at 6800 rpm.

Fordwiser, I have seen the the racing filters. Any info on them? I have been thinking about investing in a System 1, cleanable/reusable filter.

n2omike, I buy the same oil as you. 5 qt jugs at Wal-Mart. I can even get it a little cheaper. Employee discount, wife works there. I had been getting the 15W-50, just the last time I decided to try to try the 10W-30. Guess I'm back to the 15W-50 for good now. I also do the 7 qts in an 8 qt pan deal. Worth about 1/2 a tenth. But I don't have a windage tray. I run an older style DSS main girdle with the front sump Milodon pan. No room for a tray with the combo of girdle and stroker crank. Had to grind a little on the girdle to get the pan on.

Later,