I've ran both straight 50, and 20w50 in my engines , my distributor gears looked great when I had it out last winter. I am running the melonized gears, my cams have iron gears. And I have lots of oil psi. Cold oil getting on plane (engines rev to about 4k getting on plane), Im at just under 100psi oil pressure. Once things warm up they are at 75psi running with straight 50.

I'm getting close to the same oil pressure as Joe. 90 cold and 70 at temp, I took a picture of my gear, there is the slightest signs of wear on the lower portion of the tooth. I've had a distributor gear go out on me in the past, so I like to keep an eye on them. I know last summer this gear looked like new. Like others on here I run the GM melonized gear. When I was buying cams from Marine Kenetics, I asked Bob if I should be running a bronze gear. He said with an Iron gear on the cam, I should run the melonized distributor gear.

Somewhere on here there is a post about the HP loss using 50 wt oil, they did back to back dyno runs 50 wt vs 40 wt.. If I'm remembering correctly it was around 10-15 hp loss with the 50 wt. Again, I know I also had this discussion with Bob and he also said to NOT to run 50 weight. Said it it was hard on the distributor gear and you would have measurable HP losses. I know I'm done running 50 wt oil.

Ive never tried comparing the oils on the dyno. The builders on speedtalk claim the opposite, that with hydraulic lifter builds making good power, they almost always find the heavier oil makes more power on the dyno. Who knows what lifters they were running , i can see that making a difference.

Pouring the oil, i can def tell a big difference pouring a 20w50 full synthetic, and a straight 50 conventional.

I w as running 20w50 full synthetic, and running pressures were about the same as the straight 50, but the idle psi hot was lower with the syn 20w50. This year i may go back to syn 20w50. Sucks cuz can usually find the straight 50 for 4 bucks a qt at the farm store on sale, about half the cost of a full syn. 22 qts times 5 bucks a quart, over 100 bucks more to run syn. I change it no matter what about about 10 hours anyway. I believe fresh oil is the best oil

I like loose clearances so thick oil is a must...

Even Mercruiser Racing recommends their 25W-50 for their motors.
http://www.mercuryracing.com/vital-fluids/

http://www.mercuryracing.com/wp-cont...troke_gal2.png

what cam are you running?if it is a crane hyd roller it has a pressed on iron gear and uses a melonized gear.their website is confusing because the older hyd roller cams had a steel gear,that was ages ago before the days of melonized gears.

imo straight 50 oil is not the way to go.a good 20-50 like brad penn is a much better choice than straight 50 wt.is their a power loss from using a thicker oil?not much after the multi wt oil reaches 180 deg.back when i was drag racing i used 50 wt oil but i pre heated it to 160 deg before startup,50 wt oil does not flow well when it is cold.most boat engines using 20-50 would be fine with 10-40 or 15-40.imo the key is to let the oil warm up before running the engine hard.

if you buy a hyd roller cam from bob you also get a melonized dist gear with it,he always asks what dist your engine will be running,that is because there are three different dist shaft diameters and he wants to make sure he sends you the correct gear.

It is a Crane, 691 I believe, not sure what vintage...2004 or newer

what is the 6 digit number?