If a boat went 89-90 mph,lets say a average of 89.5 during various runs with 900 plus hp with 75/140 synthetic gear oil in a bravo drive how much faster does everyone think the same exact boat under same conditions would go with same brand 75/90 synthetic gear oil? For sake of argument lets assume drive is good (200-250 degrees) and hot so oil is thinned out pretty good,Smitty

Smitty,

If I remeber you correctly you have & go thru drives periodically & even bought a gear set from me at one time..

It can make a slight bit of difference. My opinion is to not change unless you are looking to get just a tiny bit more speed out of it.. Id dont see you gaining even 3-5 mph out of it... Maybe 0.5 to 1 mph would be my guess.. If you were looking to race & win, not play it safe look into it. Otherwise I'd leave it alone.. Again just my opinion.. Jamie / Lakeside

Jamie,thanks for your input. Any other input from anyone,based on opinion or experience? Smitty

How about if you add a shower to a drive and it overcools the oil? Is that ever a problem? Where and how would you measure this?

No problem.. AS far as monitoring the drive temp, I believe I can order a Livorsi drive temp sender & gauge.. jamie / Lakeside

I ran redline heavy shockproof for a season, ran the boat about noon one day pulled it and switched to M-1 75-90 put boat back in water and saw 100rpm difference. I have made 2 changes with the M-1 since.

The Redline was messy and took all night to drain. Awesome gear lube though

Do you know what weight the redline shockproof is when hot-ie-90,140,etc? Smitty

the total additional drag added by virue ofthe viscosity of 4 qts of oil in two drives compared to that of the totality of the aero and hydro of the boat would be in the 6 decimal point range...not non existant but roughly equivilent to you eating lunch before you went out or not.... remember... 1 hp is 745 watts....1/2 a toaster at full heat... you need HUNDREDS of hp more to go only a little bit faster at top speed.... so think of what that equates to in heat energy... do you REALLY think you are making another 50or so hp ... 35 THOUSAND watts of heat energy by changing viscosity by 25 % MAYBE ? nope... sorry....

the engines are different... on a 500 hp big block, thin oil at 220 deg will free up another 20 hp over cold thicker oil... pumping losses and windage... thats one reason why dry sump makes so much sense. get that oil out of the pan... for the drives you use the very very best LUBRICANT you can... the viscosity is a meaningless loss.

http://www.redlineoil.com/products_g...6&categoryID=6

they claim it performs like an 80/140 but with a film strength of greater than a 250

do the spin test, take your hand and spin the prop and see how many turs you can get with each one, i did the same thing and saw a big diff!