weights of drive oil vs speed of boat
 

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

Re: weights of drive oil vs speed of boat
 

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

Re: weights of drive oil vs speed of boat
 

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

Re: weights of drive oil vs speed of boat
 

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?

Re: weights of drive oil vs speed of boat
 

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

Re: weights of drive oil vs speed of boat
 

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

Re: weights of drive oil vs speed of boat
 

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

Re: weights of drive oil vs speed of boat
 

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.

Re: weights of drive oil vs speed of boat
 

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

Re: weights of drive oil vs speed of boat
 

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!

Re: weights of drive oil vs speed of boat
 

bcarpman,
I dont really think you can over cool the drive oil. Well lets say you boat in a warm climate. The drive oil will heat up when the motor is started, how much is the question. The viscosity of the oil will allow it to lubricate sufficently when cold.. not ice cold.. on start up. From there I believe the oil heats up as it moved around by the gears. If you have ever put your hand on drive after a hard pass, you will feel heat. More cooling is better in my opinion, and i dont believe you can over do it. Of course if you boat in water with ice burgs, then make sure you run hard all the time to keep that drive temp up!! :D

Dick

Re: weights of drive oil vs speed of boat
 

I like everyones opinions and answers so far. Heres a brief summary of what I have done and seen this season. In June I ran boat 3 different times, BEFORE installing ext box,with royal purple 75/90 gear oil,boat ran mid 89's w/30 pitch at 5900 touching rev limiter a few times at 6000,with 700 lbs of passengers in boat,50-70 gallons of fuel (it pretty much will always go this fast regardless of how good the air is,i think because its innercooled).Ran 92.8 w/32 pitch last fall with 500lbs of passengers and 30-40 gallons of fuel,it will only pull 32 pitch better than 30 if running that light,other wise it just lugs harder and runs about 89-90 w/32.Nothing was done over the winter to boat what so ever. So my baseline is boat will run mid 89's loaded down in pretty much any air temp w/30 pitch (has done this countless times) and run 90-92.8 w/32 pitch depending on load.
I installed a stellings ext box in late june moving drive back 1 foot and up 1 inch.I also started experimenting with various treatments to my lower gears to try to make them last longer. I also started using royal purple 75/140 synthetic gear oil to cushion the gears and try to eliminate gear damage from oil possibly being too thin. After these changes boat would only run 86-87 mph with heavy load w/30 pitch and high 88's to low 89's lightly loaded,ran 88-89.9 mph lightly loaded w/32 pitch,lugging motor bad,never broke into the 90's.The box also created all kinds of handling and driving issues's (porpoising,cavitation,blow out,felt bow heavy. I then added a 1" drive spacer,got rid of 80% of the problems ext box created but slowed boat down even further.boat then ran 85-86 w/30 pitch w/heavy load,87.5 with light load. Tried 32 pitch,would barely hit 85 mph,even lightly loaded. In between all this I rebuilt lower several times as gears would start to fail,I also changed outdrive oil countless times always filling it with 75/140 so as not to skew my results with lower gear longevity.
A few weeks ago I tried a 5 blade prop with and without the drive spacer,boat went slower yet AND sheared off the prop shaft from the extra load. When I pulled the drive apart to fix it I found the lower gears had virtually no accelerated wear and that my current gear treatment is actually working. I reassembled the drive with a spare prop shaft I have and filled it with 75/90 royal purple this tiime,I went to the lighter oil to see if gears would still hold up with thinner oil AND to see if boat would go any faster.I also left 1" spacer out as it only slowed the boat down.The boat with this same exact setup other than thicker outdrive oil would only ran a best of 89.9 when lightly loaded,usually closer to 89 after several runs. Took boat out yesterday,500 lbs of passengers,30-40 gallons of gas,ran 92.5 mph on first pass and 91.8 to 92.2 on subsequent passes,boat seems to have picked up 3 mph from gear oil change. There is no way the oil could have been using a extra 40 to 60 hp but believe me,I have not been able to get this boat back into the 90's all summer and I have tried! The only other change is my spare prop shaft is slightly bigger as it is a xr style.All the nasty handling quirks from running the ext box were back too of course so its coming off this winter.The obvious scientific thing to do would be to drain the oil out,put heavier oil back in and make some more runs but I ran boat up and down the river 40 miles after the high speed test to run the gas out of it for the season and I am now hearing a louder than normal clatter or ticking from the valve train or lifters so I'm not going to try to resolve it with motor still in the boat before freshening the motor this winter because it would be a waste of time when motors going to be out anyways. What do you guys think,Smitty

Re: weights of drive oil vs speed of boat
 

Wow :D

Re: weights of drive oil vs speed of boat
 

Boat pulled 200-300more rpm's than it has been with 32 pitch too. It has to be a combination of the gear oil being thinner and water being 5 degrees cooler. ambient air temp was mid 70's yesterday,it was 58 a few times when testing this summer so I don't feel it was the air,Smitty

Re: weights of drive oil vs speed of boat
 

My thoughts too.

Thanks for sharing all your info Professor Smitty ! :D

Anybody ever use that climbing gear lube stuff in race car rear-ends ? It killed some power on a few of our cars. You ever touch it ? Feels and sticks to you like some major league boogers. :eek: :D :D LOL.

Re: weights of drive oil vs speed of boat
 

I can tell you that when you spin the prop at ambient temp w/the 140 compared to 90 wt it definately feels stiffer. I just can't picture it being more than a 10 hp dif though to the prop,I am perplexed,Smitty

Re: weights of drive oil vs speed of boat
 

Scott,how much did the climbing gear lube slow you dow? I ran the 69 gto I work on and race for a friend of mine last weekend and picked up a solid tenth over previous runs from lightening the rear brakes 25 lbs (he had humungous truck drum and backing plates on it). We run 75/140 in it and I want to try 75/90 this weekend if it doesn't rain but the owner is worried it will tear up the ring gear. If there is another tenth to be had then I'm going to do it. You know,I should just do it and not tell him :evilb: ,if it beats the gears up after a few trips to the strip I'll just buy him some new gears,Smitty

Re: weights of drive oil vs speed of boat
 

Drag cars usually don't build much rear end gear oil heat, so stay on the lighter side with good synthetic. Maybe shockproof light if your worried.

Speaking of oils...Engine - hyd flat tappet ?solid FT ? Hyd roller ? Where do you shift at ? What spring psi ? What rocker ratio ?

Speaking of rear drums brakes - you have those backed off right ?

Re: weights of drive oil vs speed of boat
 

Scott,the motor in gto is a .030 over pontiac 400,aluminum rods,nodular crank,ported iron heads,ultradyne solid lifter cam,stock ratio harland sharp roller rockers,shift at 6800,pulls traps at 7200 rpms,513 gear with spool. Took truck drums off it and put some car drums on it last week before going to the track. Car picked up a solid tenth plus,ran into the almost mid 11.60's on several passes. Going to try a 4.88 gear and see if car picks up any more speed,its reving a tiny bit past power band now,Smitty

Re: weights of drive oil vs speed of boat
 

A noise in your engine? Maybe that is where the speed went when you tried the ext. box. Great info. Good luck.

Re: weights of drive oil vs speed of boat
 

Leave the box on and run my dyno and see.

Re: weights of drive oil vs speed of boat
 

I did some changes this summer...-2" IMCO shorties, 5-bladed XP5 and switched drive lubes this year from the Redline Shockproof Heavy to the 75/90 Amsoil gear lube. Just thought I'd give the lighter gear lube a try and wanted to use Amsoil.

With all the changes this year the gear lube and the 5-blade 30" props were the last things I changed. When switching from some 5-bladed 28" props to some 5-bladed 30" props I expected to lose at least 200rpm---and was told that I could even lose up to 400rpm, but the engines stayed right at 5600rpm---so, I gained some speed as well. Slightly cooler temps may have contributed to it as well, but I think the lighter weight 75/90 drive lube had something to do with it. That Redline Shockproof Heavy is some really sticky stuff. Some guys I know jokingly refer to it as "grease". :eek:

Re: weights of drive oil vs speed of boat
 

We run M-1 75-90 in our dirt track UMP modifieds, putting around 750hp through 9" ford rear ends for up to 40 laps at a time. No gear or bearing failures yet.

Re: weights of drive oil vs speed of boat
 

The ticking/clattering just started the other day a hour AFTER making the high speed runs as I was running the gas out of the motor going up and down the river so it wasn't slowing me down this season. It is something in the valve train,the motor has a tiny bit over 100 hours on it,50 of them this season,I'm just not going to try to fix it in the boat since I am freshening the motor this winter anyways and our season is over. With the 1 inch spacer out with the box on the boat still exhibited the the terrible handling effects the box created,I just drove thru them to make these high speed passes. The boat still only drove as fast or slightly slower than it did before the box so it didn't give me any speed. Boxes don't work on every v-hull and I have found out thru alot of testing and work my boat is one of them,Smitty