bobl

The P/S pump probably accounted for 5 maybe 10 HP. I believe the drive losses are greater than what people thnik. The more power/rpm the more the loss, more of a percentage than a linear amount. It's possible the mufflers are costing a few HP, but that's the best I can offer at this point in time. I've tested 3-4 engines at the prop and the power was a good 50-60 HP less than what they should have been making at the flywheel. But, I didn't have the opportunity to put them on the engine dyno. I've got a couple of projects this winter that I should be able to do more comparisons. I'll keep everyone posted.

Falcon

You have to be careful when comparing 2 "different" dynos. Both have their own calibrations and +/- percentage errors at different rpm points (electronic load cell dynos use filtering and averaging). When you use a different dyno for each one, you double the possible error factor. A dyno is a good comparison tool when using the same one, same conditions, etc. You also have to be keep in mind the drive load isn't completely the same, no propshaft thrust load, and the temp of the drive cases and oil are not the same either.
A majority of the losses in the drive are from windage and normal bearing friction which will change with rpm. Since windage losses generally increase with rpm, torque loss will go up with rpm, so a drives hp loss at 5200rpm will not be the same at 5800 rpm with the same engine hp at each. The higher rpm engine will have substantially more hp loss through the drive (more torque loss and more rpm), if the drive ratio doesn't change. Also, if using manual calculations, make sure the proper rpms are used for the propshaft if measuring propshaft torque. If you are using engine rpm and calculating propshaft rpm, even a small error (1.50 vs 1.49 ratio) can affect the hp numbers when trying to do this type of comparison.

Strip Poker 388

iTrader: (6)

Falcon glad to see you back

I would think that outdrive oil temp and weight oil would have a effect on it.

Escape Velocity

BOBL,

This is great information. Not many people have the ability to perform crankshaft/propshaft side by side comparisons using the same dyno. Also, I appreciate you sharing your experience with the Gibson mufflers. I have them on my boat and have always wondered what real-world losses are.

What gear lube was in the drive? I use Merc's Hi Performance but used Alisyn in the past, that allowed the prop to spin much easier. Also, I'm running a Bravo XR and wondered if you have experience measuring one of these. I've been told its losses are greater than the Bravo X.

bobl

Falcon, keep in mind this test was with the same dyno, same location. I mount the absorber on the prop shaft or engine stand, whichever I'm testing.

Escape, the drive had Merc lube. I've not tested an XR but will the first oportunity I get.

Strip Poker 388

iTrader: (6)

Bobl it would be nice to make a adaptor to insert in to the back of the motor like a engine alinment tool that would hook up to your Dyno,Then do a back to back test with the drive vs no drive

Rage

Strip Poker,

Your wish has already been granted. That in fact is the exact setup that BobL uses because that is the the way his dynamometer was designed to begin with. Dual purpose. The same identical torque transducer/water brake either attaches to the motor crank or the prop shaft and the computer does the rest.

bobl

I think what Strip is trying to say is a method to test the flywheel hp IN THE BOAT. Then you could tell exactly what the drive was costing. I believe the exaust routing in some boats (like Rage's Nordic) costs more power since it makes 2 sharp turns after the water mixes with the exhaust.

Falcon

It sounds like it's a good setup. I think the biggest challenge would be to prove the accuracy of the dyno at 2 different torque/rpm points. Dyno accuracy varies slightly at different rpm's and torque numbers because of filtering of the load cell. If you would look at the raw output of the electronic signal it would be varying with every cylinder pulse and vibration, they try to filter and average this out. This is still interesting and would be a good tool if you were trying to compare different drives and/or changes to them (gear lube, oil level, temp) as long as you kept all of the variables withing reason. Also, how close is this to the max torque rating of the dyno (raw torque at the propshaft is probably over 750 ft.lbs)?
Exhaust silencing on a naturally aspirated engine will almost always have some negative effect, but on a boosted engine can be less of a problem.
It will be interesting to hear more results and see how consistent the numbers are.

Strip Poker 388

iTrader: (6)

yeap. if there was some way to make a shaft that went thru the gimble ring bolting up where the out drive bolts up? may be more touble than its worth.The info is still fun to tickle the brain