496 Dyno testing and myth busting!
 

Results are in. I’ve finally completed some comprehensive dyno testing of a 496HO and various exhaust systems. It’s rather lengthy so I published it on our web site. Please check it out. I spent all the time and effort for you guys. Go to www.fullthrottlemarine.com and click on high performance projects.

Bob

EXCELLENT info!!!

high performance projects.? can't find it ?

Underneath WHIPPLE SUPERCHARGER LINK..


Undertaker

Good info by the way:D:D

Thanks Bob for taking the time on this. Can't wait for the Raylar data!

That was great info....thanks for posting!

Very nice. Much appreciated.

Love this sort of stuff. Very well done, and you accounted for some interesting variables.

Bob,

This is great testing! I'm really glad to see you running the full wet exhaust, because, as you mentioned, I think it really does skew the results running dry exhaust. Members have reported that going to dry exhaust has given them performance gains (along with huge noise gains).:D

I'm looking forward to more tests!

Michael

Good notations & testing procedures.. :) J

.

those of us waiting for dana marine exhuast
 

Full throttle marine, very awesome, this is exactly what ive been waiting for, i was very curious as to what the truth was and the fact and fiction of the dana exhaust. the 48HP sounded to good to be true, but i did order a set, or atleast put my name on the list, but now im not sure if $2400 is worth 21HP.. can someone shed some light on this? dont get me wrong they do look awesome and will shed some light.. are they better than CMI's? also im curious with this exhaust will a prop change be needed?

Bob, thanks for taking the time to do this right. Very professional and straight forward.

Nice work, Bob. Good read. One question, to date have you heard of any problems encountered after removing the turbulators on the stock exhaust?

I've not heard of any problems. Obviously Merc puts them there for a reason. Removing them increases the chances for moisture to work it's way back up the exhaust at idle.

Well....that sucks. Its true, aftermarket exhaust isnt worth the thousands of dollars they charge when used on its own. Two mph is great and all, but not for $2400.

I wish I had a set of CMI's to test, but I didn't. I personally believe the Dana's are as good as anything on the market, better than most. The lightnings I used are a very nice full tubular true header. I was surprised the Dana's outperformed them. That speaks well for them. Fact is there are no magic products out there. Eveything works together as a package.

Some boats will respond much better than others with the additional HP. Might be that the additional HP will push the hull to a more efficient ride or raise the RPM enough to get it higher in the power curve.

Here's an example: suppose your boat is turning 4700 RPM at WOT now. You add a set of headers and pick up 300 RPM and 4-5 MPH. You think wow, the headers really made a difference. However what really happened is that the headers added enough power to gain maybe 150 RPM which moved the engine up in the power band to where it generated an extra 15 HP so it moved further up the power band gaining even more HP. The headers only accounted for part of that gain. Had you worked the prop to have it peak at 5000 RPM you would have gotten some of that gain. I believe this is one of the reasons some people see more gain than others from adding headers.

Bob:

Very interesting results, especialy the effects of water in the exhaust and the loss of power through the Bravo drive. As for the exhaust results I can say that all ofour dyno testing was done dry because our facility is not able to run a wet test with our quieting system. I sure would like to see you prop shaft test a Mercury HP525 at the prop with the XR drive. Even though peak power seems to occur in these motors at about 13.6 A/F I dont think I would set up a boat to run there over extended periods. I think I would error on the side of cautiion for long term reliability and set the A/F closer to 13.0-13.2. I love the 87 versus 91 Octane comparison. confirms what I've been preaching for a long time, Higher Octane does not make more horsepower. It only needs to be higher to counter knock if it occurs. Keep up the great testing!

Best Regards,

Ray @ Raylar

Bob -

I wish you would have asked. I'm sure we could have sent you a set of CMI's to test with, although you'd probably want to keep them after you saw the results :drink:

Seriously, nice job with the testing.

Kirk

Great post Bob. Very nicely worded. Great info as well!

What about the intake side of the motor? Any replacement parts or mods that arent real expensive and are direct bolt ons? Of course paired with the exhaust.

Great testing and control of the variables. Would be nice to see the dyno difference between stock and Dana exhaust after the Rayler upgrade is performed :cool:

I'll be testing it.

Kirk, I'll be retesting after the Raylar kit next week. If you have a set that I could test with I'd be happy to do so. I could run stock, Dana, Lightning and CMI back to back. I'd certainly be willing to do it.

Great job. Finally doing what Powerboat and HotBoat rags should have been doing all these years. Oh yeah can't piss off the advertisments with truth about their product. I'll just subscribe to your thread.

Just as an FYI, so we're comparing apples to apples. I just spoke to Tyler Crockett. The CMI test that he conducted was run with no water mixing with the exhaust just as Dana tested theirs. There is no doubt in my mind that when you mix water in with the exhaust that it changes the performance of the exhaust system significantly.

Fantastic research project! If the opportunity ever presents itself, I'd like to know what the torque curve looks like with the K&N filter you show in the picture vs. the stock flame arrestor. Also, I switched from a Bravo X to a Bravo XR drive and would love to know how much more horsepower, as a percentage, it is absorbing.

disapearing 496s
 

It is a shame that GM is moving away from the 496. I suppose that there are more reasons than meet the eye for the decision but profitability at GM drives decisions and, unfortunately, marine considerations are probably not in the equation when fighting Toyota.

I been told by a boat manufacturer that Mercury has been pleasantly surprised by the success of the 496 and just when the folks who know how to make them run get fine tuning locked in it looks like the motor is going away eventually, probably sooner rather than later.

My feeling is that "bobl", Raylar and others will always find a means to get the appropriate HP and torque from what ever is out there to help satisfy our need to tear up drives. Thanks guys. Quent

What are they going to replace it with?

Bob,

Great information with interesting results. I am a bit confused at one thing. You said..

"One last Myth to bust. How much horsepower does a Bravo drive absorb? For those of you that are observant, you’re probably ahead of me. It’s certainly not 25 or 30 HP like many have come to believe. It is a percentage. In this case with a Bravo X drive, right at 10%. I’ve done testing on 600 HP engines and lost 60+ HP to the drive."

I am certainly not doubting your claim to this, but how can a drive absorb more hp at a given rpm, with the only variable being a more powerful engine? Wouldnt a drive require the same hp at 5000 rpm regardless of what is turning it? I can see the additional horsepower turning the drive to a higher rpm, thus requiring more horsepower to turn it. I dont understand that a drive absorbs power on a percentage scale.

Vinny

The load on the drive must increase to hold an engine at 5000 RPM. How 'bout this example. You run a 17 pitch prop and turn the engine up to 5000 RPM. Now switch to a 30 pitch prop and spin the engine up to 5000 RPM. Obviously it takes much more torque to spin a 30 to 5000.The 30 pitch prop is trying it's darndest to keep the engine from achieving that RPM. The entire load is being absorbed by the drive. Does it make sense that the friction created by the gears would be much greater in the second scenario than the first? This increased friction is what would be costing the more HP. If you put the boat in the water without a prop and pushed the throttle forward to achieve 5000 RPM, how much HP is the drive using now? In the case of the dyno I program what RPM to hold the engine to. If I say 5000, it keeps adding load as the power increases to maintain that RPM. The drive would be absorbing every bit of that power.

In the case of the stock 496 we went from 431 HP at the crankshaft to 387 at the prop. That's 44 HP, or roughly 10%. I recently dyno'd a supercharged small block. It made 555 HP at the crankshaft. I took the engine straight off the dyno and put it in the boat. I redyno'd it at the propshaft. This was with a standard Bravo drive, not an X. It made 490 at the prop. There were some gibson mufflers on the boat that probably added a small amount of loss, which may be why we were showing over 11% loss in this example. Hope this helps.

Bob

Vinny, there is no surprise here. The drive is nothing more than a odd shaped transmission, and transmission and rear axles in cars also behave this way (percentage of load). Think of the gear teeth dragging across each other. Put more load on the gears, and the more drag there is. Now, of course, this can change a bit at super light loads, where the viscous drag just moving the gears through the oil becomes a larger percentage of the loss, but in most operating conditions, loss is a percentage of horsepower.

Michael

What was the Torque loss thru the bravo drive? is that constant with rpm? Do you have any curves showing HP and TQ with stock and with Dana exhaust?

All the dyno sheets are posted on my web site.

Okay, so now that we know the Bravo's scrub 10% off the ponies, what can we do to lessen that.....There in lies the question of inquiring minds...Synthetic oil? Lower weight oil? Dialing in the toe/heel adjustment on twins?

Great job man...I can't wait for more test!!!!

Bob,

I know you talked about this when we did mine, what the bravo really eats. We dyno'd mine at 509hp at the prop (and i was a little disappointed) but going on the 383 buildup (555hp/490pshp) That would put mine over 560hp. I just wish i had the dyno sheets for the higher hp :D :D

Thought I would bust another myth here in this thread since it was mentioned. GM has no current plans to drop the 496 8.1L engine for the Marine or other non light truck uses. That information comes straight from officals at GM Powertrain who build and supply this engine. Thought I would stop that rumor before it goes any further. I hope the CMI's get to you in time to finish a complete comparison.

Best Regards,

Ray @ Raylar

Awesome, I was hoping that was a rumor!

I removed the turbulator rings when I polished the elbow. I heard they were more for condensation in colder climates. I live in Florida where there is supposedly less of a risk. It's about a year so far.