15 400R news

[Revolution141]

Here's why I say the DBR 300XS has more power at higher rpm than the stock 300XS. My 21 Trick with stock 300XS went a best of 106 at 6,100 w/ a 32 pitch Blaster and a best of 102 at 6,300 w/ a 30 pitch Blaster. This proves the motor was making more power closer to 6,000 than 6,500, or it would have spun the 30 up higher. Yet on my 28 w/ the DBR modded XSs, it is faster when propped to run at 6,500. I understand what you're saying, and I agree with you to an extent - but owning both stock and modded XSs and seeing the difference in the best rpm/top speed combinations leads me to believe that the DBR mods help the XS continue to make more hp past where the stock ones do.

I respect what your saying. I did however ask this very question to Dave when he first came out with the upgrades. He told me that regardless of power increase and raised limiters they still make peak power at the same rpm as standard. I'm just quoting his words to me.

[skaterjim]

might not agree with that 100%, low drag hulls will always go faster when propped past peak power
Its how long it carry's that power after peak and how fast it drops is the issue/skill in the engine design

powerabout, Dale my peak power is at 6400 but I rev to 6950 (for my best top speed) i tried proping with bigger diameter and raising engine higher, i reduced slip, rpm went down slightly below peak and lost about 4-5 mph. at 6950 rpm i am down over 20 hp but the boat carries past peak. fyi my limiters are at 7500 just cant pull it. need more power and raise peak power

[racer]

Thats a lot of weight change for 5 inches of mid section, I would think they are changing other components as well to save 60 plus pounds for 5 inches of mid. I do think it would run well on one of our 224s that we built.

[RBT]

It is called over rev, the ability to pull past peak power.

[sunshine patty]

just wait the 450 is already running in testing and should also follow soon

[WILDMAN]

Peak power on a 300xs is at 5750 rpm and is 307-308hp at the propshaft. This is according to Mercury.

[Markus]

low drag hulls will always go faster when propped past peak power

Why??

[olboatman]

Why??

Markus I would think that would be because speed is directly related to prop rpm and pitch. Gary

[powerabout]

They dont need a continuing increasing torque to go faster, they need a secong gear

[Markus]

Markus I would think that would be because speed is directly related to prop rpm and pitch. Gary

Well, then you would increase pitch...

[Markus]

They dont need a continuing increasing torque to go faster

Peak power is usually way beyond peak torque, which means that torque is decreasing, not increasing.

[olboatman]

Well, then you would increase pitch...

But if you keep pitch down you wouldn't loose acceleration and still gain speed with more rpm. Gary

[powerabout]

=Markus;2735694]Peak power is usually way beyond peak torque, which meansitthat torque is decreasing, not increasing.[/QUOTE]
Essentially thats what I said, the hull needs very little torque to push it, so a few more rpm/hp and it will go a bit faster.
Not going to happen on a v bottom.

[Markus]

Essentially thats what I said, the hull needs very little torque to push it, so a few more rpm/hp and it will go a bit faster.
Not going to happen on a v bottom.

Got it - you meant prop it above peak torque, not above peak power. Now I understand.

[powerabout]

Got it - you meant prop it above peak torque, not above peak power. Now I understand.

No I do mean after peak power
you must see those argo cats up your way with the SSt120 powerhead ( forgot what they call them over there)
look at the revs they run those to, way past peak power.
SST120 in the USA they are getting toward 9k, saying that that's circuit racing so I guess you need to compare with a kilo record and see what revs they ran at.
So torque peak long gone and horsepower as well.