How Can 300 hp Outperform 425?

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airduds
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How Can 300 hp Outperform 425?

Post by airduds » Wed Jun 03, 2009 8:13 am

Another thread got me thinking and I decided to put those thoughts on paper.

I run a ZZ383 which from the GM Performance Parts website makes:

"...425 horsepower at an incredibly low 5400 RPM..."

Now here are couple of "caveats":

"...GM's testing was completed using a GM single plane intake, P/N 12496822 and a 750 CFM Demon carburetor with mechanical secondaries. Test header specs are: 1 3/4" primairies,33 inches long with a 4-inch collectors.

GM dual plane intake P/N 12366573 may be used for hood clearance on the ZZ383/425, but it results in a decrease in peak horsepower of approximately 15-20 horsepower...."

Now consider I turn my engine 5,000 rpm max, so looking at the dyno chart my engine would make maybe 400 hp.

Now consider my carb/intake/headers/ignition isn't perfectly optimized and tuned so maybe I make in the neighborhood of 380 hp (maybe).

Now consider I'm running a gearbox that eats another 20% of that and I'm down to 304 hp available to turn the prop.

Now consider the extra weight of my block and box and it's easy to see a healthy 300 hp a/c will do everything on my hull that my engine will; and those upstack/supercharged/turbocharged, ...etc. a/c that make 340 hp (maybe more) would outperform my engine on the same hull.
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Re: How Can 300 hp Outperform 425?

Post by hmgm123 » Wed Jun 03, 2009 8:35 am

Your not comparing apples to apples. A IGSO 480 or IGSO 540 is a totally different animal than your ZZ4. And they are probably heavier than your motor too. They also have alot more cubes and a blower to boot.



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Re: How Can 300 hp Outperform 425?

Post by goldhunter_2 » Wed Jun 03, 2009 9:35 am

don't get hung up on HP numbers think about the torque produced and the weight
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JOLLY ROGER
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Re: How Can 300 hp Outperform 425?

Post by JOLLY ROGER » Wed Jun 03, 2009 9:47 am

Everbody gets way to hung up on this HP numbers game. There is a lot of factors that go into making a boat performe. You can tell alot more about someones power by lookin at the prop there turning than any hp number they quote. Iv'e seen too many 4cly run the hill to get to tied up in HP numbers.
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Re: How Can 300 hp Outperform 425?

Post by CactusJack » Wed Jun 03, 2009 10:04 am

True guys, people believe more Hp is the answer to everything. IMO, when it comes to propellers (airplane/airboat/gyrocopter) it is all about THRUST. And power to weight.

Of course you need HP to begin with, but the right reduction, the right prop.... it all counts. If you have the wrong prop or ratio, no amount of Hp is going to make it perform better.

So a well set up motor with the right cam.... the right prop diameter and blade widths for the correct ratio reduction, can often beat the pants off a 600 Hp motor with bad setup, wrong prop or ratio.... and giving the motor even more horsies, wont matter a darn.

THRUST is our target..... a good set of scales is our friend, tie the scales to a tree, tie the other side of the scales to the boat..... measure the trust.... make modifications to increase THRUST, not just add power.

Get it all right, you will have a quick boat :wink:
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grant
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Re: How Can 300 hp Outperform 425?

Post by grant » Wed Jun 03, 2009 10:13 am

Thrust is only part of it....lots of thrust on a "turd" is still a "turd"!!
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Re: How Can 300 hp Outperform 425?

Post by John C » Wed Jun 03, 2009 2:56 pm

Good point Grant. IMO what makes for a good combo is what CJ said
CactusJack wrote:power to weight.
Power to weight ratio is everything. Lots of light boats out there running real good, and it ain't because they got lots of HP. Its because they are set up right. Take a good running boat and start loading stuff into it and run it. you will see real quick just how much weight cancels out HP.

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Re: How Can 300 hp Outperform 425?

Post by cont520 » Wed Jun 03, 2009 5:21 pm

iTS ALL ABOUT SETUP YOU CAN HAVE POWER TO WEIGHT AND WHAT NOT WITH ALL THE hp IN THE WORLD IF THE BOATS SETUP LIKE A RETARD IT WILL RUN LIKE A RETARD JMO
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Re: How Can 300 hp Outperform 425?

Post by CactusJack » Thu Jun 04, 2009 6:42 am

Grant & Cont, I meant over all set up has to be right..... but if you have a boat that is a turd, and you have the wrong ratio, prop.... it will be a slow turd.... you can add 300 Hp and it will still be a slow high horsepower turd :shock:

However, if your boat is a turd & you put on the right prop, ratio (get your engine setup right) it will be a really fast turd :lol:

My point is..... Hp is important, but it is only part of the equasion as a whole. The more thrust your power plant can provide is what counts. Like the OP asked, how can a 300 hp beat something much more powerful?

Say a 600 hp boat with the wrong prop, pitch, ratio makes 500lb of thrust & weighs in at 750kg.....and a 300 hp boat with a spot on setup makes 550lb of thrust & weighs in at only 500 kg..... I think you can guess which will be the winner :lol:

Don't JUST chase Hp....... chase TRUST output, IMO :wink:
I was told I was wrong, once (not sure I believe it though)
If you can't blind 'em with brilliance, baffle 'em with BS
Airboat experience so far, limited to having bolted a gyrocopter to a flat bottom punt.... but THAT.... is about to change, bigtime :-)

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Re: How Can 300 hp Outperform 425?

Post by cont520 » Thu Jun 04, 2009 6:54 am

Thats a solid opinion and a good answer still all boils down to set up free is fast
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airduds
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Re: How Can 300 hp Outperform 425?

Post by airduds » Thu Jun 04, 2009 7:10 am

I guess I didn't do a very good job of making my original point.

I was trying to say that even though GM says my motor makes 425 hp, in all likelihood I'm probably only getting around 300 to the prop - a little less than a healthy O-520.
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Re: How Can 300 hp Outperform 425?

Post by CactusJack » Thu Jun 04, 2009 7:54 am

Airduds.... cool, I would suggest you get yourself a big set of dial type scales & do some thrust testing..... play with your props pitch (or try other props, if you have mates that will let you try theirs) IMO, the prop is what 'puts the power to the ground' so to speak.... you need to find out what the prop is doing, performance wise. You might find your prop performance plateau's out at a certain rpm and actually could decline in performance as more throttle is applied. You cant guess what a prop is doing... some scales will reveal all.

If there is a bunch of folk (or club situation) I suggest you all pitch in (or the club forks out the $) for a decent set of scales and some 'tow straps' so you can all measure and tweek you boats performances.... so if you change something (even small) you can accurately determine if your 'fix' has fixed or fu...... not :lol:

Scales are your friend, IMO :wink:
I was told I was wrong, once (not sure I believe it though)
If you can't blind 'em with brilliance, baffle 'em with BS
Airboat experience so far, limited to having bolted a gyrocopter to a flat bottom punt.... but THAT.... is about to change, bigtime :-)

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Re: How Can 300 hp Outperform 425?

Post by CactusJack » Thu Jun 04, 2009 10:52 am

Airduds, I finally read & understood your question :oops: I know what you mean now.

Yes, your engine is supposed to make 425hp..... when they designed the motor, the one they tested and finished up with made around 425hp, so thats what they called it. Yours could be anywhere from 400 - 430hp, depending on whether the motor was made monday morning or friday afternoon ...... how much attention the folks on the assembly line payed to it, you can get exceptionally good engines out of the box, or rather mediocre ones... depends on luck. Also, when the auto factory rates an engine, it is on a dyno and the engine has the same exhaust system as the car it is expected to be put in, on it. So, depending on your exhaust and modifications you have made, only a dyno could tell you exactly, and the power/torque curves associated with it.

Ok, so the reduction gobbles 20-30Hp, water pump takes 4hp, alt takes 5-6hp etc & you end up with say, 330hp from a 'supposed' 425hp.... ok, fine.

Again I say, Thrust output is key. That leaves the prop & reduction ratio to gain the useage of that Hp available. IMO, the torque is most inportant to us (at least as important as overall Hp)

Say your max Hp is at 5,700 rpm & max torque is 4,800....

Then say your prop needs to turn max 2900 rpm.... you need to have the ratio that will get these 2 things happening at about the same time.... you don't have to worry about WOT being where everything happens, you might find WOT is actually not as efficient as planning to have the engine doing 5,700 and the prop turning at its best performance rpm. I have flown peoples gyrocopters, they complain they give it WOT and the thrust decreases..... OK, so dont use WOT, use the appropriate throttle setting instead. Easy, really.

So, if you have the motor, reduction & prop speed correct...... then it is up to pitch.... this is where the scales help out heaps. Props, god love 'em) are very inefficient and very temperamental beasts. You can loose or gain 100lbs of thrust with a half a degree or less! A prop blade is actually a wing.... wings make lift & drag.... the best you can hope for is as much lift as possible with an acceptable amount of drag as a trade off. That is why you cant just keep on adding pitch.... sooner or later the drag will be too great and the lift (thrust) will drop off.... this is why I say the thrust test (scales) are so important.

Ok, so your engine (425hp) is actually making only 330hp..... set up the prop correctly and you can use all of that 330hp and turn it into thrust. Get the prop setup wrong & you may end up only being able to benefeit from a percentage of that hp.

You may be 1/2 a degree away from perfection..... when you adjust your pitch, you may go too far and miss the sweet spot and think you must need more Hp..... The scales mate, the scales will tell you whats happening, without guessing. Change blade angle 1/4 of a degree at a time, yes it is time consuming and a pain in the butt, but in the end you will get every bit of thrust out of the Hp available.... you will be suprised :wink:
I was told I was wrong, once (not sure I believe it though)
If you can't blind 'em with brilliance, baffle 'em with BS
Airboat experience so far, limited to having bolted a gyrocopter to a flat bottom punt.... but THAT.... is about to change, bigtime :-)

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