Re: 35 Lightning vs. 35 Executioner
 

I don't completly follow this, other than the fact that Mercury does state, as a disclaimer in a sense, that horsepower can vary on their productuction engines in the real world. They do not dyno check/tune every engine. That said, how would you figure that my particuliar 500's would be on the plus side of the range? Never came out of my mouth, my engines have never been run on a dyno. My assumption would honestly be that they would be average/the norm, in that my boat runs the speeds that the average/ normal 35 with 500's runs, no better, no worse, they all run 80 +/- the normal 1-2 based on real world variations on any given day. I don't understand you claining that mine are at the top of the heap, if that were true then my 35 would be faster than others out there, you claim the best it ran was 81.7 on your GPS, right there with all the rest.

Now, and correct me here if I'm off on anything. Prior to starting your "project" you did run one of the stock 500's on a dyno, and if I remember correctly, it was pretty much normal in terms of what Merc claims. You also had the benefit of a fair amount of test time on the same dyno after the engines were completed. Being able to test with dyno headers, the Gills, and the CMi's, see where they made their horsepower, and know exactly what effect every change had on the engines. You are fortunate to have a friend that not only has the equiptment, but was also willing to work with you on all the testing. I see the narrow the gap attempt here, but I haven't changed anything. My set up is the constant here. Before your project, after your project, nothing has changed.

One more thought here. Assuming that there is truth in the claim, by others - not me, that on average one needs to add 20 hp per side in a twin engine performance boat to gain 1 mph, your going from 77( + -) to your stated best of 87.8mph, calling that plus 10mph, would require an additional 200 hp per side, my math. Now in reality some of your speed gain may have come from the fact that you now turn the engines at a few hundred rpm more than before and some may be due to work on the props. Lets for this example, not spliting hairs here, say you gained 10mph. Lets assume 2 - 3 of the 10 is attributed to the rpm gain and the prop tweak, that leaves 7 -8 to credit to the horsepower. At 20 hp per side, per mph gained, you would need 140 - 160 hp per side to get there. You can push these numbers around a little any way you want, a little more mph to the rpm, a little less to the horse power, the props helped less, split the hairs if we like, but it's not going to change the thinking that much. Just where am I so out to lunch here in stating you added 300 hp ?

Re: 35 Lightning vs. 35 Executioner
 

Again, I don't think you taught me anything that I didn't know before the season began.

Re: 35 Lightning vs. 35 Executioner
 

It is MY understanding that they DO dyno run all Blue motors! I think I saw it on Powerboat TV here on OSO!

I make 630 + - with everything and the CMI's. The boat speed supports that number as well. The comparison was the difference from your 550 (which I could be wrong, but I thought you had assummed that was what you were making!)to my 630hp, hence 80hp per side difference. But, after further review, You would need to run 5300 rpms with a 6% prop slip (26 pitch prop) and 1020 shaft horsepower at 7600 lbs. to run 81.7 mph in your boat. The difference then being 240 additional hp on my 9600lb. boat running a 29.1 pitch prop at 5500 rpms with a 15% slip to run 87.8 mph.


240 horsepower 120 per side. Proven by REAL testing not bench racing. If I knock off the 2000 lbs. from the Formula, it should run 99mph! Knock the horsepower back to 1020 and the weight back to 7600 lbs and the boat should run 89 mph. That is apples to apples. Are we done now?

Dave

Re: 35 Lightning vs. 35 Executioner
 

1) Maybe something new, don't think that was the case years ago, in any case I have no clue what mine make. All I can assume is that they are normal based on all the boats like mine out there with the stock 500's.


2) The only speed formula I've ever played with works like this:
RPM divided by gear ratio, multiplied by prop pitch, divided by 1056 equals theoretical speed, apply slip factor for real speed.


3) In my case @ 5300, 1.50 gears, 26 pitch (Hydros here) the theoretical speed = 86.994 mph, multiply by .94, your 6% slip, and you end up at 81.775 mph. Now I am not sure exactly what my slip factor is but 6% works, at least on one of those real good days. Using 10% makes it 78.295 mph, probably one of those not so good days. This formula does not input weight or horsepower, other than the relationship of it to the ability to turn a given pitch to a given rpm. So I agree that I likely make 500 hp per side to push my 7600 lb, apparently very efficient, hull to the speed your GPS says it runs. Make sense to me.

4) You have lost me here.

Re: 35 Lightning vs. 35 Executioner
 

Looks like this bench theory method works out prety close also.

Re: 35 Lightning vs. 35 Executioner
 

Speed
http://go-fast.com/boat_speed_predictions.htm


Prop slip
http://go-fast.com/Prop_Slip_Calculator.htm

Put away the paper and pencil. New school...like GPS.

Dave

Re: 35 Lightning vs. 35 Executioner
 

you 2 need to start a race team :drink:

Yes, Merc dyno's all blue motors and tears them down if not at 540-530.

Re: 35 Lightning vs. 35 Executioner
 

Neat toy, I've played with it before. And if you look at the prop slip calculator, at the top, the formula get the theoretical speed is exactly the same mathematical formula I stated. I use my pencil, actualy a calculator, to get there vs you and the computer program. Yours is much quicker.

I plugged your stats into the slip calculator, 1.5's/29.1/5600 and in theory you run 103 mph. Now, thanks to technology, we know you run a real GPS verified speed of 87.8 mph. Then I took the real info we know here over to your boat speed calculator. Put in the 9600 lbs, left the horsepower blank, selected the constant of 225 in that we know you are at 15% slip, I assume that is correct, and asked it to calculate the HP. It says 1458 total. It's your toy, I"m still working with a pencil here.

Now we know thru the miracle of modern technology, your GPS, that the best my old girl could muster this summer was 81.7 mph. The theoretical speed on the old girl is 87, she realiy runs 81.7, you verified that for me, so my slip is 6%. Take the known info over to the speed calculator, and plug it in. 7600 lbs, skip the horsepower, use the 275 constant based on the 6% slip, plug in the verified 81.7 speed, and let the computer tell us what I've got. Wow 671 hp, chit, thats total, divide by 2 and the HP's are 335.5's. Do the same using the Fast V constant and they are 406's. Now plug in 7600, 1000, 275 for the constant based on the slip calculator 6% figure, and presto, the old girl runs 100 mph. But your GPS only said 81.7, what's up here. Maybe the GPS is off, I run 100 and you run 105 and you make almost 2100 hp according to your computer. Explain what's wrong here. Looks like my pencil derived statements are closer to the real world than the computer.

Re: 35 Lightning vs. 35 Executioner
 

You have to figure the constant on what you already know FIRST. I took the info from both sets of props at different rpms and speeds to average the constant (241). This is the number that should be calculated based on factual numbers. Then the other numbers can be changed for additional results. You also have to know your slip percentages and exact pitch of your props (facts) to calcuate it correctly. Thanks to Brett Anderson at BBlades, I know the exact pitch and slipage at all rpms.

Dave

Re: 35 Lightning vs. 35 Executioner
 

We would if we could figure out which hull is faster. I'm thinking his 2100 hp in my 94% effecient hull, now that would be a Cat Killer. We could be Pu$$y Lickin' Motorsports, that would make us the speedy Pu$$y Lickers, our moto could be "We've never met a pu$$y we couldn't lick". Sound like a plan Axa ?

I assume this would be on the newer 525"s, do you know if that was the case with the 500's back in 1999 or so ?