Mbam

Tomcat, your plotting of the speed/hp is a good improvement on the calculator presently on my site. I wish there was an accurate (and inexpensive) way to measure the hull power requirements.

My calculator (Speed calculator) will do the HP calculation if you enter the weight, constant and speed, in fact it will solve for any one of the numbers if you supply the other 3. The way I find it most usefull is to find the constant for a given hull/setup combo. If you have good numbers for the weight, speed and power the resulting constant is very accurate. If you then make changes to one of the other variables I have found the resulting calculations are pretty close.

The hardest part is coming up with accurate numbers. It is good to use the uncorrected HP as this most likley represents the power you actually have while running.

[ 01-18-2002: Message edited by: Mbam ]

tomcat

Mbam - Thanks. Marc. I like the simplicity of the Mercury formulas, and I like being able to work backwards to get the constant for your own hull. For example, my old Excaliburcat has a constant of 264, halfway in between a fast vee and a cat.

You and I think alike, because the ultimate answer is an on board dyno that can measure propshaft HP and therefore the hull HP required at any speed. I think it could be done. How easily and how expensive I don't know. This is a whole other subject so I started a new topic on it.

RumRunner

Tomcat
This sounds very intereasting. Are you coming up with a hull number based on performance, or your dyno numbers ? The only question I would have is are you able to correct for the inaccuracies of most desk top dyno type programs ?
Doug

tomcat

The hull constants come from Mercury if you use their formula, or from your own test results if you use the other formula. Desktop dyno numbers can be very accurate if you use the cylinder head flow data on the chevyhiperformance.com website and cam card data from cranecams.com.

Rik

Is this spreadsheet file to large to email or download from a web site?

I would like to download it and play with it.

One question, if I do not know the engine's dyno sheet, only the engines max HP and operating RPM, will I be able to use this program? i.e. Mercury 500 EFI operates at 5300 rpm.

RumRunner

Tomcat
I agree that some of the better dyno simulators are very good, but to use them you almost have to build the engine to have the right data to imput. I find that most people do not get very good numbers from the Desk Top dyno versions due to the data they imput. I deal with this on a daily bassis. My main beef with them is you can enter number that are not possible of working, and still get data.

tomcat

Rik - The program is not too big to download, but it's a one man program right now; too many things you have to know and do manually to make it work.

What I would like to do is get a streamlined version up and running on the web as soon as possible. That means going through the logic of every cell in the spreadsheet, with a computer person at my elbow telling me how it should be designed to run automatically on the web.

After that, adding an advanced version would be icing on the cake. If I do it this way it will minimize everyone's learning curve, and maximize enjoyment.

You do need a dyno curve with data for RPM range 2500 up to a max of 7000, at 500 RPM intervals. A single point will not generate a HP vs. speed curve, therefore no intersection of curves and no Max speed.

What I do is simulate the engine on Desktop Dyno using the known parts and adjusting exhaust and/or compression to get the known HP @ RPM. This gives you a very realistic curve. In the future I would like to go directly to Mercury for their dyno curves, or use dyno data from aftermarket shops that have dynoed the engine.

H2Xmark

lets do it! sounds like a great software tool.
Mark

kook

Where do you get this "desktop dyno"?

tomcat

You can buy Desktop Dyno from most car speed shops. There is supposed to be a CD with cam data available too.

I have sent a couple messages to Jeffery about putting the speed calculator on the site somehow. Stay tuned!