Incredible Performance

SS201....about 6 months ago you helped me fix my carb problems...she's still running great.

I got mine in the water this week-end and tried out the new prop and did a little stopwatch test as well. It was a little tricky doing it myself with the cell phone, not enought hands to hold the trottle, phone and wheel all at once. But I timed mine a little differently as well, I went from a dead stop to top RPM (5K) or WOT or top speed what ever you want to call it and it took just under 8 seconds on last years gas as well. My speedo's never read over 40-45 mph and need adjusted. But I figure the first time I peg the speedo they'll have to be re-adjusted again anyway so I haven't done it.

to figure speed.
RPM X prop pitch X .00946 then divide that by the prop diameter that gives you the speed at 100% then subtract at least 10 - 20 % it gives the speed. However most CC subtract 15 - 18%.

ex. 4800 rpm X 14 = 67200 X .00946 = 6357 minus 18% 521.26834 or 52 MPH.

The power valve is a key component of the power enrichment system of Holley
performance carburetors. The power enrichment system supplies additional
fuel to the main system during heavy load or full power situations. Holley
utilizes a vacuum operated power enrichment system and a selection of power
valves is available to "time" this system's operation to your
specific requirements.


Each Holley power valve is stamped with a number to indicate its vacuum
opening point. For example, the number "65" indicates that the power valve
will open when the engine vacuum drops to 6.5" Hg, or below.


An accurate vacuum gauge, such as Holley P/N 26-501, should be used when
determining the correct power valve to use.


A competition or race engine which has installed a long duration, high overlap
cam will have low manifold vacuum at idle speeds. If the vehicle has a
manual transmission, take the vacuum reading with the engine thoroughly
warmed up and at idle. If the vehicle is equipped with an automatic
transmission, take the vacuum reading with the engine thoroughly warmed
up and idling in gear. In either case, the power valve selected should have
a vacuum opening point about 2" Hg below the intake manifold
vacuum reading taken.

bill is the formula correct? it seems to be off when I plug in the numbers it comes up 5 mph lower than what I would expect. What effect would cup have on the calculation?

The formula is correct, depending on how severs the cup.In some cases it can add to the pitch a extra pich. Ex a prop with a 15 cup pitch could be in theory a 16.
Stock 81 CC
13 X 13 X .009469 = 59.0340 -20% = 47 MPH
as I said you have to rate your hull, Bass boats or flatbottom are 10%. Rermember if you havea 123 tranny you subtract 23 % from the engine RPM.

BC,
I am not familar with Acme props, sorry.

thanks


I'll have to compare with my buddies boat and see how close it is.