271 sr1 prop
 

what props are you running and what speeds and rpms are you getting? thanks

Modernized 271 SR1 1993, blue merc502 (dynoed 560 hp) Bravo1 XR Drive aprox 530 at propshaft

Tested Bravo1 24` 5450 rpm 65 mph

Testing a Bravo1 26 these days, will keep you posted

Try this site for Speed calculations and prop ca,culation

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

I choose the 225 constant from Heavy V Bottom ( I think for a 271 SR1 that should be ok)

I have used 4500 pound as weight, based on boat plus som gas and my self :-) 530 prop shaft HP (you need to know approx. the correct prop shaft HP) and 225 as constant

Theoretical Result 70 mph

My result 65 mph gives me 16% slip which is a bit high ( based on this prop slip calculator)

http://www.go-fast.com/Prop_Slip_Calculator.htm

I also know that Bravo1 is around 1,5 pich lower then what is written on the prop. My 24`are actually 22,5`

I have consider this in my calculations :-)

Gear ratio of your drive Tag.

1.50 XR Drive

I'm really not sure what the ratio is or how to find out I believe it's a stock 94 drive

What kind of engine du you have 502 or 454 Mag ?

Stock 502 efi

I have a 1992 271 Sr1 stock 502 Mag and running a 23P prop

DF what is your cruising speed and top Speed ?

Monaco20, I recently bought the boat and haven't had it out very much. Just hooked up a GPS so Ill have to get back to you with some numbers

Went out this past Sunday. Full fuel tank, full water tank and 3 on board. Was 4400RPM and GPS top speed of 45 mph. This was all trimmed up etc. Was cruising around 30 mph. It felt like the boat wanted to go more,but just couldn't get there. I was expecting to see something closer to 58. I know these aren't the fastest boats and they're heavy. I am going to empty the water tank and try it again with less weight to see what happens before messing with props.