454 performance

[Buckknekkid]

Im running 20X22 props on a 36 Sedan, anyone else?

[planb]

I own a 1972 36' sedan with twin 454's with 20 x 21 props. I have not owned the boat long enough to have a good feeling on performance and or fuel economy

[Buckknekkid]

it certainly handles well at low speed.

[f36f36]

on my 36 is 20x21 - 3blade michigan props- My mech believes they are too big??????? max rpm I get is 3900 ,,,,,,,should be 42 to 4400............boat handles great at low speeds, cruises great near 2800 rpm.......18-20 mph.....1000 hours twin 454's.......

[rossjo]

What transmissions and ratio?

[JuiceClark]

Mine are 22 x 19 four blade props with 2.5 to 1 trannys. I cruise at 3100 rpm and get just about 19 mph. When tested, the engines (both less than 200 hours 454s) got just over 4250 max rpm. It sure is a trip going over 30 mph while up on the bridge!
I was told the four blade props are a little more efficient at slower speeds and a little less efficient at higher speeds. So, I got the 4 blades since I tend to try to poke along and save gas these days.

Tony

[Buckknekkid]

Im running with some old nasty tachs, but at 2800 we are cruising along at about 18 knots. 1.81 ratio 4 blades,. Engine builder wants to see more RPM, so we are having a mech put a True Tach on and see exactly what we are turning,

[rossjo]

I ran this through my Prop Calculator:... looks like your mechanic is right ...

18,000 lbs, Avg Planing hull
34' Waterline Length
2x300 HP, 1.81:1 straight drives
4-blade, Cupped Props

=________________________________________________________
MAX PERFORMANCE
Available Power: 601.4 SAE hp ( 448.5 kW) @ 4250 RPM
Max Speed: 28.3 kts
Fuel: 36 US Gall/Hr (typical)
CRUISING PERFORMANCE
Cruising Power: 195 SAE hp ( 145.3 kW) @ 2800 RPM
Cruising Speed: 16.1 kts
Fuel: 11 US Gall/Hr (typical)
RECOMMENDED PROPELLER
Diameter: 17.6 in. Pitch: 17.5 in.
Blades: 4 Cupped: Yes
Transmission Ratio Acceptable
PROPELLER BASED ON INPUT DIAMETER
Diameter: 20.0
Pitch: 14.6
Blades: 4
ALTERNATIVE GEAR/PROP COMBINATIONS
Gear Ratio Shaft RPM Dia. Pitch
1 4250 12 10
1.2 3542 13 12
1.4 3036 14 14
1.6 2656 16 15
1.8 2361 17 17
2 2125 18 19
2.2 1932 19 21
2.4 1771 20 23
2.6 1635 21 25
_______________________________________________________
(c) boatdiesel.com

[Buckknekkid]

Now THAT is interesting, thanks mucho allthough we are rated at 350 HP, the 300 idea is on a hot summer day. Now talk about weight, this thing is loaded with 300 gallons of fuel, etc. etc.

[rossjo]

Stock Merc Crusaders aren't 350 HP w/o mods - not sure what you'e got there ... But even if they are 350HP rated, the age and heat will bring them down to a more realistic 310 or so.

Just for fun - assuming 350HP...............................................
MAX PERFORMANCE
Available Power: 698.4 SAE hp ( 520.8 kW) @ 4250 RPM
Max Speed: 30.5 kts
Fuel: 42 US Gall/Hr (typical)
CRUISING PERFORMANCE
Cruising Power: 226 SAE hp ( 168.8 kW) @ 2800 RPM
Cruising Speed: 17.4 kts
Fuel: 13 US Gall/Hr (typical)
RECOMMENDED PROPELLER
Diameter: 18.1 in. Pitch: 18.7 in.
Blades: 4 Cupped: Yes
Transmission Ratio Acceptable
PROPELLER BASED ON INPUT DIAMETER
Diameter: 20.0
Pitch: 16.5
Blades: 4
ALTERNATIVE GEAR/PROP COMBINATIONS
Gear Ratio Shaft RPM Dia. Pitch
1 4250 12 10
1.2 3542 14 12
1.4 3036 15 14
1.6 2656 16 17
1.8 2361 17 19
2 2125 18 21
2.2 1932 19 23
2.4 1771 20 25
2.6 1635 21 27

[Buckknekkid]

like I said on a hot summer day 300 is more like it. I have Crusader xl's low hours. One rebuilt at 100 hours by a Merc Racing shop that I have used for a long time . I'll see if they can remember the dyno numbers.[/img]