I have a 1990 24' (226ES) BAJA with a bravo 1 outdrive 1.50 ratio and a 454. I just rebulit the engine last season: bored .40 over forged pistions 10.0:1 comp. 7/16 chevy rods, 781 heads with oversised valves & mild porting and roler rockers. Crane cam #134561 236in/246ex dur. 553in/571ex lift. Edelbrock RPM intake and a Holley 800cfm carb. Also Paterson big tube headers with full dry pipes. I am guessing around 430HP/450TQ at the shaft at 5000 rpm. I run the engine in with the stock 23pitch 3 blade prop. I could spin it well over 5500 RPM then I would back off. I just got a 26 ptich Bravo 1 prop. and tested it on saturday. I got 67mph at 4400rpm and 3/4 gas. Heres THE PROBLEM if I give it full gas it drops to 66mph and stays there. What gives!? I was hoping to see 74 mph at 5000 wich should be my peek TQ. But I can't get there! Any suggestions are welcome, sorry for the long post.

At full throttle, what is your fuel pressure and timing set to? The prop sounds like it should be about right.

I don't have a fuel pres. indicator but I can get one, I am runing a mech. Holley 110gph 7psi pump or at least that is what they claim. Ingnition is set at 10deg BTDC at idel 700rpm. It is the stock ing. system with 24deg advance I thnik that is right? with would put it at 34deg at 4000 rpm and above right????

You saying that your rpm doesn't go any higher either? Or is it going up, but at a loss of speed like a slipping prop? Need more info on what your motor is doing when you drop the hammer.

Try a 25" 3 blade mirage or a 24" bravo prop. That should get you to where you want to be.

No, the rpm stays at 4400 rpm aprox.

whodathought,

I'm no engine expert. I checked the specs and recommended rpm of that cam with crane and also considering the oversize valves it sounds to me that you need to run that motor at a higher rpm than 5000 in order to get at the peak horsepower level. That is where you will get your max speed.

If the 23p prop you were running before was a mirage this would also explain the excessive loss in rpm when you put the 26 Bravo 1 on. You are off the torque curve of the motor.

What speed did you see with the 23p prop at 5500 rpm? If you can get your hands on a 24 Bravo 1 try that. If you see a large rpm difference between the 26 and the 24, as you saw between the 23p three blade and the 26p Bravo 1 then you are getting close to the torque band of the motor.

What prop is the 23p? if you don't know give me the part number and I will be able to tell you.

Good luck,
Matt
Throttle Up Propellers
www.throttle-up.com
[email protected]

Matt,
It was a merc. mirage plus. I got 63 mph at 5400 rpm with that prop. but it would spin higher if I left it there longer than a min. or so. I checked the mortor on the laptop dyno and it showed max TQ at 4500 ot 5000 rpm and then a drastic drop off. However the HP peek was a lot higher like 6000 rpm or so. I thought I was soposed to prop for max TQ. So do I ahve wrong cam?

Thanks for everones help,
Andy

I wouldn't panic on engine set up at this point. There is a MAJOR differance between a 23 mirage and 26 bravo 1 prop. I would try a 24 bravo 1 and see what you get. Or a 25 mirage as suggested prior. I ran a 23 mirage plus on a 502mpi and with a major increase in power I still run a 26 bravo 1. I have a deep X deminsion on drive height though. Drive height makes a big differance when you start running a 4 blade prop. Just from my testing anyway.

I could try a smaller prop. But I don't under stand why my last 1/4 throw of the gas lever makes no difference at all if fact it goes SLOWER? Is that to be expected when you over prop a boat?