Prop. testing Help (long)
 

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.:confused:

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?

if the prop is to much for the motor to handle all you are doing is wasting fuel a 25p 3 blade is easier to spin on top end but gives more slip out of the hole or in a tight turn you can lab finish the 26 p and get 2-300 more rpms out of it

LABBED 25MIRAGE PLUS
 

A 25 PITCH MIRAGE PLUS LABBED WILL BE YOUR FASTEST PROPELLER.or try a 24 Bravo-one.

Depending on set up yes this could be normal. It is kind of like over carburating a motor and they get very sluggish or respond to throttle poorly. Kind of like trying to take off or accelerate a car in high gear and low RPM. No power and if you full throttle it will bog down but if you ease in to the throttle it will take off better. Not the best splainen I know. :rolleyes:
Try a smaller prop I think you will be pleased with the outcome. Keep us informed and happy testing.
Peformance boating is test - test and more test as for set up. Unless you have the big bucks and go with a known package. :)

I would prop for 5400 rpm on top end. I think you will be happier than trying to hold it to 5000. I know the numbers but I think with that cam you will have better performance.

yep!!

Crane specs say the powerband for that cam is 3000-6000rpms. Also, with that big of cam, I would run higher initial timing. Would help idling and low end power. You would have change ignition modules to 20* advance one.

I have a smilar engine setup in a 24 Outlaw. 454Mag, rect port heads milled .20 to get 9.0 CR, mag intake, Holley 800, Crane cam #134241(226/236,.534/.553). I ran a 23" Mirage+ to 5500rpms with it. The torque is starting to fall off though. I also ran a 24" Bravo 1 and it is the perfect prop at 5200 rpms.

With that big of cam in a 454, you should spin at 5200-5400rpm at least.

BTW, did you check plug readings after the runs. You could be lean on fuel.

whodathought,

Yes, prop for max horsepower.

What is odd is the fact that you saw a difference of almost 1000 rpm between the 26 Bravo and the 23 Mirage. I would have expected about 400-500. There are many reasons for this. Two of which are, either the Mirage or the Bravo are not stock and have been modified. Or, the power curve of the motor is such that it starting to produce power in the low 5000 range.
What doesn't make sense is that your speed was higher with the Bravo 1 at 4400 than with the Mirage at 5500. Speed comes from horsepower.
I would take a close look at the Mirage and see if it has been worked, if it has that could account for the high rpm and poor speed numbers with it.
Just a couple things to think about.

Matt
Throttle-Up Propellers

Plugs! Read the plugs!
Might be running plum outta fuel. OR might be drownin it...

Plugs are the best way to know.

Only if they look right should you move to the next step.

As far as the timing issue, where you are now should be fine for WOT testing. After you have settled on a prop, etc, you may indeed want to start with more initial timing and use a different module - but it shouldnt make any diff on what youre doing now.

Thank you all for your help. I think first I am going to do is check fuel pres. to make sure my pump is kepping up with my engine. Then I will check WOT carb tuneing I guess by reading the plugs. I used to use O2 sensor with a LED indicator made by K&N on my street cars and bikes. Any thought on those for marine aplications? How do I get it into my fully water jacketed dry system? If all that checks out I was woundering if Houstion prop. could do anyhting with this prop. to make it fit my needs?

Thanks,
Andy

Darin,
Could you give me an idea what can be done to get 600 rpm out of this prop and what am I looking at fo cost? Or is it better to just sell this one and go with a 24 pitch?
Andy

Go with a 24" prop. It will increase your rpms by roughly 400, and probably more since you are getting more into the power range of the cam.
Don't be afraid to spin that engine at 5400-5500 WOT.

Torque, Torque, Torque. You are probably putting out the same TQ at 4400 rpm as at 5500 rpm. Get a 24' stock bravo prop and see where you are at and how it performs.

sell
 

I could give you the bullsnit line but you better go with a diffrent prop thats alot of rpm to be gained (properly).:D