Prop Size????

[P-Money]

I finally got the motor back in the boat a few weeks back, went out yesterday to get some time on it before the snow flies (yes, it was cold as witches tit out!!). Here's the question: The boat is a 19 foot flat, 1.18 gears, 500 cid BBC with a Dyers 6-71. I had a 11 1/4 x 16 2-blade (that I just got polished and balanced by Braaksma) on the boat. Since I'm still breaking the motor in I only ran it up to 6000 rpm. At 6000rpm the GPS said 82 mph. I'm sure the motor is good for another 1500 - 2000rpm, but I'm thinking I need to get a bigger prop. Any suggestions?

[Sangster]

Give Tom Bently a call, He's the man on props & gears...
http://free.***boat.net/gfx/menkens.jpg
[ October 28, 2002, 06:37 AM: Message edited by: Sangster ]

[superdave013]

You don't need a prop. You need to change your gear ratio.

[V-Drive Tom]

P-Money, You worrying about something you don't know yet. Run the boat some more. You are going to have to run it at Full Throttle to know. If your RPM is too high too soon,or is too high on the top, THEN you need more prop.(Or maybe just gear)
You just don't know yet.
My Grandma runs her boat at 6000 RPM!! :D
So get it up there man!!!
wink TOM..

[beaverfab]

V- Drive Tom I want to meet your Granda! :D :D By the way thanks about your post on cases I know I worked on a 10Deg. case 62000 number. j.j.

[DUCKY]

If the prop works well on the boat, DON'T CHANGE IT! Just spin it faster with more gear. You said 18's right? DAMN! Go to some 22 or 25's

[P-Money]

V-Drive Tom, your point is well taken. My intial feeling however is the rpm's are going to be spinning higher than I want. Just playing with the boat yesterday I discovered they jump right up there when you step on it. This being the case something has to change.
What do you think about stepping up to 1.22? Whats a used set of lightened gears going to cost?
And who's got some? Thanks for the help.
Ducky, whats this "DAMN" stuff all about? :D 1.18's are all you ever hear anyone talk about, thus I figured a prop change would be the way to go.

[superdave013]

P Money, you don't want to go to more pitch then what you have in your flat. More pitch will cause more lift in the back of the boat and it could start getting evil handling.
22's would be great if your racing and don't care about max rpm. Most lake racers that run good seem to run 25-29%. I bet you can still turn 29's to 7K.
I exchange gears and if you want to change ratios shoot me an E-mail or PM.
If you want to wait until summer I don't blame you but right now I have pretty much want you need if you have a 10 degree v-drive.

[GofastRacer]

You need to experiment, run the thing up to the max rpm's that you want to run, if the motor wants to keep going, go up in gear until you have enough load on the motor!, the thing to do is borrow a couple of set of gears and try them!..

[West Coast Dave]

Everybody that is talking about 18 gears are normally aspirated engines. as soon as you put the huffer on top you are going to ned more gear. People I know that are just lake boats and play racers start w/ 29's. Hardcore 1/4 milers that will spin the snot out of the engines seem to lean towards the 22's. Everybody is right, you don't want too much pitch or the handling goes away.

[Morg]

Just because everyone has an opinion here's mine.
Before you go to the big gears you might want to think about a couple of things.
What rpm is the motor spinning out of the hole? Is the prop./gear combo. letting the motor make power?
What rpm do you want it to turn at the top end? Is it spining the rpm your cam is set up for.
How deos the boat ride at the top end? Is it sitting on the tail, or is it falling onto the nose?
This is by far an exact sience. Let the boat tell you what it wants. The boat has not told you yet.
P.S. If you run the big gears, I'll line up next to you with my 427 & 15% gears.
Remember most lake races are over at 1/8 mile

[V-Drive Tom]

P-Money, You haven't said anything about how much blower you are running.(Boost) If your making 10 or 12 pounds of boost,I would still not run more than 25% gears at first. It will depend on the prop from Ron is a real mean one or not.
It depends on what you want out of the boat.
If you want it to be a real hard runner out of the hole then don't go too high with the gear.
TOM..