Nova II Bravo change X-Dim change?
06-25-2003, 05:56 PM
#1
Guest
Posts: n/a
Nova II Bravo change X-Dim change?
Buddy of mine has an '86 Wellcraft 26' Nova II that he's built some nice 383 stroker motors for. It currently runs 1.50 ratio Gen II Alpha drives turning 14.5"x23" Mirage 3 blade props both turning standard r/h. Horsepower is around 425 or 450 but he's still playing around with cam timing, ign. timing and jetting so we haven't nailed down top speeds yet.
Question is...
He just bought a couple of new Bravo drives with 1.65 ratios and is wondering what to use for an X-dimension before installing them. These drives are .5" shorter than the stock Alphas. Should he go stay with the .5" or go higher? He's been told by one person to go up 4" to get the best speed. That seems a bit high to me, but what do you all think he should do. Wish I could remember the current dimensions... sorry, crs disease. Also... what about prop size? Turn them in or out?
Thanks in advance guys! He should be registering tonight sometime.
~Scott
Question is...
He just bought a couple of new Bravo drives with 1.65 ratios and is wondering what to use for an X-dimension before installing them. These drives are .5" shorter than the stock Alphas. Should he go stay with the .5" or go higher? He's been told by one person to go up 4" to get the best speed. That seems a bit high to me, but what do you all think he should do. Wish I could remember the current dimensions... sorry, crs disease. Also... what about prop size? Turn them in or out?
Thanks in advance guys! He should be registering tonight sometime.
~Scott
06-26-2003, 08:56 AM
#2
Platinum Member
Platinum Member
STD bravo and STD alpha are the same crankshaft-to-propshaft height spec.
A bravo offers more drag than an alpha due to its thickness thru the bullet.
A NovaII will have a conservative X from the factory, and I would expect that 2 inches would be do-able with 4-blade Bravo1 props.
The boat will be slower with Bravos than with Alphas (at identical X heights).
Higher X will increase top speed until excess slippage and/or lack of bow-carrying leverage works against it. Planing performance will generally get poorer at higher X dims. Prop selection can offset poor planing performance and slippage issues. All hulls respond differently and X dims and prop selections are as much a matter of preference according to what aspects of performance are important to your friend.
Rotate in or out? In gives more bow lift and pulls the tail down. It also makes it weird when maneuvering around the docks. Out gives more stern lift and makes dockside maneuvering more predictable. As before, prop selection and driver preferences will make this decision. The best part is that it is nothing more than a prop swap on Bravos to try this out.
Bravo1 props have more bow lift. Hydromotive props have more stern lift. He may like Hydros turning in better than bravos turning out or vice versa.
Rules of thumb are all we can give you. Wish we could do more.
A bravo offers more drag than an alpha due to its thickness thru the bullet.
A NovaII will have a conservative X from the factory, and I would expect that 2 inches would be do-able with 4-blade Bravo1 props.
The boat will be slower with Bravos than with Alphas (at identical X heights).
Higher X will increase top speed until excess slippage and/or lack of bow-carrying leverage works against it. Planing performance will generally get poorer at higher X dims. Prop selection can offset poor planing performance and slippage issues. All hulls respond differently and X dims and prop selections are as much a matter of preference according to what aspects of performance are important to your friend.
Rotate in or out? In gives more bow lift and pulls the tail down. It also makes it weird when maneuvering around the docks. Out gives more stern lift and makes dockside maneuvering more predictable. As before, prop selection and driver preferences will make this decision. The best part is that it is nothing more than a prop swap on Bravos to try this out.
Bravo1 props have more bow lift. Hydromotive props have more stern lift. He may like Hydros turning in better than bravos turning out or vice versa.
Rules of thumb are all we can give you. Wish we could do more.
06-26-2003, 09:53 AM
#3
Guest
Posts: n/a
Scott, I running the same boat with Alpha SS's Which are at least 2 inches shorter than an Alpha I.
I built a pair of 409s with about the same HP. Right now I'm spinning hydromotive 22's and seeing about 60. But I have carb issues. At 60 my secondaries (Mechanical) haven't opened yet when I hit max RPM's but is still have another 1/4 throttle to go. I just need to to some testing.
But with the SS's I've had zero problems with blowing out. They hook up in hard over turns with no blow out. So I would say its safe to go 2 inches shorter. I have a pair of 25" Mirage Plus's I need to put on and see what I get.
Mcollinstn is right about the higher X's and bow lift. Its okay at cruise, I can lift the bow high enough to porpose, but running hard I would like a little more lift. The boat feels stuck down abit.
My other limiting factor in top end is my bottom paint. It was rolled so its like pushing sandpaper through the water.
Keep us informed on how your friend does. I would be really interested since we have the same boat and similar setups.
I built a pair of 409s with about the same HP. Right now I'm spinning hydromotive 22's and seeing about 60. But I have carb issues. At 60 my secondaries (Mechanical) haven't opened yet when I hit max RPM's but is still have another 1/4 throttle to go. I just need to to some testing.
But with the SS's I've had zero problems with blowing out. They hook up in hard over turns with no blow out. So I would say its safe to go 2 inches shorter. I have a pair of 25" Mirage Plus's I need to put on and see what I get.
Mcollinstn is right about the higher X's and bow lift. Its okay at cruise, I can lift the bow high enough to porpose, but running hard I would like a little more lift. The boat feels stuck down abit.
My other limiting factor in top end is my bottom paint. It was rolled so its like pushing sandpaper through the water.
Keep us informed on how your friend does. I would be really interested since we have the same boat and similar setups.
