I'm a little confused and frustrated, I was running speeds of 64.8 on GPS with a 24 4 blade bravo on a Sonic with a stock 496HO. I since have had a whipple installed and now am running a 28 4 blade bravo (which is too big) and gained about 233 hp but have only hit a high speed of 68.9.

Stock I was running about 5100-5150 rpms, with the 28 and extra hp I am only turning about 4500-4600 rpms.
I am going to put a 26 4 blade on it, will I get back to the 5100 range and will I see a major mph increase?

I was told I should see around 78-80 mph with the 658hp dynoed on my Sonic is that realistic?
Or am I looking more at 74-75 mph range?

Also why would I go down so far in rpm's with the upgrade of hp, is a 24 4 blade that much of a difference than a 28 4 blade?

I was told you gain or lose about 150-200 rpms when you go up or down in pitch which would mean if I was still stock I should be at 4300 rpms, but I added 233 hp??????

I guess I am just looking for some facts and what I should expect.

A 26 at 5100 with the same propslip you had with stock power will put you in the 70mph range. I would also think you should be in the 75-80 mph range.

hey bad-intentions what kind of gas milage are you seeing.your post sounds like the same thing that i am going through w/my pachanga.i wish i could offer some help,but i am working through it too.hang in therethe griff has posted on my thread and has helped........solved the gas comsumption problem....stay out of boost,and keep below 3000 rpm.

You do not have an added 233 hp with the motor in the boat, plain and simple. You should be able to pull a 28" prop with 600+hp. Something is not right with your motor setup. Did you install the whipple?

The 233hp he saw on the dyno is real close to what whipple shows also on there website. Even at 4600rpms he should be making 600hp and 700tq.
http://www.whipplesuperchargers.com/...sp?ProdID=1149


I have to wonder if the its getting enough fuel??????
Do you have 5 lbs of boost????

Hey B.I. I assume that you have a 26Prowler? I had an '04 & did the Whipple also. 73-74 on GPS is about all that you are going to get. On paper the numbers add up to much more, but in my real world numbers of running my boat for a year & a half that is all that I saw. About 10 mph over stock. I ended up using a 26p stock bravo prop & the boat seemed to like that prop the most. I sold the boat about a year ago, but if I can be of any help please let me know.

Well, as has already been said, it does make you wonder if the hp is actually there! What is the x dimension like? Measure from propshaft middle to lowest point on hull. If the drive is really low, and you add more power, you just bury the prop even deeper and create your own anchor.

What is the recommended prop shaft below bottom of the boat on a single Vee with Big HP????

I am having a similar problem. Huge HP, doesn't matter what prop, similar speed and RPM.

this 26 prowler with 750 h.p ran late 80's and on a good day 90. it also had a 2 " shorty.

your drives must be burried. or you have a 1 36 gear ratio and not making the rpm to make boost.

I can only give you the facts from my own 25 Outlaw. It came from the factory with about 6 1/2" propshaft to pad, and ran 67 mph GPS at 4900, 496HO, X drive, labbed Bravo 25".
With Imco ext box, the prop to pad was reduced to 4 1/2" and gives me around 80 mph from a stock 525, XR drive, labbed Bravo 28".
Best yet 81.2 mph, all day 78 mph. In most conditions, except a really hot summer day, I´m on the 5350 revlimiter when trimmed out.

For my boat, the extension box and the raised x worked perfectly.
I have more slip than before, but the boat comes up on plane as quick as it did in stock form.
I don´t feel like I´ve reached the limit (on drive height) but I´m not rushing to put a shorty on it yet. I´ve got a !" spacer, though to see if giving back one of the three inches would be good.

The figures 4 1/2" - 5 1/2" prop to pad, are typical on high power/weight 25-28ft singles.
The more power, the higher the bow will lift. As the bow gets higher, The boat rotates and the prop goes deeper. Even though the boat rides higher, the faster you go, you end up dragging more metal through the water.
If a low set water pickup can take a couple of miles off, imagine what a whole drive unit can do!
I may be be wrong on this, but these are my observations, based on experience with one particular hull!