Four blade vs five blade on 353 Fastech?
 

I have a 2004 353 Formula Fastech with 525 efi's, XR drives with Stellings boxes. I currently spin 15 5/8 x 30 pitch Maximus props. Very slow to come on plane. The props cavitate when coming on plane, and the boat porpoises constantly between 40 and 50 mph unless the tabs are half down. Top end around 85-86 gps.
I have access to a pair of four blade 32 pitch bravos. What should I expect to see with the four blade props?

First of all, that's a real good speed out of a 525 boat. What RPM?

I'm running a cut down version of the Maximus 15 5/8 28 pitch, but am able to spin them 5800 (no factory rev limiter). It is all relative.

Something is wrong if you are having trouble getting a 5 blade on plane. Any idea where the Stellings are adjusted to? If my memory serves me correctly, you can get 1-3" of adjustment up or down. Same goes for the porpoising.

Dave

At WOT i am at appx 5100 rpm. I have no idea how to tell where the boxes are set. I can throttle up very slowly with minimal prop blowout when coming on plane. The drives seem to shudder, then rpms wind up before boat levels out and props "catch". Just wondering if four blades would handle better. My neighbor is running 4 blade 32's on a ts top gun with same power and ITS boxes and is pleased with handling. Guess I will have to try them to find out.

Heavy boats need some momentum to get on plane. I usually set the power to like 2000 rpms and "let the boat catch up" be fore adding more throttle. If you throttle up to quickly you will get the cavitation / shutter. Find the spot right before that and give it a chance to break over. Once it does, you should be fine.

As for the 5100...I think you have too much diameter in those props. I'd have it cut back to gain those rpms on top. That is an opinion, I leave those decisions up to the prop experts. Give Brett a call an see what he thinks.

Dave

Exactly how my boat reacts with the shudder. Going too little RPM and the boat just snow plows and too much and it shudders, it's a balancing act for sure. For reference my best speed is 84.7, usually run 83 at 5100. Sent props to BBlades over the winter, Brett matched them (one was cut down slightly from previous owner) and put a little "English" in the blades. Not looking for more speed just consistency getting on plane.

Get it up close to 5,400. That's where the power is. I bump the rev limiter on a good day.

https://www.youtube.com/watch?v=kSUWplf6m6A

Have you run bravo 30 4 bades? That was probably what came on your boat from the factory. The 32s might be a bit much unless they are labbed.

I Know this is an older post but I have a 05 353 with 525's and boxes with 28p mercury 5 blades from the factory I run consistent 80-81 in fresh water 85-86 in salt water. I can get 84-85 out of it in fresh water but I need perfect conditions on the lake. I borrowed a set of 32p mercury racing 4 blades and the boat ran 85-86 in fresh water. Never ran it in the salt water with the 4 blades

Those are respectable numbers. Are you the original ower? I can't remember if they used 5 blades from the factory back then but in most cases labbing makes a 2" reduction in pitch. Whats your max rpm at these speeds and are the mph figures from gps?

I am the original owner. These numbers are from GPS my rpms where 5100 with 5 blades and I believe they were 5200 or 5250 with the 4 blades