Matt, I checked out your page from the link you gave here----very nicely built engine combination with the cam and AFR 315cc Cnc ported heads--almost 700hp @5500. I am sure that engine makes that boat a true runner! What kind of RPM's are you running at top RPM and what kind/size prop? I love your head and cam combination---especially with the Hilborne FI velocity stacks---AWESOME...nice job !!!

I have a pair of NA carbed 565cid engines with the AFR 315cc Cnc ported heads as well, 9.3 comp ratio---small hyd baby roller cams---my boat hauled the mail !!!

Cool blog!

Some may find your post about the need for a bypass hose in the cooling system pretty interesting. I'm not running a bypass, but I have my thermostats drilled to remove air and move some water when the thermostat is closed.

Yeah, it surprised me, for sure. I run a full flow closed cooling setup, which is great. I have full coolant flow through the engine at all times, and the thermostat just redirects it through the heat exchanger when needed. Temperatures are rock steady at 160F all the time. Along with a big oil cooler too. I’m going to explore if I have enough heat exchanger capacity to include the exhaust manifolds, eventually. For now, I want to get the map dialled in and make sure it’s all nice and reliable.

But that little bypass hose on the top of the circulating pump - I wouldn’t have believed it if I hadn’t had it happen to me. To blow the core plugs out it must’ve been making some serious pressure!

So far, I’ve seen 79.5mph at 5450 (roughly) on a stock Bravo 1, 26” pitch.

Focus at the moment is to get everything working well and reliably, map needs leaning out, ignition needs a bit more advance (am only running 30 degrees advance at the moment) and then I can start to explore performance a bit more.

I have 24,26&28” B1 props to try, wouldn’t like to guess which will be the best.

Props seem to be the most complicated factor in performance boating.

I'm feeling that boning up on Surface Prop info. Hard to even locate it.

X-dimension
setback from transom
diameter
pitch (BBlades mentioned some are not as advertised)
Cup
Rake
sufficient clean water feed
#blades
Bullet hydro shape

Once you touch on props...then engines and drives seem simple to solve the issues.

We're lucky BBlades Brett is a passionate man...or we would have lost a lot of good prop knowledge. Here on OSO and in the great perf boating community.

For our type of high performance stuff, you’re right. These days I think you can get the prop maybe 80-90% right straight out of the starting blocks, but that last 10-20% is very personal and unique, including driving styles, water conditions you want to optimise for and many other factors even on an otherwise like for like rig and that’s where someone with an abundance of experience and knowledge really becomes useful.

Yes, bravo props are not that accurate on pitch until you go with labbed ones. Somewhere on here is a thread that labels the difference between see stock vs labbed, I have it saved somewhere

Not having moving in the block as it comes to temp is a hard way to run. Hot spots can develop.

Just to be clear, we're talking closed thermostat operation, where the engine water pump is flowing water through itself, until the thermostat opens progressively, and flow is directed to cool through the heat exchanger.

Agreed. I think we're talking at odds. My closed cooling setup is full flow, so even when that stat is completely closed, the block gets a full flow of coolant circulating, it's just not going through the heat exchanger.
Nice even block & head temps. It was the small bleed off the top of the circ pump I had closed off - which means a bit of coolant bypasses the engine entirely. Since my block is full flow, I tried plugging that bleed and it blew the core plugs.

A more classic open cooling setup still has some water (re) circulating through the block when the engine is cold as a function of the stat housing design. Plus some people drill a small hole in the stat as well (me included on my motor that had this setup)
And then of course you have the pure seawater pump & bypass setup. Stone cold water hitting the front pair of cylinders - sub-optimal design unless you really need that much cooling capacity to have full flow from the seawater at all times.

So in the pic below (my setup), the thermostat is in the heat exchanger. It works great, although I don't like my setup from the heads to the exchanger, I'll make a nice compact water manifold that mounts on the engine at some point.

Interesting setup. I like getting the thermostat restriction out of the intake left and right bank manifold system.

I have not tested for it, but the water flow alternates left and right bank from one side hotter...more pressure, cuts flow to other side....and heats up...creating more pressure. Pulling the coolant out of the front of the heads direct and joining with a Y pipe is supposed to alleviate the alternating flow, that results in higher head temps.

With no thermostat there...it likely has a more even flow.

Just an update. I was running the boat last weekend and I put a pair of flaps on. They stayed on just fine. No noticeable impact to noise, which is expected, and while it was a fairly short run, they didn't burn up either on my rig (with the water dumps flowing over the mufflers)
Unfortunately I picked up a misfire, looks like a coil pack died since it'd run just fine when cold and all the way up to full engine temperature, but eventually it'd drop a couple of cylinders (wasted spark setup). By the time I had it lifted out and on the hose, everything had cooled down a bit, so ran on 8 cylinders again.
New bits on order - coils, leads, plugs etc just to switch it all out and get running again.