Cigarette Cafe Racer prop choice
 

Hoping for a little guidance here - thanks in advance.
1991 Cigarette Cafe Racer, Bravo 1, Currently spinning Bravo 1 4-blade 26P.
Rev limiter on new engines has been set at 5800 but I am barely seeing 5000. Depending on conditions / trim that will get me to low 70s. This is with fresh 550ci motors - dyno sheet below.
Wondering what direction to go in, if any.

https://cimg2.ibsrv.net/gimg/www.off...d8bcb982db.jpg

Somethings seems off, at 640hp only spinning a 26p 5k..are the drives 1.5 ?

As far as I know, yes they are 1.5

CMI headers. same on Dyno and in the boat. Dry tails because we were seeing water reversion at idle.

https://cimg1.ibsrv.net/gimg/www.off...b8e0a28441.jpg

How did you remedy the problem? Scoops on top? Ducts on the side?

Also, I should mention, it seems like the last few clicks of throttle position towards WOT do nothing to increase RPM or speed.

I have fuel pressure gauges. Both reading around 6.5psi most of the time, admittedly I did not look closely at them during my last WOT run. Next time out I'll pay closer attention and also try raising the hatch an inch or so - and read plugs after WOT run.

Haven't had a chance to run it yet - but I did notice that the inside surface of the 3 vents on each side of the hatch, had 3 layers of tight plastic mesh, which couldn't have been doing anything positive for airflow into the engine room. I removed it all.

I bet you find out Saturday how that works!

Yep, that's the plan!

a,
Any update?
MD

So running yesterday, fuel pressure over 4000 rpm drops to 5 or 5.5 psi. Opening up the hatch vents did not improve top end. I forgot to try running with the hatch up.
I checked timing today, both motors set to 38 degrees initial and locked in with no advance.

Thats a lot of timing and fuel pressure is on the light side but should be ok if it maintains it.

38 is where it made the most power on the dyno, and it also idles quite nicely for the size of cam. I did not see the fuel pressure drop below 5 at any time. Yesterday I pulled both pickup tubes out of the tanks and verified that there's no strainer/screens on them to clog. Pickup tubes are 3/8" i.d.

I have new 2 new 540's in my Cafe Racer and before installing the motors took both to Nickerson Performance since i run there carbs and spent a long day With Dean Nickerson to Dyno both motors. I run Daytona Sensor ignitions and after a bunch of runs setting up ignition curve vs carburation the sweet spot on my motors was 38 degrees. He told me you have to give it what it wants. after break in time the first initial pull was 628HP and that went up to 680 with adjustments to metering blocks and timing curve. So glad i took my motors to Nickerson and had him tune them on the Dyno, money well spent, besides getting an education i know exactly where i am at with the motors.

I had a similar issue with RPM last year struggled to get over 4700 spinning 30 Bravo's, everyone that had history on the boat said they were 1.5, I had to replace a pinion seal over the winter and upon tear down found they were 1.36. I'm really looking forward to getting out in a couple weeks. Should run like a different boat.

Engine builder asked me if the drives were 1.36. We have been working under the assumption that they are 1.5s but have not confirmed. Will put that on my list of things to check this weekend.

Are you changing props or gears ?

You know another thing is you might want to give mike a call and see what he did to the props.
At some point when you get the little issues worked out you are going to need to run it and write down RPM-Speed in 500 rpm increments trimmed to the best speed and see if Mike can bring the props in.

Maybe some Thursday I get take 1/2 a day and we will go out when the river isn't busy.

We had a gear with some damage on one drive so we have upgraded to XR gears and converted to 1.5.

Yeah, that's a good idea!

Update: Drives are 1.36:1

Also swapped to new fuel filter heads and lines/valves. Now 8 psi fuel pressure at idle.

Cool, let's do some Easter boating!
MD

Follow-up: Changed drives from 1.36 to 1.5 yesterday, still spinning Bravo 4-blade 26P props. Saw ~5500rpm and planed easier for sure. Sounds much happier too.

That 38* of timing would scare the crap out of me without an egt gauge. You might wanna check them plugs at minimum , Id be afraid those exhaust valves are getting toasted.
What it wants on the dyno for a 10 second pull doesn`t really tell you what it likes on the water.
BTW good job F-2 Sleepy, you called it :D not a 1.50 drive

I've got about 40 hours since the engine builds. I've checked plugs a few times along the way. Plugs have a clean burn, light tan/brown on insulator, but get sooty after a long idle.