blue thunder

I don't know about you Cal, but I'm think there may be a lot of rpm and speed lost in my rigging and hull. I've had a similiar result to yours (last year) and have been wondering if I may be hitting a wall due to X dimension and other issues. Audacity used to speak of that often and I think he may be very correct. Have you considered these things? I know the one rigging related change I made last year to spinning the props in made a huge difference in hull attitude.

Food for thought........

Dave

mopower

Hmmm Point well taken. But the boat (Formula 272) did exactly what it was expected to do with the 330's and would run with the best of them. I did hear of a guy on here that reversed his props(same boat as mine) and claimed to pickup 3 to 4 mph
I'd talk longer but I'm at work and have a problem at the moment...really gotta go
Cal

mopower

OK Blue I'm back. Everthings cool.
Now like I was going to say. The boat did 68/69 gps with 330s. These 540s @ 46/4700 rpms on the dyno were doing 425/450 hp. That gained me 7 to 8 mph. Just about right for a 200hp gain. I was going to try my old 25 Mirages toward the end of the season just for the hell of it but didn't have the heart to twist the engines that high. I do believe there's ALOT more speed to be gotten out of this. Just have to get my power band down to a reasonable level. I had 700ft lb torque in the high 5000s and 700 hp @ 6200
Anything will go faster given Mopower

My last boat was a 21'FourWinns Liberator with a 625hp 540 and could easily bury the 80mph speedo. That one my torque peaked around 710 ft lb@3700 and 625hp @ 5200. No gps back then. That was quite a handful You could be doing 50 and it could still plaster you in the seat. Only trouble it was a Ford

blue thunder

I would really like to know what the OSO knowledge base thinks the result would be to Mopower's situation if he advanced cam timing 4* and used pump up lifters. Would the advance bring his torque band down into the low to mid 5k range and would the pump up lifters fix his low vacuum at idle problem? At 4" of vacuum the power valve was likely opening. I think these two changes may have a good result.

Other than that Mopower, my boat was a pig with the props spinning out. Probably due to hook in the hull. Spinning in gave me a good 4mph and made the boat loosen up. What was your boats attitude last year at WOT and trimmed... bow high, low or in between and managable?

Dave

mopower

Dave,
I didn't get to it today as planned , but I think my cams are in at +4.
At 77mph and trimmed slightly over center it was quite well behaved. It held the bow up with no porpoising. That was turning out , with 28" Bravo ones.

Cal

blue thunder

Sounds good Mopower. I run a set of 27p mirages plus props. Would have been nice to give them a try on yours last year. Maybe next year we can get together on the Chesepeake and do some prop testing. That is unless you are spinning 32p props by then

Dave

KAAMA

Mo,

My personal opinion is that I believe those Comp cams of 247*/254* are too big for a 540 inch marine engine. The following info I have laid out is something I believe might help you in your decision when it comes to making a cam selection.

I had some Crower hyd roller cams 236*/244* on 114* lobes in my naturally aspirated 540's that are almost identical to the Crane 741 cam and they worked very well. In fact, the Crower cams I had were a hair milder. The Crane 741 usually comes with 112* lobe seps which is fine. My Crowers idled at about 800rpm in neutral and with 160* thermostats and Crane Hi-6M ignition box and MSD crank trigger fire it idled down as low as 550-600rpm in gear. Those cams made for very smooth shifting and manuvering around the docks, wind, water currents and boat traffic. In my 8000lb+ (dry) 32' A/T I was able to turn a pair of lab finished 32" Bravo One 4-blades to 5600rpm. Hope this helps a little.

Mark

mcollinstn

Kaama, havent seen your name in a while. Good to hear from you.

Blue - I nix the pump-down lifters. Old tech. Band-aid.
They are only helpful to increase engine vacuum at idle to near-idle. This was a plus in overcammed street cars that wanted an erratic idle but didnt have enough vacuum to operate power brakes. Modern cam profiles should provide acceptable idle qualities if matched to the correct build spec and compression. Contrary to street talk, pump-down lifters do not have enough pump down effect above 2000 rpm to provide for any torque increases worth considering. If their orifices were sized large enough to provide for that, they would be hammering the entire valvetrain to an early demise.

+4 to +6 is advised, but many cams these days are ground with the advance built in.

When I was about 25, I specced a roller cam for a really hot stage 3 440 Chrysler with a race-tuned 6 pack setup (yeah, I know, but friend was a 6 pack nut and did not want to go dominator - although the 6 pack setup was 1100 cfm so it wasnt hurting for flow). This was in a B body Coronet.

I thought about it and picked a .710 [email protected] on 105.
It was the baddest sounding thing you have ever heard (it was a race gas 13:1 motor). Idled at an angry 1500rpm.

Launching at 3500, it STILL had a NOTICEABLE soft spot and a steep power peak. Pulled hard thru 7600, but not like I had expected it to.

Realized the mistake and sent it back.
Reground it to .660 and [email protected] on 108.
Car became a monster.
Now idled at 1100 and sounded ALMOST as good.

Same car now runs a 535 inch hemi with aluminum indy heads and twin 700 Carters on a crossram. Built right and touches 900hp thru full exhaust (race gas motor again). I left the cam choice to a Hemi expert even though I have made and fixed a thousand mistakes since the 440 cam episode so many years back.

Too big of a cam in a boat is much worse than too big in a car. Just turns it into a soft turd.

mopower

Thanks Kaama , I think it's to big too. And so did my engine guy, but I believe it was James at Comp insisted it would be ok because "it's a 540 and should be able to handle it" WRONG
Comps head engineer sez it's too big too, now . Well thanks for yoour advice Talk about being a day late and a dollar short. Not to mention one lousy boating reason with a number of embarrassing moments try to dock with engines that didn't want to idle and a tide that woulldn't quit
Your #'s and the Crane 741 look a whole lot better. Something new will be ordered this week. Just have to get the power band down and the idle vacuum up and all shoud be good
And Mc. Your right , it is a turd