russ

Here's how I think the boat should ride!

Not like mine.

russ

Ran the boat with a 25 M/P unlabbed. Ran 4900 RPM's. Forgot the GPS but the speedo said 72 73 Mph. Guess I was running 67 to 68 MPH. Hopefully when I change out the exhaust will gain me another 200 RPM's then I'll have the prop worked.

russ

Added the Rev Marine exhaust and it didn't add anything. Was running 4900 Rpm's, 67 GPS, 1.5 gears, 25 M/P. That's 13.4% slip. Hopefully I can get that down some. Only thing left to try after the prop is timing. Right know it is set at 31 going to try to bump it up some since the motor is broke in.

What kind of gains have people seen when they bumped up the timing? I'm thinking the motor should be set at 34 not 31. Have to try and see. Might also try a 23 M/P prop next weekend.

articfriends

iTrader: (1)

Russ,i see you still haven't solved your dilema. My 272 is like kennyo's,it gets the most speed by trimming it to max but that is with a 4 blade prop. I will hit 77-79 mph with it trimmed normal and you can feel the vee digging in holding you back and when you start trimming it more you feel it start getting "loose and squirelly" and it picks up more speed,but it's hard to compare our similar hulls to yours because we are running blown motors and 4 blade props. Timing really woke my motor up but it is a 8-1 motor s/charged w/intercooler and responds to timing increases well (until detonation). On the chasiss dyno at baker engineering,a normally aspirated small block chevy i built peaked with 34 degrees timing,had the same power with 36 but ran hotter then lost 18 hp at 38degrees. I know you don't have a smallblock but what i'm saying is there is a certain amt of timing that will give you your max power. Add 2 degrees at a time and watch your plug readings,it is a big block so you probably won't want to give it anymore than 36 dgrees,34 sounds reasonable,Smitty

russ

Nother pic of the boat running

articfriends

iTrader: (1)

Russ,your boat looks plenty loose and aired out in the latest pic (actually looks awesome!)so i don't think how your boats planing is a issue,another member recently took a pic of mine (in upper 70's) and it was almost identical,i'll try to scan it and post it.

russ

Ran a stock 23 M/P this weekend. Ran 53 to 5400 RPM's but would only go 63 MPH. This is the 2nd 23 M/P I've ran and they both acted the same. 18% to 19% slip
Boat didn't seem to like the 23. seemed like the boat was just stuck to the water until it was trimmed way up.

The 25 M/P stock was running 67 at 48 to 5000 rpm's. 13% slip. I will bump the timing this weekend and see what happens.

Russ

articfriends

iTrader: (1)

Russ,hers a pic of my 272 at about 77-78 mph,i had extra b.s, in front cabin during a long trip a few wk's ago but compared to yours i think your also plenty loose. The only way i can get my 272 to run fast is with nose loose and the only prop's ive been able to so it with have been 4 blades at 16-20% slip,Smitty P.S.-Thanks for the pic John

Darkhorse468

Hey Russ,
The speeds you are running with the weight and other conditions seems in the ballpark. One thing I learned the hard way, and you may already know this, but I put 575hp's inthe place of my 330hp's in my 30 Sutphen. It originally ran 64mph at 5000rpms with 25 three blade cleavers. With the cleavers (hadn't had time to get the right ones yet) doing my seatrials, the boat barely got 70+mph at 4900rpm!!! And it wouldn't go higher. Fish around and found that the fuel shut offs were looking like 3/8, which are too small anyway, but really 1/4" id. The rest of the systems were all new 1/2" all the way to the carbs, but I overlooked this one critical area. After I put 3/4" ball valve type shut offs from the pickup tubes on, the motors pulled like mules WAY past 5000rpm for the short burst I gave her(their 4hours new) and got 79 mph with ALOT more to go. She also liked more trim, so it obviously fixed the problem. Moral to this story is, its the little things we overlook that kill us...(like my porous headers that held press, but failed under work. I later found possible temp. fix evidence that I didn't catch. Problem is, it was found after the motors were rapping.