cass236

I'm a little disappointed in a boat i recently purchased. captiva cuddy 236 1993, 502 mag bravo, carb 390hp. hull weight 3725 (nada). I figured with the power and the weight of the boat i should see 65-70. The boat came with a 21p mirage prop 5200 rpm. 58.6 mph. So i bought a labbed 25p, result 4200 rpm 57.x mph. Looks like i need a 23P, and i have no chance in hell of getting 65+, I would be happy with 60. Shouldnt I be able to keep up with a baja 23/4200lbs/375hp. Those seems to be running high 60's?? Or is it just the deep v hull design limiting me? Also the 21p was a solid hub, and the 25p needed the plastic insert kit. does that matter?

stevesxm

my guess would be that your alleged 390 hp is more likely closer to 275 or 290

cass236

Hmm boat seems to run good, i will go do a comp test and see what i get.

stevesxm

thats a light boat that the math says if it had your true 390 should do 70 i would think intuitively and the math suggests better than that...

on the other hand, the math also suggests that 60 mph on a typical boat like yours is about 280 hp... so my guesswork wasn't bad...

there are a million reasons that this can happen not the least of which is that there have probably been people screwing around with that motor in lots of ways before you got it. if you REALLY want the answer, yank it and sort it on the dyno... that grand or whatever it costs all at once will be a much better deal for you in the long run than throwing 250 bucks here and there at it and never finding your answer.

and lets suppose its something easy... like the jets are fat or the float has sunk... you go to the dyno and fix it and youre a star... you RUN it like that without fixing it and fill your oil up with fuel and your next post will be " gee i wore out my cam and lifters and everything else... how can that happen with so few hours ? "

be smart. fix it once.

cass236

here is what i got for a compression test. 105,100,110,132,100,135,103,115. So to me it looks like two cylinders have full compression. Why are the rest of the cylinders so much lower? Do i need a new top end, a rebuild or what>? Boat seems to run good and doesnt blow smoke or anything. some of the plugs looked wet and gunky, two of them were dry. Boat doesnt seem to be using oil and oil looks clean.

stevesxm

there is no way to answer this that will be authoratative. it all depends on what you want to talk yourself into and what you care to believe.

if you think your compression test is accurate and trust the results then they suggest that the motor is tired. rebuild it.

if you think, for some reason , that you can get away with just a top end, then do a leak down and see where the air leaks out. i'm betting the breathers start huffing like steam ship.

the fact is that the motor gives every indication of being tired but if you feel that a fresh set of plugs and a tune up might fix it then you should do that.

and if you think a fresh set of heads will fix it then you should try that too. i try not to work like that.

if it were mine, i'de pull it and freshen it complete and be done with it all at once. they are a good tough motor. doing rigns,bearings and a valve job is cheap and simple and will fix you right up.

ENFORCER24

just a side note here , its ALOT cheaper to rebuild right now before any failured have happened , as opposed to running a tired engine hard this summer and scoring a cylender or throwing a rod or breaking a valve etc etc , rebuilds get alot more expensive when failures happen.
aside from that , how many hours on the boat? if its below 400 i would lean toward top end , freshen the heads , if above 400 then you need to pull the engine and take it to a machine shop for a simple rebuild
just my .02

hoozeyurdaddy

They clam that anything more than 15% of the highest cyl. needs to be repaired, that puts your limit at 115psi for your lowest cyl. I just did a rebuild and blower install on a 232 rinker, even if you just plan on doing the heads, pull the motor, save your sell the back ache.
Larry

cass236

The boat does not have a hour meter it is a 93 though, It is in good shape and the motor looks untouched. It is 15 years old, so probably more than 400.

stevesxm

for no reason at all, i was looking at engines on ebay the other day... some guy had NEW... not rebuilt but FACTORY new 502 shortblocks for 4 grand. thats about what a rebuild will cost you more or less... now i don't know what "gen" yours is or if your heads would be compatable but its just something to consider.. the bottom line is that you should probably have it apart one way or another.