prop/engine/performance
 

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?

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

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

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.

compression
 

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.

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.

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

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

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.

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.

Update
 

I brought the boat in to a mecanic for them to do a leak down test. They did a comp test and came up with different #'s then i did, and they said the motor had no problems and felt a leak down was unecessary. So maybe i just have one of those boats that isnt designed to go fast. Is it worth the money to upgrade the motor?heads/cam/carb/header? fuel injection? 'We are probably 1,000-1,500 above sea level does that hurt me? Here is what the hull look like except mine is a cuddy with a 502.

http://cgi.ebay.com/ebaymotors/236-r...spagenameZWDVW

where are you at , i have a 23 pitch mirage plus you could borrow if your close
although , if your 1500ft elevation your probably on a lake somewhere far from me
elevation effects performance a little thinner air les oxygen , and a little more cause your running in fresh water , salt water is thicker and boats sit a little higher , less wet area = faster boat
i would lean towards 23 pitch prop , 1/4 tank and yourself = 60 mph , i'v never heard of the rinker hull being a very fast hull , but more of a comprimise between stable ride and speed
a last note , is the bottem painted or dirty ?
i ask cause i unfortunatly had to leave my boat in the water for a week and went from mid 60's to mid 40's on my performance , because growth on the bottem , i now have a project for saturday in pressure washing and waxing the bottem of the boat to get those 20mph back

20mph from growth? You must have some big barnacles on the bottom of your boat! I'm in MN, interested in selling it?

i really dont want to cause its my back-up if i crash into something with the 25p thats on it , but if you post in the "wanted" section you'll find more then a few
also look at ebay , the come across every day , its probably the most widely used performance prop out there right now

oh yea , its not barnicles , its the scum growth that fouls up the bottem on mine

the normal figure is 2% per 1000 ft of altitude in HP loss,
I'm at 6000 ft alt and deal with it every day, I run my boat at 3700ft and suffer a 15 mph loss from 700ft, so to answer your question, yes, elevation hurts you.
Larry

prop/engine performance
 

I have a labbed 23pt mirage that i will sell,had it on my baja until last year,works great ,built a 660hp motor over the winter and now this prop is useless to me,shoot me an email or call me 519 809 2800,my name is adam.