1988 25 ft convinsor

[tonywil33]

just had 454 motor rebuilt running about 400 horse power need prop help running like 4000 rpm at 60 mph with a 23 prop bravo 1 does that sound right thats all the rpms the boat has could use some input thanks

 

[keith4216]

There,s a few motor builders here that will tell you more but I,m sitting here saying hmmmmmmmmm. That motor should be turning another grand in rpms and seeing 60 at 4000 I,m assuming thats not gps. I have close to the same set up and see 65 spining the same prop at 5000 rpms. Im not sure but you might have a motor issue not a prop issue.

 

[JimK]

You might want to check the tach against a mechanic's test meter. Sometimes it is as simple as the little switch on the back of the tach not being on the correct setting (for instance - 6cyl instead of 8cyl).

 

[tonywil33]

my motor guy said get rid of the quadrajet and put a 750 holley on does this make sense to you guys just wondering?

 

[lcboater]

A bravo1 runs in even pitches so it should be a 22 or 24.How many blades does your prop have,if it is a bravo it will have 4. 4000 rpm's would probably be in the 60 range but you should be closer to 5000 rpm's.

 

[jazzy]

sounds like you have more than that going on not to ask a stupid question but you are trimming up the outdrive do you have your vacuum lines hooked up i believe that carb has vacuum secondaries and you wouldnt get much past that point without using the secondaries

 

[tonywil33]

have a 3 blade prop tried a 25 and ran about 50 at 3200rpm going to try some things out this weekend to get the rpms up.the boat did seem to run strong just no rpms in top range pulls right up out of the hole just no top end rpms.i believe the boat came with a 23 pitch prop factory and turned like 4800 i no it has more than 330 hp

 

[Big Red]

For one thing you need a GPS not a water filled dream-ometer

Your boat new with a 23P prop at 4800 rpms ran 62.7 mph with a good driver with seat time that could keep the slip rate down where it should be.

4000 rpms with a 23P prop with a good driver is 52.3 mph

3200 rpms with a 25p prop with a good driver is 45.5 mph

If you did not build your torque numbers up on your engine and just added horsepower your gain is not good.

How excatly did you get 400HP from your 330HP engine what mods did you do.

 

[tonywil33]

ok here we go 454 mark 5 block stock lower end set of oval port heads closed chamber summit cam i will have to get numbers running stock intake and quadrajet carb. set of custom marine headers the big ones boat wont go over 4 grand on gps at 59 mph..i have someone checking into the block and numbers on the heads..other than that the boat runs great no rpms we put another tach on it to check rpms.... any input

 

[Big Red]

The summit cam is the problem throw it in the trash can and find a marine "motor guy"

 

[tonywil33]

thanks big red also just found out the heads suck also.found other sources have to run it the way it is for now until the season is over.thanks every one for the input