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convincor speed

stclairriverblaster

stclairriverblaster

Member
hey guys. i finally got her on gps and she topped out at 66.7 mph at around 4800 rpm. but couldnt get it to spool any higher than that unless i trimmed way up but then it would slip badly.

the prop is a bravo 1 24 pitch and i have the 1.36 gearcase

when i got back in i realised my fuel pressure was around 4.5 psi at idle. oops:poke: is the shortage in fuel pressure the reason for it not wanting to rev out.. i thought this motor would have no problem spinnin this prop:cheers:
 
What motor you have in your boat and what HP you pushing? I just put in a 540 in my convincor and am turning a 25p mirage plus to 5000rpm. This weekend I'm going to try a bravo one 24p. A buddy of nine has a 253 with a HP 500 and he is turning a b/1 24p and running about 5000rpm.


I am running 7.5 for fuel pressure that's what nickerson's recommended.
 
its a slightly modded 454.. .070 over forged pistons. 9.5:1 compression. 128cc combustion chamber. longer eagle rods. full arp fastners fully balanced rotating assembly. roller rockers roller lifters. merlin heads 5 angle valve job. full msd igniton with mechanical advance
 
stock fuel pump should feed that motor but i went through the same issues with my repower are your plugs showing lean after wot runs i ended up upgrading to a holley blue pump with a regulator are you using all of the stock stainless lines theyre probably too small and there is a check valve in the pickup from the gas tank that you can take out it is very restrictive also but i have to ask what rpm is your motor set up to run to also you can try a smaller prop and see where it runs just to check to make sure the motor is running up to max rpms did you put upgraded exhaust on that will make a huge difference in how your motor runs you have those great flowing heads but then have to try to ram that exhaust through the stock manifolds
 
i have a red top fuel pump that im hoping just needs a rebuild.
plugs havent pulled em yet all the lines are aftermarket and anl fittings

i have cmi big tube headers
 
if that fuel pump is a holley red it has a built in regulator set at 4.5 psi. you probly want a holley blue with no regulator. amazon.com has them fairly cheap. you need at least 7 psi I believe.
 
brian752 said:
What motor you have in your boat and what HP you pushing? I just put in a 540 in my convincor and am turning a 25p mirage plus to 5000rpm. This weekend I'm going to try a bravo one 24p. A buddy of nine has a 253 with a HP 500 and he is turning a b/1 24p and running about 5000rpm.


I am running 7.5 for fuel pressure that's what nickerson's recommended.
Click to expand...
What speeds are you getting?
I have the hp500 and a 253 Convincor and run anyday about 70 - 72 gps with a 26 Bravo at 5200rpm. The best i've seen is 74.6 with a 25p, 3 blade Mirage.
 
I also have a 253 with a hp500 built into a 540 xr drive and see 72-75 gps tryed alot of 3,4,5 blade props and even a imco -2 lower and never got close to the holy grail of 80mph, was my goal at onetime.
 
glen george said:
I also have a 253 with a hp500 built into a 540 xr drive and see 72-75 gps tryed alot of 3,4,5 blade props and even a imco -2 lower and never got close to the holy grail of 80mph, was my goal at onetime.
Click to expand...


What prop you are you running and how is it handling. I'm still trying to find a good prop to run. Had a mirage 25p plus but it likes to blowout. Had that running at 5000 at 74.8 mph GPS. I would like to try and run a 26p bravo one or a 25p hydromotive quad 4 x you have any luck with the hydromotive? Let me know thanks.
 
Im running a mercury labbed 24P b1 at 5300 rom 73.5 gps , i have a labbed 28p coming this week, i did not like the 3 or 5 blade props , 4 blades are the way to go, bravo 1 I liked beter than the hydromotive also.
 
ok i have a strange feeling that my tach is way off
second.. my timing doesnt want to advance fully and bounces around from 10 inital to around 25 very unsteady when i raise rpm.. need to check timing chain. or distributor for play. msd pro billet with new components)and 7al2 box

it says im doing around 4300 rpm@ 67.6 mph.. that gives me around 6 percent slip.. which is obviously wrong..

i figure i get around 16 percent slip and that would put me around 4800 rpm @67 mph.. im thinkin my motor doesnt have many horsies up top and would like a bigger prop. but first i need to get a decent tach
 
stclairriverblaster said:
hey guys. i finally got her on gps and she topped out at 66.7 mph at around 4800 rpm. but couldnt get it to spool any higher than that unless i trimmed way up but then it would slip badly.

the:cheers: prop is a bravo 1 24 pitch and i have the 1.36 gearcase

when i got back in i realised my fuel pressure was around 4.5 psi at idle. oops:poke: is the shortage in fuel pressure the reason for it not wanting to rev out.. i thought this motor would have no problem spinnin this prop
Click to expand...

If there's any question about your fuel pressure, then I would suggest checking it at WOT (wide open throttle). And make sure you still have 4.5 psi. If you've got a pump with a regulator in it and it's 4.5 at idle and it stays 4.5 all the way to full speed @ WOT then it's OK.. If it drops off...then you have a fuel issue.
As far as props....I've tried many different ones. I'm running about 500 Horsepower in a 251 Convincor. Right now my favorite prop is a 26 Bravo 1 turning about 4700-4900 rpm and about 70-72 mph depending on temperature and weather. (1.5 ratio outdrive.) Hydromotives are good. I've also got a 29 Tempest Plus thats....just OK... it drops my rpms about 2-300. and mph goes down about 1-2 but cruising speed goes up at a given rpm.
Check you fuel pressure at WOT.
 
did you check the little dial on the back of the tach i had some similar issues with my tach and im guessing that a lot of bouncing around turned the dial to the wrong setting but i reset it and its like new again
 
well called barry grant because he modded the carb.. and come to find out i have a stage 3 1050 cfm four barrel holly .. so yeah i got plenty o fuel lol
 
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