What really is the WOT on a 7.4L - no really

[Elk Chaser]

The Seloc manual says that the WOT is 4200 to 4600 on a 7.4L Bravo.<br /><br />However this spec.........<br /> http://www.marinemechanic.com/specs/mc-454SC.htm <br />says it is 4800 to 5200<br /><br />Holy bat dung Bat Man that is a huge difference in WOT. <br /><br />I was running on the assumption that I should be at the 4200 to 4600 range (based upon my manual) <br />and now I'm not so sure about that. <br /><br />Anybody know the answer for sure?

 

[f_inscreenname]

Re: What really is the WOT on a 7.4L - no really

I always thought with a middle of the road prop it would be 4600rpm’s.

 

[Airpacker]

Re: What really is the WOT on a 7.4L - no really

The 7.4 with cast crank and pistons was rated at 4600 maximun rpm. I can tell you that you can spin it at 5000 but I would not run it over that. 4800 to 5200rpm is for a 454 mag with a steel crank and forged pistons.

 

[WSUDERMAN]

Re: What really is the WOT on a 7.4L - no really

Don't forget the valve train. @ 5200 + with stock springs you might start to see some float....

 

[kcole683]

Re: What really is the WOT on a 7.4L - no really

Doesn't Mercruiser put a plate on the engine with this info anymore?<br /><br />My old 1985 merc. has a plate with tune up specs and WOT info etc.

 

[Bondo]

Re: What really is the WOT on a 7.4L - no really

Holy bat dung Bat Man that is a huge difference in WOT.

It's Also a Very Long, Expensive ways from 330hp, to 425hp, or 525hp.................... <br /><br />Stick to Your Manual........

 

[Elk Chaser]

Re: What really is the WOT on a 7.4L - no really

OK, but I am due for a new manual, the Seloc is gettimg very worn out (had it through three boats now) and it is not specific to the 7.4L. <br /><br />So when I buy a new one I can base my assumptions on the WOT listed in that one............ <br /><br />Engine was rebuilt and I was told it's built stock mercruiser, however it has raised pistons and aluminum roller rockers, performer intake, holley carb, thunderbolt ignition, rv/truck cam and I'm not real sure what else unless I tear it down. No plate telling me anything anywhere on the engine and even if it had one I could not really rely upon it.<br /><br />I'll stick to the 4600 max and go from there.

 

[Bondo]

Re: What really is the WOT on a 7.4L - no really

So when I buy a new one I can base my assumptions on the WOT listed in that one............

Yes,<br />IF you buy 1 for the 330hp, Standard Merc. 7.4l..... <br />IF your motor Is/Was a Standard Merc. 330hp,<br />You have a Standard Duty, Cast Crank, 2bolt Mains...........<br />Then You'll Still have to stick to the 4600rpms........<br />It Appears that your overhaul Might have upped your hp a Little,<br />But, Your Still running a Basically Stock motor......<br />Changing Manuals will Not give you the Heavier Hardware Needed for the High Output 425hp, or the 525hp motors, which run at Higher RPMs.......<br />Your motor,+ the 2 listed on the page you show with Higher WOTs, Share the Same Displacement .......<br />But, Little Else...............

 

[LubeDude]

Re: What really is the WOT on a 7.4L - no really

Most have bult in rev limiters, not sure about your vintage though, 4,600 is good though, your cam isnt going to produce any more HP past that anyway.

 

[Elk Chaser]

Re: What really is the WOT on a 7.4L - no really

Thanks guys, I appreciate your help.<br /><br />I completely understand the horse power differences I guess I did not relate the top numbers in the chart (link above) to be HP. My dumb mistake.<br /><br />Nope, no built in rev limiter that I know of, (thunderbolt ignition have one?) matter of fact I installed a motor protector but it is set up at about 4600 to 4800 or so.

 

[GL2238]

Re: What really is the WOT on a 7.4L - no really

I have 7.4MPI 2001 with B3. Motor only turns max at 4100 fully trimmed (26" SeaRay Sundancer). All diagnostics check A-OK. Another SeaRay and two Wellcraft with same I/O and block run 4300-4600. Props are the same on all four boats.<br /><br />Could rev limiter be at fault?<br /><br />Gerald