311 Speed with 502's?
 

Hi Guys,
Ditched my 330's for 502 MPI's. Before they went in had valves done on both to be on the safe side.
With the old motors, I was turning 22P Bravo 1 four blades going 58 at 4400 RPM's on GPS. I now have on 24P Bravo 1's four blades turning 4800. My GPS isn't working now so I don't know exactly how fast I'm going (speedo says 64). The tachs are original so they're not the greatest. Any of you guys running the same power set up? If so, what prop is best, and what should RPM's be? I'm looking for 70!

You should be real close to 70 with that setup. In our 89 311 we upgraded from modified 330 motors to 502 MPI that we swapped out the MPI system for dart intakes and carbs from an HP 500. With labbed 24 Hydromotives we would see between 70 and 71 @ about 5200 RPMs (on GPS). Drives are turning out.

Hopefully someone running bravo props will chime in. Not sure if they are turning drives out or in? When I tested 24 bravos I had low rpms and slower speeds turning drives out, and turning in was similar to the hydros.

Sharpened stock hydromotives seem to work the best for me so far.

I've got a 89 292 but the speed between it and a 311 is almost the same. I've got a pair of 425 454's in my boat so it should be very comparable to your engines. With stock 25 pitch Hydro's I get 68-69 MPH @ 5000 rpms. With Labbed 25 Bravo's (24 castings)- 68 MPH is my best @ 5200 rpms. The Bravos were labbed at Mercury and I've been talking with Brett at BBlades and he says the labbing recipe is wrong so there is more potential there.

If you have a smartphone, down load a GPS speedometer app. There are plenty that are free. The one that I have found to be the most accurate is SportsTracker. One thing to remember is if it's 90 degrees and humid your speed will suffer. Last week when I was hot (90 and humid) 64 is all I could get out of my boat, yesterday it was 70 and I was back to 68-69. Good luck and let us know what you find out.

Thanks for the feedback. Haven't had a chance to get out. Will reset GPS and see what it's really at this weekend. Someone here said they were turning 26 B1's with same power. sounds a bit much, but a buddy has a set so I will try them too. Formula, are you saying that you were hitting 70 with the 24 Bravos turning in?

Got twins runs 62 with 330's so i would think 502's should push u to upper 60's, when ya coming to buffalo?poker run in three weeks

Best I saw was 68.8 with 24 bravos turning in, but under 35 mph I had a horrible cavitation for some reason. Really sucked for our night time speed limit.
That's why I was hoping someone else running bravos would chime in. See if they had similar results?
For reference, with upgraded cams from marine kenetics and bigger carbs, we turn 5300 with stock 26 Hydromotives. I don't think I can swing 26 bravos.

I don't think you'll be able to turn the 26 B1s.

i had a 91 311 with 502's - bravo boat with drives turned out (tried it in as well) the boat would run 71-72 gps. 24 pitch prop.

Chris- were you running Bravo props?

yes i was

Do hydros turn higher than b1? I have 26p b1's can turn 5200 gen 6 502's with some work done to them,,,and dry exhaust

I have a 1993 336 with 502s approx 425HP a side. Turning 24P Bravo 1s best speed 65.5 GPS at 4800. Ran 67-68 at 5000 with 25P Mirage. 24s will get to 4500 quicker than the 25s. Problem is too much stern lift for me..

I had a chance today to try different prop set ups. And GPS is working now.
First run for reference with B1 24's at 5000 RPM was 64
Put on B1 26's. Couldn't turn them. It (way) longer to get to speed and saw 63 at 4500 RPM
Back to 24's turning in and saw 63 at 5000 RPM. Cruising with shifters in reverse is weird by the way!!!

I did notice that drives have about 3" of play back and forth independent of each other and no, I do not have a tie bar. Would that shave a lot of speed?

Also, the port motor is a but low at 5000 when the starboard motor is at 5100. Don't know if this is a motor thing or if 23 Yr old gauges just don't quite read accurately.

My other thought is these boats really don't go 70 with stock 502's, and I'm chasing a ghost LOL!
Happy to hear your thoughts guys.
Any thoughts?

Get a set of 25 mirage + 3 blades and you might see 3-4 more mph..also make sure your top cap bolts are tight on the bravo drives..just a caution they do come loose..

You really need a tie bar then set the toe in about a eighth of an inch.

I have a 90 311 with MPI 502’s I was wondering what is the diameter of your prop. I’m running a 27 pitch three blade right now and I’m getting about 68.

The MPI 502 was not original to the boat. Is this a Bravo setup or was it originally a 420 TRS boat (I think you could still get a TRS 311 in 1990).

The documentation that I have from Formula says that the 390 horse 502 Magnum/Bravo runs right at 69 MPH (radar) at 5k RPM. It did not have the prop listed, but my guess was that it was spinning a 25P Mercury Mirage 3-blade (23P would overrev I'm pretty sure).

My 88 had 502 MPI 415s and it ran 69-71 depending on water , weather, and weight. I had to trim the drives (TRS) way off the scale to get there and it took a lot of room to do it. RPM would typically run right at 4700 with a 27P Mirage maybe a tad more.

The 311 with its rocker hull needs a lot of power, trim, and rougher water to go fast. Friends with some pretty strong 311s have come to me saying their boats are supposed to run upper 70s/low 80's and could only get low 70's out of them and no RPM. I would ask about where they were trimmed up and they'd say about 6, 7, maybe 8 on the indicator card. I would tell them to trim it to where it starts to fall off and then bring them back in a touch - basically way off the scale. When the stern gets light and starts to dance around a little, you're in the zone. Over a good distance there's another 5-6-7 MPH to be had. I very much recommend having hydraulic steering on these boats.