TomZ

iTrader: (2)

What's up folks?!

I've been going through the 311 working on upgrades here and there (sound system, LED lighting, cleaning cleaning cleaning), and now that the warm weather looks to be here to stay we're really starting to have some fun with her!

One observation that I wanted to bring up is around getting the props right. I know that this has been gone over quite a bit already, but my boat seems to be a bit of an anomaly in the fact that she has a pair of Gen VI 502 MPIs mated to B/W 72C transmissions and TRS drives. I'm thinking that power-wise, she's somewhere in between the output of a set of 454 mags and the original 420s she came with (but with more torque than either set up). Ted G and I were already discussing this some on Facebook, but I though I'd open it up top a wider audience. Now this could be that I do not have the boat trimmed out all the way (my last run I flat out ran out of room), but with the 23P solid hub Mirage props that I'm running, I'm hitting the rev limiter at 5200 and seeing 64 MPH on GPS. She may have been climbing a little more, but like I said I ran out of room. I see 420s running right around 70 at that RPM and the same prop; I'm seeing 16% slip with mine while the 420 sees around 9-11%. I'm trying to wrap my head around why? Regarding trim, I know that as I was running her, trimming would bring up the RPM so I know it was having an effect (that's how I got to the rev limiter). I don't think these things make much power over 5K RPM so having them up that high is a waste. I'd think though that RPM is RPM and that if she could spin to 5200 with the 502s that she'd get pretty close to what the 420s were doing. Formula says the boat should go a tenth or two under 70 with a 502, but I believe that's with a Bravo (I do not think there were any 502s in front of TRS drives made).

My thinking is to bring the RPM down to 4800-4900 with either a set of 25P Mirages or maybe some 4-blades. I have access to a set of 27P Mirages but they may be a bit too much. Distant Thunder has offered up his 26P Bravos to try in the next couple weeks.

Any thoughts?

aquaforce

My 357 had TRS with the O.E. 420's that got stroked. It had 24 bravo1 props.
Maybe the 26's could work with your shorter boat.

TomZ

iTrader: (2)

Definitely going to try them.

Anyone have comparisons to how the 502 runs versus the 420? I'm assuming there's more toque available because of the 48 CID difference.

Mr Maine

My 272 with 330s ran 4500-46rpm 64-65 with 25 mirages, non plus so 9 to 10 percent slip.

My 311 ran 70 at about 5200, 5250 with 23 mirage plus, so 9% slip or so. 420s with roller cam upgrade.

Are you running plus or non plus 23s? I think you should be at about 68 with your setup. The trs is a bit slower than the bravos. For some reason your slip is a bit high for a twin but there should be 4mph left in there. Are the engines strong? I know you had some firing order issues but how were the leakdown numbers?

TomZ

iTrader: (2)

The props are 23 Mirages, not pluses.

The engines are good. I never did the leakdown tests. They ran (and continue to run) so well that it seemed pointless. After finding all the stuff that was deliberately done to mess them up, just wasn't necessary to do anything else but run them. The boat gets on plan with no issues and accelerates hard. RPM is RPM. If something was up with them, I think we'd be chasing it in the other direction. In my opinion she's about 3-400 RPM over-propped. The question is why?

TomZ

iTrader: (2)

To clarify... I would think that the 420 would have a leg up over the 502, but perhaps not in the the RPM range that it operates.

Mr Maine

The pluses have more cup and bite harder than the non pluses. What are you trimming to? I want to say mine drives are level at about 3.5 and i trim up to 7.5ish wide open

TomZ

iTrader: (2)

Honestly, I'm still trying to get that all figured out. The drives are level at 3; she was climbing RPM with trim and then hit the rev limiter. No matter how she's trimmed she' reachs 5K RPM with no hesitation.

I'm not as concerned with the top-end as I am with cruise, but having a solid 69-70 MPH boat is a plus... not that it's anything to really brag about these days but still!

Mr Maine

I hear ya, just throwing some ideas out. My boat was about a mph slower with 25 pluses. But as you have said you may have more torque to turn them. If you were closer you could try mine.

SB

iTrader: (1)

Your under propped hitting the rev limiter.

No way toknow how fast it will go with hitting the limiter.

502MPI's run fastest if I remember right, right at 5,000rpm and OE rev limiter is 5150.