Should I get my props labbed and polished?
 

I've lost 3 - 4 mph on my 502 since I bought my Cobalt 2 years ago and the only really thing I can think that has happened is my props aren't running true anymore.

I just got done replacing manifolds and exhaust collectors on the boat and in the process I yanked the catalyst. I know I'm not really gaining any significant performance with those changes but should I consider labbing and polishing the props on my B3?

If so, anybody know any reputable lab shops in the Tampa area? And should I ask them to try and get me another 200 RPM? Or add some cup?

Unless the props are damaged, I doubt that is the cause for 3-4mph loss. Have you lost rpm at WOT??

I would look toward the health of engine first. Do a leak down test.
Second, check for hook in the bottom of the hull.

I would PM 12meterjoe on here. He is designing and testing some new props.

as griff said,new props are not the answer,sounds to me like the boat is down on power,new props will only confuse him more.

I'm about 4600 RPM at WOT

What we're you Before? Do you have a lot of stuff that has collected on the boat and adds weight? Have you changed plugs, fuel filter Etc? What does the prop look Like?

Padraig

does the boat stay in the water or on a trailer?

For 75hp Johnsons

How clean is the bottom of hull, outdrive and props (growth)?

What does your spark plugs look like ???? Wet - black - tan or ???

Also prob in needed of spark plugs and possible wires ?.

Compression test numbers are ?

Very Clean flame arrestor and throttle body ?

Fuel injectors needing to be flow tested and clean ???

Well I TOTALLY missed that your 502 in which MERC calls it an 8.2 CATALYST ENGINE. Your engine is a 2010 and up year model -- Not what every else here thinks it is ( the older 502 1993 thru 2000 )..

WOW and WOW --- you took off the catalyst system, manifolds and risers and what did you do to the PCM or NOT do for a correct calibration ???

YOU CAN NOT RUN THE ENGINE ON A STOCK LOCKED calibrated PCM from MERC. when you took off the their exhaust set up and catalyst system. You are going to damage the engine with the stock tune with out those stock OEM parts that were engineered into the calibration from MERC. .

Tech speaking MERC calls this the 8.2 EC engine FYI MERC never brands this engine a 502, why I missed it being a CAT engine to begin with per your calling it a 502.

You are actually down 400 RPM's not 200 rpm's per removing the stock parts for your app.

The 8.2 EC engine is max 5000 rpm's.

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