Crankshaft or Propshaft HP?
 

Are Mercruiser's current horsepower ratings taken from the propshaft or crankshaft? For example, I was under the impression that a 496MAGHO has 425 propshaft horsepower. However I just received Mercruiser's latest product brochure and under engine specifications they state "Performance obtained and corrected in accordance with SAE J1228 crankshaft power." I'm confused.

Re: Crankshaft or Propshaft HP?
 

As far as I can tell Mercruiser uses propshaft horsepower ratings with their standard engine line and crankshaft horsepower with there racing engines. This is somewhat misleading because a 496MAG HO 425 propshaft HP and 500 EFI 500 crankshaft HP should read 470 HP when comparing apples to apples. How about the 377 Scorpion? How different is that from the MX 6.2? Looks like only 30HP from were I'm standing. That it is quite an increase in price for 30HP. Any insight would be appreciated.
Rob

Re: Crankshaft or Propshaft HP?
 

I thought they are all rated at the prop shaft.

Re: Crankshaft or Propshaft HP?
 

checkmate454mag,
Have you water tested your new 540? I also wanted to ask you about mid speed porpoise in the 259 Convincor. It seems if I have the boat loaded with people I cannot avoid a mid range porpoise, between 35-45mph before the boat achieves a comfortable set. Have you experienced similar ride characteristics? How do you avoid it?

Re: Crankshaft or Propshaft HP?
 

I your running a 3 blade try a bravo prop. It helped me quite a bit. If you need more add tabs. I run a set of 380S K-planes. With those down I can plane with no porpoise at any speed above 20mph.

Re: Crankshaft or Propshaft HP?
 

I currently run a 23P Mirage Plus prop. What pitch bravo prop would you recommend with a stock 454MAG?

Re: Crankshaft or Propshaft HP?
 

If your rpm is right, a 22" bravo is the correct one.

Re: Crankshaft or Propshaft HP?
 

Talk to the guys at hydromotive about your porposing. IF you spin a 4 blade, lab finished, it will take away your porposing and because of the lab finishing you will not loose and MPH versus a 3 blade. Plus there will be no blow out when you hit the throttle to get out of the hole. Check it out, Pretty cheap solution. They are very knowledgable.

Re: Crankshaft or Propshaft HP?
 

I've had hydromotive 4 blades on as well. It will also help the porpoising, but I found their prop to be a little slower for me.

If you lab either prop properly it will increase your top end, but it usually won't change the porpoising much.

Re: Crankshaft or Propshaft HP?
 

I agree with the above statements. A good labbed prop and tabs will cure your problem.

I have run the new power one time so far. The results are not too good yet. It turns out I am over propped. I tried a 27" P-5X Hydromotive. I could only get 4800 rpm @ 75.5 mph gps 80mph speedo. I need to get about 800 more rpm. This weekend I plan on trying my labbed 26" Bravo. Hopefully, it will yield better results. Then I can settle in somewhere with the right prop. Maybe somewhere around a 25" P5-X, but I am not sure yet.

Re: Crankshaft or Propshaft HP?
 

Vinny,

Why did you choose a P5X? I would think your hull would like more bow lift than a P5X can deliver. Did you have it trimmed higher than last year to hit top speed?

Re: Crankshaft or Propshaft HP?
 

Dave,
I went with the P-5X on Throtle-Ups recommendation. The boat did ride a bit different. Like you said, not as high from the bow. I'll see what my Bravo wheel gives me. Of course, the weather doesn't look good here for the weekend.

Re: Crankshaft or Propshaft HP?
 

The reason I'm testing a 5 Blade is to hold 1300HP and use a 2" shorty drive. Without a shorty drive, I can't see how a 5 blade could help a checkmate. But stranger things have happened.

BTW the weather here looks bad too. %#@*&

Re: Crankshaft or Propshaft HP?
 

I am beginning to think that I may have made a mistake with going to a 5 blade. My thoughts were to get a bit less slip over a 4 blade. Besides, Throttle-Up thought it would work as well. It still may, only further testing will tell. Luckily, they will exchange the prop for a different style and or oitch.

Re: Crankshaft or Propshaft HP?
 

What slip did your bravo have last year? You may want to talk to Brett at BBlades.com. I've dealt with him for years, and he's been very knowledgeable on checkmate hulls.

Re: Crankshaft or Propshaft HP?
 

I got 9% slip with the Hydromotive and 14 1/2 % slip with the Bravo. I am not sure how or if the Imco lower drive I have on now will effect the slip numbers as compared to standard Bravo 1 H.P. drive from last year.

Re: Crankshaft or Propshaft HP?
 

From my testing a nose-coned lower will usually reduce your slip. Since there is less blowout, Especially at high speed. Your slip results are very similar to mine. If you want to use the 5 blade you will most likely need to raise your drive height about 1". I realize that would require a 2" shorty with a spacer. It's only money........

Re: Crankshaft or Propshaft HP?
 

This weekend was another bust weather wise. I plan on taking some time off from work this week to give it a run with my 26" Bravo. I'll let you know. I am going to try to avoid going to a shorty.