Couple questions

Blackbart5

Seaman
Joined
Jun 8, 2015
Messages
68
Hello all......have a couple questions, 1- I have a '97 Mariah 252z shabah 7.4 /b3. My flame/carb cover is black with red lettering. I have seen some same year/engine covers that are black with light blue lettering?? Is there a difference between the two engines even though they are the same size and year? ........next question, my pitch on my props are 28's??? How or where can I tell what factory is suppose to be? This seems kinda high to me. Boat hits 2/300rpms shy of bottom end of rpm range.
 

Fun Times

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May 16, 2009
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8,776
The two different colors typically indicates (for both I/O and O/B) if the engine is set up for either fresh water or salt water....Red being fresh while blue = salt (AKA the big Blue.;)

http://www.ebay.co.uk/itm/mercruiser...-/151519709787
https://www.bing.com/images/search?q...2CD9EAD1AFBB78 (< or search online1997 mercruiser 7.4l engine blue decals)

If you're not reaching your RPM range, then typically dropping pitch size would help gain more RPM....28P does seem a bit high.
Being that the original Mariah is no longer in business since 2001, it would be difficult to say what came on "your" boat from new as the company may have held onto a build sheet to your boats hull ID number.

So you may have to do some trial and error, prop calculations or you might get luck and try your question on the Mariah Owners Club too should someone have the same boat/engine models as you.

The guys here are really good at getting you within the RPM range you need to be in....Just post all the detail you can about your boat, engine, drive gear ratio and go from there. Also be sure to check out the Read This First!! sticky in the Prop Questions and Topics here on iboats.
 

tpenfield

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Messages
17,620
4400 - 4600 rpm's would be the WOT range. If you are hitting that, then all is good. If you are lower, then the 28 pitch set is probably too high.

​Thing about Bravo 3 prop sets is that they are about $1K, so you don't see too many folks changing them out from what came from the factory.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Hello all......have a couple questions, 1- I have a '97 Mariah 252z shabah 7.4 /b3. My flame/carb cover is black with red lettering. I have seen some same year/engine covers that are black with light blue lettering?? Is there a difference between the two engines even though they are the same size and year? ........next question, my pitch on my props are 28's??? How or where can I tell what factory is suppose to be? This seems kinda high to me. Boat hits 2/300rpms shy of bottom end of rpm range.

Howdy,

I have a 1997 7.4L + Bravo III in my 87 Fourwinns 211 Liberator. (It was removed from a 98 24ft Bayliner) It's also a 1.81:1 drive and I have 24 and 26p props for it
I get about 4400 RPM with the 26's and a little over 4600 with the 24p props. I also have a 3x4 24p propset but I am not impressed.



97 7.4L engines include several models. ( reg 7.4 [carb], 7.4LX EFI , 7.4LX MPI (all rated 4200-4600 RPM)

There was also a 454 Mag MPI (4600-5000 RPM)

Your serial number will reveal exactly what you have.........


What is your drive ratio, speed (GPS) and RPM at WOT ? (for your size boat, I'll guess 1.81:1 ratio?)

If your WOT RPM is 200-300 RPM below 4200, (turning 3900-4000 RPM) You are over propped. You need to switch to 26p or 24p propsets.


Select prop pitch to obtain 4600 (if that's your max) at WOT when loaded at the weight (people, gear fuel) you will operate.

Running over propped will slow your holeshot, top speed performance and can possibly damage the engine due to lugging (from possible detonation)

Regards,


Rick
 
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