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What engine do i have?

Old 03-09-2012, 02:00 PM
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Default What engine do i have?

I recently bought a new boat with the merc 454 bravo 3 and im finding conflicting information about the motor. The person i bought it from said it was the 300hp but when i look it up by the serial number everything is telling me its the mag. The serial number is 0f282609 any info on what it is and possible up grades would be great.

Thanks in advance
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Old 03-09-2012, 02:26 PM
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it does come up as a magnum if it is you have forged internals and rec heads lots of upgrades possible i am sure someone else will chime in but it looks like a magnum to me what carb and intake manifold does it have is it a high rise or does it look flat?
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Old 03-10-2012, 09:32 PM
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Serial Number 0F282609 is a 1994 GEN V MERCRUISER 7.4L BRAVO III Model Number 474H1F0GT with a Propshaft Rating of 300 HP.

The link below is going to be your engine parts catalog for this engine, Anytime you look up a part number that you may need, make sure you or your Merc dealer reads the notes, You need the Bravo 3 parts, not the Bravo 1 or 2, There is a difference on some of the engine parts for this model.
http://www.mercruiserparts.com/selec..._nbr=821723+92

The service manual for this engine is going to be merc part number 90-8232242, (it covers 1993 THRU 1997) (AKA, S.M # 16).

To help find out exactly what type of engine you have, Take a look at the first link below, find your letters on the engine block & match the #'s up in the S.B, (See page 6) then read all of page 3A-4 in the second link below.
http://www.boatfix.com/merc/bullet/97/97_06.PDF
http://www.boatfix.com/merc/Servmanl/16/16A3R2.PDF

Page 3A-4 will read like this below, but in a chart. Good luck.
DISPLACEMENT 7.4L 454 MAGNUM 502 MAGNUM / 8.2L
Bore 4.25 (108) 4.46 (113.28)
Stroke 4.00 (101.6)
Compression Ratio 8.0:1 8.6:1 8.75:1
Heads Cast Iron
(Oval Port)
Cast Iron
(Rectangular Port)
Intake Manifold Cast Iron (Note 3) Aluminum With Brass Inserts-High Rise (Note 1)
Block Cast Iron (4 Bolt Main Bearing Caps)
Rods Forged Steel
Pistons Cast Aluminum (Note 2) Forged Aluminum
Crankshaft Cast Steel Forged Steel
Camshaft Cast Iron (Gen V) Steel (Gen VI)
Note 1: 7.4L / 454 and 502 Magnum Multi-Port engine is equipped with a cast aluminum intake manifold with
brass inserts.
Note 2: 7.4L Bravo Three engines with engine code
UB with serial number OF1589289 and lower will have forged pistons.
XX with serial number OF159290 and higher will have cast pistons
Note 3: Serial numbers OD838819 thru OF800699 are equipped with cast aluminum intake manifolds.
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Old 03-12-2012, 01:54 PM
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Great motor, it will run for years/decades with no work, mine has.
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Old 03-16-2012, 12:45 PM
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Thanks for all the info. It is strange because its only rated as the 300 hp but it has the alum intake and mag carb?? Why would they do this on the bravo 3? is it just the way the engine makes power? is the bravo 3 less efficent their for the engine make more crank hp then the standard 300 but is rated the same because of the bravo 3?

I hope that all made sense because my mind is all confused
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Old 03-16-2012, 04:49 PM
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This was what Merc installed on the B3 equipped 7.4 engines. Rectangle port intake on oval port heads....

Originally Posted by Jbsk731
Thanks for all the info. It is strange because its only rated as the 300 hp but it has the alum intake and mag carb?? Why would they do this on the bravo 3? is it just the way the engine makes power? is the bravo 3 less efficent their for the engine make more crank hp then the standard 300 but is rated the same because of the bravo 3?

I hope that all made sense because my mind is all confused
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Old 03-19-2012, 08:09 AM
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You look to have what Merc called a "Performance Tuned" BIII . The changes were done to increase mid-range torque in the BIII application, specifically for pulling high load on large cruisers. Had the Mag intake on small oval heads, different carb calibration and a recurved distrubutor module. Some (but not all) had forged internals.

From the August '93 PowerBoat:
The Bravo Three uses a Performance Tuned V-8 that can be bought only with this drive as a system. The 7.4 PT's high rise mag intake, tweaked 4 bbl carb, and timing adjustments are designed to improve torque in the critical midrange.
I had one in my PQ, but the block was changed out some time back for Mark IV replacement block w/ cast internals.
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Old 03-21-2012, 09:48 AM
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ahh very interesting. gotta love manufactures that do these little things that drive the do it yourselfer up the wall! Any ideas on suggustions to gain a little hp with this set up?
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Old 03-22-2012, 10:53 AM
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IF you have the forged internals, you have a platform that can go up fairly well in HP. If yours are cast, like mine, you are limited to around 5000 rpm, and maybe 75-100hp more. Try for more on cast internals, and experience says things go boom. But frankly, unless you ditch the BIII, huge HP won't help, they hit a wall around the mid 60s.

The path forward is the same - ditch the peanut port heads for lg ovals or sq ports (depending on goal), change cam, and possibly intake. Unless you change the exhaust, you will severly limit cam selection (and power).

None of this is cheap. OTOH, your existing 7.4 will run practically forever with routine maintenance.

Just curious - what speed/rpm are you seeing now?
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Old 03-27-2012, 10:47 AM
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i am currently running 54.6 gps with a 2/1 ratio and 28p bravo3 props im not looking to go insane but would like to see 60s
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