moving from 496 mag to 496 HO
 

Hello,

I have a Baja 275 and the engine blew on me late this season (496 mag). I have ordered and will be installing a new 496 HO. I was wondering if anyone can chime in on what type of performance increases I can expect? Increase in speed? Acceleration? Is there a difference in sound?

Thanks for your input!

your picking up 50 hp, I would guess 2-3 mph if that, more cam in the HO, so maybe a little more thump

Yeah.
2-3 sounds about right.
i really liked my HO, has a nice lumpy idle.

You will need the ecu reprogrammed for the HO

I have a good spare 496 HO Ecm no longer needed. I have sold the boat it was for. If interested please contact me at
847-204-7876
Jeff

The HO is in and ready. Does anyone know if I will need a different prop?

What prop do you have now?

Break the engine in first, then see where the rpm is at WOT, if you're running up on the limiter you may want to change it.

Same prop as I run on my 275 with HO. What I've seen on Merc's break in:

20-Hour Break-In Period

IMPORTANT: The first 20 hours of operation is the engine break-in period. Correct break-in is essential to obtain minimum oil consumption and maximum engine performance. During this break-in period, the following rules must be observed:

Do NOT operate below 1500 rpm for extended periods of time for the first 10 hours. Shift into gear as soon as possible after starting and advance the throttle above 1500 rpm if conditions permit safe operation.

Do NOT operate at one speed consistently for extended periods.

Do not exceed 3/4 throttle during the first 10 hours. During the next 10 hours, occasional operation at full throttle is permissible (5 minutes at a time maximum).

Avoid full throttle acceleration from IDLE speed.

Do NOT operate at full throttle until the engine reaches normal operating temperature.

Frequently check engine oil level. Add oil as needed. It is normal for oil consumption to be high during the break-in period.

After Break-In Period

To help extend the life of your Mercury MerCruiser power package, the following recommendations should be considered;

Ensure that propeller allows the engine to operate at or near the top of the specified WOT rpm range (Refer to Specifications and Maintenance) when at full throttle with a normal boat load.

Operation at 3/4 throttle setting or lower is recommended. Refrain from prolonged operation at WOT rpm.

Change the oil and oil filter. Refer to Specifications and Maintenance.

Not likely. The HO is rated for 200 rpms than the standard 496. The HO has a 5150 rev limiter so as long as you below that its fine.

For the HO you really want to keep WOT at 5000 rpms for stock apps and the NON HO ( mag ) at 4800 rpms.

496 throttle plate is 75 mm for both apps --- MAG and HO.

the mag has a bypass of 0.100 and the HO has a 0.200 in the throttle plate.

Just some extra info on top of