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4.5 200 / 4.5 250 differences....

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Mike94ZLT1

New member
Hello everyone, new member here. I recently picked up a new Monterey 204FS with with 200HP 4.5 in it. I'm pleased with the performance, but the gearhead's curse is creeping over me, and I want to tinker. What do I need to do to get that extra 50HP?

I dug through their parts catalog tonight and can't find a difference in part numbers. The block is the same. The heads are the same. The cam is the same. The intake and TB are the same. The springs are the same. The rockers and lifters are the same. The injectors are the same. All the major mechanical parts are the same.

The only difference I saw anywhere was in the operating range. The 200 redlines (per MerCruiser's website) at 4400-4800 rpm and the 250 redlines at 4800-5200 rpm. I'm not sure why there is a 400 rpm variable, but it is irrelevant. I'm almost positive the difference lies in the PCM and the tuning. The 200 has the same rotating assembly and parts to support the additional RPM, the same injectors and pump to supply the additional fuel, and the same exhaust to exhale through.

I would bet anything a tune would get us our missing 50 HP. Thoughts?
 
The ECU can be programmed.....but since its a mercruiser engine, you'll likely have to have a dealer do it.....there may be some independent shops that have acquired the tunes but not likely....
 
Think your only options are to find a Merc dealer to reflash the ecu if possible or buy the 250 hp ecu.

Went through a similar situation with my brothers Yamaha 50 hp outboard, lower head and engine is the same as 60 ho ... same except for ecu and a restrictor plate in intake. Taking out the restrictor plate netted 3 mph of top end per gps
 
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