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More HP in 7.4 MPI's?

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Old 08-12-2016, 04:49 PM
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Originally Posted by Griff
In a correctly tuned engine, Carb vs MPI fuel economy is minimal. Maybe 5-10%
And the reason why for guys who arent really engine guys is IF your carbed motor is jetted correctly , which is normally for a much narrower temperature range and altitude than most cars there is very little difference. So most of us boat between 70-90 degrees so your carbed motor doesnt have to be able to run right at 20 degrees, it can be jetted for 70 or 80 degrees. And another dirty little secret about the crude EFI Merc used before all these 555 ho motors is even though there are altitude, intake air temp,baro correction tables in a mefi 3 ecu, many of them are all set to zero so they dont correct anything anyways, they almost might as well be carbed.
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Old 08-12-2016, 04:55 PM
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I believe camshaft is different. ECU will have probably have to be programmed. Talk to a programmer like Mark Boos or etc before assuming no tune will be needed..
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Old 08-12-2016, 05:55 PM
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We had a 454MAG EFI that would vapor lock in the heart of Summer. Now we have a carbed blower motor and it is much easier to start regardless of conditions, go figure!
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Old 08-12-2016, 11:18 PM
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Originally Posted by jsoderbe
So, I bought these, thanks ICU!

Does anyone know if the 7,4 Mag MPI with 385 HP is the same engine internally as my 7,4 Mag with carbs and 365 hp?


Regards,

Johan
MPI's use a roller cam. Carbed have flat tappet cams.
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Old 08-13-2016, 02:17 AM
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I am sure carbs work in the US, but over here in Europe a carbed bigblock is worthless. They have a bad rep for power, fuel consumtion and reliability. There are no mechanics that work on carbed engines anymore, just the new breed of OSB mechanics. And, fuel is about $6 a gallon, so people just dont buy carbed boats anymore. Right or wrong, I just follow the market. I honestly think this boat will be worth $15k more with MPI's than carbs!

The engines need to be refurbished anyway, after 680 hours, and they need to be out of the boat for this conversion. The boat ran in Kentucky, and have been in Sweden for about 5-6 years now, so I would consider this a fresh water boat. I hope I can re-use the blocks.

Isnt this the perfect reason to upgrade the cams? I think I will start a new thread about this.

Thanks guys for all your ideas and support!


Regards,

Johan

I
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