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How to ID the heavy duty 300 six

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Old 02-20-2012, 08:41 PM
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How to ID the heavy duty 300 six

Hello,
How do you identify the 300 six heavy duty engine from the standard engine? I have a 78 F150 4x4 that has a GVW of over 6000 pounds. it should have the heavy duty engine but, I don't know what engine I have.
Thanks, Joel
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Old 02-20-2012, 08:52 PM
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As far as I know, the HD 300 was the same as the regular 300. The only differences are a different exhaust manifold (the outlet goes straight down instead of curving towards the rear), some had a forged steel crank shaft (but not all), and there's some debate as to the possibility they had a different cam. Other than that, there isn't a whole lot of difference between the two.
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Old 02-21-2012, 08:39 AM
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I doubt a F-150 ever had the HD engine unless it was swapped in. The HD 300 would be found in a F-600 class truck.
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Old 02-21-2012, 09:57 PM
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Hello Harte3
Actually, the 1978 Ford truck shop manual says trucks with 6000 gvw has the heavy duty 300 six.
Regards, Joel
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Old 02-22-2012, 05:27 PM
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I should know the difference as I took care of a bunch of these in a fleet. The p 500 had a different head than the 600. It seems to me the 600 had sodium cooled exhaust valves the exhaust manifold as someone else said the forged crank as far as I know the cam was the same except it drove thru steel timing gears{and they were not noisey}. All those engines were reliable and had good long lives if maintained. We had some abusive drivers and they held up. Newspaper fleet GVW ment nothing, when I'd see them loaded up I often got into some difference with the delivery supevisors. kotzy
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Old 02-22-2012, 07:29 PM
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Most of the HD engines I've seen also had lower compression then the standard 300's. They had different pistons ( they were either a shorter compression height or larger dish ) .

Really there isn't anything too special about the HD's unless you had one of the early ones with the forged cranks.
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300, 49l, crank, duty, engine, exhaust, ford, forged, hd, heavy, id, identification, inline, manifold, straight

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