EFI 351 HD???
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Joined: Dec 2002
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From: USA
EFI 351 HD???
Information I have here on my truck (92 F350 CrewCab 4x4, originally a fed gov't truck, but with California emmissions) states that the engine is a 351 HD. What is the significance of this 'HD'. I have not heard of that before. I have heard of 'HO', but I thought that was only in Mustangs or cars, not trucks. What is the real story here (?), and if this engine is different than a regular 351, what is different about it?
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Joined: Aug 2001
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From: New England
EFI 351 HD???
I have a friend that swears there are two different 351w motors offered in the F-Series trucks. He tells me that there is a 351w and a 351HD. The HD has larger intake runners and larger (header like) exhaust manifolds. But I have not seen this, so don't quote me on it. He is a mechanic, so he should know what he is talking about.
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Postmaster
Joined: Dec 2002
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From: USA
EFI 351 HD???
[updated:LAST EDITED ON 31-Dec-02 AT 07:12 PM (EST)]I'll have to check out my exhaust manifolds and see if they look any different than other manifolds I have seen. The truck is definitely over 8500 lbs GVWR. I gotta say though, if this is the 'HD' 351, I'd hate to be stuck with a regular 351... this engine is, in my opinion, a gutless dog. Gimme back my Chevy Big Block!! LOL 
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From: New England
EFI 351 HD???
I do have a little more info on the 351w HD. I still haven't seen it but after talking to my mechanic friend again, he described it a little more. It seems that the intake tubes are larger and the throttle body is larger. A normal 351w has two tubes going to the throttle body, these tubes are about 3" in diameter. The HD also has two tubes but they are almost twice the size of the regular 351w. He also mentioned something about it being a different "letter" motor. The 351w is an "H" motor (?) and the HD is an "R" or "W" motor. I think he is referring to the letter in the VIN. It also has larger tubes in the exhaust manifolds. I will have to see this thing. He saying is has endless torque and a real monster power curve. I will keep researching.
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Joined: Jul 2003
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From: West Paducah, KY
EFI 351 HD???
I have a 351w EFI HD in my 1989 Econoline 150 Converion and found this out with the VIN using one of those VIN search engines to check the background. Ive seen pictures of the H type exsaust manifolds and they look nothing like the ones on my motor and the intake tubes are larger. The problem is I have found no information except for the reguler engine that was 210hp@3600rpm and 325lb/ft@2800 witch is all the info I could find for that model year.
Last edited by griffe150; Jul 24, 2003 at 09:19 PM.
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Joined: Aug 2002
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From: Colorado
EFI 351 HD???
It's my understanding the "R" code HD motor is rated 240hp @ 3600 with 345lb/ft @2800 for vehicles over 8500 GVW. The "H" motor found in most F-150's is rated (supposedly) 215hp @ 3600 and 325lb/ft@2800.
Yelrihseam
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Joined: Jul 2002
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From: Bend,OR
EFI 351 HD???
so if i was poking around the junkyard what years should i keep an eye out for this motor and how would i know its the HD . I am gonna be swapping a 351HO this fall and if this HD intake is bigger with larger throttle body it would be a nice find and help wake that ho motor up a little bit more im sure.
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Joined: Jun 2002
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From: Dallas, Texas
EFI 351 HD???
My truck decodes as an HD model.
I don't believe it has anything to do with the hp ratings. My truck is under 8500lb gvw. It did not have tubular headers (they were big, heavy, cast iron manifolds) and the standard 5.8 intake is used. I have mass air so the two air inlets that run from the tb Y-into the MAF. The two tubes are no bigger in diameter than those on my friends 91 SD 302. I do however have extra leaves in the rear as well as an oil cooler.
I don't believe it has anything to do with the hp ratings. My truck is under 8500lb gvw. It did not have tubular headers (they were big, heavy, cast iron manifolds) and the standard 5.8 intake is used. I have mass air so the two air inlets that run from the tb Y-into the MAF. The two tubes are no bigger in diameter than those on my friends 91 SD 302. I do however have extra leaves in the rear as well as an oil cooler.
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Joined: Jul 2003
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From: Lapeer, MI
EFI 351 HD???
My Bronco also decodes as an "HD". It has heavy duty springs, quad shocks (the better to dampen front end undulations while towing) up front, tranny fluid & eng oil coolers, and factory tow pkg.
There are no visible differences between the throttle body, intake and exhaust manifolds on my Bronco as compared to my ClubWagon (which does not decode as an "HD").
I am fairly certain that HD simply means Heavy Duty and is related only to chassis options, not engine options. FYI, my Bronco which decodes as an "HD" has the same "H" in the VIN...
As far as "monster torque", I assure you that the "HD" is also a slug... Take whatever 351W you can find, and start with all the usual mods if you need "monster torque".
There are no visible differences between the throttle body, intake and exhaust manifolds on my Bronco as compared to my ClubWagon (which does not decode as an "HD").
I am fairly certain that HD simply means Heavy Duty and is related only to chassis options, not engine options. FYI, my Bronco which decodes as an "HD" has the same "H" in the VIN...
As far as "monster torque", I assure you that the "HD" is also a slug... Take whatever 351W you can find, and start with all the usual mods if you need "monster torque".
Elder User
Joined: Jun 2002
Posts: 678
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From: Dallas, Texas
EFI 351 HD???
Originally posted by BroncoDave
My Bronco also decodes as an "HD". It has heavy duty springs, quad shocks (the better to dampen front end undulations while towing) up front, tranny fluid & eng oil coolers, and factory tow pkg.
There are no visible differences between the throttle body, intake and exhaust manifolds on my Bronco as compared to my ClubWagon (which does not decode as an "HD").
I am fairly certain that HD simply means Heavy Duty and is related only to chassis options, not engine options. FYI, my Bronco which decodes as an "HD" has the same "H" in the VIN...
As far as "monster torque", I assure you that the "HD" is also a slug... Take whatever 351W you can find, and start with all the usual mods if you need "monster torque".
My Bronco also decodes as an "HD". It has heavy duty springs, quad shocks (the better to dampen front end undulations while towing) up front, tranny fluid & eng oil coolers, and factory tow pkg.
There are no visible differences between the throttle body, intake and exhaust manifolds on my Bronco as compared to my ClubWagon (which does not decode as an "HD").
I am fairly certain that HD simply means Heavy Duty and is related only to chassis options, not engine options. FYI, my Bronco which decodes as an "HD" has the same "H" in the VIN...
As far as "monster torque", I assure you that the "HD" is also a slug... Take whatever 351W you can find, and start with all the usual mods if you need "monster torque".
New User
Joined: Jul 2003
Posts: 9
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From: West Paducah, KY
EFI 351 HD???
Mine has Trans oil cooler and and heavy duty cooling. Don't have quad shocks. Mine decodes as HD but I have H in the VIN 8th digit. It also has a heavy duty tow package. The Decode reads Ford 5.8L V8 EFI HD Incomplete Chasis. This of course is a conversion van.