Motor Swap??
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New User
Joined: Sep 2003
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Motor Swap??
A friend told me to get a 70 or 71 400 V8 for my truck, as it would mount up and have about double the power(due to being made before government detuning). Anyone here know about how hard it is to do the swap and if the 400 will bolt in place of the 351M in a 79?
Posting Legend
Joined: Sep 2001
Posts: 30,255
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71 was the first year for the 400. An engine that old will be mostly worn out. A rebuilt motor will most likely have the detuned guts in it.
The 400 has the same block as the 351M. There are a few 400's that have a small bellhousing pattern to match the 351W.
The 400 has the same block as the 351M. There are a few 400's that have a small bellhousing pattern to match the 351W.
Elder User
Joined: May 2003
Posts: 549
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The 400 came out in '71. The hp for that year was 260 at 9.0:1 cr. In '72 the industry changed the way they measured hp. The hp rating dropped to 168 hp with 8.4:1 cr, using the same cc heads. The '71 motor does not have double the power. '71 and earlier motors were rated by bare motor output. In '72, when the rating changed, the motors had the waterpump, alt, powersteering pump, ect... on the motor using production tune up specs. There is really about a 60 hp difference between the '71 and '72 if the hp were to be measured the same way on both engines.
To find a '71 in good condition, built to factory specs, will be hard. IMO a better way to go would be to find any 400 (they are cheap in the salvage yards) and rebuild it using '71 cleveland pistons machined to fit the 400. Going to straight up timing gears help the motor too. The guys in the 400 forum can tell you more on that.
As far as the swap goes, it would be pretty much a straight forward swap.
To find a '71 in good condition, built to factory specs, will be hard. IMO a better way to go would be to find any 400 (they are cheap in the salvage yards) and rebuild it using '71 cleveland pistons machined to fit the 400. Going to straight up timing gears help the motor too. The guys in the 400 forum can tell you more on that.
As far as the swap goes, it would be pretty much a straight forward swap.
