Old 01-21-2023, 07:45 PM
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arbys arbys is offline
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If I were to replace the 326 HO 4 speed in my 66 LeMans would you go with a 389 or a 400? What advantages does the 400 have over the 389?

Last edited by arbys; 01-21-2023 at 08:06 PM.
Old 01-21-2023, 07:58 PM
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Mr Twister Mr Twister is offline
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I like 400 engines, but the 389 would be more "period correct"

Last edited by Mr Twister; 01-21-2023 at 08:06 PM.
Old 01-21-2023, 08:22 PM
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b-man b-man is offline
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Eleven cubic inches plus a better cylinder head and valvetrain design.

The availability of pistons that are reasonably priced is a big advantage for the 400 engines, good 389 pistons are scarce and expensive in comparison.

1964 Tempest Coupe LS3/4L70E/3.42
1964 Le Mans Convertible 421 HO/TH350/2.56
2002 WS6 Convertible LS1/4L60E/3.23
Old 01-22-2023, 05:56 AM
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1963 and earlier 389 blocks wont hold the starter.
1964-66 389īs may be bored out to 400 std.

400īs is still plentiful, 389īs is not.

1966 GTO Tri-Power
1970 GTO TheJudge
Old 01-22-2023, 12:53 PM
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Sirrotica Sirrotica is offline
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65 and 66 389 have thin wall cast blocks, plus the connecting rods were strengthened in 1967 over 1966 by adding a rib on the big end next to the rod bolt.

Then there's what Bart said about the heads, and valvetrain being improved also. Unless you needed to have a 389 for class rules, I would go for a 400, hands down.

Brad Yost
1973 T/A (SOLD)
2005 GTO
1984 Grand Prix

100% Pontiacs in my driveway!!! What's in your driveway?

If you don't take some of the RACETRACK home with you, Ya got cheated

Old 01-24-2023, 06:49 PM
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geeteeohguy geeteeohguy is offline
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A '66 326 HO 4 speed LeMans is a rare enough bird (and way cool) that I would leave it alone. Put an 068 cam in it and bolt on a tri-power and you're all set.

Old 01-24-2023, 10:58 PM
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65madgoat 65madgoat is offline
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I vote leave the 326 HO in and build that up some. But if you must, just go to a 400 stroker then.

Old 01-25-2023, 12:43 PM
rohrt rohrt is offline
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