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Old 02-21-2006, 08:46 PM
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pontiac 389 or 400

I have a 37 Pontiac 4 door sedan. I was originally looking at putting a Pontiac 389 in it. I have found a local car with a 400 in it. My reasons for going with these engines is for nostalgia. I think it would be cool to put a muscle car era engine in my 37. Questions raised to me by coworkers included options for trannies, and which one would have the most aftermarket parts available. From what I've seen they both seem to have rebuild and performance items available. If anything it looks like parts for the 400 are cheaper. This may be a fluke in my research. What are ya'lls opinions? What would it take to use a newer 5 speed man like a T-5?

Thanks for the info


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Old 02-22-2006, 12:04 AM
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Hello Rufus... I was VERY involved with Pontiac motors. The only difference between the 389 and the 400 is the 400 is overbored. The only reason for this was the cars were getting heavier at the time and Pontiac simply bored out the 389 for a little more horsepower and torque.
I had a 1965 GTO that I bought with the original 389 Tri-Power and a blown motor. I dropped in a 400 from a 1969 GTO and used my tri-power.
When the 400 came out they put smooth valve covers on it and it makes the motor look a little different too. For some reason Pontiac changed the intake manifold slightly in 1965 the 1964 and earlier had the same ports, etc. but changed some cooling passages around. So, if you had a 1964 Tri-Power and wanted to use it on a 400 you would have to swap the heads too.
Nice thing about Pontiac they used the same basic motor from the 326 cid through the 455! You can build a 455 from a 389 or 400 Motor by using a 455 crankshaft and cutting down the mains.
Hope this helps! If you have any other questions let me know.
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Old 02-22-2006, 05:48 AM
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Pontiac changed either the valve angles or the valvetrain geometry in 67 (maybe both). If you try to put the earlier valve covers on an 67 up engine, you will end up with 16 new bumps. Don't ask me how I know. If you are putting 400 heads on a 389 engine, or vice versa, you would probably want to verify the valve to piston clearance. If the angles are different, you may miss the relief pockets. Other than that, any performance part listed for a 400 will fit the 65 up 389 (earlier ones as well as long as you look out for the slight oddities like the manifold cooling passages as pointed out by wulff406).
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Old 04-01-2006, 03:39 AM
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the bastaed years

Everybody is about right. 65-66 are a hair off. in several places,not all of which I remember either. The manifold bolts had a few differences for several years- the boss needs to be there if you have to drill and tap a hole if you need it. Usually the ex manifols. The intake manifolds had the same problem on occasion. The Ramair trials may not even been any better, but check them out. the 389- 421 of 65-66 and 428-455vs 400 had a few minor differences . Mostly check the bolt holes. My biggest concern is the intake maniflold- particuarly 3 deuces. The center carb. is larger in 66 and maybe ,probably 65. However I sure feel that they were the same in 65 and earlier. I am sure that 65 or pre 65 all three are the same size. There's one in the floor without the carb's, the holes are the same. some of these go farther back. I have 2 EWdlebrock's in the floor, 64 65 don't fit I think. I would guess that the 66 intake fits 389 to 400. 428 has a larger center carb. The 66 3D's fits 400. some of the swapping around might require changing heads and carbs together. 3D's are more of a matter of style more than anything else. after that things got to be a little more uniform youcould swap heads and maniflodstogether effectibely. Ram Air is still out there,I would have to go one by one myself. I have the books from back then somewhere. Swapping around like this might mean changing carb jet sizes to get air to fuel right. I would always reccomend checking valve clearance when doing this type of swapping,also if you free up exhaust flowlike duel pipes and definetly headers. I don;t remember 421 in the car. I think it was a crate engine. I think a 64 came out at 465 HP. I have a 326 around they were good family car engines. I don't know anything about 350's but they should have been good family sedan engines. I always liked the ohc 6 that came out in 67, i think. sport version had triple split cast ex manifolds, and 4 barrel carb. Ahead of its time. The big engines needed bigger valves,and always remember long strokes useually mean broken rod bolts in pontiacs so redlines were low.
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