# 389 or 400



## beer guy (Oct 22, 2014)

I am seriously thinking about replacing the engine in my 66 GTO (currently has a 350 Firebird engine) and I don't know whether to go with a 389 or 400 Pontiac motor.
My criteria for selection is (in no apparent order):
1) Ease of boosting hp and torque
2) Cost and availability of engine.
3) Durability
4) Availability of parts
5) Least amount of costs to modify

I recognize the 66 came originally with a 389 but it seems to me that they are harder to come by and while I want to be reasonably true to the 66 it isn't a moral imperative for me.

Any thoughts?


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## BearGFR (Aug 25, 2008)

Well, since you asked... 

It's hard to beat a stroker motor built out of a 400, as long as you start with the earlier model year castings. They're strong - stronger than the larger journal 421/428/455 blocks.

I built a stroked 400 (461 inches) for my 69 using the original numbers-matching block. It has run a best to date at the track of 11.86 @ 113 mph.

Bear


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## beer guy (Oct 22, 2014)

*earlier model castings?*

What years are we talking about? I read somewhere that 74 and later 400's aren't the best. Or is it 75 and later?


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## geeteeohguy (Feb 2, 2008)

What Mr. Bear said. Get a '67-'74 400 and build it up. I personally like the 389's, because of the mystique, weird displacement, and history. Today, they are harder to build, more expensive to get parts for, and not as easy a route to follow as a 400 based build. That said, I just LOVE the 389 tripower mill that's in my '65.....and it 'gets with the program', too!


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## DSMTiger (Nov 17, 2012)

geeteeohguy said:


> What Mr. Bear said. Get a '67-'74 400 and build it up. I personally like the 389's, because of the mystique, weird displacement, and history. Today, they are harder to build, more expensive to get parts for, and not as easy a route to follow as a 400 based build. That said, I just LOVE the 389 tripower mill that's in my '65.....and it 'gets with the program', too!


I agree with geeteeohguy. Most people associate GTO's with the 389 (probably because of the song). I like to see 64-66 GTOs with the 389. That's just me. But, if you are going after a big build with big HP, early 400 is good and there are more of them available.


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## Mr. P-Body (Jan 20, 2011)

It's important to understand, parametrically speaking, there is virtually no difference between 389 and 400. A .060 over 389 IS a 400. Cranks interchange. Rods interchange. 

Butler Performance offers a variety of pistons using the 389/421 bore sizes in the more popular strokes. Reasonably priced, Ross, VERY good.

Most "things" that can be done with 400 can be done with 389. The earlier blocks (pre-'64) are VERY strong. Adaption is required to make them fit an A-body (starter, trans). 389s are more prone to "freeze" cracks in the middle, where the "third" plug is added to 400s. All the Pontiacs use the same head bolt pattern and deck height.

Use what ever block presents itself at the best price. Avoid the '75-newer "557" casting for anything serious. It's fine for a 500 HP streeter, though.

389 heads, however, cannot be "stretched" to perform anywhere near the level 400 stuff can be. Whole different chapter...

Jim


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## Red1970GTO (Jun 25, 2011)

There is no replacement for displacement. Since all the Pontiac engines are the same exterior dimensions, go with the biggest one you can afford. A nice stroker 461 or a 455 HO/SD, etc.


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## geeteeohguy (Feb 2, 2008)

While Mr. P-Body is absolutely correct, 'parametrically speaking'. 'Romantically speaking', saying 'It's a 389' or "It's a 421" has more cache than saying 'It's a 400'...at least in the early cars. And I've owned .060" over 389's that were 400 inchers. But the casting number and codes on the block, and my soul, knew it was really a 389 at heart. It's all about what it started out as, what it originally was. I could stroke my 389 to 440 cid, etc. I would still refer to it as a '389'. For 34 years, it's been a 394 cubic inch engine, but it's always been a '389' in engine code and spirit! All this nonsense aside, do what Mr. P-Body said: get a good block and go for it.


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## BearGFR (Aug 25, 2008)

Jim!!! Great to see your tracks on here again. How's the healing coming along?

Bear


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