Newbie Question

Can I put a 400 motor out of a 77 trans am and muncie trans in my 66 GTO and what kind of horsepower can I get out of this 400?  

Yes, as long as the GTO originally had a Pontiac motor it should bolt right in. And as long as the GTO was a manual to begin with, the muncie would also fit. It may need some changes to the linkage and some other mods. Is the GTO a floor shift or column shift?

That's the short answer. Give us all the details of what engine/trans combo was in it and what type of modifications were done to the 400. The 77's came from the factory with 180 HP.  

i think there might be an issue with how the motor mounts are attached to the side of the block.. but i think there are special mounts or brackets to adapt..  perhaps its going old motor into a newer chassis..  

1964 to 1969 Pontiacs engines were all "2-holers." Blocks cast in 1970 to the last of the run (1978) had 5 holes per side, at least in theory.  
Horsepower sells engines and torque wins races

The GTO was a WW block 389 long gone and a mucie 4 speed. I would want to be able to rebuild the engine to 1966 stock or better than stock horsepower and torque specs which in this case is 335 to 360 horse 400 ft pounds torque. is this possible or am I better off finding a closer to period correct engine?  

Anything is possible.  I know for sure the older blocks were much stronger than the newer stuff.  A lot more nickle in the blocks.  I would go older,  400 or a 455..   Lotta fun,  Bill  
68 GTO  455/462
498.9 HP 558 TQ

If there was a Muncie in it to begin with that's a plus. Getting the '77 400 up to the specs of the '66 389 will require quite a bit of work. The 77's were detuned from 200HP in 1976 due to the increasing emmission regulations, and the blocks were not as strong as pre 1973 blocks. Achieving the higher HP ratings can be done and is done all the time, it's just going to take some cash and a well thought out combination of modifications.

There have been many previous threads on perking up the later 400 blocks. If you go into search you will find all kinds of posts on just what you are doing.

We are here to help with any details.  

Thanks for the info Everyone! One more Question. . Are all m21 four sppeds basically the same meaning can slide one in my car from a later year I still have a bell housing for my 66.  

In mid 1975 the 400 blocks were weaker because they had less material in the blocks main areas.  
Horsepower sells engines and torque wins races

One other issue that I think may need to be addressed is the transmission. Is it from the 77 Trans Am too? If it is, then it's not a Muncie M21, it is option code M21 which was a Borg Warner T-10. There are differences in length and the diameter/spline count of the output shaft. Just thought you should know before you go buying parts that won't fit! The T-10 is a good trans and should work well if it's in good condition. I had a few over the years and the main roller bearings tend to get noisy and synchro rings can get worn with years of use. They are reasonably easy to work on with a good manual.
Steve  
A little help... 'cause we don't all have to learn the hard way!

The Muncie was discontinued in 1973, when the Borg Warner Super T-10 replaced it.
The T-10 is every bit as strong, if not stronger than the corporation Muncie.
Reason.,. 9 side cover bolts instead of 7. The case wants to spread in this area under high horse and heavy loads.
The Muncie uses a TH-350 output shaft and the T-10 the bigger TH-400 shaft.

 
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P. Engineer, Engine Builder

 Hi People,
 Both gear boxes are good gear if not abused by idiots.