301 to 350 small block swap

The Th-400 is a very strong transmission and is used behind alot of engines that produce lots of torque.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

There are a few things to consider when swapping to TH400 from a Th350. First the driveshaft will need to be shortened and the yoke replaced with the correct larger diameter piece with more splines. The trans crossmember will have to be moved back to accomodate the new trans mount position. The shifter arm on the trans detent must be swapped from the TH350 and the shift cable bracket from the th350 can be cut and welded to fit the different spacing of the th400 pan bolts or buy a th400 bracket. Also the th400 doesn't use a kickdown cable, it uses an electric switch that is activated at full throttle. You can use a switch from an earlier firebird or use the switch that activates the Air Induction hood flap on 79-81 Z-28 Camaros. If you don't use a switch you will have to manually downshift the trans. These are small changes that are easy to make and are well worth it for the extra reliability. I have one in my Formula and the only other change I can suggest is a street/strip shift improver kit.
Steve  
A little help... 'cause we don't all have to learn the hard way!

alright guys, got the bird in the yard this evening. didn't get under it yet but it def needs a floor and the trunk patched, i've called bout the 400 but it has a fresh rebuild on it and i can't afford it now, but i might have found a 455 out of a 71 bird, guy just emailed me about it so don't really have much info on it. what kind of work am i looking at to put that bad boy in my engine bay? and i'm not sure if the birds came with different suspension to handle the bigger motors cuz this one is an 80 espirt so originally a v6, any thoughts would be appreciated, thanks!!  

Installing a 455 is the same as a 350 or 400 Pontiac V8, externally they are all the same dimensions. As for front suspension, aside from springs and sway bars all firebirds and Ta's are the same. Just use a set of springs for a 78 TA with a 400. Be sure to address the floor and frame issues before bolting in a huge amount of torque.
Steve  
A little help... 'cause we don't all have to learn the hard way!

Hi There!
   This is Adonis from Italy!
 Im new in this site!
  Ditto with the Pontiac engine. I swapped out the turbo 301 in my '81 Trans Am a while back and put in a Chevy 350. Yes, the parts and support are more available, but I never achieved the same torque. The motor mounts have to be moved for the Chevy engine, it will need a different transmission, A/C brackets are different, and oil will leak from the timing cover no matter what you do.

Thanks!...

 See you soon Guys!...  

I just put a 400 into an 80 Trans AM and it was harder than I imagined.  Everyone told me that is was an easy fit – “Just drop it in”   No matter how I tried the mounts would not line up right and I ended up taking my best guess on the location and drilling new holes in the cross member.

Blackbird72 Wrote, “The best block for your application is a 70-75 no.481998 400 block, which has the 5 mounting holes per side- this bolts in to your chassis and is stronger than the no. 500557 block”; sounds like good advice and I wish I knew about this sooner.

Definitely go with a Pontiac and good luck.  

hey guys, though i'd post an update, i ended up picking up a 455 and plan on giving it a good machining. gonna stick to stock specs for the most part this time around and do a performance build later on down the road. So the plan is a basic clean up at the machine shop, some new bearings (rod, main and cam, check out the bottom end cuz there were two different heads on the engine when i bought it, a #64 and a 6x-8, donno if it was run that way so i'm gonna get everything checked. Picking up a set of 6x-4's and gonna run those, just don't have my cam picked up yet cuz i gotta see what gears i have in the car. It was originally a v6 car and the original rear end is it. donno what they came with but i also have the rear end out of the firebird the 301 was taken out of. donno what gears those are either.So thats where i'm at, debating on going all out and doing the .030 the first time and buying new forged pistons and rods or running it how it is for a while then doing the complete do over all at once (heads and all)  

You can find out the gear ratio from the numbers on the top side of the rear axle, passenger side.  These are often covered with rust and gunk but wire brushing the top of the tube, and using a mirror and flash light will reveal them.  The numbers will id the axle ratio and tell you if it's posi-traction.  

Some of the others may be able to give you some other suggestions to find the gear ratio  

+1 Mr Milt

However, I have found that sometimes the stamping can be faint or altogether unfindable. Then you need a book or website with the codes. Then it has to be unmodified, and in its original car for that to be correct. If thats your case, this is the best way to know what you have. A posi will have a tin tag that states "limited slip lube only" attached under one of the cover bolts, as well.

More rednecky backwoods methods would be...
You can always pull the cover and count teeth.   Divide the number of teeth on the ring gear by the number of teeth on the pinion gear. Or get a general idea by marking the driveshaft and seeing how many turns it takes to turn a wheel once. Jacked up in the center of the housing, trans in neutral, generally speaking, if you turn one tire the other turns the same direction on a posi, and opposite directions on a pegleg. Just my two cents, none of it gospel.  

+1  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

id,,,
Your last sentence sums it up best to determine a posi from non posi carrier.
Unless the posi clutches are shot, and then all bets are off.
Usually even cooked clutches create enuff drag to feel as if both axles want to turn the same way.
Some GM 10 bolt carriers came with a "wind-up" limited slip, with a thimble on a long, fine threaded shaft that spun and at threads end engaged both axles.
This setup was very poor and ended up being junk.
 

pretty much nothing I say is gospel. Unless its about bodywork

Theres a ton of what ifs involved. Gotta look inside to "know" know. Y'know?

 

If you go with the Pontiac 400, be sure to get all the accessory brackets etc. The deck height on 301 is different than 350-up Poncho v-8. th400 will hold a ton of power as it has larger shaft size than th350. Just remember, you dont want to build it twice, so if you look a little harder and find a 455 engine, get it. There is no substitute for cubic inches.  

i ended up picking up a 455 but didn't manage to get the accessory bracket with it so i guess i'm going to have to go on the search for those or pick up new brackets from summit racing. Well guys thanks for everything and i will keep you guys updated as i'm building and of course there will be more questions to follow.  

If you are searching wrecking yards, look for any mid 70's Pontiac powered car, the 350's, 400's and 455's from about 70 onwards all use basically the same accessory brackets. Try to get a complete set of brackets/pulleys/power steering pump from one engine and you'll save time and headaches.
Steve  
A little help... 'cause we don't all have to learn the hard way!