350 to 400 motor swap (new to Pontiacs)
 

Just traded for a 72 Lemans 350, 2bbl, 350 trans. The old girl has seen better days and the guy who was working was not the best shade-tree mechanic. I need to pull the motor and trans to clean-up the re-engineered wire harness and to check for other fixes that may have been applied.

I know where I can get my hands on a complete pan to intake Pontiac 400, 4bbl that came out of a Trans-Am (not sure which year), and they say the motor ran when it was pulled. Since I will have everything out, I figure an upgrade is in order. Being new to Pontiac, I wanted to get your input on what kind of things I should be looking for or known issues that I can fix while I have everything out.

1) Is there anything that wont swap from the 350 to the 400? Brackets, distributor, starter, exhaust manifold, ect...

2) As I take the 400 apart to check the crank, rods, cam, ect..., is there anything is inherent to Pontiacs that I should be looking for?

3) Is there any weak-links in a 400 that I should look to beef up before I put it back together?

Guess I should also state this is to be a Street Cruiser that I will drive to the local 1/8 strip for bracket races. Fast is cool, but I would rather be reliable and consistent. Any input is welcome. Thanks. :D

answear for question one is yes, everything will swap from the 350 to the 400, even the heads if you choose to use them

1) Is there anything that wont swap from the 350 to the 400? Brackets, distributor, starter, exhaust manifold, ect...

Mike,

Everything will swap from the 350 to the 400 exept the cranskaft (different balance but same stroke) and the the pistons. Look closely at the flywheels. There was a different regsiter bore (the big hole in the middle) Vs. the early and late cranks. The flywheels interchange other than this fact. You will know when you have the right one because the other one will not slide onto the crankshaft.

Early heads had one less accesory bolt hole, but other than that, all the brackets will interchange.

Once you have dated the 400 and post the head casting codes (numbers are on the center exhaust outlets) we will all have a better idea of what parts you will need to get a pump-gas friendly compression ratio.

For what you describe, a basically stock rebuild, with emphasis on cleanliness and good quality parts, including a mild camshaft, should give you more than enough power to have fun with in a street cruiser.

Welcome to the forum!!!...Robert

Thanks for the responces. It's nice to know that I will be able to re-use some of the parts. For right now a stock-ish rebuild is all I am looking for. Maybe down the road, after I had the chance to drive the old girl, I may look for some for umph.

Made a phone call and the 400 block is a XZ with 4X heads. After looking at Wallace Racing's Engine Code list, my best guess is that its a 1973 motor.

Year Engine HP Engine code Trans CR Cam Head Code BBL Carb No. Misc
1973 400 200/230 HP XZ A 8.0 066 4X 1-4 7043266 Block Casting # 481988


I will make a trip after work and find out the date from the VIN number on the front of the block.

The date code will be cast into the back of the block on the shelf near where the distributor sticks up. That and the block casting number, located on the bellhousing flange at the rear of the block underneath the passenger side head will positively identify it.

If I was in your shoes, I think I'd use the 350 heads on the 400. When you have them rebuilt, have the larger 2.11/1.77" valves installed and have the pressed rocker studs pulled and the holes tapped for 1/2-13 threads. ARP makes a stud with the 1/2-13 base thread and the correct 7/16" top thread. This will bump your compression ratio up into the high 8:1 range, to maybe right about 9:1 depending on the actual chamber volume of the heads. Perfect for pump gas and better than the stock 8:1 of the 4X heads.

As to weak links - the connecting rod and it's weak bolts are the weak links in the Pontiac engine. No matter what you do, be sure to replace the rod bolts and have the rods resized and magnafluxed. Better yet would be one of the sets of budget forged rods available for under $300 from some of the Pontiac vendors. This will ensure your engine doesn't throw a rod and wipeout all the money and time you invest in it. It also allows room for further performance enhancements if you want to go that route further down the road with no worries about breaking a stock rod.

And, as the others said, everything from the 350 will swap right onto the 400 except pistons. The crank *will* swap and may even be the same casting number, it's just balanced differently for the smaller 350 pistons so you'd have to have it rebalanced if you wanted to use it.

I took a look at the 400 last night and its all there. Could not get the date code from the front due to the fact the water pump and fan assembly is still on the block. It even still had the old exhaust manifolds and heat shields attached. Best I can tell, it has never been taken apart.

Will, I did not see your post until after I got back from looking at the motor. I will see if I can get the date code from the back next time that I see it.

Again, thanks for all the help guys.