I am working out the numbers for a 305-400 swap. The 400 is a mid 70s 4-bolt nothing unusual about it. I'll be keeping the TPI and using a mild cam 210/218 .450/.460.

I am trying to find out about some details for the swap and would appreciate hearing from those who have successfully done the 400 swap. Here are some questions:

- how do you deal with the single main seal to two-piece main ?
- does the WC T-5 fit the 400 crank ?
- what do you do about harmonic balancers ?
- will the 305 flywheel fit/work ?
- do you need a 400 oil pan or can you use the 305 oil pan ?

If you have any other 400 swap experiences to relay I'd like to hear those as well.

thx in advance,
RP.

 

1. You get the right flywheel, which is the one for a 83-85 305, and have it "unbalanced" to the stock 400 spec.

2. Yes. The trans couldn't care less how many CID are in the jugs as far as fit is concerned. Just FYI, I have a 91 T-5 in my 83, with a 73 400.

3. Use a 400 one. You lose the timing mark, and if you care, you'll have to make one during your buildup.

4. Not if your motor came with a WC T-5: it's 87 up, so your flywheel won't bolt to the older motor. See #1.

5. You have to use an ealry model oil pan, because the dipstick is on the other side and the pan has a place for it; and because of the rear main seal thing. I use the Z28 pan on my 400, that's for the 6-quart system. That particular one requires a windage tray. Any LH dipstick pan from a A, G, or F body will work. Any other chassis (Caprice, truck, etc.) it's anybody's guess whether it will work or not. The dipstick that goes with it will not work, unless you use headers; the tube will have to go right through the middle of the exhaust manifold on these cars. Alternatively you can use the pan & dipstick assembly from a 78 El Camino 305 (I have one of those too), that application has the dipstick plugged into the pan rather than through the block.

You will have to add one starter bolt hole. Don't pay any attention to anything anyone tells you about "it ought to work" or any other drivel of that nature, or about some starter that they "heard" might work; it is BS and lies. The bolt pattern that your starter requires did not exist when the 400 was being made. No starter will work, no nosepiece will work; if you put a bolt into the bolt hole that's there, it would go right through the middle of the starter drive if there was any such starter, so it's clearly impossible. Starter bolt holes are special, so have your machine shop drill it for you before you have a fully assembled motor in your car and you're laying up under it with a starter in your hand wondering how it can possibly fit. You will probably find that the weenie little stock POS which can barely budge your 305 may not be able to move a 400 at all; I highly recommend a mini-starter. I have the CVR one on my 400, it spins the motor at least 3 times as fast as the stock one spins a 305.

Sorry to hear you're keeping the TPI; the up side is that it will protect the 400s bottom end from ever seeing any significant stress, but the down side is that it will also deprive you of the full enjoyment of a large motor, which can only be truly appreciated when the induction system meets the flow requirements of the number of cubic inches, unlike TPI.

Enjoy!!!!