[Rapdron]

I am putting together a 67 YD code 400 for my 66 Bonneville.
The block code by the distributor is 86133, with a build date of A267
It has a stock bore, new rings and a Summit 068 cam & lifters
The motor came with 143 heads with 10.5 compression
I just installed a set of 6X4 heads to reduce the compression, but there is a problem.
The original 400 push rods are now too short.
What push rods do I need to make these cylinder heads work?
I just had the heads rebuilt by a local machine shop, and would like to keep them if possible.
Sorry, obviously not too familiar with Pontiac motors.
Any help would be much appreciated.

Thank you, Ron

[b-man]

You simply need to match the pushrods to the heads when doing a head swap.

The 143 heads are the old style 20 degree valve angle like the heads on 326/389/421 engines which use a pushrod about 8.71” in length.

You need the later pushrods that should be 9.145” long for your newer style 14 degree heads.

1967 was a transition year where both styles were used, the lower performance engines used the old style for the most part.

[steve25]

In 67 the 400 motors In the big B body cars still got fitted with the 389 / 421 type heads so as posted in the above you need the 350/400/455 length push Rods .

The other thing also is that your Intake Manifold from your motor will not seal up right at the Exh crossover area.

More important is the fact that the 89 CCs of those 6X-4 heads and your stock 400 Bore will only provided you with a much too low compression for the 068 Cam of 7.6 to 7.9 with those 389 type Pistons!
Your really going to need to wack those heads .060" to get your compression up, or only run something like the 067 Cam or the like in a aftermarket type.

If your block is not assembled yet you need to mock it up and also see how much it can be decked to get the the Pistons .005" out of the Bore.

[Rapdron]

Steve
I am not too familiar with the Pontiac V8 motors.
I love Pontiac's, but this is the first one I have tried to rebuild myself interchanging different year parts.
I have run and built most Chevrolet V8's from a 55 265 in my Nomad, to a 402 (396) in my 70 Monte Carlo.
They were an easy motor to work on, but I am lost when it comes to Pontiac V8's.
I built a 68 428 for my 66 2+2 that turned out to be a great street motor, but that's it.

I thought that the original 143 heads were advertised as 10.5 c.r. which I thought was too high for 93 octane pump gas. I had read that the 6X4 heads would bring the compression ratio to around 9-9.25.
I agree that 7+ is way too low.

What heads would you suggest would be a good option to lower the c.r. from 10.5 to around 9?
I have at least a half dozen sets in stock to choose from, but don't remember them all now.
Obviously, the 143's, a set of 46's from a 69 428, and a set of 670's from a 67 GTO I had years ago.
I have a 69 cast intake that the numbers show to be a Ram Air 3, but it looks to be just a stock manifold that I plan on using with this 400.
I have a 66 tri power intake and carbs that I eventually plan on using with the 428.
will that intake work o the 68 motor? It currently has a stock 69 intake with a set of # 13 heads?
Sorry about all the questions, just learning at 71 .

[Goatracer1]

As long as your 428 has the original heads the 1966 Tripower will work fine. It will also work with any other heads from a 1965 through 1971 engine. It can be made to work on 1972 and up heads but it's not a bolt on. The RA3 manifold is nothing special. It also will work on 1965 thru 1971 heads. There are several heads that might work but you should measure your engine's and head gasket's volume. Then measure the heads to find something close. Remember the heads will change after a valve job.

[steve25]

A perfect head for a 400 when you want to end up with a 9 to 1" to a 9.5 to 1 ratio is a 1968 to 1970 high Comp head with a 72 to 74 CC chamber.

[Rapdron]

Steve
I have both a set of # 13 and 670 heads, both measure at 72 cc
My original # 143 measure at 75 cc which are rated at 10.5 CR
How would installing a smaller chamber head lower my compression to 9 - 9.2 ?

[John Milner]

That 10.5:1 was really just an advertised compression ratio. Those engines were really in the 9.5:1-10:1 range.

[steve25]

I would do what's needed to the 13s and run those since they burn cleaner and thus need less timing then the 670s do.
When you have the valve job done on them just be sure to have the machinist leave a nice wide .060" to .070" wide Exh seat and there will be little to no issue with valve seat recession over the long haul if spring seat pressure do not top 120 psi.

[Rapdron]

Thanks everyone for the reply
I will have the 13's done and install them on the 400.
Happy New Year Everyone.

[1969400HO]

You can get pushrods ordered in .050 “ increments .
Butler performance can make them any length you want though, but will need to do the basic measure process.
There are plenty of YT video showing what to do and how to etc.