Pontiac 461

We’re going to take you through the process of building one of the most popular modifications for classic Pontiac V8s, a 400 bored and stroked to 461 cubic inches. It is going into a stock ‘68 Firebird street car with power brakes, so it will need good street manners. This is a budget build so we used as many stock parts as possible. Check back often to see how the build progresses!

hunting cabin

We headed up to our parts cabin to locate a suitable block

hunting cabin

Getting closer!

hunting cabin

Found it! a standard bore 1974 988 casting 400 block. This block was already magnafluxed and hot tanked. Perfect!

So we found the perfect block for this build. We’ll put that aside and begin the work on the 6X-8 heads our customer supplied. They are from a 1979 400 engine. These smog era heads have large combustion chambers to keep the compression low on the 400s. On a larger displacement Poncho these heads are known to work quite well, with a little help from Zeke’s of course! Take a look as we show you the complete process of building performance cylinder heads from stock smog era iron. The flow numbers will impress you!


Disassembling  the 6X-8 heads.

Disassembling the 6X-8 heads.

Into the hot tank for a little bath in some acid.

Into the hot tank for a little bath in some acid.



Magnaflux testing for cracks. A magnetic particle dye solution is sprayed on the heads. Here you can see Race holding the handheld electro-magnet over the surface. If there are cracks, he’ll see them in the fluorescent dye. These heads checked out good!


Next step is to check the threads. Race found one that needed some attention. Easy repair with a helicoil.


Here Race installs brass valve guides.


Honing valve guides to exact clearance specs.


machining down the valve guide boss so valve (PC) seals can be installed.


Porting process begins with race cutting the port throats.



Race bowl blending by hand.


Close-up of Race doing his thing.




Take a look at the difference, we’re optimistic of some good flow results!


Another before and after comparison.


So how did we do? We measure a steady 265 cfm on the intake port! This 461 will breather nicely!