[bonnebird]

I picked up a complete 455 at a clearance sale recently,looks like it has never been apart it is a 1973 vintage with 4x-1h heads. When I removed the carb I noticed 2 holes in the bottom of the primary wells. What are these for and do they harm performance at all

Thanks

Bert

[Ronc455]

1973 was the first year for the egr valve. Those two ports you can see are for the exhaust gas to go into the intake manifold.

[MarkS57]

Originally Posted by bonnebird

I picked up a complete 455 at a clearance sale recently,looks like it has never been apart it is a 1973 vintage with 4x-1h heads. When I removed the carb I noticed 2 holes in the bottom of the primary wells. What are these for and do they harm performance at all

Thanks

Bert

Wow, a Yank 455 Pontiac at a clearance sale down under? That's cool!

Most will agree the stock 73 EGR intake is a good piece depending on what you are going to do with it. What are your plans?

Cheers!

Mark

[Sirrotica]

If the EGR was hooked up and functioning properly, it does cut the performance somewhat. They've done flow testing and dyno testing on the factory EGR manifolds, against the non EGR manifolds. There is little to be gained by switching to the non EGR over the EGR equipped. The one you have will run very close to an earlier intake. There is only one OEM year you can use in your heads that came without an EGR valve, that would be 1972.

When these cars were close to new, we just rendered the EGR inoperative by disconnecting the vacuum hose running to the diaphragm. If we wanted to be sneaky about it, we would use the metal cap from the end of the glass fuse, and push it inside the hose to look like it was hooked up, but in reality it was blocked internally.

[mgarblik]

Originally Posted by bonnebird

I picked up a complete 455 at a clearance sale recently,looks like it has never been apart it is a 1973 vintage with 4x-1h heads. When I removed the carb I noticed 2 holes in the bottom of the primary wells. What are these for and do they harm performance at all

Thanks

Bert

Those holes were officially called "floor jets" in GM service information. Possible winning answer for some obscure engine trivia contest. They were not needed on the secondary side because when you opened up the throttle enough to use the secondary side of the Q-jet, the mixture was so rich EGR gasses were not needed .

[bonnebird]

Thanks for the reply's,
Im probably not going to use this manifold I was just curious about the "floor Jets" not having seen an EGR manifold before. This motor when rebuilt will be going into a 1962 Bonneville. I have a set of 45 casting heads that im going to clean up install larger valves and screw in studs and an earlier 4 barrel manifold that I have already modified.

[74Grandville]

only downfall of the 73 intake manifold is weight.

[Skip Fix]

Yes they are heavy suckers! I had a 73 SD intake heaviest one I've ever had! The later EGR passages for dump under the primary bores at the carb flange.

[grandam1979]

Looks like you have a lot of time into your intake mods?