[Cliff R]

"I used the 2801 on forum advice"

You just plain got some BAD advice.

Using a 2801 cam in a 455 is like having a 2800 cam in a 350 build at 8 to 1 compression. It's a tiny cam and best suited for very low compression and smaller engines, and in the big 455 it's going to make a lot of cylinder pressure and raise octane requirements.

I do NOT believe that retarding that cam is the solution here, I'd rate is as more of a "crutch" fix instead.


"My carb 7028262 I think, does not have a ported port"

Most Pontiac carburetors after 1967 have ported vacuum at the front port in the main casting just to the right (as viewed from the front) of the fuel filter housing.

As with all Q-jets that had a ported source for the advance, it is very well located, and supplies FULL MANIFOLD VACUUM to the distributor with the slightest movement of the throttle.

So basically the only difference between full manifold vacuum and the correct ported port is no timing coasting and at idle with ported vacuum to the advance.

For a high compression 400 engine base timing on pump fuel will have to be pretty "low", or you may run into difficult hot restart issues. This assumes the cam is stock, and not some aftermarket cam with tight LSA and enough overlap to kill off vacuum signal at idle speed.

I have never once found that we had to run very much initial timing on an early high compression engine with a stock cam in it. Most are fine with the timing at or close to stock specs. With aftermarket cams, larger than stock and/or tight LSA, more times than not we'll have to increase timing at idle some. At the same time we'll add idle fuel as well, as the engine simply isn't pulling (vacuum) as hard on the carburetor and the stock idle system may not supply sufficient idle fuel to the engine without some help.

Anyhow, that's getting pretty off track for this thread. The easy fix here would be to install a larger cam and all the problems would go away. I've found very few of these types of issues that could be cured by retarding the camshaft, as that usually brings in negatives in other areas as well, like sluggish off idle performance and degraded idle quality, "lazy" in the mid-range and often less power at every rpm......Cliff