[DogMeister]

Originally Posted by JLMounce

I'm assuming this is not running timing control through the Sniper?
When you added the sniper did you make any changes to the ignition system from where it was set with the QJet?
Have you verified 60psi of fuel pressure during WOT application?
Does your Holley in-tank pump sit in a sump, or is it sitting in a tank designed around having a carb with fuel bowls?

I think there's way too much advance in your vacuum can. That should likely be limited to around 12 degrees. Fuel slosh away from your pump (if it's not in an internal sump) would certainly cause surging by way of intermittent fuel starvation.

The cam in this is exceedingly small for the size of the engine and the compression it is running. The smallest cam put in a 455 in the early 70's was the 066 and that was put into engines with advertised compression around 8:1. I don't think you can rule out some detonation being cause for some of the surging either. While a TBI system does have a certain degree of charge temperature cooling, it doesn't have the same effect as a carburetor does on the intake charge temp. The carb may have been working in your favor in that regard.

One thing you could do to test that theory is to put some higher octane fuel in the car. If you can get a couple gallons of 100 or 104 in the tank to test with, you may be able to glean if that's an issue. Given the setup, I'd add some WOT fuel as well. I'd want that closer to 11:1.

If you can get and post a datalog, that would be helpful. I'd want to at least see AFR, Throttle Position, MAP, RPM and Fuel Flow.

Yeah I don't know what's going on with the vacuum advance. The only change from prior operation with the carburetor is the new vacuum can since the old one had a hole in the diaphragm. And, well, obviously, the EFI. There should be no vacuum advance at rpm. The can worked fine when installed. Going to see what the manifold vacuum is at idle vs. rpm and make sure the can is releasing.

Even with the dinky cam it ran flawlessly with the carb. The tank is not baffled, but the surge rate was probably not due to fuel slosh since it was happening on straight line level ground .

On the last test run I turned on data logging but shut the car off before turning logging off so it didn't record. This EFI stuff is new to me...