TWM 8 stack plenum too small?

[kobrabytes]

I am running TWM/FAST on a KC 427 FE (527 CI). My ECU came set up in speed density mode. It had plenty of power but had poor idle and lots of back fire. I've since moved to Alpha N.

The TWM manifold only has around 6lbs of vacuum at idle. Reading the fast documentation it says that you should use Alpha-N on motors that have below 10 lbs of vacuum.

"Alpha-N mode is often used on naturally aspirated racing engines with very long-duration camshafts that produce little or no engine vacuum at an idle. It is sometimes difficult to achieve decent drivability or idle quality with an engine of this type using Speed/Density mode because the amount of pressure in the intake manifold is almost the same at an idle as it is at wide open throttle. If your engine will not have more than 10 lbs. of vacuum at idle then choose Alpha-N mode."

I've been working on the program for several months and now have a VERY well running engine. Sold idle, power is back up where it was in speed density, no backfire, and it tolerates altitude very well. I live at a base of 4200 ft. I went on a cruse Friday up to 8000 with no negative effects. Previously that would have been a fouled set of plugs, and poor performance at altitude.

I'd still like to get on a dyno to see where the HP is and peak it. As for the A/F ratio I've "guessed" based on recommendations from this forum. It seems that I am pretty close. I pull dead even with another Kirkham with an equivalent setup, except the other car is carbureted. Once I set the A/F table up I made many logging runs and tweaked the fuel table to get the correction into an acceptable range.

Some of the other guys on the forum have done more elaborate things with the an IAC and a larger plenum. I figured that I'd give Alph-N a shot before I made things more complex, it's worked rather well for me.

len