S/C RV8, modified extra air valve (cold start)?

[V8 Fettler]

Flapper EFi. Cold idle is erratic, low rpm with hunting. Current workaround is to introduce additional unmetered air at the extra air valve for about 2 minutes = strong, steady idle at about 1k rpm during early warm-up (good auto creep!). Has anyone with a supercharged flapper RV8 had to increase the hole size through the disc of the extra air valve? The valve is working, I can see the hole in the disc when the engine is cold, although I haven't timed how long to close.

Other options are to (electrically) delay the closing of the extra air valve or add a manual extra air valve.

Delicate operation of the accelerator during early warm-up can overcome the problem, but it's a bit cumbersome.

[Wedg1e]

Ah, auto creep. Many's the time I almost ran over a funeral director walking in front of my Granada hearse on a cold morning

[adam quantrill]

Mine doesn't really idle at all when stone cold but I just put up with it - it's fine after 2 minutes running.

[V8 Fettler]

Thanks Adam, 2 minutes first start of the day is the problem area. I would guess that a manual gearbox car is driveable like this, auto generally lurches and stalls.

[V8 Fettler]

Wedg1e said:

Ah, auto creep. Many's the time I almost ran over a funeral director walking in front of my Granada hearse on a cold morning

Granada hearse = banger racer supreme! The creep is strong on my Rangie, I wonder if the supercharger is boosting at idle?

[mrzigazaga]

V8 Fettler said:

I wonder if the supercharger is boosting at idle?

At idle It would hardly be classed as "Boost" but It can interfere with the "Negative pressure".....Especially when the idle is high..

Vacuum or Boost is the result of high pressure forcing itself into low pressure environment

High (positive) pressure naturally forces itself into a low (negative) pressure environment in order to equalise pressure. Therefore, a pressure difference must be initially created for air to move from a high pressure to a low pressure environment in order to produce vacuum or boost.

For example,
To produce vacuum a lower (negative) pressure environment below atmospheric pressure must be initially produced inside the engine (ie: when a piston moves down the bore it reduces the pressure in the cylinder) while the higher atmospheric pressure outside the engine remains constant.

To produce boost a higher (positive) pressure environment above atmospheric pressure must be initially produced outside the engine (ie: when an air pump compresses the air it increases the atmospheric pressure) while the lower pressure inside the engine remains constant at a given rpm.

[adam quantrill]

Actually if you connect a vacuum gauge to it you won't see any difference - at idle it's all vacuum.

The blower doesn't really do anything until 80% open throttle, at any speed.