What would happen, if you used smaller diameter hose for the vacuum lines than what is to spec. I would assum the engine wouldn't be getting enough air, or incorrect readings on the ECU? I have a whole bunhc of hoses at work that are available to me, so if I can get around it, I wouldn't bother spending more money on lines. Any thoughts?

 

Gm uses a lot of short plastic lines under the hood. Sensors like the MAP, and vacuum switches for EGR and EFE and such. They maintain that the vacuum lines are "tuned", by length and diameter, so that a specified manifold vacuum will take a predictable time to pull a vacuum in a known volume (the working end of the EGR valve f'rinstance). As far as our cars, it doesn't look to me like the length of our plastic vac hoses are as critical, but I wouldn't change the ID. Some of the more learned engineers on this board may have opinions here.

 

A very large line would cause a long time to pump down, but smaller lines should do no harm as you are not really moving much air. Many times MAP sensors have restrictions in the line to reduce signal fluctuation. The line volume would seem small in comparision to the manifold volume.

I'd say go for it, you don't have much to lose.

Art