What is VGIS?

potsurfriend:
"I have heard this mentioned a few times here before and tried doing a search on it and found nothing. Just curious what it is and how it works... "

mtlswift:
"Variable geometry intake system(?)... it varies the path of through the intake manifold (usually 2, a long and a short path) based on rpm. Longer intake usually means increased air velocity so it helps aid torque at lower rpm. At higher rpm too long of an intake path can starve an engine, so it changes to a shorter path to increase flow.
I think the changeover occurs around 4500 rpm for the Aveo..."

Nemasys:
"Is there a way to make it come on earlier then 4500rpm? "

mtlswift:
"Crack the ECM?? might not be good torque-wise... "

exodus:
"Wouldn't be benificial for Hp either, I don't think

It's set where it is for a reason. At lower-mid RPM you want the long narrow intake path so that the air is "charged." At higher RPM the engine starts sucking in the air faster than it's getting charged (sans forced induction), so an extremely short and fat intake path is ideal.

I really wouldn't consider anything below 4,500rpm a high engine speed. "

precisionboost:
"Don't even think of fooling with the VGIS system..... it's crossover point is in the best spot.

My friend owns a tuning company (which owns a Dynojet ) and it just so happens he had an Aveo for about 6 months before picking up a 350ZX from his brother in law.

For the hell of it one night we threw the Aveo on the dyno and fooled around with it..... one of the things we did was manually trigger the VGIS system.... the result was power loss each and every time.

In the end.... the factory ECU cross over point was the most efficent.

So...... it has been proven on a dynojet that changing the VGIS point with do nothing for your Aveo. "

Nemasys:
" Wow heh thanks that answers the question "

precisionboost:
"No problem..... just thought I'd get in here and mention something before people start thinking that they can make power by disconnecting it ( drops by about 10hp!!! )

My friend was going to have lots of fun with his Aveo..... but his brother in law offered him a 350ZX for $15,000 ( it had been stolen and insurance refused to pay for damages)

Most of the stuff missing was things he would have replaced anyways.... seats, stereo, shift knob, few other bits and pieces.... I think he had to replace one fender... but other than that it was still in perfect condition.

Needless to say it's too bad he got rid of his Aveo.... but we did have some fun with it before he sold it off for next to nothing. "

khan4rtist:
"so does that mean we have 2 intake paths?? 1 short and 1 long? "

ontarianfrog:
"Yes that is what it means....One thing I just thought of...If you put on a short ram or a CAI, wouldn't that change the length of the intake and affect performance in a bad way?

If the VGIS is set for the stock air box, then wouldn't you need to recalibrate it to work with the new intake, since the overall length of the air path changed? "

exodus:
"A change in intake length and diameter can always impact performance in a negative way. In this case I believe that the manifold, where the sperate paths are, is too much of a bottleneck for it to matter much. When it comes to the VGIS anyways."

and then it was locked on the old forum.....which was good because if you didnt understand it by then, then you weren't ever going to understand :lol:

great info, thanks for getting it together aveosam

Also, I have a question...with VGIS would adding an Oil Catch can instead of the PCV Breather mod be a better idea for keeping oil residue out of the intake while still keeping the needed vacuum pressure?

i believe so....never liked the PCV breather mod