well im in the engine performance section of my schooling and im thinking about picking up a type II manifold and maybe gutting and polishing it for a project to for my lab grade.... just what would be the benifits of taking out a VIS system in a manifold??? if it will kill your low end torque by shortening the runner length why do it??? as im thinking if your racing youre never that low in the rpm range anyways but does it affect daily driving in a bad way. as i understand one is set to open at a certain rpm and another is a variable one which means it opens depending on how hard you press in the throttle pedal. ive seen the new chart regarding the 3.2 vs 3.5 and i understand disconnecting the VIS system took away from his torque which lead me to making this thread.... till now i was set on gutting a type II IM and thowing it in the legend. can i please get input from those who have done so.
dgandul
I don't really see the logic in deleting it myself... looking forward to some explanation by folks who have.
well from everything ive read from the performance section is it shortens the runner length... swift even went into making them "2 inches short like the NSX guys".... how does that help us down low with torque since torque is the craze
For you guys with 3.2's especially autos, VIS was designed for you.
It has two sets of vacuum butterfly flaps that are closed when the engine starts up and is idling. At certain rpms around 3k and later at 4k they open separately.
Imagine two large flaps on either side of each other then one smaller one in between. The two sides are the lowend flaps that open around 3k and then the single smaller one opens around 4k.
VIS is designed to lengthen, shorten, slow and speed air velocity traveling through the manifold's plenum. All closed lengthens the air path thus creating lowend TQ, opening all flaps shortens, thus speeding up air velocity, creating topend hp. The transition of opening two flaps first then the last flap later, tries to give the most efficient lowend transitioning to mid and top.
The most topend power can be achieved with out VIS, however lowend daily drivability suffers greatly especially on a 3.2 auto. The manuals are a bit more resilient, because of the ability to rev at will, but still will suffer good loss of TQ.
3.5's already have loads of TQ from the extra displacement, overwhelming the FWD. I've found they need as much air in/ out as possible. Removing the VIS entirely has been proven effective in my case with a highly modified 3.5. Having VIS on a modified 3.5 will only add TQ and thus make it hard to keep traction. I will go as far as to construct my own version of the intake plenum soon, for an increase in air volume, like swift had done.
Hope this explains it all. This is all off the top of my head, im pretty sure i got it right.
~Dv8
It has two sets of vacuum butterfly flaps that are closed when the engine starts up and is idling. At certain rpms around 3k and later at 4k they open separately.
Imagine two large flaps on either side of each other then one smaller one in between. The two sides are the lowend flaps that open around 3k and then the single smaller one opens around 4k.
VIS is designed to lengthen, shorten, slow and speed air velocity traveling through the manifold's plenum. All closed lengthens the air path thus creating lowend TQ, opening all flaps shortens, thus speeding up air velocity, creating topend hp. The transition of opening two flaps first then the last flap later, tries to give the most efficient lowend transitioning to mid and top.
The most topend power can be achieved with out VIS, however lowend daily drivability suffers greatly especially on a 3.2 auto. The manuals are a bit more resilient, because of the ability to rev at will, but still will suffer good loss of TQ.
3.5's already have loads of TQ from the extra displacement, overwhelming the FWD. I've found they need as much air in/ out as possible. Removing the VIS entirely has been proven effective in my case with a highly modified 3.5. Having VIS on a modified 3.5 will only add TQ and thus make it hard to keep traction. I will go as far as to construct my own version of the intake plenum soon, for an increase in air volume, like swift had done.
Hope this explains it all. This is all off the top of my head, im pretty sure i got it right.
~Dv8
Good explination, I am not sure what happened to my Microsoft paint (to copy/paste pics tp upload but it is also explained on page 275 of the SM (fuel and emissions section.
then really there is no use for removal of the VIS in a 3.2 AT or MT unless you want your car to be a dyno queen???? really in a race the loss of soo much low end torque is going to make the HP useless because the race would already be over. which would benefit FI people since this is the next step for legends
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