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Discussion Starter · #1 ·
i am polishing up an intake manifold for my car and remember reading that with the VIS diconected that someone gained more power... so i was wondering if i were to take the flaps off of the VIS unit would that be beneficial or no? i had one person tell me no becuase air velocity would be horrible and would not be ideal for a daily driver. but i want to get some more opinions...(the more the better)
 

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Type2-L said:
What is VIS? Isn't that a company that makes body kits and carbon fiber stuff?
lol well it is, but thats not what hes referring to...

hes talkin about VIS (Variable Intake System), where in the Legend's intake manifold, it uses flaps between the upper and lower plenums to regulate the amount of airflow going into the cylinders in 3 different stages, depending on what RPM range youre in...this was pretty much the precursor to VTEC, and serves the same purpose.


(the right side is towards the front of the engine)

(excuse me if i get the numbers wrong :lol:)
Up until 1500 RPM, all flaps are closed, and the air travels way to the back of the manifold, then up into the intake runners and then into the cylinders. This is optimal for most low-end torque.

Then around 3300-3400 RPM, the two side flaps open up, allowing air to move more freely up into the intake runners and into the cylinders, which is better for mid-range performance.

Then around 4000-4300 RPM, the flap in the center opens along with the other 2, allowing maximum airflow into the runners, which helps in giving high-end performance.

NickD said:
The VIS is closed by default on the Type I and Type II intake manifolds. Leaving these open all the time would give you erratic idle, cold start issues and poor low-end performance.

In fact, performance will be horrible because the engine will be getting too much air at the low RPM range which the ECU won't compensate for properly. The oxygen sensors will then detect the engine running lean and trigger the ECU to run in "safe mode" which will degrade performance.

Even if you manage to overcome this you will have to deal with degraded low-end torque which the VIS is designed to solve.
and yea, the performance would be horrible since this system is designed to keep the engine's performance balanced throughout the entire RPM range. And thats just if you unplug the vacuum lines to turn VIS off...there was one idiot on A-L.com who removed his flaps entirely (which was alot worse than just unplugging stuff), and royally screwed himself over [link: hehe]

stop by A-L.com, and do a little searching over there for "VIS", and there were quite a few opinions from highly respected members as to why VIS is needed...
 

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Gride_Cruiser said:
:werd: The VIS is necessary. That thread by Legendtyperkon just make me laugh every time. One wouldn’t take out the VTEC to make more hp right (and I'm just talking on the extreme side)?
This system is NOTHING like vtec. Get that straight.

Anywho. Unless you have other modifications, you have no use for removing the VIS. The only reason it is there is to balance out the a/f ratio.

If you are an intake/exhaust/chip kind of guy, leave it. You will get better gas mileage
 

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RangerJoe said:
This system is NOTHING like vtec. Get that straight.

Anywho. Unless you have other modifications, you have no use for removing the VIS. The only reason it is there is to balance out the a/f ratio.

If you are an intake/exhaust/chip kind of guy, leave it. You will get better gas mileage
OH no no...i never said it was like vtec...i was saying it'd be like having vtec and wanting to remove the vtec to make power. And I also emphasized (on the extreme side) i guess my comparison is not a very good one...obviously i know they're very different systems.
Thanks
 

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Discussion Starter · #7 ·
wow after reading that thread, i feel like a reatard for even thinking about it. "i thought id get mad hp yo" lol
 

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Discussion Starter · #9 ·
that is true, thanks for all the responses. when i diassembled the manifold on the VIS section there is a little pocket with a bunch of oil in it? what kind of oil do i need to put back in it?
 

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you dont count....

anyway, Dave, everything I have ever heard about VIS says it is for a/f stability first and foremost. I do not know any other benefits to having the system are, but there are bound to be some.

What do you mean by sonic tuning?
 

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Sonic tuning increases volumetric efficiency--the measure of flow through a given diameter pipe--because of a pulsing/resonating effect.
The more sonic tuning, the more efficient a setup becomes. Pipe diameter and length are huge factors in sonic tuning.

You know most of this already; hence why you are working on the y-pipe :)

k.h.
 

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I think RangerJoe was talking about Daddymac who said "this was pretty much the precursor to VTEC, and serves the same purpose."

It's not like VTEC but Daddymac knows that :mhihi: what he means was, before VTEC came out this was a PRE-VTEC type system. That essentially served the same purpose/result. VTEC is a lot more advanced/efficient/better results... but before VTEC we had VIS ;)

...

DV8 removed his VIS but he doesn't count because of the VAST amounts of HP he has over the stock system, and the many other modifications done to his car. For most of us, we will not get any result from removing VIS. Port N' Polish would give us better results on the intake manifold.
 

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I'm acutally tring to have my manifold filled in so there arent any dips and valleys.

i really think the RL manifold flows better with a P&P.



~TRu Hybrid
 

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Well DV8 lol you really dont count because with the increased stroke you've inherently increased torque production so VIS on your undersquare engine is pretty redundant.

with the Legend's 90x84 there's need for sonic tuning and velocity amplification to increase cylinder filling.

thread is pretty much done though...everyone's said the same thing :rofl2:
 

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B&O Legend said:
Well DV8 lol you really dont count because with the increased stroke you've inherently increased torque production so VIS on your undersquare engine is pretty redundant.

with the Legend's 90x84 there's need for sonic tuning and velocity amplification to increase cylinder filling.

However with the increase in TQ, i could use as much air as possible thats why i opened the manifold up to create volume. I really think a manual legend would benefit from no VIS.

~TRu Hybrid
 

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Dv8 said:
However with the increase in TQ, i could use as much air as possible thats why i opened the manifold up to create volume. I really think a manual legend would benefit from no VIS.

~TRu Hybrid

under full or generous throttle a 4000+rpm no doubt...

but at 50mph in 5th gear it would be hurtin bad. i wonder though, how much torque you'd end up giving up with that flow speed lost due to missing VIS.

only one way to find out lol.
 

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B&O Legend said:
under full or generous throttle a 4000+rpm no doubt...

but at 50mph in 5th gear it would be hurtin bad. i wonder though, how much torque you'd end up giving up with that flow speed lost due to missing VIS.

only one way to find out lol.

If someone is driving around in 5th gear @ 50mph then they should shred their licence and take up biking.

~TRu Hybrid
 
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