Intake runner actuators: Are they worth the trouble?

I’ve noticed a lot of newer engines incorporate intake runner actuators, presumably to optimize the shape of the intake manifold for the engine operating condition. I can see how the change would help a race car win a race, but don’t understand why it would be used in an ordinary passenger car. What are the motivations for the increasing use of intake runner actuators?

My 03 vue has an opel 3.0 v6 with variable intake runners. Has long path at low rpm to help torque. And reroutes to shorter runners at higher rpm for top end help. I’ve never gone over 3k rpm so I think it is unused.

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Maybe it is mostly an advertising thing? Or maybe there are emissions benefits?

The upper intake is a large casting with a removable lid. You can take off top to access runners/flaps or you can lift entire manifold to reach lower intake. I think the flapper motors are electric driven. At low rpm the bits don’t do much. They default to long runner mode.

YES!!! if done correctly, it gives the performance guy/gal (not the average driver) the best of both worlds, low end torque AND upper end HP, the actuators are like a blend door that basically makes the runners long or short… Kinda like a VVT changes the cam in degrees related to the crankshaft to move the power up or down in the rpm range… The performance problem with a VVT system is you are limited on how much more lift and duration you can add (bigger cam) with out having a piston to valve interference, but by changing the intake runner length, there is no internal interference issue to deal with…

For a lot of the members on here, y’all will never know the difference, but if you shift in the 5-6K+ range, you WILL be able to tell the difference vs one or the other… This mainly applies to street or street/strip driven vehicles, a track only drag car is only mostly worried about the upper RPM range… This is Dyno proven…

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Variable cam timing widens the power band and improves efficiency across the rpm band. Variable intake runners do exactly the same.

It improvement in volumetric efficiency helps fuel economy and power in everyday driving. It is not a gimmick any more than variable valve timing or variable valve lift is.

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Well, this would explain why, on the basis of having driven my '97 Escort a good 300K+ miles, I couldn’t say a thing about it! I guess I’d have to delete the IMRC module to find out! Torque…HP…5-6K rpm shifting? Not what you think about tooling around in the single cam Escort. Pure, no frills transport. :laughing: (I’m sure it mattered sometimes in ways I wouldn’t know about, including for fuel efficiency).

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The only vehicles I have really never shifted at just below red line sometimes, is the old Chevy truck and the Infinity, and I redlined the Infinity a few times when it was younger, but dad in his older age slowed way down and now I am a little nervous of the transmission not liking it much, after hibernating a few years in the garage the 1st time I got it up to 80 and then got in it a little the #3 COP didn’t take kindly to it… :laughing:

But everything else has always been fair game… and lasted with no major issue, however I did loose the water pump hub and pulley off the shaft at 6K rpm on the Vibe/Matrix one morning on the way to work… lol

Having driven vehicles with and without VVT, I cannot really feel the difference in performance, and I don’t really see a difference in fuel economy. With no VVT, there is less complexity, and fewer potential problems…especially when buying a used car which may not have been maintained well.

Since I only drive vehicles with an automatic transmission, I am mostly interested in torque at lower RPMs, which is what gets you moving from a standstill. One does not need VVT or variable intake runners to achieve that. Also, once you get into models with VVT, you can no longer use diagnostic tools such as a timing light, or make any mechanical adjustments like you could on older models.


Whether or not you can feel the difference doesn’t change the facts. Lets look at a 2.5 L SOHC Dodge Daytona from 1990. 21/29 city/highway fuel economy with a 5 speed, 100 hp/135 ft-lbs.

Now we look at a 2015 VW Jetta 2.0 L. 25/34 city/highway with a 5 speed, 115 hp and 125 ft-lbs with its single overhead cam, variable valve timing, direct fuel injection and no variable intake. So more power and a bit less torque but greater mpgs from a smaller engine.

Because you don’t NEED to use a timing light. You can read it directly off an OBD scanner. New tools for modern cars.

Now I know you LOVE those 90s Chrysler products and that’s OK. 25 years of development makes for big improvements. But the newer stuff is better in all respects.


How to remove intake.
Step 1. Do not remove top lid.
Step 2. Remove intake bolts in 4” deep holes with 6” driver.
Almost zero reason to ever remove top lid.
Variable runner design does have some benefits.
And it’s fairly troublefree.

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Interesting comparison, but it would be more interesting to the topic at hand comparing two otherwise similar engines & similar weight & shape cars, one using intake runner control and the other not.

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There is one issue with these. Nissan used them on it’s Sentra Spec V and they had a history of the little screws that hold the butterfly valves in place falling out and ruining the engine. My son took his apart and squeezed the exposed threads with a pair of pliers so they could not back out.

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Interesting that this is the customers responsibility, every engine has a throttle body and the screws don’t fall out.