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I don't understand. What does "long" mean in this context?

The manifold length is cut shorter when the butterfly closes?
simply, yes, work out the flow pah if the butterfly is closed.
The "long" intake runner effect on bottom end hp is achieved by the expansion chambers. This runner length effect however is a detriment to fuel demand at high rpm air flow needs. That's what I'm reading.

So the short version is, the butterfly valve eliminates the "long runner" advantage at high rpms. Is that about right?
Almost, but it might be the way i'm reading your answer. I think you have the gist of the way it works tho which is good.....The butterfly eliminates the long runner disadvantage at high revs, at high revs you want a short intake path, at low revs you want a longer path to allow the air velocity in the intake to assist in getting more air into the cylinders.
I can read your statement the other way and understand why you used the word advantage, but whichever way the main thing is long at low revs for more bottom end power, short at high revs. If you have a long intake at high revs, you can actually starve the engine for air as the intake pulses can set up "standing" waves which actually act as "plugs" preventing air flow. This was a regular thing on the early carbed drag and racing engines, leading to the invention of the dual plane manifold for bettter performance.
 

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Discussion Starter #22
The butterfly eliminates the long runner disadvantage at high revs, at high revs you want a short intake path, at low revs you want a longer path to allow the air velocity in the intake to assist in getting more air into the cylinders.
Thank you. That's the best explanation I've seen so far.

I read elsewhere that you can indeed run the butterfly valve directly off the intake vacuum but you might not get the full benefit of the short intake path. Not sure why. But it seems like it would still be worth a try.

To see this in operation I think what I'll do is plug the butterfly assembly into the RHD vacuum port on my 2.5L daily driver - the larger port that's pinched off in LHD cars. Then I'll reduce it down to the smaller port size with some hose fittings, and maybe I'll test it both with- and without the tank, but in both cases I'll bypass the intake runner solenoid valve. I suppose I could also record live data with my scanner. Together, these tests should give me a pretty good idea if the VSV will cause other problems like a lean condition code in my 2.7. Plus I'll be able to observe when the valve opens and closes with engine speed. I'lll try to post some video.

I'd rather do a dry run than assemble the 2.7 engine in my Tracker with the VSV installed, only go have to pull the whole thing apart if the engine doesn't run right.
 

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As long as you aren't sucking air from anywhere into the inlet then you shouldn't get a lean code no matter what you do. Sucking on a diaphragm as long as its intact wont worry the car one bit.

My bigger concern would be running the runner butterfly off the inlet manifold directly as it will try to close as the throttle opens as the manifold vacuum will drop Just when you need it to be open.
This is why its fed from a vacuum tank and controlled by a solenoid valve thats rev controlled from the ecm. You could cobble together a rudimentary controller i suppose based on revs, with a set switch point around the 3500 rev mark initially. Know any electronic geeks? Frequency counter chip set to toggle at a set point to drive a relay to turn the vsv off to close the butterfly above a set point.
 

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Discussion Starter #24
You could cobble together a rudimentary controller i suppose based on revs, with a set switch point around the 3500 rev mark initially.
What would you think about a simple inline vacuum relief valve between the manifold connection and the butterfly assembly? One that would delay opening until a preset vacuum pressure is achieved?
 

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What would you think about a simple inline vacuum relief valve between the manifold connection and the butterfly assembly? One that would delay opening until a preset vacuum pressure is achieved?
I'm not sure that would work you need it to open at low revs and remain open until about 3500 rpm under acceleration. Ok at idle or closed throttle as there's plenty of vacuum to pull the butterfly open, but as you press the gas, vacuum in manifold drops. When you reach cruising speed vacuum rises again. Your method will make it open at cruising as well which is not what you want. You need to control it electronically based on revs, or via a switch on the dash.
 

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Discussion Starter #26
I ran those tests on my 2.5.

From the side port I mentioned, I pulled about 52 pounds at idle, and it settled in around 60 pounds at 2500 rpms.

Then I removed the gauge and installed the valve, with the canister, on the same port, bypassing the solenoid. The butterfly is normally open with the engine off. At idle the butterfly closed immediately, and it stayed closed throughout the rpm range, up to 3000. I didn't see any point in going any higher.

I appreciate your explanations. If I can't figure out a way to prevent the diaphragm from cracking open mechanically until about 55 lbs of vacuum, then I doubt I'll pursue this much further. I don't want to lose the long runner effect at low rpms and I can't see installing another 'power" switch I never use.
 

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As interesting as this discussion may be, I'm not certain that it's applicable to the XL-7 intake - please take a second look at the intake manifold - if we define the intake runner as the "pipe" leading from he throttle body to the intake valve, then each of the three cylinders in the bank will have a different length runner, in fact, each of the six cylinders may have a different length runner, and more to the point the butterfly valve does not impact the length of the runners.

If we define the intake runner as the "pipe" leading from the plenum to the intake valve, then we have what is probably six equal length intake runners, and again, the butterfly valve does not impact the length of the runners.

Either way you look at it, and I believe the second is more appropriate, the length of the intake runners is fixed.
 

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As interesting as this discussion may be, I'm not certain that it's applicable to the XL-7 intake -
I'm not sure what you're getting at here. There are several different conversations on this forum alone about shortening the runner length of an xl-7 2.7 engine using this valve. It's called a intake runner control valve. They must have installed it for a reason. Some say 10hp boost. Some say torque boost. I surely don't know.

So we look to the experts. 2013GV says yes, you say no. I don't know what to make of all this.

So while yes it's very interesting, I've decided it's not worth the hassle. I have a couple of junk 2.5 engines I may try to fix someday. Maybe I'll fiddle with it then.
 

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I'm not sure what you're getting at here. There are several different conversations on this forum alone about shortening the runner length of an xl-7 2.7 engine using this valve. It's called a intake runner control valve. They must have installed it for a reason. Some say 10hp boost. Some say torque boost. I surely don't know.
Read the discussions - and let me say right now I haven't - and then engage brain.

Re-read my post - what are you defining as the length of the intake runner? I have suggested two definitions, and also indicated which I feel is the correct one. I have also pointed out that the butterfly valve does not change the length of the runner as defined by either definition.

I'm not suggesting that the valve doesn't have a purpose, I'm not suggesting that it doesn't improve torque or horsepower, but based on the position of the valve it's not changing the length of the intake runners.

All I'm doing is suggesting that you think about what you're reading and not accept it as gospel - don't accept my scepticism as gospel, I may be wrong, but I sure as heck believe that that whatever that valve does, it does not change the length of intake runner, and for what it's worth, I own a Suzuki with a variable length intake manifold - or as Suzuki calls it, IMT - Intake Manifold Tuning.
 

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I took a look for the threads that discuss shortening the runner length on an XL-7, couldn't find any, but I did find this, which might explain the additional power.

different motors

By the way - my version of the WWEPC describes it as "VALVE, INTK CONT".
 

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Fordem, it does change the length if you look at the totality of the inlet manifold. While the "length " from the throttle butterfly is fixed down both sides, its the addition of the length across the front of the engine that makes the difference. Its the increase in flowing volumetric capacity that changes the pulse resonating in the manifold leading to the added air velocity at low revs.
 

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Fordem, it does change the length if you look at the totality of the inlet manifold. While the "length " from the throttle butterfly is fixed down both sides, its the addition of the length across the front of the engine that makes the difference. Its the increase in flowing volumetric capacity that changes the pulse resonating in the manifold leading to the added air velocity at low revs.
Let me start by asking this question ...

Valve open - what's the length of the intake manifold?
Valve closed - what's the length of the intake manifold? Does it actually change? Bearing in mind that the valve is at one end of the surge tank, is there a disadvantage or advantage to the banks having unequal length manifolds?

Now can we address the definition of an intake runner? From the valve to the common or shored space, aka the intake plenum. Opening or closing the valve does not affect the length of the runner.

Yes, the valve has some impact on intake manifold tuning, but it is not a variable length runner.
 

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Let me start by asking this question ...

Valve open - what's the length of the intake manifold?
Valve closed - what's the length of the intake manifold? Does it actually change? Bearing in mind that the valve is at one end of the surge tank, is there a disadvantage or advantage to the banks having unequal length manifolds?

Now can we address the definition of an intake runner? From the valve to the common or shored space, aka the intake plenum. Opening or closing the valve does not affect the length of the runner.

Yes, the valve has some impact on intake manifold tuning, but it is not a variable length runner.
I agree, its not a "variable length runner" in the true sense like the 2.4's have, it fulfills the same function in the V6 models by altering the "length" the power pulses in the manifold have to travel, and interact at the point the butterfly opens or closes. While it is strictly a "tuning" device, it produces the same or at least a similar result to the system in the 2.4's. The calculations in determining the wave propagation are way above my head but as we all know with cost being king, if it didn't do something measurable, the manufacturer wouldn't have fitted it.There will be a reason why its located at one end of the cross connection rather than in the centre, there again, the calculations will have been done.

Mainfold tuning is an art, and I can tell from experience that my HG has a dual plane high rise manifold for better bottom end and street driving, the race engine has a little stumpy manifold with a common plenum as it runs most of its time at 6000 rpms on the track, and its got naff all power down the bottom end. I put the factory manifold back on and it acts like the ute but has a woeful top end.
I have 840 ish HP in the race car, and 400 in the ute, the ute has way more get up and go than the race car.

I would be interested if he did hook it up and had it close at about 3500 rpm and whether the difference was noticeable.
 

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Discussion Starter #35
I would be interested if he did hook it up and had it close at about 3500 rpm and whether the difference was noticeable.
If you're asking me - no, I decided to use the stock 2.5 intake on my 2.7 swap. I may come back to this some day after some further brain engagement.
 

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I have no doubt that it has a worthwhile impact, and would love to know more about how it works, and at what rpms it opens & closes, BUT, because it does not change the length of the runners, any attempt to explain it as such, just confuses the matter.

Over the past three or four days, I have made several google searches for how that particular system operates and found vey little detail, on the other hand I have found other explanations for where the additional power may have been created.
 

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Discussion Starter #37
where the additional power may have been created.
Are you referring to the larger exhaust mentioned in post #6 of "different motors" as the source of addl power?
 

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I have no doubt that it has a worthwhile impact, and would love to know more about how it works, and at what rpms it opens & closes, BUT, because it does not change the length of the runners, any attempt to explain it as such, just confuses the matter.

Over the past three or four days, I have made several google searches for how that particular system operates and found vey little detail, on the other hand I have found other explanations for where the additional power may have been created.
Fordem,

If you want some insomnia curing material, heres a study on plenum volume and its effects. In the situation we are discussing here, its more about pressure wave interactions (Helmholtz resonation) in the plenum than length, but its still interesting, if somewhat dry, reading.

Its an interesting subject, but I will defer to the engineer's in white coats for how it all works.
 

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