The Lotus Cars Community banner
1 - 18 of 18 Posts

·
Banned
Joined
·
6,941 Posts
Discussion Starter · #1 · (Edited)
The other day I mentioned that our airbox has a flap that is controlled by the ECU. This flap opens up another entrance into the airbox where our airfilter lives. According to the Service manual, the flap stays closed on the regular cam. This means that air can only enter the airbox through the long runner that sucks air by the scoop behind the driver's door. Generally speaking, long runners encourage torque at lowish RPMs. On the High cam, the ECU allows the airbox flap to open up. This provides two passages for air to enter the airbox, the existing long runner plus the just opened very short runner on the underside of the air box. I ran the car with the flap open all the time at all revs. And with it running stock which means flap closed on the normal cam. Below is a quick comparo showing the g-force versus the road speed in 2nd gear going up an uphill highway on ramp. This follows the shape of the car's torque curve. G-force can be felt as that push in your back. Road speed is from the GPS and S/B accurate to about 0.1 MPH.

This was just a quickie test during lunch time with one run apiece. Looks like stock won, especially at low road speeds at under 3000 RPMs. There would also be part throttle benefits, but these were not measured. Above about 5800 the curves tracked each other as expected as this is in the high RPM range where the dual inlets would start to be used when the cam kicked in. It would not surprise me if the flap changed state at other times/loads/conditions.

 

·
Registered
Joined
·
39 Posts
Interesting, I intended to purchase the reverie carbon airbox upon it's release. Your investigation makes me wonder if there will be any gains from a new airbox as the butterfly valve will no longer be there. I would obviously hate to lose any torque.
 

·
Banned
Joined
·
6,941 Posts
Discussion Starter · #3 ·
>>>Interesting, I intended to purchase the reverie carbon airbox upon it's release. Your investigation makes me wonder if there will be any gains from a new airbox as the butterfly valve will no longer be there. I would obviously hate to lose any torque.<<<

I have a carbon fiber intake and runners on my E30 M3. It helps the top end but definitely hurt the low end below about 3500. You can get some of that back with ECU tuning.
 

·
Banned
Joined
·
6,941 Posts
Discussion Starter · #6 · (Edited)
>>>Which line is which? Black stock, and red with open flap? Or vice versa?<<<

Black is stock. Slight sound change but in my case not too huge of a difference as the Lotus Stage 2 exhaust is no wall flower.
 

·
Registered
Joined
·
323 Posts
Stan

Air Box at the Toyota engine?
So far it has only a plenum or intake manifold and this plenum ends one side at the throttle body the other side at the 4 equal length intake pipes.

The length of these pipes and also their diameter is relevant for torque (see scavenging effect)

You must be writing about the air FILTER box. But I doubt that a flap in there can influence the torque curve but possibly the intake noise.

Would be good to see a picture of that “airbox” and its flap valve.

Ruediger
 

·
Banned
Joined
·
6,941 Posts
Discussion Starter · #8 · (Edited)
>>>Air Box at the Toyota engine? So far it has only a plenum or intake manifold and this plenum ends one side at the throttle body the other side at the 4 equal length intake pipes. The length of these pipes and also their diameter is relevant for torque (see scavenging effect) You must be writing about the air FILTER box. But I doubt that a flap in there can influence the torque curve but possibly the intake noise. Would be good to see a picture of that “airbox” and its flap valve. <<<

The Celica guys have found slight torque curve differences too when you play with the flap. Air box is often used to describe the box where the air filter lives, and I did mention this in the first post sentence 2. But I will try to be clearer...

You can get effects similar to those found when you vary the geometry of the intake manifold. But they tend to be weaker, secondary effects by comparison.

It's hard to get a PIC of the flap unit as you can't see it from under the hood. But you can reach your hand under there and feel it, work the flap and so forth. It lives on the dirty side of the air filter panel and is on the bottom of the further half of the airbox in the PIC below. You can see the long intake tube that Lotus attached to the same airbox piece. Our airbox seem to be a Toyota Matrix unit BTW. I'd have to take a closer look, but we may be seeing part of the rectangular passage the flap uses and lives within, under the metal box clip in this image.

 

·
Registered
Joined
·
323 Posts
Ok I called your picture airfilter box before storing it.:)

In that file I found another picture where a true air box will be required.




That airbox will cover the 4 trumpets, whose dimensions are really relevant for torque above RPM.

The airfilter arranged upstream of that airbox works as a silencer for the intake noise and should be fed with air as cold as possible and also should have a very large surface to minimise pressure drop = flow resistance. Ram air would help to reduce that pressure drop. But this effect is not far from zero at 60 miles per hour.

(I never understood the theory behind the Hurricane Air filter Box so far, perhaps this threads helps me now.:) )

My Miata originally had resonance chambers in between air filter and plenum to reduce intake noise.


Ruediger
 

·
Registered
Joined
·
2,195 Posts
I didn't see anyone else say it.. so Thanks Stan!

All the pontificating and supposing in the world doesn't add up to one well-conceived test with some measurements and charts.

How did you lock the flap into one position or the other? Does the ECU mind if you disconnect it and control it yourself?

Do you know if the ECU modulates it at all, or does it only have two useful positions?
 

·
Registered
Joined
·
2,925 Posts
There is no doubt in my mind that this is sound engineering... and I don't mean strictly the audio kind of sound. I designed and built an intake for my MR2 Spyder (1ZZFE engine) that had two tubes, one long and one short. I put a 5.0 Mustang throttle body in the flow of one tube. The butterfly valve was going to be closed by a solenoid. I never put in the solenoid or the RPM switch that would activate it, but I manually opened and closed the butterfly valve, testing with a G-Tech. I tried the valve in both positions (so it would block off either the short or long tube) and fully open, fully closed, half open, and about 1/4 open. (The difference in my design, compared to Lotus, was there was no airbox and the MAF was closer, but the principle was the same.) Each tube had its own conical filter. The tubes came together in a Y just a short distance before the MAF. There was no choice in that because of space limitations.

Results: With both tubes open, idle was erratic (due to turbulence of two streams converging) and there was a loss of low-end torque (too much air). Even with one tube 1/2 way open, it did not do a 1/4 mile as fast as with just the short tube open. Best torque was acheived with just the long tube open. Best throttle response, mid- to top-end (3500-7300 RPM) HP, and 1/4 mile time was with just the short tube open.

Next step: Had to decide between two throttle bodies tied to same solenoid, toss the TB and make something with a flap, or go to a manually reconfigurable design where you shuffle parts around and always have one tube plugged. I chose the last option because of cost and time to devote to it. Lotus chose the second one. It is a good design.

For anyone interested, what I found with my reconfigurable intake was that the short tube, about 12" total length (less than optimal for very high RPMs such as in the 2ZZ... you'd want it even shorter), plus a resonator, gave such impressive performance from about 3500RPM up that I left it configured that way all the time. The long tube would have to have been increased in diameter anyway, so I tossed it. What I ended up with I call the BCH Racing intake (initials of myself, the guy who made the custom diameter aluminum tube for me, and someone who inspired me). It is the best darned intake out there for the Spyder and will be sold in limited quantities fairly soon. You guys don't need that, though. It is the wrong inside diameter for a 2ZZ.

It looks to me like Lotus gave you a pretty much unbeatable intake, provided the opening and closing of the valve, length of tubes, and diameters are appropriate. The only thing I can think of that would beat it would be something for those who like to drive around on the hot cam all the time... just a plain old-fashioned short ram. Short and straight with a good conical filter at the end, positioned in the coolest part of the engine bay.
 

·
Banned
Joined
·
6,941 Posts
Discussion Starter · #12 ·
You can see the long intake tube in this shot. It's the black thing to the left of the airbox (and motor) that has a "7" shape from this view. The flap device lives under the airbox and is part of the box half on the dirty side of the filter.


 

·
Registered
Joined
·
2,925 Posts
Oh, I see that it is a little different than I imagined. I was fixated on my (unbuilt) flap design idea that would close off either one of two tubes. This is different. If I understand it correctly now, all that does is let more air in when it has to breathe more at high RPMs. You would not want it open at lower RPMs, as the graph bears out.

I think this could be improved upon. Two tubes with different lengths and slightly different diameters with a pair of flaps mechanically tied together controlling which tube is open. For a brief period, both tubes would be partially open. Conical air filter on end of each tube. One MAF in the common part of the tube. Get around turbulence problem by:

Add a little chip to simulate what the MAF signal would be if there were no turbulence. It would know when the transition happened. Don't connect ECU control signal to *your* flapper(s) because you would want a somewhat lower RPM switchover. Just use a "window switch" (a chip that has lower and upper limits you can set via resistors... used for NO2... transition to above upper limit, output will open a relay or whatever and it will stay open until you transition back down below the lower limit... this is so it doesn't oscillate when you are at a mostly constant RPM). The MAF simulator chip you could program by with data you would get from measuring, on a test bench with a longer tube, airflow way downstream of MAF (farther than you can actually place it... you want the short tube to be *short*).

More complicated. More expensive. If my theory is correct, it would only work a *little* better. Improvement would be mostly in lower half of RPM range. This all assumes that the Lotus flapper is strictly an on/off affair, too.

Then again, maybe this is all a "pipe dream".
 

·
Registered
Joined
·
323 Posts
>>You can see the long intake tube in this shot. It's the black thing to the left of the airbox (and motor) that has a "7" shape from this view. The flap device lives under the airbox and is part of the box half on the dirty side of the filter.<<

Somebody has a workshop manual where the hidden flap device may be shown in some systematic drawing?

In the meantime you may read :

HTTP://WWW.CIRCLETRACK.COM/TECHARTICLES/98018/

and also read /see

http://w1.873.telia.com/~u87316815/Audi/motor/Saugrohrumschaltung.pdf

translate Schaltsaugrohr = Variable length intake manifold
and :




http://www.histomobile.com/histomob/tech/2/73.htm

http://autozine.kyul.net/technical_school/engine/tech_engine_2.htm

where you read that ” Toyota's 2 litres Variable Intake engine also has a manifold longer than another “ and see that bad picture





THAT `S WHAT CAN BE DISCOVERED IN THE BLACK BOX SHOWN ABOVE?:)
 

·
Banned
Joined
·
6,941 Posts
Discussion Starter · #16 ·
Ruedigger I think that dual path picture is from a different motor...like the 1ZZ which is stronger than ours below 6000.

Here is a picture of the flap unit from a Celica. Ours is different as we seem to use a Matrix box but the flap itself is the same. The flap itself is white in the PIC below, it is a butterfly setup like a throttle.



On the top of the airbox you can see a electrically controlled vaccum valve and some hoses. The flap can be either closed or open. When open, air can enter the air filter box from either the flap passage or the normal long intake tube. When closed, air can enter only through the long intake tube.

According to the Service Manual the flap is opened when the high cam is engaged and is controlled by the ECU. It may also move at other times as Toyota seems to do this but this is not known in our case.
 
1 - 18 of 18 Posts
Top