Tuned intake runner arc length

[geniusanurag]

Hi
I have calculated the tuned intake runner length from the helmotz equations of pressure waves. The confusion that have arised is whether this length is the curved arc length of the runners or the effective lenth calculated from taking into account flow looses into account (from fox and mcd - fluid mechanics). In case its effective length, even 350 calculated length could be fitted into 150 mm arc length runner. i have doubt here that i have mixed two different theories. I would be glad if anyone could help me overthis as we need to manufacture it within 2-3 days and i dont have access to any reading material or source of information.

[geniusanurag]

Hi
I have calculated the tuned intake runner length from the helmotz equations of pressure waves. The confusion that have arised is whether this length is the curved arc length of the runners or the effective lenth calculated from taking into account flow looses into account (from fox and mcd - fluid mechanics). In case its effective length, even 350 calculated length could be fitted into 150 mm arc length runner. i have doubt here that i have mixed two different theories. I would be glad if anyone could help me overthis as we need to manufacture it within 2-3 days and i dont have access to any reading material or source of information.

[absolutepressure]

I'm not sure why you think that if you have an arc instead of a straight line your runner can be a shorter length. The wave will travel at the same speed no matter the shape.

I used the equation

L=(theta*C)/(0.012*N)

where theta is essentially the phase difference of the waves after the opening of the valves. The only thing you need to know with repect to that is experiments have shown that values inbetween 85 and 90 degrees produce the greatest results. C is the speed of sound in air. At 60F C=343m/s. N is the number of rpm's you want to tune the intake for. 0.012 is a constant. It might be conversion factor, my book wasn't too clear on that. (Advanced Engine Technology, Hiesler).

So that's speed of sound in m/s and theta in degrees which will give you length L in mm.

That length is the distance from the back of the valve to the opening of your runner, so the runner you have to manufacture, Lmanf=L-Lport.

I have a 60 degree bend in my runners for fitment. All I do is take the length of the center line of the curve.

What rpm are you tuning your intake for? 350mm seems pretty long. I have mine tuned for 8500rpm and mine are at 302mm. That's almost a foot, and I'm thankful my ports are about 5 inches deep.

[geniusanurag]

I want to tune it at 7000 rpm, though i think i wont be able to manage an arc length of more than 275mm as we have decided to go with a vertical arrangement of intake.
By the way I didnt got what was that theta that you took as 85 in that formula.

[Superfast Matt McCoy]

There are several equations that predict the appropriate length for a VE boost at a given RPM, but they vary greatly in their prediction. For 7000 RPM I have about 275mm from Planter and between 400mm and 1100mm from Ricardo. This is one of those things that you need to test.

On a more important note, if you tune for 7000 RPM, you're going to have a drop in power around 9000RPM. The pressure wave will reach the valve just as it closes and you'll just have a resonating pressure wave going nowhere.

[geniusanurag]

What if I tune the exhaust at 9000 rpm. Then I would get a flat torque curve for a greater range and would have the engine cut off at 11000 rpm only.

[absolutepressure]

I'm pretty sure there's no flattness in your torque curve at any two consecutive points, and I don't even know what engine you're running. But I kind of understand what your trying to say. I'm not sure how McCoy found that you'll have less power at 9000rpm...I'm guessing it's a simple modification of the equation, but my brain is just chillin right now.

Another thing to watch out for is helmholtz tuning. I thought that it was something to look into, but it's only advantageous at low rpm, like below 4k, and becomes severely disadvantageous above that. The waves in the plenum start creating a lot of destructive interference with the pressure waves, and actually can create negative pressure waves at some point. You might want to run your dimensions through that equation to make sure your intake isn't accidentally tuned for an rpm that will hurt your upper range.

Probably the flattest torque curve in the world right now is the one that the 2.0L turbo ecotec engine produces. It's got a torque "curve" so flat you could store ball bearings on it.

[Jersey Tom]

Ask yourself this - which has a much bigger effect.. intake tuning or exhaust tuning?

What causes the pressure wave at EVO, and what causes one (if anything) at IVO?

[BeaverGuy]

Yes curved runners will affect your effective runner length(physical length plus port length plus some length ahead of the runner in the plenum, ussually about 0.5 times the runner diameter). However, I'm not sure of an empirical relationship but I have seen the effect on the dyno. As for length calculations at 7000RPM I have effective lengths of 330mm and 460mm which for our setup in '05 is about 200mm and 330mm of physical length. Also, in contrast to Matt's claim that you would have a drop at 9000RPM my calculations for your length of 350mm has a second peak at 9000RPM. I would also disagree slightly with his reasoning as having a high pressure wave arrive just after IVC shouldn't result in a torque decerease, but it surely isn't beneficial. But you will have an RPM where the low pressure wave will hit right before IVC and that will have a detrimental effect.

Having all these different number shows just how imprecise it is when you are using empirical equations. It also shows how important it is to have as much time with a dyno as possible.

I totally believe you can use the exhaust to flatten the torque curve by filling in where you have intake dips. It works and when done in combination with adjusting your plenum volume you can achieve very flat portions of the torque curve. The '06 engine has one region where the variation in torque is only 2 Ft-lbs over a 2700RPM range and another spot with a 2 Ft-lbs variation over 1300RPM. It also achieved 85% of peak torque, 6 Ft-lbs variation, from 7600RPM to 12000RPM with a peak of 41 Ft-lbs at 8300RPM.

As far as which is more important intake or exhaust and where you are getting your Wave pulses from. The wave pulse originate at the when the respective valve opens and hopefully arrives shortly before the valve closes. You have a low pressure wave that originates at IVO and becomes a high pressure wave on reflection and hopefully arrives shortly before IVC. This way you have a higher average pressure differential as opposed to trying to get the high pressure intake wave to arrive at intake opening and the low pressure exhaust wave to arrive at exhaust opening. And I would say that the intake has the largest impact. If you can change the location of the primary torque peak by 1000 RPM with a 4" change in the length of exhaust as I have seen the intake do, I might say they are equal. But I haven't seen the exhaust do anything to the primary torque peak unless it was tuned to the same RPM as the intake.

[Jersey Tom]

I have seen on our cars, much more dramatic powerband changes with exhaust tuning than intake. Makes sense to me..

EVO is a little before BDC, at which point after the power stroke there is still a good amount of pressure built up in the cylinder. Valve opens, strong pulse of gas is sent down the exhaust runner, reflects, comes back up.

IVO is what, a little before TDC? Maybe a little after? (I'm not familiar with many cam profiles off hand) Where does the strong 'vacuum' pulse come from?

Between 03 and 05 we had tried very short intake runners (05), very long runners (04), and intermediate runners (03), all with pretty much the same exhaust lengths. Power would never come on before 7500-8000 rpm and would go to say 11000 or so.

06, we lengthened the exhaust primaries a good couple inches and ran the 03, 05, and finally 06 (similar to 03) intakes on it. In all cases, power came on around 5500 rpm and would go till 9500 or so. Unfortunately I don't have dyno plots with me, and wasn't much of an engine guy before this year.

[JuicedH22]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">
Probably the flattest torque curve in the world right now is the one that the 2.0L turbo ecotec engine produces. It's got a torque "curve" so flat you could store ball bearings on it. </div></BLOCKQUOTE>

Tomorrow I am going to post up the tq curve I created on our 2005 car power comes on late (something resolved since then), but flat as a board from 7k to past 12k

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by absolutepressure:
Probably the flattest torque curve in the world right now is the one that the 2.0L turbo ecotec engine produces. It's got a torque "curve" so flat you could store ball bearings on it. </div></BLOCKQUOTE>
Probably electronically limited to protect the gearbox, then...
Regards, Ian

[Chris Allbee]

I hate to sound like i'm disagreeing with everyone here, but it would make sense to me that with a restricted intake that begins to produce standing pressure waves as low as 9k you should be able to realize big gains by improving intake efficiency. If you aren't seeing much change from varying the intake runner lengths then you may have an issue with the plenum or restrictor designs. I liken it to trying to make anti-roll bar adjustments on a sloppy chassis. You just won't see the benefits until you sort out the foundation, in this case the restrictor/plenum. I know this is kinda long, but I really think the runner lengths are at least as important, if not more so, than the exhaust lengths in determining the location of peak power.

[Jersey Tom]

Care to elaborate on what you mean by generated standing pressure waves from 9k?

[Chris Allbee]

There are pulses, or pressure waves if you will, in the intake at all times. We all know that. With a restrictor in place often times people ignore what happens on the backside of that and just focus on a steady-state flow through the restrictor. Well as you have your pressure driven flow into the intake you also have the propagating pressure pulses from the valves trying to flow out of the restrictor into the atmosphere. The incoming pressure waves act against those out-going waves promoting stagnation and a drop in the mach number. If you think about this for a while you will come to the conclusion that there is more than just the absolute amount of air that can flow at Mach 1 through a 20mm orifice that is restricting inflow to the plenum and engine.

The 9k figure is a generalization about when this effect will come into play, it will actually depend a lot on your individual intake design.

[absolutepressure]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
Ask yourself this - which has a much bigger effect.. intake tuning or exhaust tuning?

What causes the pressure wave at EVO, and what causes one (if anything) at IVO? </div></BLOCKQUOTE>

The way I look at it, with as unrestrictive as our exhausts are, and the little valve overlap we run, doing more to get what's in the chamber out isn't the biggest help.

Now, to increase the amount of a/f going into the chamber to make more power, that's where the real gains are.

But that being said, why not do both? It's as easy as 1,2,3.

[Bill Kunst]

Abs-
which engine are you running, the r6 or the f2? I am not sure what the r6 has, but we pt an additional 22degrees of overlap into the f2 for a total in the 110 range, i think. I would have to check back to see what the overlap is on a stock f2 to be sure.
Bill