Hey Louie,

Here's my father-in-law's response:

Hi Adam,

Here's some of my thoughts, which involve several points:
The speed of sound is directly proportional to the square root of Temp. This is a fundamental relationship that arises from the molecular properties of air molecules continually banging into one another. Temperature is in fact the macro parameter that measures the energy of these molecules. Pressure and density become involved as macro descriptors of how a volume of gas behaves when it is is compressed and/or subject to pressure. Pressure multiplied by the inverse of density is proportional to Temp. So if the combustion chamber dynamics is governed by small high speed waves , ie sound waves, the Temp is an important factor, but sq. root relationship to temp keeps it a smaller effect. The answer regarding the speed of sound at altitude is indeed, that it is totally an effect of the lapse rate in Temperature as altitude increases. While it is also true that pressure and density decrease, they are not causative. Temperature is.
But there is a second possible dynamic which could be a factor in the overall piston dynamics as well. I would call this a "pump/fill/empty" dynamic. This would be more related to the pressure and density change of the gas and less dependent on the sound waves. More like the dynamics of filling up a bicycle tire with a hand pump.
There are undoubtedly elements of both the mechanisms of 1. and 2. taking place. It's not clear to me, which would be dominant, which is why I thought that if you could do some controlled testing you'd get the data you need. I sketched a little curve vs. engine rpm. to the extent that you see a pronounced peak in the power produced at a specific "tuned" frequency , it would indicate to me that the sound waves play an large role in the dynamics. But I couldn't say that ahead of time, without much further thought and discussion with someone who has done analysis and experiment with such piston dynamics.
Not sure if that is too helpful, but if you run a few careful tests, I think you'll get some of the answers you're looking for.

Best wishes in your development,
Mark

 

I must say, all you engineers sound alike.
(I've heard the same thing said about us attorneys)

 

So so I trust the real length of the tube calculated from the 3rd wave resonance math?

 

Ummm. Well, the original part of this study was to explore if intake tubes should be a different physical length for a pressurized intake at around 3 bar vs. 1 bar. I haven't found the definitive answer yet. We can understand that the speed of sound is constant with different fluid pressure. However, the speed of sound as it relates to the length of the intake tubes gets more complex. The air through which the sound wave travels in the tube is itself moving at up to significant % of mach, or sometimes not moving. The speed of the sound wave as it relates to the physical intake tube changes dramatically along the length of the tube. There is also the frictional loss, and the denser the fluid, the more loss. I'm checking some of my intake design books to see if I can find some reference to difference in design required by forced induction. So far, other than vague mention, I don't see anything specific.

 

Thanks for getting involved Louie. You too M... I mean Z.

 

Brendan,
I checked my intake design books and find very little different when designing an intake for forced induction or for N/A. Especially as it pertains to the runner length. There was a statement that said the Helmholtz resonance effect manifold could be helpful for centrifugal or turbo charged FI, because it would give a torque boost at the lower RPMs. That's like the S4 manifold with the flap closed. When designing such a manifold, use shorter and larger diameter tubes than you'd use for a N/A engine. That was to reduce the flow loss due to wall friction. No specifics were given. If you recall, the Helmholtz resonance uses the intake tube volume with length not being a factor. Evidently, you'd keep the same volume, but have larger and shorter tubes. I think the intake tube length as you are using them (sometimes called ram tubes) wouldn't change whether FI or N/A. I do have a hunch that the power drop you see in EAP when you have longer tubes is due to flow friction loss. That loss at the upper end may go away if you increased the diameter of the tubes. Of course the larger tubes would give you less "ram" effect at lower RPM due to the lower velocity which is the same as on a N/A engine. EAP has some neat diagnostic features. One is charting the port pressure. You pick an RPM and it'll give you the intake port pressure for different crankshaft rotation degrees. At the "tuned" RPM, you want to see a positive pressure spike just as the intake valve opens to get the charge moving past the opening valve into the cylinder. Just before the valve closes, you want another positive pressure peak in the port to keep the charge in the cylinder as the piston is rising and the valve is closing. Usually, the positive port pressure peak is higher when the valve is closing than the one when it is opening. You might check port pressure and see what it looks like at different RPMs and different runner lengths at both 1 bar (N/A) and when under different boost pressures. See if the occurrence of the critical positive pressure waves happen at the same RPM with different intake pressures. It's pretty easy to see when the pressure waves are correct when you are "on the pipe". You can also check mach number of the intake flow. I can't quite remember at the moment, but I think at greater than about mach 0.6 your intake flow losses are going to be high and indicative that you need larger diameter tube. That mach number is probably at 1 bar pressure and may differ at 3 bar.

 

I think the original runners are less than 2 inches on the S4 manifold. I kept the runners at exactly 2in in EAP because that is the tube I have access too (ross machine racing), and its nice thick walls may come in handy. It is also what works well with the bell-mouths that he sells.

This intake may actually end up getting turbo pressure instead of CS pressure.

Do you really think EAP is providing proof of the tube-losses? Well, I should say that instead of guessing, I should re-download the program (and pay for it permanently this time) and find out about those losses. The port size is still 49mm, so I am afraid to increase the runner size too much, or the port entry will then be too steep of a decrease.

 

it's good that you're keeping this in mind, as you would not want the intake tubes to be larger (diameter) than the intake ports---

port matching is good thing.







--Russ

 

The heads are on the engine. Its already built. Its not planned to take them back off when I just put them on. And large ports are not what a street-driven car needs. 1000hp, however, may need some serious runner thinking.

 

in this case, you have set your limits---although some would question 1K hp in a street driven car (I would not, but some folks with more sanity than I would.....).






--Russ

 

What the hell. If a 2L mitsubishi exlipse 4cyl can do 750 and 850 street driven, we sure as hell can do a measly 1000 on 5 freaking liters. Hell, remove the parasitic from todd's SC setup, and he already near there, crank.

 

Brendan,
It's just my opinion but, I think my project and yours are very similar in that
the last thing we need is more bottom end torque. I think anything over 450
lb-trq on the street with even the stickiest street tires and you've got a very serious traction problem. Now, let say your mtr might make a max of 650 trq .

but at the lower rpm range with a mtr like that your still going to be making twice as much as a stock mtr. I think you should design your manifold/runner
length as if it were a form of traction control. Start with a short runner because
your already going to have a traction problem. Try to get the chassis to hookup
with an aftermarket ECU that has traction control and get some very sticky tires.
Even with that your going to fighting the wheel spin. As your starting to hookup
and gaining more mph the short runner manifold will be coming on line and
gradually feed more power as the speed increases and as your able to put it
down. If you build a long runner manifold all your going to end up with is a car
that has an on-off switch for a gas peddle. Build it so as the mph increase it
matches the rpm's as they come up (if you know what I mean) ramp the Hp/trq
up gradually and have it peak higher up in the rpm range so you'll be able to
actually use it because your traveling fast enough to have the traction.

 

I agree Joe. I just didn't want to get something that is worse than stock when off boost or just getting on boost. The lengths of runners for 3rd wave resonance at 6500rpm is still 17 inches. I have no intention really of making them that long. MAYBE I can fit 8 inches past the port, making a total of 12.

Mine as you know is still "just" a 5L. Though if I were to build something a bit bigger, I would still use the same manifold. Maybe have time to do the ports on that magic dream hypothetical engine.

I have decided to put this 2V I am building separate from the 5L into the 78 body that I painted and just use the best stuff I have for the car and have a car to drive sooner. I will either use the 82 or 86 body for the car that will get this engine or I will use it for the 78 if I blow up the 4.5L. I gotta get a car I am proud of on the road soon. This plan buys me time to not rush the important stages of the 5L - Intake, IC, pipes, Boost method, and tuning. I can do it at a leisurely pace when I know I have a sorted car to drive every day.

 

Is the frictional loss from surface level boundary layer making the actual moving portion of the air too small?

***

From:

http://www.gofastnews.com/board/tech...ort-areas.html

 

Hi Brendan,
I've spent the afternoon working with EAP trying different things trying to compare results of different runner lengths, different boost amounts, trying to make some sense of it all.
First, it appears that changing from the standard S4 intake, on a stock S4 motor, to an individual runner type intake with 8" runners (12" total length including port length) would cost some torque at 3000 RPM, but not a lot since the IR intake is overall more efficient. Changing from 8" runners to 12" runners doesn't help torque below about 3500 rpm, but does hurt it above 5500. With 8" runners, the torque peak is at 4750 and with the 12" runners it's at 4500, but 15 lb ft higher. Increasing runner length to 17" (overall 21" including port length) does help the mid range a lot and you get a 26 lb ft increase at 3000 over the 8" IR length. The torque peaks between 3500 and 4200 gaining 40 lb ft over the 8" runners. However above 5250, the long runners just die. At 6000 rpm, the long runners are down 55hp as compared to the 8" runners.

Moving on to boosted S4 motor using S4 cams and S4 valves, but with IR intake shows some interesting info. I used a Vortech V2 S trim. EAP has about 20 different SC choices, but I think this one is a popular type.

10 psi boost using 8" runners gave between 10 and 30 ft lbs more tq than even the 17" runners N/A between 3000 and 4000. The torque peak was 480 lb ft at 5250 and peak power 510 hp at 6000. Not bad. Lengthening the runners to 12" didn't help tq below 3500, increased it by about 10 lb ft 3700 to 4700, and decreased it above 5500. Power at 6000 was down 20hp with the 12" runners. Next shortening the runners to only 4" did lower the torque below 5750, but only by about 5 lb ft. Above 5750, the short runners gave more power for 18 more lb ft and 21 more hp at 6250. Peak power was 528 between 6000 and 6250.

Next, I tried 15 psi boost. For the boost change from 10 psi to 15 psi, I had to lower the compression ratio from 9.5 to 8.5:1 or EAP would give strong warning about detonation. 15 psi boost using the 8" runners gave another slight boost in torque at the low end as compared to 10 psi boost due to more boost being generated at the lower RPMs. Again the 4" runners showed no real loss in tq below 5750, but an improvement above 5750. The difference was about the same as at 10 psi boost with gains of 20 ft lbs tq and 22 hp at 6000 RPM. Peak power at 6250 was 575 hp. Peak tq was 525 at 5000 rpm. Increasing runner length to 12" gave about 10 more lb ft torque between 3500 and 5000 over either 4" or 8" runners, but above 5000 was worse. At 6000 the tq was 43 lb ft lower and hp was 49 less as compared to the 4" runners. I tried different runner lengths too. Less than 4" showed a loss everywhere except at the very top, end. Longer than 4" would cut down the tq above 5750 rpm more and more the longer the runner was, but not much improvement below 5750.

For 20 psi boost, I had to lower the compression ratio to 7.5:1. The torque from 2500 on up was better than at 15 psi boost due to the higher boost even though the comp ratio was lower. Again the 4" runner seemed best. Shorter wasn't any good, and longer decreased power above 5250 rpm. The power peak came at a lower RPM at this higher boost. At 5750 it made 595 hp. Torque was 550 at 5000. I think the EAP modeling begins to fall apart above 15 psi boost. I noticed the power to run the compressor increased dramatically. At 15 psi, it took around 70 hp. At 20 psi boost it took 120 hp. The engine power output between 15 psi and 20 psi didn't rise as much as it should have either. There are a lot of SC specs to enter that I didn't know so used the default values. Things like island cfm, pressure ratio, efficiency % are probably way out of whack when you get up to 20 psi.

I'm not sure if this excersize helped learn much or not. It does appear that long runners on a SC engine may not be the best, and the long runners didn't help low end torque as it did on a N/A engine. But, even the centrifugal type SC makes enough boost at 3000 rpm to help some over a N/A engine. It's also apparent that a very useful motor could be had with stock compression (do nothing to it internally) at up to 10 psi boost. I think we already knew that. Go up to 15 psi and you'd better do something to lower the compression ratio. I'd say that 15 psi would likely be the practical limit to have quite high hp, but still have a torque value that would give some reliability to the drive train. Above 15 psi and strange things are likely to happen. One of which is shredding everything behind the flywheel.

Back to runner length. I remember talking to someone who was experimenting with the TS SC systems. He was improving on the basic Andy Keel manifold. Some things helped and some things didn't. Andy's manifold has no runners beyond the ports. He added runners to help channel the air and keep mixture robbing from happening between cylinders. I think the manifold with runners lost 30 hp as compared to the no runner manifold. For Brendan's manifold, I'd suggest making it with stub runners, but designed so added length could be tried. This may be a situation where nothing really tells the story but experimentation.