New Product: High-Performance Intake Runners for the 32v 928
07-09-2010, 12:44 PM
#16
Nordschleife Master
Nice product that will allow for many different configurations.
This may be nitpicking, but I don't think that's what is usually described as the Helmholtz effect in intake manifold design. The Helmholtz resonator intake manifold usually has a closed resonating plenum that receives equally spaced, non-overlapping pulses. For example, the S4 snakes' nest manifold operates as a Helmholtz resonator when the flappy is closed. When the flappy opens, the pulses overlap and the manifold is no longer a Helmholtz resonator.
Building a manifold that would usually be described as a Helmholtz resonator with your runners would require a complex pit of snakes on top of it and two separate plenums. Given the hood clearance, this is not a practical option for most of us.
I will caveat a bit. In some sense, even an open velocity stack design exploits some Helmholtz effects, if you consider the cylinder itself as the Helmholtz resonator. If this is what you mean, then I am just nitpicking about the commonly used terminology of calling an intake manifold a Helmholtz resonator only if the manifold plenum acts as the Helmholtz resonating cavity.
Here's my impression of what's going on with the ITBs: When the throttle is wide open, a typical ITB system acts like a straight runner. For WOT operation, the ITB throttle location is approximately irrelevant, at least as long as the cross-sectional area of the runner doesn't vary dramatically. Only if the throttle plate causes a lot of turbulence is there any advantage from placing the htrottle plate further from the port. In contrast, for part throttle operation, it's best to place the the throttle close to the port. Now, I am not an expert on the topic, so someone in the know may want to fact check this and report back.
Careful engineering also allows the pressure waves known as the “Helmholtz effect” to increase flow at the back of the intake valve just as it opens, thereby increasing volumetric efficiency by as much as 10%. To take advantage of this, proper intake bells must be used to create the pressure wave reversal to send the pulse back to the valve from where it came.
There are two methods of “natural supercharging”, that is, increasing the velocity of the air at the back of the intake valve. The first is the Helmholtz Effect, using proper inlet bells to reverse the pressure wave in combination with intake runner length to time the pulse so it arrives at the back of the valve just as the valve opens;
Building a manifold that would usually be described as a Helmholtz resonator with your runners would require a complex pit of snakes on top of it and two separate plenums. Given the hood clearance, this is not a practical option for most of us.
I will caveat a bit. In some sense, even an open velocity stack design exploits some Helmholtz effects, if you consider the cylinder itself as the Helmholtz resonator. If this is what you mean, then I am just nitpicking about the commonly used terminology of calling an intake manifold a Helmholtz resonator only if the manifold plenum acts as the Helmholtz resonating cavity.
Taper and intake runner length are often overlooked in ITB setups, where the ITB’s are mounted directly to the heads or very close thereto. In our design, the ITB’s can be mounted atop our runners, and benefit from the midrange torque that the runner length provides and the velocity increase from the tapered runner.
07-09-2010, 12:50 PM
#17
Developer
Thread Starter
Thanks, Dave.
There are few who know the true cost of developing a new intake casting - and I know you are one who know this all too well.
I needed it for my car, I enjoy the R&D, and I hope some others might find it useful.
There are few who know the true cost of developing a new intake casting - and I know you are one who know this all too well.
I needed it for my car, I enjoy the R&D, and I hope some others might find it useful.
07-09-2010, 01:03 PM
#18
Developer
Thread Starter
The Helmholtz Effect does not require a closed plenum to exist.
It does require a proper bell-mouth on the inlet end for the pressure wave to reverse and go back down the runner, and very smooth transitions (at the transition from intake runner to head, for example).
A lengthy bar stool conversation can be had about whether boosted engines benefit from the Helmholtz effect, or only naturally aspirated ones. My own opinion is that the physics are unchanged on a boosted engine, the valve still slaps shut into a rushing stream of air, the pressure wave is still created, and the Helmholtz effect is still real.
It does require a proper bell-mouth on the inlet end for the pressure wave to reverse and go back down the runner, and very smooth transitions (at the transition from intake runner to head, for example).
A lengthy bar stool conversation can be had about whether boosted engines benefit from the Helmholtz effect, or only naturally aspirated ones. My own opinion is that the physics are unchanged on a boosted engine, the valve still slaps shut into a rushing stream of air, the pressure wave is still created, and the Helmholtz effect is still real.
07-09-2010, 01:51 PM
#22
Rennlist Member
that flow test is pretty meaningless, right? I mean, you have the stock S4 intake, with the side covers off, and it would hardly equate to anything meaningful, comparing to straight stubby runners in a box fed by two intakes. I dont think ANYONE doubts this will flow more. but that flow bench test didnt really reveal much. Also, what comes out of the "Boxes"? two intakes that are joined by a "Y" pipe and then a stock MAF? I hope so. I dont think you need all that after market tuning and componentry, to make some big hp with your set up. sure , in boosted applications, but for NA, I would think that this could be close to the CF gains . I think you might be losing some of the midrange HP and torque, due to the lack of the Heimholz resonator effect, and the shorter stubby runners, but for racing, it migth be ok. certainly when i used a spacer and changed that part of my stock intake, it killed mid range torque that I DO use in racing by near 50hp! so, needless to say, the spacers were removed to put back to stock. However, the peak HP didnt change that much either. we (S4 and other 32valvers) need a nice bolt on aftermarket intake like the BMW and other guys have access to!
07-09-2010, 02:04 PM
#24
Three Wheelin'
Carl, at the rate you are going modifying a 4 cam 928 engine is going to be as easy as building a small block chevy!!!! Any part needed will be available off the shelf. Well done.
07-09-2010, 02:10 PM
#25
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
Not to hijack this thread, but what's the port diameter on 32v engines? I am looking at a set of Suzuki GSXR throttle bodies I can cut down, but they are about 40mm and are tapering down to like a 38.
07-09-2010, 02:14 PM
#26
Developer
Thread Starter
Carl, at the rate you are going modifying a 4 cam 928 engine is going to be as easy as building a small block chevy!!!! Any part needed will be available off the shelf.
Kibort: the final total runner length of these runners for this application came out to 10.85". Its not as short as you think. And it was not left to chance. To have a shot at the LSR, I need max HP at redline, not before it. So I would agree, my configuration would be different than someone elses.... but then thats the whole reason for seperating the intake runners from the plenums. Now you are free to finish your manifold as you need for your application.
07-09-2010, 02:17 PM
#27
Developer
Thread Starter
but what's the port diameter on 32v engines?
The port at the head is oblong, but after our porting process, the average is 54mm dia.
07-09-2010, 02:29 PM
#29
Developer
Thread Starter
About 45mm, but thats an approximation. Again, the port is oblong.
However, I can tell you that at the top of the intake runner (where you would mount your ITB's) it is 2.25" or 57.1mm
However, I can tell you that at the top of the intake runner (where you would mount your ITB's) it is 2.25" or 57.1mm
07-09-2010, 02:37 PM
#30
Three Wheelin'
Join Date: Feb 2009
Location: Washington "Dc"
Posts: 1,810
Likes: 0
Received 0 Likes
on
0 Posts
This is awesome. And thanks for sharing. R&D like this is an investment of time and $$ that most would keep to themselves.
We are very fortunate to have people like Carl sharing their hard earned knowledge to us pubbies.
If I ever get a Lebron style paycheck you will be the guy to build my 'dream car'.. Wow! CanI say WOW ?
