----- Original Message -----
Sent: Wednesday, September 17, 2003 12:01
PM
Subject: [FlyRotary] Intake
questions
Greetings,
I'm probably about to
prove that I haven't paid any attention to any of the intake construction
threads, but here goes... I know there's special length that will tune
the intake to make more power. Ed knows what this is, but if he tells
us, he has to kill us (a slow painful death, involving 60 slides)
:-)
My general question is
this- does it matter if this runner length is before, or after the
throttle body? I'm using the TWM throttle body, which is completely
separated into two sides. If I kept the air inlet to the TB as separate
tubes for a particular length, would that count towards the tuned
system?
The reason I'm thinking
about this of course is pre-planning for the almost inevitable removal of my
turbo. If I end up using a stock cowl, I'll have space in the left
cheek for intake stuff. I've seen a very short intake manifold that
sticks straight out to the side about 4 inches or so, then the TB would stick
straight out another 4 inches or so. While this is simple, and compact,
it would certainly not be good for our power band, so I started wondering if I
could "tune" it with individual pipes on the inlet side of the
TB.
Thanks,
Rusty (Scotty, I need
more power!)
The short answer is that
for the DIE effect, you need the runners between the TB and intake
port
For you Rusty, you have
to sit throught the presentation TWICE! The answer is (I love this ) is-
it depends. There are numerous approaches to "induction tuning" (as
you now) , there are even more theories from the yard tree to the NASCAR chief
mechanic's favorite one. Depending on whether you adopt "Organ Pipe",
"Helmhotz", "Finite-Amplitude Wave theory" Or WHAT, you are likely to get
different answers.
However, there are a
couple of things that appear to fall out of most theories and
practice.
1. Long small tubes
make for good low-to mid range torque and power, but tend to fall off at
higher RPM. Now define "small", Tracy Crook's engine probably has some of (if
not the smallest) diameter tubes and has done 214 MPH.
2. Short large
tubes tend to make good High RPM range torque and power (mainly power) but
tend to suck at low - mid rpms
3. Airflow velocity
in the tubes should be at some minimum velocity for good combustion chamber
stuffing with air/fuel mixture. The min velocities I have seen in
literature range from 180 ft/sec to mach 0.6 (now that helps narrow it down
doesn't it?)
The basic bottom
line seems to be that you can't have everything and trying to get it will most
likely end with a poor set up. I orginially had a very similar set
up, at 4 injector TMW throttle body sitting on a Racing Beat webber system
manifold. Dual 2" dia throats ready to turn 10,000 rpm. Well, as I
learned, the set up that's golden for 10,000 rpm sucks at 5500 rpm. My
second manifold was one I build copied after Tracy Crooks (with some changes
of course). Even my low power 1986 NA 13B showed a climb improvment of
300 fpm and top speed increased 10 MPH with the new manifold. My nominal
static with a high pitch (68x72) prop was 5200 rpm which I consider
good - but on cool days I could turn it as high as 5800
static. I took off one 28F morning turning 5800 rpm from take off
roll to 3000 msl with a fuel flow rate of 20 GPH indicating I was
producing over 200HP. Never thought to look at the VSI with my eyeball
glued to the rpm and fuel flow meter, but I got to 3000 ft before I was much
past the end of the runway.
On the other hand, my top
speed didn't seem to change! This type of thing
is what got me started
researching this DIE effect for an answer.
The secret seems
to be to clearly define what you want (compromise!) out of the engine, then go
about refining your intake system to fit those needs.
BUT, if you intend
to employ this Dynamic Intake Effect (DIE) that you will hear (at least twice
{:>), the the answer is you must put your runner length BETWEEN the
trottle body and intake port. Let me make one point clear about DIE, it
is an adjunct to a basically good intake system. If your basic induction
system is D.. S... then DIE will not pull the situation out of the
mud.
If you have a
basically good intake that provides good airflow (no doesn't have to be the
perfect system) then DIE can indeed add enough increased torque and power to
make it worthwhile. Do you need it to fly a rotary sucessfully -
certainly not. But, if you want to twitk the most HP from you
installation with the minimum weight, I believe you will find DIE potential
highly interesting.
Also it turns out
there is no one magic runner length for the DIE effect and the length for this
effect depends not only on the rpm point you select for this effect
to occur but also on your particular engine specifications - there that sounds
mysterious enough, I think.
So show up,
Rusty. Fly, drive, swim or walk but be there.
Best
Regards
Ed
Anderson