andrew-theasby
|
| posted on 28/9/09 at 09:48 AM |
|
|
best airbox design
Following on from my recent thread on filters i wondered about making an airbox so i can put the filter in a better position. The Height from the
base plate will have to be the same in each design due to space so which of the following designs would be the best one to go for?
Thankyou.
 
Rescued attachment airbox design.jpg
|
|
|
|
|
smart51
|
| posted on 28/9/09 at 10:05 AM |
|
|
B or C. Research has shown that sharp edges on trumpets like in pic A have slightly worse airflow than if the rolled edge extends 180° from the
trumpets axis. You don't have to go as far as B. C is also good. If there is plenty of space around the trumpets then B gives you more volume,
which in turn gives less vacuum on each intake of air from the box to the engine. If the trumpets are close to each other and close to the sides then
there's not much to be gained so C may be easier.
The airbox I made was like B.
[img][/img]
|
|
|
BenB
|
| posted on 28/9/09 at 10:11 AM |
|
|
You'ld also be better off having a tapered top to the plenum chamber, otherwise the air flow through the chamber will vary from trumpet to
trumpet (unless you have a large amount of empty plenum at the opposite end to the inlet. Somewhere I've got a diagram showing drag co-efficient
for various trumpet designs, I'll try and find it and post a link...
|
|
|
andrew-theasby
|
| posted on 28/9/09 at 10:21 AM |
|
|
From rampipe to the top is about 50mm in the smallest place which is why i thought about B. Is max volume always going to be best? I also considered
having a filter on each end but wasnt sure if this would complicate things, different temps, flow etc?
Which way should it taper? should it be wider or narrower, further away from the filter end? Thanks
|
|
|
BenB
|
| posted on 28/9/09 at 10:30 AM |
|
|
It should be narrow at the "far" end IE the opposite end to the filter. BUT you want to make sure that there's at least a choke's
width between the mouth of the trumpet and the top of the plenum (otherwise you can strangle the air inlet- unless you get lucky with pulse
tuning).
You really want a plenum at least 1.5* engine capacity. You don't really need a filter at each end but if you can't make a tapered plenum
you'ld be better off having some "spare" chamber at the far end of the chamber (beyond the last trumpet).
Here's the link promised
 
throttle trumpet design
|
|
|
smart51
|
| posted on 28/9/09 at 10:49 AM |
|
|
quote:
Originally posted by andrew-theasby
Is max volume always going to be best?
The volume of the chamber, the length and area of the inlet pipe form a resonant enclosure. Ideally, you'd tune the system to match your
engine. At resonance, you get extra engine filling (a bit) so you can fill in holes in the lower torque curve. A larger box has less effect on the
engine at resonance but makes less restriction on engine breathing. The idea is that if you take 0.5 litres of air out of the box to fill a cylinder
on your engine, the pressure drops a bit and causes new air to be drawn into the box through the filter. The larger the box, the less the pressure
drops, for a given air filter restriction.
Make sure the top of the box is at least 1 trumpet throat diameter from the outer edge of the trumpet. 1.5 time or more is better. Otherwise your
airflow will be restricted.
|
|
|
andrew-theasby
|
| posted on 28/9/09 at 11:10 AM |
|
|
Thanks, Im suprised by 11 being best there. So C with really short rampipes like 11 would be the best of both worlds then as id get more height/volume
in the airbox too. What about the theory of longer ram pipes keeping the peak torque down, would the improved airflow outweigh this? or is 11 not
meant to be used with a backplate on?
 
Rescued attachment best airbox trumpet design.jpg
|
|
|
BenB
|
| posted on 28/9/09 at 11:26 AM |
|
|
You can tune the length for better low down power just as you can put a plate very close to the trumpet throat and get more power. But short of
amazingly complex calculations, these are trial and error approaches which will require some way of assessing how the changes have helped power. And
of course if you're on carbs each change will require re-jetting or mixture adjustment.
The short length, 1-1.5* capacity with choke diameter max between trumpet throat and plenum gives the best outcome most of the time....
|
|
|
andrew-theasby
|
| posted on 28/9/09 at 11:43 AM |
|
|
Thanks, it was just that summary of the important bits i was after, i wont be developing it, i just want to make one thats of the right style rather
than one that loses power, but i think ive got the main bits now in that last drawing. Cheers
|
|
|
brianthemagical
|
| posted on 30/9/09 at 02:31 PM |
|
|
What length is the inlet system going to be, either as it is, or the shortest and longest reasonabley possible.
|
|
|
