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smart51 - your airbox
Bob C - 18/3/07 at 12:15 AM

It's truly hideous but.... I'l probably want to make one soon - any chance you could put a sketch of its innards in your photo archive?
some notes about design calculations would be handy too (e.g. it's tuned to 4200 rpm - how's that worked out then?)
cheers
Bob

smart51 - 18/3/07 at 08:45 AM

Perhaps I should replace the photos of the wooden prototype with pictures of the GRP finished article.

Attached is an excel spreadsheet of the tuning calculations. There is a relationship between the volume of the box and the diameter / length of pipe thay governs the magnitude of the tuned effect but I couldn't find that in the internet. I suspect that the smaller the diameter of the pipe (and the shorter its length to maintain the tuned frequency) the more resonant it is.

As for pipe diameter. I tried a 2" pipe, thinking that the exhust is 2" so it should be OK. No. Changing from a 3.5" pipe to a 4.5"pipe had no noticable effect on the road but from 3.5" to 3" mae it run a bit lean above 11,000 RPM. My R1 engine has 4 x 40mm choke carbs, for comparison.

as for the internals of the box, it's just a box. try to keepall the edges smooth, especially in the direction of airflow. Also, try to keep the face of the box at least one carb diameter away from the carb's bell mouth. I didn't on the first prototype and it restricted airflow massively. every couple of mm extra made a noticable difference.

Bob C - 18/3/07 at 03:51 PM

Great, thanks

tks - 18/3/07 at 03:53 PM

how did you compare?

how did you measure those differences??

Tks

smart51 - 18/3/07 at 04:44 PM

quote:
Originally posted by tks
how did you compare?

how did you measure those differences??

Tks


I ran it on the road and felt how the engine ran. It seemed OK with an 87mm ID pipe but with a 50mm ID pipe it wouldn't run above 8000 RPM. I then had the car on the rolling road. It was running lean with the 87mm pipe and I went up a jet size, so the 50mm pipe must be so restrictive that it took the engine from a bit lean to too rich.

smart51 - 19/3/07 at 05:35 PM

Here's a pic of the new box. I'm going to duct some air to it, as you can see, but am not sure what to do. Rescued attachment airbox.JPG
Rescued attachment airbox.JPG

Guinness - 19/3/07 at 05:55 PM

Looking good Smart51

As regards air flow, could you not make a box around the filter, with an open top, trim the upper edge in flexible edge seal to the underside of the bonnet and then have a NACA duct in the bonnet.

Judeperformance have something very similar on their Zetec powered car.

VortX
VortX
nose
nose

Mike

[Edited on 19/3/07 by Guinness]