Air Intake Question

[diesel]

This question relates to another thread that I didnt want to hijack.
Could I take a flexible metal tube and run it from my 30mm Delortto into the frame breathing hole in my S1 and attach a home made foam filter at the far end? its an Avanti currently running on an aluminium mesh fiter (a placebo more than anything else). More generally what performance effect if any would lengthening the intake tract have? I mean in theory I could have a ten foot snorkel Stuck out the back couldnt I? fnar fnar

[Grumpy225]

Your post got me thinking about intake flow theory and I found this

http://www.zzperformance.com/blog/intak ... -theories/


It's based on 4t testing but I think there are some intresting findings. Specifically bends in the air flow tract really slow down the flow (not good for power). Considering you are planning on running a bent tube from your carb to another bent tube (a restricted hole in the frame with 2 more turns) it looks like you might be sacrificing a fair amount of air flow to a top end that is designed to make a good amount of go. Kinda like putting a stock exhaust on a TS1. I do remember reading up on air box design and utilizing an intake pulse to gain more flow but I think the inherent limits of the small Lambretta motor make it unusable or impracticable.

[john]

It's made me think now... Scooter runs lovely so no problem yet. I have the Spanish toolbox with vented door ( half tool box is filter box) now for years I have run a remote filter and removed the original along with hose, just leaving outlet stub open.I was just about to fit a regular toolbox to give myself extra tool space.... But now wondering whether I will restrict the air flow into the engine bay, enough to make a difference,bearing in mind that the Spanish frame does not have the hole in the frame loop under the seat like for Italian type air box ... Any thoughts please ?

[RobD]

You could build an airbox to act as a holmheltz resonator and if you got the size and shape right it would give you a small increase at one specific rpm but it would be a lot of work for a comparatively small gain. Some of the bigger bike manufacturers have designed airboxes along these lines to alleviate problems (flat spots etc) at a specific rev range in the past. It was a long time ago that I read up about this but I think one of them might have been the early SV1000?

Lambretta's don't go fast enough to benefit from any ram air effect as this doesn't have much benefit below 100mph.

If you could build an airbox to provide a good size (as big as possible) reservoir of cool still air then that's probably about as good as you'll get.

I've often wondered about the wisdom of running open mouth carbs with a hole in the panel. Yes you get the coolest air but it can't be consistent. If you think about how a carb works, then the flow of air through the carb sucks fuel through the jets. So when you're wizzing down the road and the engines sucking in air through the carb, the air rushing past the carb mouth is trying to suck the air/fuel mixture back out. So if you've got an airbox it makes it easier for the engine to breath and your jetting more constant regardless of what gear you're in as long as it's not a restriction. The compromise is the size.

So fit a massive rickman top box from a c90 on your back rack and run a pipe of constant internal diameter tube (the same ID as the carb bore) from that over as straight and as short a distance as possible to the mouth of the carb.

I doubt you'd feel a tangible performance difference from any of these measures alone but if you tested with an AF meter it should allow you to jet leaner therefore making a bit more power. A dyno though very good indicator doesn't replicate the air flow at speed around the scooter.

A remote filter is probably the best real world solution, gives you the protection of having a filter and removes the restriction of the standard airbox. The area under the loop and panels acts as a big albeit hot airbox.

[Doom Patrol]

I'm not really up on the technicalities of this sort of thing, but I've always suspected that the Spanish could have been on to something with their tool / air boxes. I wonder if you could go further with the idea and turn the toolbox into a massive air filter. You'd have the advantage of an unrestricted path to the carb. I think Scooter Loopy John did something interesting along these lines by blocking off the existing intake, dumping the internal filter and attaching an external filter directly to the airbox which then sat inside the toolbox. Hopefully he might come on and tell you about it himself.