Airboxes and inlet tract length

[sharky]

I am going to use an airbox on my project as I am over trying to set up CV carbs on pods...
My motor is about low down grunt and works best with a box.
To achieve this I am looking at using approx 150mm long pieces of 2" silicone hose to connect the carbs to it.
Can anyone see a problem with this ?
Will the long inlets have an adverse effect ?

[Tony OW31]

yes they do have an effect, are you using stock cams?, if so they might be too long at 150mm, if you plan on using an inlet cam with a bit less duration than stock then they might be ok. In my experience the tract length between carb and airbox was critical, get it wrong and it becomes really difficult to get the fueling right. The longer they are, the harder it makes it to tune, I never got to look in to it fully because I discovered early on that the shorter I made them, the better.

[sharky]

Cheers Tony....I found some stuff on googly...Apparently if they are too long you get a sort of blow back effect that puts the fuel/air mix back into the airbox (possible 'Big Bang') and then sucks this mix through as if it was air...adding more fuel from the carby thus making it to rich...so you can have a rich/weak seesaw effect at a certain rev point that won't go away...

Sooo...being xmas and JD inspired I took a saw to the stock box, added in a bit of work with the hot air gun and Bingo...stock box now fits...all be it in 3 pieces instead of 2.....But I have a cunning plan [}:)]

[80s freak]

And what might that be Baldric? And does it involve fish?

[Chris41]

What I've done B4 Sharky is to find sets of airbox to carb adaptors that fit and use all the straight ones and make the box to match by cutting and plastic welding a similar shaped one

[sharky]

quote:And what might that be Baldric? And does it involve fish?
Only if they're carbon fish...

[livewire]

There's a fair chance that the oem manifold length will match the standard cam/ head/ exhaust combination fairly well.
Particually on a sports orientated engine.

[Stocky]

You are creating a sort of velocity stack effect with pipe like that, you need to get more internal area and try to make it just one tube so all the cylinders share it. Then it's like making the airbox bigger. Good for low end power too.