11 replies to this topic

[087dave]

Hi all, i have a 998 engine with a sw5 cam, stage 1 kit, stage3 head,HS4 carb with no air restrictions,
lightened flywheel, but was told to get a stub stack to even
further improve air flow
so my question is are these stack as good as people say????

Cherrs

[Bungle]

you haven't said what air filter you use

a stub stack fits inside something like a K&N panel filter

it's like a little ram pipe and is used to smooth the air into the engine

Visards yellow bible would make good reading for you

[087dave]

you haven't said what air filter you use

a stub stack fits inside something like a K&N panel filter

it's like a little ram pipe and is used to smooth the air into the engine

Visards yellow bible would make good reading for you

Hi thanks yes i should have said i do have a k+N
so do they work?

[Bungle]

you won't feel the difference but according to visards book you could pick up a couple of hp

[huw_jenks]

you won't feel the difference but according to visards book you could pick up a couple of hp

I'm sure Vizard goes further and says that without a stubstack or rampipe a pancake/cone filter is useless!

It's because as the 90degree turn into the mouth of the carb restricts the air meaning that your carb is actually not 1.5" any more. Putting on a stubstack smooths out this turn and means more air can flow.

Edited by huw_jenks, 05 February 2011 - 07:59 PM.

[087dave]

you won't feel the difference but according to visards book you could pick up a couple of hp

I'm sure Vizard goes further and says that without a stubstack or rampipe a pancake/cone filter is useless!

It's because as the 90degree turn into the mouth of the carb restricts the air meaning that your carb is actually not 1.5" any more. Putting on a stubstack smooths out this turn and means more air can flow.

Thanks Very interesting

[bmcecosse]

A low cost alternative is to flare out the mouth of the carb - with a good radius all the way round. The restriction of air flow is the vena contracta - and is relieved by the flaring - or the radiused inlet stack.

Edited by bmcecosse, 05 February 2011 - 08:43 PM.

[087dave]

A low cost alternative is to flare out the mouth of the carb - with a good radius all the way round. The restriction of air flow is the vena contracta - and is relieved by the flaring - or the radiused inlet stack.

Thanks when you put on the stack on to the air filter plate
do you need a gasket
cherrs

[bmcecosse]

No!

[Cooperman]

On the rollers my 'S' with K & N filters on twin H4's gained about a tiny improvement at over 6000 rpm when stub stacks were fitted. They may have smoothed up the low-end power, but it's so lumpy it is hard to tell.
Radius-ing the carb face inlet with around 3/16" radius is probably as good for a road car. They might work on a race car where a few tenths of a second per lap is important.

[Turbo Phil]

Any sharp edge is a big no no as far as good airflow is concerned. So if you have one I'd fit it, otherwise radiusing the carb mouth will get the job done.

[Timty]

how do you radius the carb mouth is it a case of filing the edge of the carb or is it a bit more complicated?