Ram Pipes and K&N filters

[pmth95]

The ram pipes on my DHLA carbs are 48mm with just 15mm clearance to the filter plate. Shouldn’t there be more clearance using smaller length pipes?

 

[drdoom]

Probably so. I ran K&N's on DCOE's when I had my Elan, can't recall the distance from bell mouth to plate, nice audible bark when you leaned on the throttle though. Have since read plenty on the lousy filtration K&N's provide so likely moving over to pleated paper for my Esprit.

[NG5]

Yes there should be more clearance.

As a rule of thumb the case lid should be the carb dia or more away from the top of the ram pipe, ie 48mm.

Any less and the plate will restrict airflow and it has an effect on how the carb works which varies car to car and how close it is.

Having the plate too close can affect the power curve and how the carb is jetted, but just to make it more complicated, reducing the length of the trumpets also affects the power curve and the carb jetting! A longer filter should be 1st choice if it will fit.

[rgh0]

I would look at fitting the standard airbox and filter. Agree you need 1 to 1.5 times the carb diameter to the closing plate above the trumpet. to not restrict air flow

[semi42]

I fitted a similar K&N setup,  the car just didn’t perform well.

went back to standard, never looked back

[drdoom]

An alternative for those who just can't resist the aftermarket filter solution is to use the OEM airbox assembly and attach a conical filter over the wheelarch at the end of the air trunking. Be sure it is fed with cool air for best effect.

Cheers 

[skiing]

From what I have read on the forum etc, the key thing as dr doom said is the cold air aspect -

Having the K and N filters on each carb without the airbox causes the carbs to suck hot air from a cramped and hot engine bay - apparently retarding performance (and I would guess causing hot running issues when in traffic or not moving rapidly) - this is why most people suggest using the stock air box (sometimes with a sports filter inside - I have a K&N in mine). This means the air feed to the carbs comes from outside the car and is as cool as possible. 

People also shorten the air feed pipe which goes to the airbox from it's standard circuitous route to get more of a 'ram air' effect for the ear into the airbox. This downside or upside of this - depending on preference - is the induction noise increases. 

[skiing]

On further research, the airbox of an S3 actually sucks air from the right hand vent in the boot space which is filled via a hose from the left hand ear into the left hand vent in the boot space. The ram air modification changes this of course - but still not as warm as direct from the engine bay I guess! 

[drdoom]

Ram air is a bit of a chuckle for our purposes, in order to attain a meaningful head of pressure means travelling at quite some rate of knots and one might well question what would be the state of air pressure along the body surface where the scoops reside. Quite important to draw air from the coolest source, as stated. There is another important aspect to the airbox which is the resonant tuning effect arising out of its carefully determined volume. This has been tested against various alternative layouts and found superior in terms of power output.

Cheers