30 replies to this topic

[h9hpj]

I have seen 2 different takes on this.

1. 6 holes around 3/4 - 1 inch drilled on the base of the airbox

2. 6 holes drilled through the side.

 

My questions are:

Which is the best in terms of position - Base or side?

Where exactly should they be - air intake side/opposite side etc?????

 

My aim is to keep the noise to a minimum as I have just removed the droning cone whilst also improving performance a touch.

 

Thanks for any suggestions - including leaving well alone (I currently just have the airbox and stock filter waiting for a k&n air filter to arrive and stubby little intake - no extra hot air duct thingy!

[D 'n A]

Depending on your spec I would say dont bother... but if you are set on this I would go for the base.

Round of the holes to cancel whistling noises.

[JXC Mini GT]

Have a read of Calver special tuning article on air filtration before you make a decision.

[beardylondon]

https://www.calverst...air-filtration/

[Steam]

As said by others, I would not bother, the intake snorkel is plenty big enough. Ditch the hot air duct and temperature flappy paddle though.

[Marky Tizz]

Mine is done exactly like this:

 

 

As per Calver. Has been like that for 13 years and runs wonderfully. K&N replacement element, freeflow manifold to twin box RC40. No idea if it actually made a difference as we did it all at the same time but it looks cool!

[ACDodd]

It’s a no brainer, I use this example when I deliver my su training to dyno operators, drilled airbox is better in every case and the bigger the engine it’s fitted to the more it’s needs drilling.

Ac

[Steam]

It’s a no brainer, I use this example when I deliver my su training to dyno operators, drilled airbox is better in every case and the bigger the engine it’s fitted to the more it’s needs drilling.

Ac

AC
Is this because the standard airbox has limited flow in standard form.

[h9hpj]

Thank you all for your help - From my observations and recent videos I have been watching, if AC says something, all should listen. K&N arrived today so weekend it is! 

[Catch1]

Hi all, In my experience, drilling holes to the bottom hasn't noticeably increased performance on a stock 998. Instead I machined up a ram pipe that fits over the opening to the airbox. The design is based on the optimum ram pipe airflow geometry which pulls in air from 360 degrees including from behind the opening. Above all else it tidies up the airbox and makes it look less incomplete with the steel flappy paddle intake missing.

[Ol timer]

Hi all, In my experience, drilling holes to the bottom hasn't noticeably increased performance on a stock 998. Instead I machined up a ram pipe that fits over the opening to the airbox. The design is based on the optimum ram pipe airflow geometry which pulls in air from 360 degrees including from behind the opening. Above all else it tidies up the airbox and makes it look less incomplete with the steel flappy paddle intake missing.

Any chance of seeing a photo of your ram pipe setup

[Catch1]

 

Hi all, In my experience, drilling holes to the bottom hasn't noticeably increased performance on a stock 998. Instead I machined up a ram pipe that fits over the opening to the airbox. The design is based on the optimum ram pipe airflow geometry which pulls in air from 360 degrees including from behind the opening. Above all else it tidies up the airbox and makes it look less incomplete with the steel flappy paddle intake missing.

Any chance of seeing a photo of your ram pipe setup

 

What is your email address? I'm struggling to add images to this vintage forum interface haha.

[ACDodd]

Yes the lid can also be seen to be squeezed inwards as the revs rise because a vacuum is formed inside, when the engine is being revved. This causes the fuel enrichment due to being starved of air. Drilling holes are adding extra snorkels increases the airflow reduces the vacuum and allows more air to pass. The carburettor calibration needs adjusting to compensate or the effect will be negated by a potential lean running situation. On a 70hp 1275 a standard one will be costing you 5hp easy.

Ac

Edited by ACDodd, 26 May 2022 - 06:58 AM.

[gazza82]

What is your email address? I'm struggling to add images to this vintage forum interface haha.

Try "More reply options" rather than just "Post" ...

[Catch1]

 

Hi all, In my experience, drilling holes to the bottom hasn't noticeably increased performance on a stock 998. Instead I machined up a ram pipe that fits over the opening to the airbox. The design is based on the optimum ram pipe airflow geometry which pulls in air from 360 degrees including from behind the opening. Above all else it tidies up the airbox and makes it look less incomplete with the steel flappy paddle intake missing.

Any chance of seeing a photo of your ram pipe setup

 

Here's a quick render of it. Ill grab some photos next time i'm under the bonnet =)

 untitled.85.jpg   13.64K   11 downloads