Yes true. You can dremel all the plastic moulding "obstacles" out of the way inside the filter and then run the cool air flow up with a plastic hose which helps the flow tremendously.

I think the basic issue is that the intake horn of the filter housing just isn't big enough, there isn't enough good flow between the outer wall of the housing and the fitler element, or both. Basically a tracheotomy. 

The six holes were drilled pre filter on the bottom side of the filter housing closest to the rocker cover, kinda contradicts the cool air is best theory drawing all that hot air off the exhaust area. From memory it was based on a 1 1/2" carb but not sure which one.

//www.acmespeedshop.com/index.html

He machined the big radius stub stack so that its outside diameter fits neatly inside of a standard clamp-on K&N Cone filter housing.

Super easy on/off, and super smooth flow, and smallest possible packaging (and fewest number of component parts).

He used to list them on his website, but not currently. Maybe out of stock? Give Hap a call if interested.

Norm

That sounds like the dashpot goes to the top when mashed and the vacuum that does it stays on full until you lift off. Or conversely, it doesn't rise fast or far enough, causing an extended accelerator pump effect, and lifting off allows the equilibrium to catch up.

(the line "every drive is a tuning session" sounds obsessive, but we understand!)

Yep. I'm not sure where and how big the six holes need to be, but I'd imagine they'd need to be outside the filter element diameter, pre-filter. Also don't remember which carb size/type it was based on.

I've got a wideband installed on Betty, so every drive is a tuning session.

Oddly, if you go WOT the mixture goes massively rich and won't lean off until you come off the throttle and gently reapply.  Until the engine is spinning reasonable fast, she won't accept full throttle.
Without the wideband, I'd have assumed she was leaning out and would have put a richer needle in...

Didn't KC or one of the other Mini guru's also do an article comparing cone filters and other filter set up's to a stock air cleaner set up ? If memory serves me correctly the stock air cleaner with a K & N filter and six holes drilled in the underside of the box flowed better than any cone set ups. I run a stock set up on my 1098 Estate with a cold air intake pipe down to the grille area and it runs spot on.

Years ago, Kieth Calver did a study and article on sub-stacks in Minis. His findings were that anything more than very short (somewhere around !/2" if I recall correctly) gave no improvement. The net purpose was to provide smooth flow as far as the bridge, and to do that , all that was needed was something to smooth the flow. Anything more increased air resistance along the wall of the horn. (I found the pic on the web... not mine.)

"...I bought the car with a k&n cone already installed. While reading MM's tech section on air filter reviews, it mentioned the flat spot caused by sucking in too much air. So i wanted to test the Ram pipe instead of getting a original air box, and see if there's any acceleration/response improvements in the mid range..."

You really shouldn't believe everything you read...

I've been running my twin HS4s with K&Ns for over 20 years and can't say I've noticed a problem (but then it was set up opriginally by someone who knows what they're doing).

There's no such thing as "sucking in too much air".  There's only one way to increase HP - suck in more air!  The trouble lies in getting the correct amount of fuel to go with the extra air.  

The effect of the K&N can be easilly checked.  Just remove it...  Theoretically the mixture may go slightly leaner - as you get even more air without the restriction of the air cleaner.  However, my experience is that a (clean) K&N does not restrict air flow in any measurable way.  

There are some opinions that the cone shape has some effect on the air flow due to the normal pressure pulses being partially reflected... I think that's what they're getting at anyway.  My car doesn't show any changes with or without the filter so.......

Don't get me started on dashpot oil choices.....

Cheers, Ian

Image Gallery

This is another Volvo setup I use quite a few years back. Forgotten the model now, so see your local Euro wrecker.

OP said 998 engine, so the carb wants to be a HIF38 / HS4 (1 1/2"), and don't know if there's an elbow for something that small out in the wild. Maybe someone who's seen one for that size will chime in.

Norm

Norm

Trouble is with the K & N and a tube it will be less restricted which obviously improves air flow something it does not need with the current needle. Try the choke trick when it stumbles just pull out the choke 1/2" or so and see if it improves. The wideband will sort out the mixture problems for sure.

Make sure that filter is on the right way, some owners install them upside down and cover the two necessary holes mentioned previously.

From my experience a "flat spot"  such as mashing down the pedal and a feeling like the carb is catching up is caused by a lean condition.  If you feel like you have the right needle maybe the problem could lie with a vacuum leak such as a broken breather or vacuum advance line.  Maybe try checking the points, spark plugs, and timing before adjusting the carb.  Just some recommendations before you dive into building that cool looking intake.  I must admit it looks pretty cool!

Thanks guys.

It's a 998 engine. As for dashpot oil, I've gone through 50 weight, Marvel mistery, now i'm using Royal purple ATF (had it lying around). The ATF seems to give the best results so far. 

The pic is the top 10 recommended for my setup from WINSU. Many of them needs to be ordered from SUCarb UK. I do have AAU and #7, currently running 7, it seems to respond better for the drives. Can't give accurate numbers until I get a wideband AF.

I bought the car with a k&n cone already installed. While reading MM's tech section on air filter reviews, it mentioned the flat spot caused by sucking in too much air. So i wanted to test the Ram pipe instead of getting a original air box, and see if there's any acceleration/response improvements in the mid range.

What type of engine is it?  Im guessing its a 1000cc since it has an HS4 carb.  I personally think a heaver weight oil leads to poor performance.  I have the WINSU full program if you want me to run all of your specifics and tell you what the recommended needles are.  The holes are designed to be open and utilize atmospheric pressure to operate the dashpot in conjunction with vacuum from the engine.  I wouldn't recommend covering them.

How will this help the flat spot ? Did you do a needle change when you fitted the K & N filter ? As the new filter flows better you need a richer mixture, to see if you need a richer needle you can just move the needle up slightly into the piston which will make it richer through the range or pull out the choke slightly while accelerating.

You could drill into the carb sideways or from the top, but you'd want the holes protected by an air filter somewhere.

Check with an A/F meter that it is going lean on acceleration. I thought mine was too (1293 with twin HS4s & foam filters) but it was actually going rich.
My solution- I used ATF in the dampers in winter, and ran em dry in summer.