Induction pipe length
#1
04-26-2016, 10:36 PM
Induction pipe length
I was trawling through some old threads last night and found an old post where the previous owner of my XJR (forum name = On Edge) had posted some dyno results for my car. (https://www.jaguarforums.com/forum/x...pulley-105701/ post #7)
In the post he points out the importance of a longish smooth pipe between pod filter and air flow meter.
When I first got the car I bought a new K&N pod which was slightly longer than the old one, so I threw away the pipe the old pod was mounted on - it was on an extension that looked like some pipes of white PVC water spouting (painted black) joined together to step down the pod to the airflow meter , with a slight bend in it.
This left just the remnant of the pipe from the back of the airbox that clips to the AFM. I clamped my new filter to this. It sits back a bit from the headlights but I thought it close enough to still get plenty of cold air.
Having read On Edge's old post, I went to the carparts place today after some careful measuring, and bought a silicone hose coupler with an internal diameter of 76mm, some clamps, and an aluminium pipe with a slight bend, and external diameter of 76mm.
I shortened the aluminium pipe a bit so it will all fit, and fitted the alloy pipe up flush to the plastic pipe just before it clips to the AFM. The internal diameters of the alloy and plastic pipes are almost a perfect match.
This gives a smooth intake from pod to AFM of about a foot's length, versus about 3-4" before.
I've just driven my son 12 miles to an appointment and I'm typing this post in a Dr's waiting room... I think , subjectively, the car is going better with this longer pipe. More power and better pick-up in the gears. I shouldn't have chucked the old drainpipe extension, but it wasn't smooth and had a few steps/joints which would have made some turbulence.
In the post he points out the importance of a longish smooth pipe between pod filter and air flow meter.
When I first got the car I bought a new K&N pod which was slightly longer than the old one, so I threw away the pipe the old pod was mounted on - it was on an extension that looked like some pipes of white PVC water spouting (painted black) joined together to step down the pod to the airflow meter , with a slight bend in it.
This left just the remnant of the pipe from the back of the airbox that clips to the AFM. I clamped my new filter to this. It sits back a bit from the headlights but I thought it close enough to still get plenty of cold air.
Having read On Edge's old post, I went to the carparts place today after some careful measuring, and bought a silicone hose coupler with an internal diameter of 76mm, some clamps, and an aluminium pipe with a slight bend, and external diameter of 76mm.
I shortened the aluminium pipe a bit so it will all fit, and fitted the alloy pipe up flush to the plastic pipe just before it clips to the AFM. The internal diameters of the alloy and plastic pipes are almost a perfect match.
This gives a smooth intake from pod to AFM of about a foot's length, versus about 3-4" before.
I've just driven my son 12 miles to an appointment and I'm typing this post in a Dr's waiting room... I think , subjectively, the car is going better with this longer pipe. More power and better pick-up in the gears. I shouldn't have chucked the old drainpipe extension, but it wasn't smooth and had a few steps/joints which would have made some turbulence.
Last edited by AL NZ; 04-27-2016 at 12:15 AM.
#2
04-27-2016, 09:46 AM
Al,
I have read about the importance of induction length before, but always in relation to the length from the throttle plate to the inlet valves. If I understood it correctly, longer distances are better for torque, and shorter for power, and a number of designs allow for the distances to be varied under different engine load. That said, I can't see how distances before the throttle plate would matter, but thinking about it, two things occurred to me. Firstly, as you suggest, if the extension allows you to access colder or ram air it would be a positive. Secondly,
If the pipe is long enough to allow the airflow to stabilise after being drawn in through the filter, it will present a more consistent flow to the MAF, which I can only assume is a good rather than a bad thing. Probably not transformational, but worthwhile.
I have read about the importance of induction length before, but always in relation to the length from the throttle plate to the inlet valves. If I understood it correctly, longer distances are better for torque, and shorter for power, and a number of designs allow for the distances to be varied under different engine load. That said, I can't see how distances before the throttle plate would matter, but thinking about it, two things occurred to me. Firstly, as you suggest, if the extension allows you to access colder or ram air it would be a positive. Secondly,
If the pipe is long enough to allow the airflow to stabilise after being drawn in through the filter, it will present a more consistent flow to the MAF, which I can only assume is a good rather than a bad thing. Probably not transformational, but worthwhile.
#3
04-27-2016, 02:27 PM
I think you're right, countyjag. that was the point I was trying to make - I should have spelt it out more clearly. I don't think the exra distance is changing the temp too much; I think it is the longer smooth tract that reduces turbulence from the pod and makes the airflow at the AFM more laminar and consistent.
I wonder if there would be still more benefit from some internal spirals (like gun rifling) , similar to the outside of tall industrial chimneys, to stabilise airflow? I can't make such a thing, but it would be interesting to see.
I wonder if there would be still more benefit from some internal spirals (like gun rifling) , similar to the outside of tall industrial chimneys, to stabilise airflow? I can't make such a thing, but it would be interesting to see.
#4
04-27-2016, 02:47 PM
Veteran Member
Don't sell yourself short; cut a slinky to appropriate length and stretch it out in there!
#6
04-27-2016, 04:21 PM
Al,
I know that a number of cars have moveable swirl flaps in the inlet manifold, which must be connected to getting the airflow optimised, but I have not come across any upstream of the MAF, and would guess that if there was a gain to be achieved, the manufacturers would have taken it. As you say, I think laminar flow is likely to be the ideal at this point.
That said the science in this area is well beyond my pay grade, so there might be something.
In terms of pursuing more cooling of the intake charge,I suspect the inter cooler might yield proportionately more benefit.
On a related topic, do you find the oil from your air filter contaminates the MAF over time?
I know that a number of cars have moveable swirl flaps in the inlet manifold, which must be connected to getting the airflow optimised, but I have not come across any upstream of the MAF, and would guess that if there was a gain to be achieved, the manufacturers would have taken it. As you say, I think laminar flow is likely to be the ideal at this point.
That said the science in this area is well beyond my pay grade, so there might be something.
In terms of pursuing more cooling of the intake charge,I suspect the inter cooler might yield proportionately more benefit.
On a related topic, do you find the oil from your air filter contaminates the MAF over time?
#7
04-27-2016, 04:38 PM
I last cleaned the K&N about 15000 km ago and it is overdue for another clean
I don't over-oil it , just a light coating which it soaks right up. I resist the temptation to put on more.
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