Induction questions
Discussion
Can anyone help with advice re the following...
I have a mid engined car which currently takes a cold air feed from a side mounted nacelle just above the sill, behind the passenger side door.
Now this layout means that the air flow to the engine spends most of it's time within the confines of the hot engine bay and also due to it's position I'm suspecting that the initial flow is "dirty".
It would be a relatively simple modification for me to replace the existing rear quarter glass with perspex, mount a NACA duct in this and then use that as the primary cold air feed for the engine. This would offer the advantage of a shorter induction run and that the majority of the induction run would be in a cooler environment.
Now the question is...
NACA ducts are good at deriving air feed with minimal impact to the aerodynamic flow from lamina air flow. The position of the duct would place it on the vehicle's flanks about a 2/3rds of the way back and relatively high up. What is the collective opinion on such an approach?
The induction run created by such an approach would be shorter but may neccesitate the introduction of a bend in the run (not 90 degrees but say 45 degrees) - what sort of effect would one expect this to have on air flow (I know it will dirty up and potentially slow the flow down but how sever could these effects be)?
I could be talking cr*p so anyone who actually knows about this stuff feel free to point out the error of my ways :-)
I have a mid engined car which currently takes a cold air feed from a side mounted nacelle just above the sill, behind the passenger side door.
Now this layout means that the air flow to the engine spends most of it's time within the confines of the hot engine bay and also due to it's position I'm suspecting that the initial flow is "dirty".
It would be a relatively simple modification for me to replace the existing rear quarter glass with perspex, mount a NACA duct in this and then use that as the primary cold air feed for the engine. This would offer the advantage of a shorter induction run and that the majority of the induction run would be in a cooler environment.
Now the question is...
NACA ducts are good at deriving air feed with minimal impact to the aerodynamic flow from lamina air flow. The position of the duct would place it on the vehicle's flanks about a 2/3rds of the way back and relatively high up. What is the collective opinion on such an approach?
The induction run created by such an approach would be shorter but may neccesitate the introduction of a bend in the run (not 90 degrees but say 45 degrees) - what sort of effect would one expect this to have on air flow (I know it will dirty up and potentially slow the flow down but how sever could these effects be)?
I could be talking cr*p so anyone who actually knows about this stuff feel free to point out the error of my ways :-)
Naca ducts look nice but i was always led to believe they were only much use on aircraft at speeds of 450 mph plus.......Are you telling us the whole sordid truth on your engine capabilities????
Seriously, id have thought that the intake should be positioned in a high pressure area to derive best advantage from any ram effect you may be able to gain, and with a slight lip to the leading edge of the vent to drive air into it by protruding into the air stream.
Dont forget that keeping the intake close to the ground results in cooler, denser air being picked up also, but then theres always water ingress
to contend with.
Seriously, id have thought that the intake should be positioned in a high pressure area to derive best advantage from any ram effect you may be able to gain, and with a slight lip to the leading edge of the vent to drive air into it by protruding into the air stream.
Dont forget that keeping the intake close to the ground results in cooler, denser air being picked up also, but then theres always water ingress
to contend with.First step for me would be to make up a replacement window panel out of perspex or whatever, then do some tests using a manometer to see what the airflow pressure is like in the location you are planning for the NACA duct.
As Deltafox says, NACA ducts are not particularly efficient at low speed so I think you'd want to place one in an area where there is some positive pressure over the opening.
There is plenty of published information on the airflow characteristics of NACA ducts, though, to help you with sizing.
As Deltafox says, NACA ducts are not particularly efficient at low speed so I think you'd want to place one in an area where there is some positive pressure over the opening.
There is plenty of published information on the airflow characteristics of NACA ducts, though, to help you with sizing.
The problem is that the logical location is probably some where at the front of the car (say high up on the bonnet just shy of the windscreen which is normally a high pressure area) but...as the car is mid-engined that would introduce a lot of plumbing to say the least!
I agree that the only real way to find out is to try it which is what I think I'm going to have to do.
Looking at the existing system the inlet is inside a side mounted nacelle, high-up and partially obscured by some plastic moulding. Definitely needs some more thought...
I agree that the only real way to find out is to try it which is what I think I'm going to have to do.
Looking at the existing system the inlet is inside a side mounted nacelle, high-up and partially obscured by some plastic moulding. Definitely needs some more thought...
If you are after any forced induction effect them a NACA duct still needs to be presented at an angle for it to do anything.
I have the same 'issue' on a mid engined car but mine is fortunate in having completely pointless air intakes to the engine bay that I can tap from. May not be positive or even neutral pressure but being cool air is far more important anyway, especially if you can't compensate for the extra ram pressure anyway!
I have the same 'issue' on a mid engined car but mine is fortunate in having completely pointless air intakes to the engine bay that I can tap from. May not be positive or even neutral pressure but being cool air is far more important anyway, especially if you can't compensate for the extra ram pressure anyway!
And, are you getting the air OUT of the engine bay effectively?
If have just dremelled (badly) some vents into my rear bumper to aid removal of air.
Out of interest I have also been talking to MIRA about some time in their wind tunnel. This is a LOT cheaper than you might expect, especially if you don't a potentially unsocial slot or they are quite.
If have just dremelled (badly) some vents into my rear bumper to aid removal of air.
Out of interest I have also been talking to MIRA about some time in their wind tunnel. This is a LOT cheaper than you might expect, especially if you don't a potentially unsocial slot or they are quite.
I wouldn't be too fussed about ram air pressure, the difference between best and worst case at 100 mph is minute. What is most important is temperature, you want to make sure you stay away from the wake of any heat sources at the front of the car. Also worth avoiding turbulent air as this will increase drag in the intake, the air filter is a very effective way of killing turbulence so fitting your air filter out by the intake is better (from that point of view) than back at the engine. But heat is the really big issue that overrides all the others.
Down the side of the vehicle the air pressure changes considerably also .. you ever seen a curtain sided wagon going on a motorway? the front section billows out as there's a low pressure created just aft of the front edge of the trailer, then the next section billows in as the pressure rapidly increases again .. you need the manometer approach to make sure you're not moving into an area of low pressure with the intake.
Also don't forget that on a hot day the ground is very warm, so having the air intake right at ground level is counter-productive especially if you have any bleed-back of engine bay warm air back to teh sides of teh car body again .. I'd favour a roof mounted scoop if it was my car, if only because any changes you make are going to be so slight you'll not feel them or possibly never be able to measure them and roof scoops look so damn sexy
Also don't forget that on a hot day the ground is very warm, so having the air intake right at ground level is counter-productive especially if you have any bleed-back of engine bay warm air back to teh sides of teh car body again .. I'd favour a roof mounted scoop if it was my car, if only because any changes you make are going to be so slight you'll not feel them or possibly never be able to measure them and roof scoops look so damn sexy
Valid points about getting air/hear out of the engine bay. Currently considering replacing the rear glass with perspex and then creating holes in that.
I'm going to try the NACA duct approach in the side panels after some less than scientific testing and reasoning last night (there is some value in very dirty roads if you want some indication of air flow direction...)
I'm going to try the NACA duct approach in the side panels after some less than scientific testing and reasoning last night (there is some value in very dirty roads if you want some indication of air flow direction...)
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