View Full Version : Ram air (maths inside)
dhdev (Oli)
19-09-08, 10:23 AM
Right, leading on from a thread in General chat, i want to try and clear some things up. I'll post what I think is correct and if anyone can poke holes/correct then please do!!! I'm trying to learn!
If my nova is travelling at 50mph and 7500rpm, then to get Ram-air I need more air to be 'rammed' than the engine is consuming. Each piston consumes air once every two rotations. So my 1.6litre engine will consume 0.8litre of air every revolution (presuming a complete fill of air, obviously some is fuel, but i'm unsure as to whether this works as theory?) So per second that will be 7500/60 = 125revs per second, therefore 0.8x125 = 100litres/sec. 100litres/sec converts to 100,000 square centimetres/sec. So travelling at 50mph, I'd be moving forwards at (50/60)/60 (from miles per hour, to miles per min, to miles per second), then multiply that by 160934.4 to get to centimetres per second instead of miles per second. That gives a forward speed of 2235.2cm/s.
Soooo if I need to get 100,000cm^2/sec into the intake, i'd need a funnel that was 100,000/2235.2 = 44.74cm^2. Then anything above this speed would produce 'Ram air'
Correct?
DaveyLC
19-09-08, 10:36 AM
Its a twisted science, you also get inlet mixture turbulance issues and you can even end up creating a suction effect accross the mouth of the intake because of the areodynamics of the car.
Your engine is at peak Veff (assuming non turbo) when its at peak torque... This is when the Veff is as close to 100% as possible (some N/A tunes can get to over 100% but its rare).
peak power is usually between 80 and 90% Veff, but the rate of comsumption is increased due to engine speed. But still assume say an 85% cylinder fill per intake stroke and multiply by RPM etc.
Thing to also consider with the funneling is that the funnel to force X volume of air through might alter the temperature so the mass of air changes which could tend the engine lean (plus mapping a ram air setup will be a coooooont of a job as there will be times you want to venture to 7.5K when UNDER 50mph meaning that will be too rich and lose you power. Net gain might be zero :(
Its worth experimenting with, although you would ideally need some top notch data logging gear to work out if you had gained anything on the road lol
dhdev (Oli)
19-09-08, 11:16 AM
Your engine is at peak Veff (assuming non turbo) when its at peak torque... This is when the Veff is as close to 100% as possible (some N/A tunes can get to over 100% but its rare).
peak power is usually between 80 and 90% Veff, but the rate of comsumption is increased due to engine speed. But still assume say an 85% cylinder fill per intake stroke and multiply by RPM etc.
Thing to also consider with the funneling is that the funnel to force X volume of air through might alter the temperature so the mass of air changes which could tend the engine lean (plus mapping a ram air setup will be a coooooont of a job as there will be times you want to venture to 7.5K when UNDER 50mph meaning that will be too rich and lose you power. Net gain might be zero :(
Its worth experimenting with, although you would ideally need some top notch data logging gear to work out if you had gained anything on the road lol
So the 100% cylinder fill is optimistic, meaning that the 'Ram' would happen lower...
Agreed you'd need to use some kind of MAF sensor really...
Top speed would be a good indicator as to whether it was working surely? Obviously won't give you any in gear stuff, but would certainly show if you were making more HP.
dhdev (Oli)
19-09-08, 11:19 AM
Its a twisted science, you also get inlet mixture turbulance issues and you can even end up creating a suction effect accross the mouth of the intake because of the areodynamics of the car.
As long as the inlet was placed in the stagnant high pressure area at the blunt nose of the car, the effect should be increased. Would only 'suck' if the entry was placed somewhere silly.
Surely any turbulence is likely to be minimised by the time its travelled down the ram, associated pipework and into the airbox?
If you were to use a properly sealed and pressurised system, you may see some effect
but its all highly technical stuff!
Thats the thing, the RAM effect will up the cylinder fill to nearer 100% (if not a little more if its done well) so a MAF is vital for this little operation imho.
You could get a good "feel" for the gains by doing an cruise run logging speed, engine speed and throttle position (and maybe MAP). Then fit the RAM stuff and do the exact same again. The difference in required throttle position to sustain X rpm will be a gauge as to any extra power you are generating. Obv no real numbers but its a good guide.
dhdev (Oli)
19-09-08, 11:54 AM
My main reason for the post was to clear up the usual pre-conceptions that you have to be doing Xmph for it to work, when in my mind it didn't work like that!
But maybe there is potential for helping out the baby XE when it starts to struggle against the air, could this be the death of the big block :eek: lol
Welsh Dan
19-09-08, 12:27 PM
As long as the inlet was placed in the stagnant high pressure area at the blunt nose of the car, the effect should be increased. Would only 'suck' if the entry was placed somewhere silly.
Surely any turbulence is likely to be minimised by the time its travelled down the ram, associated pipework and into the airbox?
Would the base of the windscreen be a better place? its also a high pressure area, but you'd need less pipework and bends.
Would the base of the windscreen be a better place? its also a high pressure area, but you'd need less pipework and bends.
little to no "ram" effect though...
I think the Xmph thing was for the Swindon stuff which was pulling in soooooo much air anyway that to ram it in would require far greater speeds than seen on track (and to not require an emmence funnel that would cause huge drag etc).
just below the windscreen (scuttle area) i supposed to be a very good place to gain the ram air effect. there is a company which specifically makes air filters for honda civics which use a big scoop protruding from the scuttle panel. i'll try n find there site, from what i can remember it was tried and tested to be the best place to get the gains...
Edit: look here http://type-r-owners.co.uk/forums/showthread.php?t=26070
CK its called a gruppe M Ram air systeM
I had one on my last DC5
Works extremely well
craig green
19-09-08, 02:12 PM
I wouldnt rely on anything Honda owners develop.
I wouldnt rely on anything Honda owners develop.
How blinkered can you be, really!
Any justification?
craig green
19-09-08, 02:53 PM
How blinkered can you be, really!
Any justification?
I'm not a fan of the 'new Escorts' & its just wound you up......
Take my comment as you please. I didnt mean anything by it. ;)
It doesnt wind me up as such, and thats far from justification
just makes me laugh how just because some cunnt doesnt like a particular model of car, means that the manufacturers stuff cant be relied upon!
I wouldnt trust much that some vauxhall "tuner" monkey came up with lol
Might need to have a look see at the honda stuff... take everything on its own merit :D
considering the gruppe m , on a standard engine, can see up to 15bhp in some cases on its own, its hardly some monkey kit!!
well worth the price tag too if you ask me
Welsh Dan
19-09-08, 03:24 PM
CK its called a gruppe M Ram air systeM
I had one on my last DC5
Works extremely well
Thats the sort of thing I meant.
considering the gruppe m , on a standard engine, can see up to 15bhp in some cases on its own, its hardly some monkey kit!!
well worth the price tag too if you ask me
I never infered the kit was made by a monkey.... my comment drew a line through 95% of vauxhall tuning being done by monkeys who know, no better etc. lol
oh i know mate, wasnt aimed at you or the vauxhall 'tunaz'
just stating fact lol
craig green
19-09-08, 04:48 PM
It doesnt wind me up as such, and thats far from justification
just makes me laugh how just because some cunnt doesnt like a particular model of car, means that the manufacturers stuff cant be relied upon!
So I'm a cunnt...... whatever.
Who made you a moderator all of a sudden? Step away from the keyboard!
how does calling you a cunnt make me a mod?
personal opinion and all that!
Forget ram air, think leaf blower (http://video.google.com/videoplay?docid=-8976258647561292563&q=+dyno+leaf+blower&ei=ET0PSIfuKZW05AK428yyBA&hl=en)
Bikes have been using ram air effect for years (lots of them) and yes it works. The gains arn't massive and there will be an optimum size for the opening (directly in the air flow).
However it's hard to guess how air will behave around the car at speed (that's why wind tunnels were invented).
It's well worth looking in to and experimenting with. Have fun!
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