wow!

started looking into Ram Air systems as a cheap way of getting more power…
… the truth of the matter seems to be a difficult to get to…
lots of flashy carbon fibre aftermarket anodised tube thingys to bolt into hondas and the like but very little information or explanation to justify the effect and an equally large number of people saying

nah, it’s rubbish – nonsense!

well… i started a question on the volkzone forum here and the replies have been coming in thick and fast…

generally the opinion is Nah! but i happened upon a page here at vararam.com with a fairly in depth technical explanation.

i summarised it on the vz forumlike this……

you raise some very good points, as i said earlier I don’t know about this stuff but am trying to find the ‘truth’ of it all.

from some recent reading ive been going through that delves into it fairly well (find it here)

it looks like this (sorry if i summarise this wrong..)

atmostpheric pressure (1bar) = 14.65psi. when your N/A engine starts running it creates MAP with a theoretical max of 14.65 psi (at some point in the rev range) but due to practical inefficiencies usually operates up to 2.0psi below 14.65 psi (atmos pressure) but as the revs climb this NEGATIVE pressure at the manifold increases. a ram air system has two qualities, cfm & psi. given that air is feeding from the highest pressure point of the front of the car (say +0.4psi @50mph) and supplies sufficient cfm (not a problem) then the manifold pressure returns to 14.65psi (1bar)

there is no theoretical boost beyond atmos pressure here but the actual increase at the manifold could be as high as 2psi…

(some figures i’ve seen state up to +0.176 psi possible from standard RAM system (ignoring (as paul rightly points out, very clever fluid dynamic designing to create pressure multiplyers in the system))

so, if my engine develops 200bhp with manifold pressure of say 13.65psi (only a 1psi loss)
then i’m developing 14.65HP per psi

so if i can flow enough air through the ram system to get back to normal atmospheric pressure (+1psi) then i’ve gained 14.65HP. if i can get +ve pressure at the manifold of 0.175psi then i’ve added another 2,5hp to the figure.

if i add in the cooled charge effect (apparently between 1.5-2bhp for every 6-10 degree drop in charge temp)
-in the bus the air is drawn straight in from the engine bay (and it gets WARM in there) from the ECU temp monitor in the engine bay i could be looking at 20degrees or more then i can add another 3-4bhp to the equation.

so
14.65 HP for return to 1bar at manifold by increased cfm
+ 2.5 HP for 0.176psi increase in MAP
+3HP increase for cooled charge =

20.15hp increase !
for the cost of a length of duct and some gaffer tape…

as a BIG caveat, i agree totally with paul about the problems of actually designing this to work efficiently at all, and the figures above are fairly loose and based on the outline of very few other sources BUT! i think i understand where the power MIGHT come from. based on this i think i might be doing some more investigation

at the end ofthe day i’ve had a great evening, i want to pursue this for two main reasons.
1 i get to read some techy stuff, learn a little more about fluid dynamics and do some mathematics, then play with holesaws and gaffer tape and then make my bus go faster
what could be better than that ?

well, the other reason is even better, i apply some new technology, i get to cut K3WL Lo0k1nG NACA ducts into the rear windows on the bus, go faster on the strip and KNOW why and how it works !

and it feels like a big fat one in the eye for the VW re-enactment society 🙂

until next time race fans !