Rolling Road on 24/11/2007

[rs4v8]

Shame you didn't have a phantom black one, just for future reference, black's always quicker

Noticing the fan he has there - bikes virtually all have ram air inlet ducts which cause an overpressure at the intake manifold. You'll never get this effect with a fan stuck in front of the vehicle as the volumetric flow will not be anywhere near as much as say 70mph (unless you are good mates with Frank Williams or Ron Dennis and can get your car in their windtunnel).

Seeing as how air is taken from a duct at the front of the car (a high pressure zone when the vehicle is moving through the air) the inlet duct will be at a higher pressure than static atmospheric pressure. This could fairly easily explain why the car is down on power compared to quoted BHP as there is no 'micro supercharge' effect. This air flow is precisely what your mass air flow sensor is measuring.

No overpressure = not enough air to engine as measured by MAF sensor = less fuel injected by fuel injection computer = less power.

This is why a K&N filter gives more power, more air to engine.

Quoted BHP is 414 - you are seeing roughly 380, an 8% drop but in static air flow. In order to get an accurate figure you'll have to be able to force feed the intake air at a pressure representative of forward movement.

It would be very interesting to see audi testing thier engines. I'd put money on it that they are force fed on the bench.

[audijohn]

Clive atthows is forced and brand new.

[t_urbo]

Those runs have been taken in 3rd gear, if they were taken in 5th gear you would see a 15hp improvement (approximate). The RS4 has two maps, one for gears 1-3 and one for gears 4-6.

So the Daytona is infact around 393.3 hp (which is exactly what mine was) and the Avus is 400.3 hp.

Anyone having RR done in the future should ask for two runs, one in 3rd and one in 5th.

Still the same old story though, both down on manufacturers claimed outputs. When are we going to see an RS4 producing slightly more than promised.

[rs4v8]

You've just confirmed what I was saying. 3rd gear would be what? 60-90mph as a rough guestimate, 5th will be well above that. Try sticking tour hand out the window at over a ton. Your hand will be blown backwards. This is the pressure which should be in your intake (or very close to it, a wee bit less due to frictional loses across the filter and round the bends). Without this your engine is being starved of air as rather than being force fed it is having to suck air though the pipes. Not enough air means not enough fuel and a power output less than expected.

Where's this Clive Atthows audijohn?

[audijohn]

You've just confirmed what I was saying. 3rd gear would be what? 60-90mph as a rough guestimate, 5th will be well above that. Try sticking tour hand out the window at over a ton. Your hand will be blown backwards. This is the pressure which should be in your intake (or very close to it, a wee bit less due to frictional loses across the filter and round the bends). Without this your engine is being starved of air as rather than being force fed it is having to suck air though the pipes. Not enough air means not enough fuel and a power output less than expected.

Where's this Clive Atthows audijohn?

He is based in NORWICH, salhouse road.
http://www.cliveatthowetuning.co.uk/

[rs4v8]

Bugger, bit of a trek from inverness!!

[t_urbo]

Shame you didn't have a phantom black one, just for future reference, black's always quicker

Noticing the fan he has there - bikes virtually all have ram air inlet ducts which cause an overpressure at the intake manifold. You'll never get this effect with a fan stuck in front of the vehicle as the volumetric flow will not be anywhere near as much as say 70mph (unless you are good mates with Frank Williams or Ron Dennis and can get your car in their windtunnel).

Seeing as how air is taken from a duct at the front of the car (a high pressure zone when the vehicle is moving through the air) the inlet duct will be at a higher pressure than static atmospheric pressure. This could fairly easily explain why the car is down on power compared to quoted BHP as there is no 'micro supercharge' effect. This air flow is precisely what your mass air flow sensor is measuring.

No overpressure = not enough air to engine as measured by MAF sensor = less fuel injected by fuel injection computer = less power.

This is why a K&N filter gives more power, more air to engine.

Quoted BHP is 414 - you are seeing roughly 380, an 8% drop but in static air flow. In order to get an accurate figure you'll have to be able to force feed the intake air at a pressure representative of forward movement.

It would be very interesting to see audi testing thier engines. I'd put money on it that they are force fed on the bench.

Sounds good in theory, but it practice it does not work quite like that with the RS4 B7, although it does with other engines.

1. The driven air as you put it produces less pressure than what the piston produces.

2. The air box has an outlet in the bottom (not part of the flap) which allows exess air to escape when travelling at speed under non load conditions.
Due to the fact it has this additional hole which is routed to the front wheel, there will never be any pressure build up within the air box/ inlet manifold.

Dispite what you are told a K&N filter does NOT allow more air flow than your STD paper filter all the time you run a NEW or clean paper filter.
K&N filters allow more flow only when your paper filter becomes partially blocked with dirt.
What a K&N filter will do is oil your MAF for you.

[rs4v8]

Shame you didn't have a phantom black one, just for future reference, black's always quicker

Noticing the fan he has there - bikes virtually all have ram air inlet ducts which cause an overpressure at the intake manifold. You'll never get this effect with a fan stuck in front of the vehicle as the volumetric flow will not be anywhere near as much as say 70mph (unless you are good mates with Frank Williams or Ron Dennis and can get your car in their windtunnel).

Seeing as how air is taken from a duct at the front of the car (a high pressure zone when the vehicle is moving through the air) the inlet duct will be at a higher pressure than static atmospheric pressure. This could fairly easily explain why the car is down on power compared to quoted BHP as there is no 'micro supercharge' effect. This air flow is precisely what your mass air flow sensor is measuring.

No overpressure = not enough air to engine as measured by MAF sensor = less fuel injected by fuel injection computer = less power.

This is why a K&N filter gives more power, more air to engine.

Quoted BHP is 414 - you are seeing roughly 380, an 8% drop but in static air flow. In order to get an accurate figure you'll have to be able to force feed the intake air at a pressure representative of forward movement.

It would be very interesting to see audi testing thier engines. I'd put money on it that they are force fed on the bench.

Sounds good in theory, but it practice it does not work quite like that with the RS4 B7, although it does with other engines.

1. The driven air as you put it produces less pressure than what the piston produces.

2. The air box has an outlet in the bottom (not part of the flap) which allows exess air to escape when travelling at speed under non load conditions.
Due to the fact it has this additional hole which is routed to the front wheel, there will never be any pressure build up within the air box/ inlet manifold.
Dispite what you are told a K&N filter does NOT allow more air flow than your STD paper filter all the time you run a NEW or clean paper filter.
K&N filters allow more flow only when your paper filter becomes partially blocked with dirt.
What a K&N filter will do is oil your MAF for you.

1. Really? I thought this is why engines had valves, cams and timing belts? When the cylinder is in compression the inlet valve closes and the pressure generated by the piston doesn't escape back to the inlet manifold (otherwise you'd not really get much power as the bang which occurs wouldn't drive the piston would it....?)

The air only flows into each cylinder during the very small period of time where the inlet valve(s) open during induction phase of the cycle, at this time if the air is at a pressure greater than ambient then effectively you'll get more in, allowing you to squirt in more fuel (this is partly why supercharging and turbocharging work). The maximum pressure generated by the piston at no time overcomes the pressure of the inlet air as the inlet valve creates a physical barrier between the two at maximum cylinder pressure to prevent back flow.

If this is happening in your car then it'll be very sick indeed.....

2. Perhaps you have noticed that the small hole you mention is not the same size as the one the air enters the box through or the one from the box to the engine. Perhaps this might lead to an overpressure, admittedly if not one which is the same as which is measured at the front of the car but you will be seeing an overpressure there at speed.

3. K&N's will only oil your MAF if you put too much on during cleaning. Fact. Several cars and bike later and no oiled MAF. How often do you change your nice OEM filter??

[mrdeli]

I'd certainly be in favour of full power in all gears - extra power in 5th gear is pretty useless to me.

[t_urbo]

If you will be seeing an overpressure at speed why does the additional flap operated intake open at higher rpm?

Surely this would not be required with all this pressure you talk of.

The flap is there to allow additional air to be SUCKED (by the pistons) into the engine at higher rpm.

[rs4v8]

Have to be honest didn't realise there were different maps for different gears. Pretty interesting. Makes sense too if you think about it. It'd be fantastic to be able to switch it from full power to something like an 'eco mode' where gear selection / revs dictate the fuelling.

[rs4v8]

If you will be seeing an overpressure at speed why does the additional flap operated intake open at higher rpm?

Surely this would not be required with all this pressure you talk of.

The flap is there to allow additional air to be SUCKED (by the pistons) into the engine at higher rpm.

I would imagine this is exactly the same as the reason why you'd want the exhaust flaps to open at high RPM, in order to allow gases to flow through the engine more easily. Less restriction = more power.

At low revs you do not want or need this extra flow. If an engine has to suck air (to which I think you mean draw a vacuum in the intake manifold)during the induction phase then it'll not be performing very well. The only sucking (vacuum drawing) should be in the cylinder bore. The RS4 engine operates at such high revs and the pistons travel at such high speed(apparently approaching that of an F1 car) that the extra flap opens at high revs in order to allow the air to enter the cylinder without restriction, I imagine to specifically prevent a vacuum in the inlet manifold. Bear in mind that the inlet valve is only open for a few milliseconds so the engine needs as much assistance as possible to be able to breathe correctly.

Jap bikes have been doing this for years. Bike engines rev far higher than car engines and one of the challenges is getting enough air into the cylinder in the given time. This has been solved by using what the japs named ram air, collected via ducts at the front of the fairing where the speed of the bike creates a high pressure zone at the front of the bike, effectively the same as the intake pipe on the RS4.

When you say 'all this pressure' in what I am sensing is a sarcastic tone, I am talking tens of millibar above static atmospheric pressure, not even close to what a turbo or a supercharger would achieve, as you rightly say, there's a hole in the air box (and I'd even add the plastic pipes aren't even properly sealed till after the filter).

Lastly, how can MTM create their car using what is effectively a bolt on supercharger with no real internal mods and a gain of around 100bhp if the RS4 engine doesn't like being force fed air and prefers to 'suck' air during high revs.

I'm not wanting an argument here chief Just trying to provide an explanation as to why people are seeing a measurable deficit in expected BHP to that quoted by Audi.

[rs4v8]

Here you go t_urbo, some light reading.....

http://www.fireblades.org/forums/genera ... m-air.html

[55JWB]

Intersting as my plots show the operator used "shoot 08" mode not "shoot 44" I have since been advised that is the correct mode, so hopefully I will see the same kind of numbers as you guys next week....

Jason

[GrahamS4]

The gear used also seems a good point for the B7 RS4. Normally a gear good for 80-90 seems popular, but I think 4th sould be ok.

Re talk of air flow ablove - of course the air from the fans is not as good as being on the road.

Did any of the B5s log while on the dyno at Thorneys? Was the max MAF reading down on what you see on the road?