Renich Carbon fibre Ram Air Duct

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The concept is simple, the denser the air the more power, the colder the air less retardation and reveal the true power.

This is true however you're never ever be colder than ambient (taking pressure out of the equation) so you will not gain any power just keep what you have for longer. So for tuning and power plot purposes this is a red herring.

To prove the concept is easy take a funnel and cut the small end off so that it is the same size a peace of tube. Hold both out of the window in turn and see which has the most resistance. The greater the resistance the greater the air pressure must be.
The larger the leading edge of the funnel the more air is forced into the same space. Try this at 40 and the confirm that Ram air only works at 120mph. admittedly the faster you go the greater the effect, as I stated at the beginning the fans on a dyno only spin at 60 mph.... This is the exact reason that when you tune a turbo car you have to ensure that it receives enough cool air to perform. If anyone purchases the Kit simply do two runs, one with the standard fan set up and one with a fan pointing directly into the duct. I know you will see a difference. On the road you won’t have the issue of air displacement as the air will be uniformly hitting the face of the car. In fact Ricks homemade version should prove the point depending on the shape of his duct!

This is a common misunderstanding of what is going on.
The force is greater because more air molecules are hitting the larger surface than the smaller one. Pressure is largely irrelevant in this case however yes the air pressure in front of the funnel may be fractionally (and I mean fractionally almost too small to measure at road speeds) all that happens is that excess air will spill out over the edges of the funnel rather than be compressed. The assumption that a big scoop funnel will increase pressure is based on the fact the air has no other option on where to go but this is false.

Air like most things doesn't like being compressed and will in preference move somewhere else if it can. Now a funnel will taper down to a narrower point and what will happen here...
It's classic example of a venturi effect - instead of what you may think would happen (the pressure increasing) the air instead flows faster. This faster air will have a lower pressure than what you started with so what you end up doing is causing a reduction in pressure by having a big funnel.
This is why cars have a large airbox as the idea if for the air to slow down and gain some pressure. If you have like in the RS4 an airbox with multiple air intakes it's not really possible for the pressure to increase as it'll just spill out into the other air intake feeds.

As for the fans being closer - thats more down to air losing speed after the fan. Move the fan closer the air will be travelling faster when it hits the airbox intakes.

So given that CAI won't add numbers (just maintain them) and the ram air is of marginal benefit at very high speed I can't see how on face value that this will add 30 odd hp with 60mph fans.

[S4Player]

Sorry pal I'm questioning your dyno dynamics rolling road figures the dyno dynamics rollers don't pick up the power split on the b7 very well. Your car ran 442ps at Mrc? Well done I ran 565ps and 695nm . I'm making sense pretty clearly there's no way your 'ram' cold air feed is giving you 30bhp simples. Most of the lads on here run caf's which cost about 40 quid in parts and do exactly what yours does just because it's carbon fibre doesn't really make it any better

[MB2]

We used to run ram air on our bikes and to make it work properly ended up with the front of the tank removed, a cover over the area that used to be the front of the tank, flatslide carbs with velocity stacks on them & 2 huge hoses connected to the front of the fairing. Even then it was considered to only really work at high speed & could only really be proven by the speed/gearing the bikes could pull at Bruntingthorpe vs the bhp on the dyno, but I guess in the days of speed limiters this is harder to test now.

Danny if you have dragged yours then maybe you have calculaed the expected bhp back from the timing figures ?

Agree, the only way to tune a car is to get a dyno you can trust and make changes & analyse the results although it can be a lot cheaper to trawl the country's dynos until you find one with a result you are happy with...

[S4Player]

http://www.youtube.com/watch?v=04mz1CbxRlg 11.77@123mph
http://www.youtube.com/user/TheChipsno1 ... rmwOtcdfbI 11.85@121mph

[RTS BRAT]

FAO: MB2, DannyRS4 and adsgreen


Guys maybe you’re right concerning the venturi affect, but all I do know is that two separate dyno's gave to comparable figures, with the same map. So if you trust dyno dynamics, or you trust the type of dyno MRC uses “they both gave the same figures when converted”.
Afters these figures were confirmed, the only changes made was a remap, inlet manifold spacers and the addition of the Duct. Maybe the faster airflow ensures that induction temperatures remain cool at low speeds (eradicating retardation) and at high speeds the ram air takes effect as you explained?!?

But it does not change the fact that the dyno (chart) isn’t lying, if that’s the case then both DMS and MRCs dyno’s lie. I am always very meticulous in measuring gains I get from the Car, both on the dyno and on the track, the visible difference is clearly evident, as for the physics I leave that up to you. But no matter how you look at it, I have a combination that has broken the accepted rule.

I daren’t stress the fact that the car was using 20” wheels instead of 19’s .
What is the take on this when the same car is dyno’d on two different set of wheels, would 20” gain or lose me power?

[RTS BRAT]

Sorry to burst your bubble but your spec is old hat on here,I ran that level of tuning and power ages ago,you have a 440ps level of tune which is very good and transforms a standard car for sure but 470 it isnt,perhaps it is on dms dyno in which case we could all add 30ps,I think we are all very aware of the principles you are explaining as some like myself have been running these mods and more for some time.

What power output do you have now, and what mods have you done??


There maybe only one way to confirm this..... CATS, vanes and all

[sonny]

Have a browse at this list, its a bit out of date but will give you an idea http://forum.rs246.com/viewtopic.php?f= ... s&start=45

[Rick_RS4]

when is the next rr day, we can all go to settle this and leave our handbags out.

[sonny]

when is the next rr day, we can all go to settle this and leave our handbags out.

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Mine has made 456 on mrc's and has no CAI or fancy airbox duct.
So what you're saying is that as mine made more than yours on MRC's I'll see 470+ on the other rollers?

[RTS BRAT]

Mine has made 456 on mrc's and has no CAI or fancy airbox duct.
So what you're saying is that as mine made more than yours on MRC's I'll see 470+ on the other rollers?

No... I'm saying forget the rollers!!
Lets just fill them to the brim with fuel and we'll go side by side and do some 3rd and 4th gear runs!?

[MB2]

FAO: MB2, DannyRS4 and adsgreen


I daren’t stress the fact that the car was using 20” wheels instead of 19’s .
What is the take on this when the same car is dyno’d on two different set of wheels, would 20” gain or lose me power?

I can't imagine how the diameter of the wheel affects the bhp of the car as surely they can't affect the output of the engine ?

[RTS BRAT]

FAO: MB2, DannyRS4 and adsgreen


I daren’t stress the fact that the car was using 20” wheels instead of 19’s .
What is the take on this when the same car is dyno’d on two different set of wheels, would 20” gain or lose me power?

I can't imagine how the diameter of the wheel affects the bhp of the car as surely they can't affect the output of the engine ?

But can we agree that it, will affect acceleration?

[MB2]

I don't think I can, as the rolling radius of the wheel diamenter must stay the same so the total wheel size hasn't actually changed, just the ratio of wheel to tyre.

[RTS BRAT]

The concept is simple, the denser the air the more power, the colder the air less retardation and reveal the true power.

This is true however you're never ever be colder than ambient (taking pressure out of the equation) so you will not gain any power just keep what you have for longer. So for tuning and power plot purposes this is a red herring.

To prove the concept is easy take a funnel and cut the small end off so that it is the same size a peace of tube. Hold both out of the window in turn and see which has the most resistance. The greater the resistance the greater the air pressure must be.
The larger the leading edge of the funnel the more air is forced into the same space. Try this at 40 and the confirm that Ram air only works at 120mph. admittedly the faster you go the greater the effect, as I stated at the beginning the fans on a dyno only spin at 60 mph.... This is the exact reason that when you tune a turbo car you have to ensure that it receives enough cool air to perform. If anyone purchases the Kit simply do two runs, one with the standard fan set up and one with a fan pointing directly into the duct. I know you will see a difference. On the road you won’t have the issue of air displacement as the air will be uniformly hitting the face of the car. In fact Ricks homemade version should prove the point depending on the shape of his duct!

This is a common misunderstanding of what is going on.
The force is greater because more air molecules are hitting the larger surface than the smaller one. Pressure is largely irrelevant in this case however yes the air pressure in front of the funnel may be fractionally (and I mean fractionally almost too small to measure at road speeds) all that happens is that excess air will spill out over the edges of the funnel rather than be compressed. The assumption that a big scoop funnel will increase pressure is based on the fact the air has no other option on where to go but this is false.

Air like most things doesn't like being compressed and will in preference move somewhere else if it can. Now a funnel will taper down to a narrower point and what will happen here...
It's classic example of a venturi effect - instead of what you may think would happen (the pressure increasing) the air instead flows faster. This faster air will have a lower pressure than what you started with so what you end up doing is causing a reduction in pressure by having a big funnel.
This is why cars have a large airbox as the idea if for the air to slow down and gain some pressure. If you have like in the RS4 an airbox with multiple air intakes it's not really possible for the pressure to increase as it'll just spill out into the other air intake feeds.

As for the fans being closer - thats more down to air losing speed after the fan. Move the fan closer the air will be travelling faster when it hits the airbox intakes.

So given that CAI won't add numbers (just maintain them) and the ram air is of marginal benefit at very high speed I can't see how on face value that this will add 30 odd hp with 60mph fans.

Are you saying that the Gruppem has no effect on performance as this has a duct for ram air and also keeps the OE funnel going to the top of the main Radiator? Surely the duct is no different in concept, the venturi effect that you describe must also be true for the GruppeM??
See the link below...

http://www.europeancarweb.com/tech/prov ... ewall.html