Renich Carbon fibre Ram Air Duct

[RTS BRAT]

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.

I had the same discussion and originally had your view, but the centrifugal forces are greater due to the material (metal) be further away from the centre. Thus it take more energy to rotate the wheel.

[RTS BRAT]

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

Nicely phrased!!!

[RTS BRAT]

Have a browse at this list, its a bit out of date but will give you an idea http://forum.rs246.com/viewtopic.php?f= ...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

Sonny are these your figures ?:

441ps, Sonny, BMC filter, Full Milltek (non res 200cell cats), Manifold, Remap and valves cleaned, MRC

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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

There is no venturi effect here as the size of the "ram air" duct is constant. You get a venturi effect when you have a funnel of a larger diameter going into a smaller one as per your previous example stating it would raise manifold pressure (when it wouldn't).
As for the link - those results are exactly what I mean. *Less* than 10hp over a simple filter change. Given the stock is a crappy paper thing and the K&N is a proper oiled filter thats hardly surprising.
Most of the GruppeM benefit is more likely down to the much larger airbox and internal airbox design rather than any ram air effect (which we've already said you're not going to see at all on a dyno with 60mph fans!).

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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.

I had the same discussion and originally had your view, but the centrifugal forces are greater due to the material (metal) be further away from the centre. Thus it take more energy to rotate the wheel.

Centrifugal "force" has nothing to do with this. I think you are actually referring to "increased polar moment of inertia".
The funny thing now is that if you "got" 470ps with heavier, bigger wheels then like for like you're actually saying that you're way above this so like for like your car is actually nearer say 480ps?
This will also mask drive train losses as once you have a heavier wheel spinning then pysics says that the wheel will want to stay spinning. As the only thing that would slow the wheel down is due to transmission fricition losses then this suggests that if the dyno operator calculated drivetrain losses with a coastdown test with the larger wheels fitted then is would underestimate this making things read slightly high.

As for dyno results - dynos' lie. They lie all the time.
There are so many variables that you can run them back to back and get different results. Hell even the best dyno's have a degree of accuracy in the region of +/- 2-5%. with 450bhp thats potentionally 20hp or so.
Flywheel numbers are fun for the pub but posting the raw wheel numbers is a better form of comparison. Hell, even cahnging the tyres by 5psi can throw the results out a huge amount. I've heard of dodgy dyno operators at tuning companies doing this to help fudge the results.

[RTS BRAT]

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.

I had the same discussion and originally had your view, but the centrifugal forces are greater due to the material (metal) be further away from the centre. Thus it take more energy to rotate the wheel.

Centrifugal "force" has nothing to do with this. I think you are actually referring to "increased polar moment of inertia".
The funny thing now is that if you "got" 470ps with heavier, bigger wheels then like for like you're actually saying that you're way above this so like for like your car is actually nearer say 480ps?
This will also mask drive train losses as once you have a heavier wheel spinning then pysics says that the wheel will want to stay spinning. As the only thing that would slow the wheel down is due to transmission fricition losses then this suggests that if the dyno operator calculated drivetrain losses with a coastdown test with the larger wheels fitted then is would underestimate this making things read slightly high.

As for dyno results - dynos' lie. They lie all the time.
There are so many variables that you can run them back to back and get different results. Hell even the best dyno's have a degree of accuracy in the region of +/- 2-5%. with 450bhp thats potentionally 20hp or so.
Flywheel numbers are fun for the pub but posting the raw wheel numbers is a better form of comparison. Hell, even cahnging the tyres by 5psi can throw the results out a huge amount. I've heard of dodgy dyno operators at tuning companies doing this to help fudge the results.

If this is the case, why do you all swear by MRC? even though I have proven that on two seperate dyno's with the same set up gave me near enough the same figures?

p.s. check your mail.... PM

[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

Sonny are these your figures ?:

441ps, Sonny, BMC filter, Full Milltek (non res 200cell cats), Manifold, Remap and valves cleaned, MRC

Yes there my old figures, replied to your PM

Most if not all are using one rolling road as a bench mark, and that rolling road is at MRC. MRC pioneered work on the B7 RS4, hence why most of us use them.

[MB2]

OK, I can see what you are saying (although had never really thought about it a lot) the extra metal will probably weigh more than the tyre it replaces & so the wheels may take longer to spin up, but as adsgreen says will take longer to slow down - I still don't see how this can have the slightest difference on bhp/torque unless the car was only given say 10 seconds to spin the rollers so ran out of time to accelerate your heavy wheels. Although I do wonder if the heavier wheels with more stored momentum could change the drivetrain losses calculation, I can't accept that adding weights to my wheels would change the bhp the motor can produce - I could remove the wheels use the drive shaft to lift buckets of water from a well & I think I would still have my 420 bhp (or whatever it is).

It isn't that we all think MRC's dyno is wonderful, just that it is one that many cars have been tested on, including yours and provides a benchmark to compare against. Somewhere between MRC & DMS you gained 30 bhp and considering how much people will spend in the search for bhp it is only natural to wonder where that came from - if 20" wheels gave 30 bhp then every manufacturer would be fitting them to all their cars tomorrow.

[RTS BRAT]

OK, I can see what you are saying (although had never really thought about it a lot) the extra metal will probably weigh more than the tyre it replaces & so the wheels may take longer to spin up, but as adsgreen says will take longer to slow down - I still don't see how this can have the slightest difference on bhp/torque unless the car was only given say 10 seconds to spin the rollers so ran out of time to accelerate your heavy wheels. Although I do wonder if the heavier wheels with more stored momentum could change the drivetrain losses calculation, I can't accept that adding weights to my wheels would change the bhp the motor can produce - I could remove the wheels use the drive shaft to lift buckets of water from a well & I think I would still have my 420 bhp (or whatever it is).

It isn't that we all think MRC's dyno is wonderful, just that it is one that many cars have been tested on, including yours and provides a benchmark to compare against. Somewhere between MRC & DMS you gained 30 bhp and considering how much people will spend in the search for bhp it is only natural to wonder where that came from - if 20" wheels gave 30 bhp then every manufacturer would be fitting them to all their cars tomorrow.

You have completely missed the point.....
445ps (=438.90 hp), MRC .........The car was Dyno'd again with DMS, and confirmed 440hp (=446ps) with MRC map.
After which point I had the spacers fitted and the Kit and then a remap. Nothing else changed, not tyre pressures not wheels nothing just those three things

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I don't swear by mrc's rollers but as above many people here have been there so it serves as a fun method of comparison.
All I was interested in was that when my car arrived at mrc it read less than 400 and a few days later nearly 450. I don't care about the actual numbers but it's harder to argue against the same car on the same rollers within a short space of time. For me things got better so was happy.

Re:heavier wheels - makes a huge difference. The only reason f1 cars are fitted with carbon brakes is that the unsprung mass is much lighter which adds acceleration and braking performance.

[RTS BRAT]

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.

I had the same discussion and originally had your view, but the centrifugal forces are greater due to the material (metal) be further away from the centre. Thus it take more energy to rotate the wheel.

Centrifugal "force" has nothing to do with this. I think you are actually referring to "increased polar moment of inertia".
The funny thing now is that if you "got" 470ps with heavier, bigger wheels then like for like you're actually saying that you're way above this so like for like your car is actually nearer say 480ps?
This will also mask drive train losses as once you have a heavier wheel spinning then pysics says that the wheel will want to stay spinning. As the only thing that would slow the wheel down is due to transmission fricition losses then this suggests that if the dyno operator calculated drivetrain losses with a coastdown test with the larger wheels fitted then is would underestimate this making things read slightly high.

As for dyno results - dynos' lie. They lie all the time.
There are so many variables that you can run them back to back and get different results. Hell even the best dyno's have a degree of accuracy in the region of +/- 2-5%. with 450bhp thats potentionally 20hp or so.
Flywheel numbers are fun for the pub but posting the raw wheel numbers is a better form of comparison. Hell, even cahnging the tyres by 5psi can throw the results out a huge amount. I've heard of dodgy dyno operators at tuning companies doing this to help fudge the results.

Check PM, as I explained I'm rather disapointed that assumptions are made, and more to the point. Why would I allow myself to be cheated??
Anyway hopefully this can be settled once and for all very shortly!!

[sonny]

Ring time...?

[Timster]

Ring time...?

Blimey, you are drunk aren't you Sonny. Not even any foreplay?

[P_G]

RTS BRAT, can you get more pics posted up of the new sports rad and duct? I'm interested in seeing more details without shooting you down.

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Ring time...?

Don't start