Learned something very interesting about how McLaren and one other team (Ferrari? can't remember) do tuning with their new rear diffuser.  They're using exhaust flow to increase the effectiveness of the rear diffuser, so that requires as much exhaust flow as possible over the diffuser at all times.

So the throttle plates are always open between 90%-100% according to the tv commentators.  That way, the engine is always pumping air over the diffuser.  Fuel and ignition timing is used to control power.  It's almost like a diesel! 

No more engine braking really, but I guess the KERS can help with that.  But they probably still had to beef up the rear brakes.

Ah, yes, you're right.  It was Renault.  I don't think there's necessarily a fuel penalty, but getting proper combustion is probably tricky as the A/F ratio has to be in a reasonable range.  So to do that, maybe there are conditions where they have to spray more fuel than would be necessary if they used the throttle plates to regulate mass air flow.  Then just retard the ignition timing to regulate power.  Just making guesses.

 they are using the over run on the engine to keep the exhaust gases flowing.. that's why it gurgles off throttle.

www.youtube.com/watch

you can hear it pretty well on this vid.  most of the teams are using it now.

btw this isn't new technology. it's been around since the early 80's.  and the FXMD NSX used it on their aero package too.

Very interesting about using the exhaust flow to basically make the car a ground effects car.

It's not the use of exhaust flow working in conjunction with the rear diffuser that I find interesting as you guys have pointed out it's old tech, it's the fact that the throttle plate never closes more than 10% from fully open. 

Usually, the throttle plate controls the mass flow rate of air.  You measure that, you inject fuel somewhere in a range around stoich and it burns.  For the fuel to burn, the A/F ratio has to be in a range around stoich.  Go too rich or too lean, and it won't burn.  So here's the issue.  Maybe you're at an operating point where the throttle plate would typically be open only 20%, but now the lowest it will go is 90%.  So it's pumping way more air than is required which would make for an overly lean A/F ratio that will not burn.  So how do they get around it?  I guess the only way is to spray the proper amount of fuel, which would typically be too much for requested power, and use ignition timing retard to limit the power.  Or, maybe only spray fuel in 2 or 4 cylinders to reduce power and leave the others deactivated.  Hmm... that seems to make more sense as no fuel would be wasted.

 Not only is this old tech, this is old news - Ferrari, RB and Mclaren were doing this last year - including the special engine settings to sustain flow with the overrun. Nearly everyone this year is running an exhaust blown diffuser now, but Ferrari and RB seem to have the most extreme solutions.

Posted By l4mbch0ps on 03-29-2011 12:57 PM

 Not only is this old tech, this is old news - Ferrari, RB and Mclaren were doing this last year - including the special engine settings to sustain flow with the overrun.

Got any links to info on the 'special engine settings'?  That's the part I'm intrigued about.... I only have my guesses as to the method so far, so I'm curious as to what's actually done.

Posted By spdracerut on 03-29-2011 07:21 PM

Posted By l4mbch0ps on 03-29-2011 12:57 PM

 Not only is this old tech, this is old news - Ferrari, RB and Mclaren were doing this last year - including the special engine settings to sustain flow with the overrun.

Got any links to info on the 'special engine settings'?  That's the part I'm intrigued about.... I only have my guesses as to the method so far, so I'm curious as to what's actually done.

If anyone would know, it would be Mark or Eric.  Since they are working in the high end ecu market. 

here is Scarbs analysis from last year

scarbsf1.wordpress.com/2010/07/10/r...s-q3-pace/

Posted By sticky667 on 03-30-2011 08:18 AM

here is Scarbs analysis from last year

scarbsf1.wordpress.com/2010/07/10/r...s-q3-pace/

That appears to be old tech now.  In his explanation of the method thought to be used by Red Bull last year, the throttle is only partially open to provide just enough air to burn a little fuel.  The fuel is burned when the exhaust valve is open so that the expansion of the fuel/air mixture due to combustion drives the flow over the diffuser.  So not a lot of mass flow of air, but a whole lot of energy.
 

So now the throttle is always 90%-100% open resulting in a lot more mass flow of air.  So how are they tuning for what would have been part throttle.  I guess it can be a bit rough because F1 cars aren't at part throttle that often.

Mark, thanks for the datalog.  I'm not too surprised less than 20% of the time was spent at part throttle.  I read or saw about a datalog from MotoGP bikes and it's interesting to see the difference between requested throttle position by the rider and the actual throttle position of the engine.  It really highlights how important the engine calibration guys are.

Posted By l4mbch0ps on 03-31-2011 01:15 PM
It's likely that the 90% figure is exaggerated?

Well, I'm pretty sure that's what the TV commentators said.  Looking at this rule:

5.5.3 The minimum and maximum throttle pedal travel positions must correspond to the engine throttle minimum
(nominal idle) and maximum open positions"
 

90% throttle open can be the position of the engine throttle at idle   So to get it to idle, I would guess they would only fire 2 or 4 of the cylinders instead of the full 8.  Where do F1 engines typically idle?  10k rpms?

90% throttle open can be the position of the engine throttle at idle So to get it to idle, I would guess they would only fire 2 or 4 of the cylinders instead of the full 8. Where do F1 engines typically idle? 10k rpms?

7-10k rpms as far as i know, depending on when (pre-race, pitstop, etc.)

I don't understand your point though. Do you mean they set the engine up to idle with the throttle plates at 90%?

Assuming the tv commentators are correct in that 90% value.

The way I read the rules, the minimum throttle position is defined as the throttle body position where the engine idles.  So, if you want the minimum position to be 90% open, then you have to figure out a way to make the engine idle at that throttle opening.