The MCS has such a flat torque curve, should Ijust the RPMs up to the 7,000 before shifting to get the most power? On a related topic, once I get up to speed, should I drive in the lowest gear that I can to get the best mileage?

 

The lower the gear selected the more torque multiplication your transmission will give you. In general and almost always, you will achieve the fastest acceleration by running the engine to just before the rev-limiter kicks in as the torque at the wheels in 1st at any RPM is greater than the torque at 2nd at any RPM.

As long as the engine is running smoothly you should get the best milage with the highest gear(lowest numerical gearing).

 

I would say no. Rev it up a bit on a down-shift though (ie from 5th to 4th or something).

I would say yes. You get much better milage going 60 in 6th than 60 in 5th.

Do you have the R56 or a previous MCS?

 

Thanks to both of you for the info. I have a 2007 MCS.

 

As I understand it, to maximize fuel mileage, you want to be at torque peak, but not any higher revs than necessary. So that'd be around 1700 (driving revs, not shifting at that point) on the MCS. Higher revs offer more hp, but to generate that higher power you'll be using more fuel.

If your question is when to shift whilst getting groceries the answer should probably be: Whenever you want to.

If you want to know what's best for the car, I'd shift WAY before 7k unless I'm driving in a competition. Driving to redline all day long is stressful for any motor. Because this car has bags of torque down low, I'm tending to shift early, and I believe it's paying back with increased gas mileage.

 

Here is what I do...
Never shift under 2000 rpm, as you don't want the engine to lug. So in heavy traffic at lower speeds, I actually shift around 2500 - 3000 rpm. That way, the tach drops back two about 2000 in the next higher gear.

For sporty driving and/or fast getaways... 4500 - 5500 rpm is great and will get you moving. I would not go much over 5500 ever on purpose. The rev limiter is set for around 6000 something, don't know what yet because I haven't reved my motor that high yet. But shifting at 4500 in all gears gets you to 100mph very quickly.

Hope this helps. These rpms seem to be a good comprimise between quick acceleration and good fuel economy. With alot of city driving, I am getting almost 30mpg, and once on the highway, over 35mppg and once in a while over 40mpg.

 

On some engines, if you don't rev them high enough from time to time they tend to build up deposits. Is that old technology, or does that still hold? How about with the turbo engine of the MCS?

Anyone remember Bill Cosby's routine about his conversation with the mechanic on having to blow the carbon out of his first Ferrari, "...on any side street."? Something like redline in 2nd gear. I don't recall what speed that was, but they would do 80 mph in first.

 

Power peak is 5500rpm so max acceleration comes when you keep the car close to this peak - that means shifting around 6000 so it drops back to just below 5500 in the next gear

 

With 1700-2000 rpms as your lowest, there's not really any point to going above ~5500-6000 rpms. This is going by the torque curves others have published. If I remember correctly, torque actually starts to fall off above 5500, so what's the point? The only reason to keep the car up at the high revs would be if it's inconvenient to shift, like in the apex of a turn, or just before hitting the brakes for a turn. Less shifting means more time under acceleration! Higher revs def mean more gas.

Robin, to be honest I don't remember any problem with carbon buildup using prem fuel and running the car up to what feels good, assuming modern fuel management. If you run it at 2200 rpms all day, yes there'd be a prob, but I don't think many of us should have That prob! By the way, I think that particular F car was carburated. Diff kettle of fish. Bad fuel metering. My current 930(old turbo Porsche) pretty much has raw fuel out the exhaust at idle to about 3500 rpms and it's got early fuel injection. That old thing will get deposits for sure without running it out occ.

Mark

 

Yup, those were the days when Ferraris typically had six dual Webers.

 

I agree for normal driving. But for all-out max acceleration you need max power. That means keeping it close to the power peak of 5,500 which means going near the red line before shifting.

 

FLKeith,

FWIW, hp seems to peak @4500 rpms and stays flat and even tails off @~5700. Torque peaks even earlier and has a sharper fall-off. It then depends on how many rpm you lose going to each higher gear. I'm still waiting for my MCS, but my spirited test drive felt that, for me at least, there is little point to run it up much above 6000.

Anybody who's autocrossed a new one or done a track day have anything to add?

Cheers,
Mark

 

bjacobso, +1 to what Keith said, if you're looking for max rate of acceleration. As the physics of racing interested me years back, I researched this. Though "push into the seat" (i.e. force, thus rate of acceleration) in any one gear is directly relate to torque curve so it is at max at the torque peak, the maximum rate a vehicle can accelerate through multiple gears when traveling a set distance is a function of power. Max performance accelerating through the gears is when you shift to keep the RPMs around the power peak.

Counter-intuitive yes, when you figure max push into the seat is at a max at the much lower RPM of the torque peak, but the speed of the application of work (moving a weight) is force at a rate of motion. So as long as you can apply more force to the contact patch of the tires while holding a lower gear, then the force that would be applied to the tire's contact patch if you up-shifted, you'll maximize acceleration; which happens around the power peak. That is proved true as well with a great automotive simulation program called CarTest2000.

Rate of fuel usage does go up with RPM. So yes, lowest gear will give you the best mileage at a set rate of speed.

 

A friend of mine is a mechanical/aerospace engineer, and has an old Saab 900 turbo w/ a stick - damn thing has serious mileage on it and still runs great. Sweet color too - metallic green. He told me that the key to good mileage in a standard transmission is to keep the tachs really low. So, even if you're just cruising around at like 30-40 mph, you could opt to be in 5th/6th gear and keep your gas consumption way down. Of course, the car won't take off quickly in that gear. I'm certainly no expert myself. For all I know it's hard on the engine to do that for other reasons that I don't understand?

 

Years ago (proably about 15 yrs ago), I got a formula for optimum shift point from Road & Track magazine. Basically you up shift at the point where the RPM will fall into where the peak torque would be in the next gear (the calculation involves the gear ratio of each individual gear). But with the torque on the R56 being so flat, there's really no particular shift point.

 

Correct me if I have this wrong, but I was under the impression that torque gives you acceleration, and HP is what is needed to keep the car moving against wind resistance, etc. So, if you are traveling at 60 mph you need a high enough rev. to produce the HP to overcome wind resistance.

In watching the mpg readout on my ScanGaugeII (you can set your tach to read out mpg) I found I was getting as good or better mpg readings at 3,000 rpm as 2,000 rpm. This was at speeds between 50 - 65 mph.

So, my conclusion is that low revs. = better mpg is too simplistic a rule.

 

Because the assumption disregards engine load. 2000rpm in 6th represents a bit more load than 2000rpm in 5th (due to torque multiplication). More load = fuel dumped into the lines.

 

In fact, torque and HP are directly related. Roughly speaking, HP = Torque * RPM. Torque is a measure of force, and HP is a measure of work (which here can be thought of as force applied over time).

If you're driving at a constant speed, the force needed to maintain speed doesn't vary with the RPM, so it makes some sense that your MPG didn't vary. At 3000 RPM the work required per RPM is less than at 2000 RPM, so you probably just kept the throttle lower. This probably explains the roughly equivalent MPG.

 

So, with a flat torque curve, HP would climb as rpm climbs. The torque for one revolution of the engine remains the same regardless of how many rpm, as long as it is in the flat area of the torque curve. At 2,000 rpm, the engine is capable of 2/3 the amount of work that it can do at 3,000 rpm.

If the engine isn't doing enough work at 2,000 mpg to maintain 60 mph, one is going to have to put their foot in it to maintain speed, thus lowering the mpg. Therefore, one can't assume that a flat torque curve means that one can drive at any speed with the minimum rpm required to get onto the plateau of the torque curve, as has been suggested earlier in the thread.

In other words, low revs. = better mpg is too simplistic a rule.

 

HP is what gives acceleration - more HP at the same speed always means more acceleration.

Torque is roughly HP/RPM. You need more power to get the same acceleration as the speed goes up so, if you stay in the same gear, you get maximum acceleration at the toque peak.

It is not intuititive but these two are consistent with each other. You get max acceleration in a specific gear at the torge peak but, to get maximum acceleration at a specific speed, pick the gear that gives max HP.

Getting max MPG is a totally different question - for this you need the gear where the engine is at its most efficient for the level the throttle. This is not always the highest gear.

Keith

 

How is that different than what I've been saying?

 

the enclosure maps wheel torque at the axle as a function of gear and rpm

the question is, is there any point above 2000 rpm where wheel torque is greater in the next higher gear?

the answer is, nope...

 

I don't follow. How does your question relate to the rest of the converstation? Not sure I get your point.

 

the OP question was "should Ijust the RPMs up to the 7,000 before shifting to get the most power?"

power, if defined as acceleration of the vehicle, occurs because the axle twists the front tires - generating thrust at the contact patch

that twisting force is torque, measured at the axle

for example in the case of 2nd gear the axle is generating 1,200 ft/lbs of torque at about 4,000 RPM

that's max - would i accelerate faster if i changed to third? if not, then is there ANY point where changing to third would cause me to accelerate faster?

well... if i follow the 2nd gear curve (pink, 2nd from top) off to the right i do see that the axle torque finally falls to about 1,050 ft/lbs as the RPM hits the limiter

BUT if i change to 3rd the absolute BEST i can do for wheel torque is about 900 ft/lbs - again, at the engine's torque peak of 4,000 RPM

so for maximum thrust i would wind the p*ss out of 2nd and not change to 3rd until i had to, because even at the redline 2nd pulls harder at the contact patch!

the same is true for each pair of gears - although the gaps get narrower, there is NEVER a point where one of the higher gears can generate more torque at the axle than the next lower gear...

(sorry for the long explanation)

 

What CMT posted is called a "thrust chart", and it's the definitive tool for determining optimum shift points for maximum acceleration.

Because the torque curve is so flat, upshifting from *any* gear to the next-highest gear, at *any* rpm is going to leave you with less torque at the wheels than you had in the prior gear.

For other cars where the torque falls off faster at higher rpm, it's possible that even though you lose some torque multiplication in the transmission/differential by upshifting, you gain back more than you lose because the torque output of the engine at the new lower rpm will be higher enough to make up for the multiplication loss. This would have shown up on Charlie's chart as adjacent lines crossing.

So in a case like this, the best shift point for maximum acceleration is the engine's redline.