Can we get a longer 7th gear?

[kenwelch]

Originally Posted by bruce.augenstein@comcast.

I have to seriously declare that I just don't get this. I believe BMW has declared that Valvetronic reduces pumping losses, but I don't see how. Can you explain this?

Bruce

These are links that will help you with understanding the valvetronic system. The intake valve opening is used to change engine rpm’s instead of using the throttle plate. With low rpm’s the intake valves open a small amount and with greater throttle the intake valves are opened more. You will find the pumping loss description in the Valvetronic Manual.

BMW Valvetronic Training Manual link:
http://prodcds.bmwuniversity.com/lib...ALVETRONIC.pdf

Newer version Valvetronic used in the BMW N20 engine:
http://f10.5post.com/forums/showthread.php?t=856538

Link including video of valvetronic operation:
http://www.bmwforums.info/general-gu...-what-why.html

[bruce.augenstein@comcast.]

Originally Posted by MrStinky

What don't you get? Just like ITB decreases pumping loss over single traditional TB.

I assume you mean individual throttle bodies by using the term ITB, but just how would those decrease pumping losses. You're still pulling against an almost completely closed throttle plate at cruise.

With Valvetronic, you nudge the intake valve open a smidgeon, so the piston still has to overcome a significant partial vacuum. The restriction just happens at the intake valve instead of the throttle body or bodies.

I couldn't find an answer by reading the manual, either.

Does someone actually know how Valvetronic reduces pumping losses? I would seriously like the answer.

Bruce

[bruce.augenstein@comcast.]

Originally Posted by kenwelch

These are links that will help you with understanding the valvetronic system. The intake valve opening is used to change engine rpm’s instead of using the throttle plate. With low rpm’s the intake valves open a small amount and with greater throttle the intake valves are opened more. You will find the pumping loss description in the Valvetronic Manual.

BMW Valvetronic Training Manual link:
http://prodcds.bmwuniversity.com/lib...ALVETRONIC.pdf

Newer version Valvetronic used in the BMW N20 engine:
http://f10.5post.com/forums/showthread.php?t=856538

Link including video of valvetronic operation:
http://www.bmwforums.info/general-gu...-what-why.html

OK, I appreciate your posting of this information, but still can't find a reference as to exactly how Valvetronic reduces pumping losses. The only reference I find is "By shortening the duration of the intake instead of throttling, pumping losses are reduced...", but that certainly doesn't cover it. No matter what, you're providing a restriction to intake flow, thus forcing the piston to pull down against a partial vacuum. What am I missing?

Thanks.

[kenwelch]

Originally Posted by bruce.augenstein@comcast.

OK, I appreciate your posting of this information, but still can't find a reference as to exactly how Valvetronic reduces pumping losses. The only reference I find is "By shortening the duration of the intake instead of throttling, pumping losses are reduced...", but that certainly doesn't cover it. No matter what, you're providing a restriction to intake flow, thus forcing the piston to pull down against a partial vacuum. What am I missing?

Thanks.

In the Valvetronic Manual (first link provided above) read and study the graphic on page 5 and top of page 6. There is a test next week

1. There is no intake manifold vacuum or minimum only for "crankcase ventilation and evaporative purge systems". In a conventional single throttle body engine you are working against the intake vacuum with each cylinder sucking through the same opening. MUCH less partial vacuum on the valvetronic engine than a conventional engine.

2. Vacuum for power brakes and accessories is provided by a vacuum pump powered by one of the camshafts.

3. With two intake valves, cam timing "overlap", and the benefit of exhaust flow through a tuned exhaust system there is less resistance (pumping loss) in the valvetronic engine shown by the right side yellow section "B" of the graphic on page 5. The conventional engine graphic is on the left side of the page.

4. The documentation is by BMW for training their technicians. They would not have added all the extra hardware if there was no benefit to engine efficiency.

[Craigy]

I would also love a lower 7th gear. And a decently sized fuel tank, preferably 20+ gallons.

IMHO I think the car is severely lacking an overdrive gear. With seven speeds BMW should have used one of them for highway cruising at 80-90. A simple overdrive gear would save dramatically more fuel than the dreadful stop/start system.

I don't think that a low 7th gear would have in any way affected the image and overall performance of this car, and the highway mpg advantage would have been far more dramatic.

As for complaints this is pretty minimal but if I was able to make 1/4 or 1/3 fewer fuel stops in any given year I would be very grateful.

[Edward]

How about if they kept the ratio the same through all gears and simply added a final 8th OD gear that isn't designed to help the car get up to any max speed, but instead there to throw into for fast cruising.

[Craigy]

Originally Posted by Edward

How about if they kept the ratio the same through all gears and simply added a final 8th OD gear that isn't designed to help the car get up to any max speed, but instead there to throw into for fast cruising.

I wouldn't mind that as well. I would imagine there is some size/weight penalty to keep adding gears though... but if they already do 7 I can't see how 8 would be that much more difficult.

[bruce.augenstein@comcast.]

Originally Posted by kenwelch

In the Valvetronic Manual (first link provided above) read and study the graphic on page 5 and top of page 6. There is a test next week

1. There is no intake manifold vacuum or minimum only for "crankcase ventilation and evaporative purge systems". In a conventional single throttle body engine you are working against the intake vacuum with each cylinder sucking through the same opening. MUCH less partial vacuum on the valvetronic engine than a conventional engine.

2. Vacuum for power brakes and accessories is provided by a vacuum pump powered by one of the camshafts.

3. With two intake valves, cam timing "overlap", and the benefit of exhaust flow through a tuned exhaust system there is less resistance (pumping loss) in the valvetronic engine shown by the right side yellow section "B" of the graphic on page 5. The conventional engine graphic is on the left side of the page.

4. The documentation is by BMW for training their technicians. They would not have added all the extra hardware if there was no benefit to engine efficiency.

OK. You've not covered it here, but the "By shortening the duration of the intake..." sentence I quoted a bit earlier finally got through to me. I assumed Valvetronic opened the intake valves a minor amount at cruise, but that is apparently not the case. Except at idle (where it actually does open the valves just a smidgeon) what Valvetronic actually does is open the valve a normal (or similar) amount - much faster than "normal", and then, later in the intake stroke, it closes the intake valves.

The net result is that the piston faces a reduced early vacuum on the intake stroke (because Valvetronic can open the valve really quickly compared to normal cam-lobe operation), and then a more normal high-vacuum condition nearer the end of the intake stroke when Valvetronic closes the valves early. The net is reduced overall average vacuum over the entire intake stroke, with the obvious benefit of reduced overall pumping loss.

This is all possible not strictly because Valvetronic can open the valves a reduced amount, but because it can open the valves more quickly than a normal cam-lobe operation safely can - gleaned from reading all of the publications you've thoughtfully provided. Thanks again.

I know that nobody here has been able to directly explain how Valvetronic precisely reduces pumping losses (including me until now), but does anybody have any problem with the above explanation?

Bruce

[kenwelch]

Originally Posted by bruce.augenstein@comcast.

OK. You've not covered it here, but the "By shortening the duration of the intake..." sentence I quoted a bit earlier finally got through to me. I assumed Valvetronic opened the intake valves a minor amount at cruise, but that is apparently not the case. Except at idle (where it actually does open the valves just a smidgeon) what Valvetronic actually does is open the valve a normal (or similar) amount - much faster than "normal", and then, later in the intake stroke, it closes the intake valves.

The net result is that the piston faces a reduced early vacuum on the intake stroke (because Valvetronic can open the valve really quickly compared to normal cam-lobe operation), and then a more normal high-vacuum condition nearer the end of the intake stroke when Valvetronic closes the valves early. The net is reduced overall average vacuum over the entire intake stroke, with the obvious benefit of reduced overall pumping loss.

This is all possible not strictly because Valvetronic can open the valves a reduced amount, but because it can open the valves more quickly than a normal cam-lobe operation safely can - gleaned from reading all of the publications you've thoughtfully provided. Thanks again.

I know that nobody here has been able to directly explain how Valvetronic precisely reduces pumping losses (including me until now), but does anybody have any problem with the above explanation?

Bruce

Remember also that the valvetronic engine does NOT have intake vacuum like the conventional engine. The piston is NOT sucking on a vacuum chamber (intake manifold) with 18 - 21" of vacuum. The intake is closer to atmospheric pressure so the intake effort of each piston is less.

[kenwelch]

Originally Posted by bruce.augenstein@comcast.

Lastly, do a little reading on pumping losses, would you? On the intake stroke, each piston has to pull down against a significant vacuum at cruise (because the throttle is nearly closed), and that effort robs power from the cylinder that's firing at the time. These losses may account for a 10-15 horsepower loss at cruise (out of the 50-60 you'll need to cruise at 80), meaning you're using fuel to do nothing more than power the next piston on its intake stroke. At full throttle, pumping losses are minimized (perhaps two or three HP), so you're effectively having to feed fewer HP to maintain cruise, thus maximizing fuel economy.
Bruce

You explained pumping loss very well here.
Remember that the valvetronic engine is not having to "pull down against a significant vacuum at cruise" because the throttle plate is nearly fully open.

[M3AG]

Originally Posted by Alex07M3

Yeah but I think the DCT guys have best of both world, shorter gearing for better accel. and taller 7th gear for highway cruising! The only thing they don't have is the fun to drive!

+1

[navybum]

This is one of the few things I would change on this car. I have the 6MT, and the car reaches the limiter in 5th. 6th is only there as a highway gear anyway, it would be nice if it was taller to give quieter, more efficient cruising.

[bruce.augenstein@comcast.]

Originally Posted by kenwelch

Remember also that the valvetronic engine does NOT have intake vacuum like the conventional engine. The piston is NOT sucking on a vacuum chamber (intake manifold) with 18 - 21" of vacuum. The intake is closer to atmospheric pressure so the intake effort of each piston is less.

Yes, I remember that. BMW has not been shy about that particular fact.

[sensi09]

A longer 7th would help on the highway, but would make mpg in the city that much worse. 7th is perfectly usable at say 50mph which you would lose with a longer gear.

[Craigy]

Originally Posted by sensi09

A longer 7th would help on the highway, but would make mpg in the city that much worse. 7th is perfectly usable at say 50mph which you would lose with a longer gear.

Just use 6th then (barely a difference 6th to 7th), or drive faster to take advantage of a longer 7th

[CptSlow]

Originally Posted by Eddien123

You may also correct me if I'm wrong, but I believe the cars with a top gear like that are the Panamera and the Cayenne which are not performance cars (unless you get the turbo models.) Point is, they start as family 4 doors and get reverted to performance cars. My other point was the M3 was a performance car and BMW didn't need to give it good fuel economy they just needed it to be fast.

I'm not an engineer and can't "argue" with the science experts here, but I will say, as a Cayman S owner, and my closest friend a 911 owner, that you are incorrect about the tall 7th gear, at least on PDK equipped cars. I can cruise at 80, at 2100 rpm, and get 31mpg, by shifting to sixth and maintaining the same speed, I see 25mpg at around 3100 rpm. Seventh gear is provided merely as a highly efficient cruising gear. As a matter of fact is certain "sport" modes, the PDK logic will not allow a shift to 7th gear. Top speed of 175mph is possible in either 6th or 7th.

I can't speak about their 6MT.

[Eddien123]

Originally Posted by CptSlow

I'm not an engineer and can't "argue" with the science experts here, but I will say, as a Cayman S owner, and my closest friend a 911 owner, that you are incorrect about the tall 7th gear, at least on PDK equipped cars. I can cruise at 80, at 2100 rpm, and get 31mpg, by shifting to sixth and maintaining the same speed, I see 25mpg at around 3100 rpm. Seventh gear is provided merely as a highly efficient cruising gear. As a matter of fact is certain "sport" modes, the PDK logic will not allow a shift to 7th gear. Top speed of 175mph is possible in either 6th or 7th.

I can't speak about their 6MT.

No i understand but like I said, an engine in a 911 is most definitely strong enough to do that. I was blown away when I saw how low the highway revs were in the cayenne and 911,

[Hujan]

Originally Posted by Craigy

I would also love a lower 7th gear. And a decently sized fuel tank, preferably 20+ gallons.

IMHO I think the car is severely lacking an overdrive gear. With seven speeds BMW should have used one of them for highway cruising at 80-90. A simple overdrive gear would save dramatically more fuel than the dreadful stop/start system.

I don't think that a low 7th gear would have in any way affected the image and overall performance of this car, and the highway mpg advantage would have been far more dramatic.

As for complaints this is pretty minimal but if I was able to make 1/4 or 1/3 fewer fuel stops in any given year I would be very grateful.

Originally Posted by Edward

How about if they kept the ratio the same through all gears and simply added a final 8th OD gear that isn't designed to help the car get up to any max speed, but instead there to throw into for fast cruising.

Either would work for me. I pretty much never use 7th except on the freeway, so I wouldn't mind it a bit taller. I tend to cruise at 85 and with ZCP tires and stock wheels that's around 3,300 RPM, which is about 500 RPM more than ideal, IMO.

Cruising at 85 at 2,800 RPM would be great. Keep 1-6 the same, but make 7 a bit taller. Or keep 1-7 the same but at an 8th, very tall gear for highway. It would be nice.

[CptSlow]

Originally Posted by Eddien123

No i understand but like I said, an engine in a 911 is most definitely strong enough to do that. I was blown away when I saw how low the highway revs were in the cayenne and 911,

I had an E92 M3 for a few years, though, and fail to see the point of why a "cruising" gear wouldn't work on it. JUST for highway cruising.

[pkimM3r]

Who cares. Thats why they have a 328i.

[elitex]

Originally Posted by track_warrior

BMW M responds: "No because race car"

[Eddien123]

Originally Posted by CptSlow

I had an E92 M3 for a few years, though, and fail to see the point of why a "cruising" gear wouldn't work on it. JUST for highway cruising.

Yeah I agree that's odd. I doubt you'll use 7th on a tight circuit. It seems like 1-6 could be high revving track gears and 7th should be for cruising but how can I argue with M? Haha