Auto vs. manual throttle response/rev speed...

[ecrabb]

OK, I've asked about the "sluggishness" of my ZHP throttle in another thread (http://www.zhpmafia.com/forums/showthread.php?16249-Throttle-hesitation). To recap, what I'm referring to is sitting in the car at idle, stabbing the throttle throttle, and the response is slow to non-existant... I stab the throttle, and I can hear air in the throttle body, it sounds and feels like the ECU is tilling the engine to rev, and there's fuel and air, and the RPM's go up some - just not much. The best metaphor I can think of is that the engine is connected to a big, heavy flywheel... It's like mass/inertia is keeping the engine from revving.

In that old thread, pretty much everybody unanimously agreed it was the crappy fly-by-wire throttle map/response, and that a Shark Injector, SprintBooster, or other tune with throttle remapping would correct the issue. I stored it away in my data bank and wrote it off for after I have my wheels and tires redone this spring. Important stuff first, then on to the really fun stuff.

Fast forward to a couple of nights ago. I had to restart my wife's E83 X3 in the garage and shut it down, so I revved it up a little for fun. Wow! Not only is it night and day, but the X3 revs like a frickin' F1 car compared to my ZHP! I mean, the difference is incredible. Now, the X3 is an '07 LCI with the N52B30, so a totally different engine, and no doubt BMW improved the throttle response between '04 and '07. Still, should they be THAT different?

So, I started thinking... The X3 is an automatic, so then I started wondering about flywheels. Because that's what it seems like... Like my ZHP has a 100-pound flywheel and the X3 has like a 50-pound flywheel. I know there's a big difference between stock and performance flywheels, and that one of the main benefits of a light-weight flywheel is throttle response and faster acceleration. I looked it up, and our stock dual-miss flywheel is 25 pounds, while a lightweight aluminum flywheel is only 10 pounds.

So... Then I started wondering... Is there a big difference between flywheels on autos and sticks on our cars? Does anybody have significant seat time in both auto and 6MT ZHP to know if the throttle response is different between the two?

Cheers,
SC

[terraphantm]

I noticed the same thing when driving my mom's E46 330xi compared to my ZHP back in the day. What I can tell you is that the auotmatics and manuals have the same software, so they use the same throttle curves (granted there may be some maps that are only used in auto mode and vice versa).

Your instinct about the flywheel is correct. Since automatics have a torque converter, they don't have a flywheel in the traditional sense. They just have a flex plate that doesn't weigh much (< 10 lbs). Most manuals have flywheels around 25-30lbs. You can install a lighter weight flywheel and get some of that off-idle throttle response back, but then your clutch will engage much less smoothly. Also, remember that this really only applies when you're in neutral. When the cars are in motion, the drag that results from the torque converter and driveline will make the automatic more sluggish overall.

With regards to the N52 specifically, even in manual guise, that thing will probably have more responsive throttle than the M54. Valvetronic allows for the valve lift to be controlled directly -- so there are even less pumping losses than an ITB-equipped car.

[ecrabb]

Thanks! Glad I wasn't totally out to lunch.

Definitely want to do Shark Injector, and if I decide to keep this car long-term, I think an LSD and lighter flywheel would both be on the to-do list.

Cheers,
SC

[BMWCurves]

I don't know much about lightweight flywheels, but I have heard that you may experience more clutch/gear chatter at idle. Just something to consider.

Some info from UUC: http://www.uucmotorwerks.com/flywheel/gear_rattle.htm

[az3579]

I don't know much about lightweight flywheels, but I have heard that you may experience more clutch/gear chatter at idle. Just something to consider.

Some info from UUC: http://www.uucmotorwerks.com/flywheel/gear_rattle.htm
Yes. The chatter is usually very noticeable and is audible when the clutch pedal is not pressed and the transmission in neutral. Otherwise, you don't hear it when the pedal is pressed or if the car is moving in gear. I used to get people asking me "what's wrong with your car?" at stoplights, which was amusing at times.

I absolutely loved the performance of my E30 with the lightweight flywheel. It revved VERY quickly, and made rev-matches a lot faster. It accelerated faster due to its eagerness to rev. If you don't mind the chatter, then this is an excellent performance upgrade.

sent from my Droid Turbo

[ecrabb]

Yeah, I knew they chattered, but then my OE clutch chatters a little. How much worse on a 1-10 scale is it?

Mine is certainly noticeable sitting in my driveway, though it probably wouldn't be sitting in traffic.

SC

[az3579]

Yeah, I knew they chattered, but then my OE clutch chatters a little. How much worse on a 1-10 scale is it?

Mine is certainly noticeable sitting in my driveway, though it probably wouldn't be sitting in traffic.

SC
Where my ZHP chatters at a level of 1 (can't be heard from the outside but only from the inside - barely), my E30 chattered probably at about 5-7, depending on whether it was loud or quiet that day.

sent from my Droid Turbo

[Simmsled]

Drive a 99 323i or 328i with cable-action throttle. Feels like freaking lightning in comparison to ZHP drive by wire thunder.

[KevinC]

Sharking my ZHP improved the throttle response A TON. It now feels like an old school non-drive-by-wire car. Sharking the M5 had an even more dramatic effect, as it employs euro fuel mapping, which is apparently a mess on the US-spec M5. Result is it's a ton easier to drive smoothly.

I wholeheartedly recommend Sharking a ZHP.. not for alleged power gains, but for greatly improved drivability and responsiveness.

[ecrabb]

As always, great feedback, guys! Clearly, I just need to shut up and get the throttle remapped. Thanks!!!

SC

[BMWCurves]

Sharking my ZHP improved the throttle response A TON. It now feels like an old school non-drive-by-wire car. Sharking the M5 had an even more dramatic effect, as it employs euro fuel mapping, which is apparently a mess on the US-spec M5. Result is it's a ton easier to drive smoothly.

I wholeheartedly recommend Sharking a ZHP.. not for alleged power gains, but for greatly improved drivability and responsiveness.

I can't say I felt much of an improvement with my Shark tune. There were little improvements here and there, but it was not night and day for me. Still, I'm glad I got it, and glad it worked out well for you!

[az3579]

Sharking my ZHP improved the throttle response A TON. It now feels like an old school non-drive-by-wire car. Sharking the M5 had an even more dramatic effect, as it employs euro fuel mapping, which is apparently a mess on the US-spec M5. Result is it's a ton easier to drive smoothly.

I wholeheartedly recommend Sharking a ZHP.. not for alleged power gains, but for greatly improved drivability and responsiveness.

Interesting. I have to agree with:


I can't say I felt much of an improvement with my Shark tune. There were little improvements here and there, but it was not night and day for me. Still, I'm glad I got it, and glad it worked out well for you!

I didn't notice a huge difference either. The changes were very minor in my case as well. I wonder if a proper, custom tune would improve it by a significant amount... hmm...

[BMWCurves]

I didn't notice a huge difference either. The changes were very minor in my case as well. I wonder if a proper, custom tune would improve it by a significant amount... hmm...

Agreed, although I've always assumed that you can't really coax that much out NA engine by tuning alone.

[ecrabb]

Agreed, although I've always assumed that you can't really coax that much out NA engine by tuning alone.

It really depends how much the original design left on the table.

With some turbo cars with a conservative program, all a tune has to do is bump the boost a couple PSI, tweak the air/fuel, add a touch of advance, and you can pick up 30, 40, or more HP, at the expense of a little long-term reliability and having to absolutely burn only premium or risk damage.

Modern naturally-aspirated designs typically have much less headroom in them from the manufacturer.

I wonder if some of the variability in impressions on the Shark Injector is what adaptations people had before they sharked. If you had some conservative adaptations, and sharked, you might really feel like you really got some pep. If you had a pretty aggressive adaptation, then sharked, then you probably wouldn't notice much beyond the throttle map.

I also wonder if some of the variability is the auto/6mt differences. From my reading, auto guys probably notice even less improvement.

Cheers,
SC

[BMWCurves]

Yup! That's what I meant by NA (naturally aspirated).

[az3579]

Agreed, although I've always assumed that you can't really coax that much out NA engine by tuning alone.

I wasn't referring to power, since I know there's nothing to really be had in that department. It was a thought based purely on throttle pedal response.

[KevinC]

The main difference Sharking caused for me was the throttle tip-in response - any power gain is not really noticeable. But that one improvement was well worth the cost of admission for me. It's really a big improvement.