<sigh>

absolutes in car forums:
1. d!ck measuring
2. auto and manual debates
3. intake and exhaust questions
4. auto and manual debates
5. d!ck measuring

i know that when i grab a stick and row it though gears it doesn't make me feel ghey...wait...what?...

 

Drivetrain losses are difficult to quantify by using dyno graphs. First, there’s too much variation. You can dyno several different 6MT cars and get a lot of variation. Same holds true for 7AT cars. So to make an accurate comparison, you’d actually have to play with the averages. And even that wouldn’t be entirely accurate because there’s also so much variation between actual dynos.

One very accurate way to determine drivetrain losses is something called a “coast down” test. Unfortunately, there don’t seem to be many people who know how to do coast down testing on a dyno.

I’m not sure if you ever heard of the 1999 Mustang Cobra debacle or not, but owners of these cars were screaming that their cars didn’t make the “advertised” HP after running them on the dyno. There was so much variation that nobody knew for sure what kind of HP the cars were averaging. The numbers were all over the place. Well, that’s when coast down testing started to become a very popular way to measure drivetrain losses. When a lot of angry customers are threatening a class-action lawsuit, it becomes very important to know how much HP is “lost” to the drivetrain in order to determine the actual HP output of the engine.

In the end, Ford did acknowledge that the ’99 Cobra was short on HP and they made a few changes during a recall campaign to fix the issue. BTW, all of those cars were manual trans, as an automatic wasn’t offered. But the reason I’m telling you this is because a simple dyno graph doesn’t tell the whole story. There will always be an advantage for MT cars when it comes to drivetrain losses over a conventional automatic transmission vehicle, all else equal.

 

I agree. I went with MT knowing that anytime I want a more of an experience I can whip out the old 76 280z...no powersteering makes you work more

 

No power steering means you work less... except when you're parking.

 

I agree with most of your post although much of it doesn't really apply in this context and I know all about dynos. The whole AT vs MT issue has been hashed out on the forums often and I dont want this to start turning this thread into an AT vs MT debate which often involves people making statements based on antiquated facts, which in my opinion you are doing in your posts. Furthermore that was not the intent of the topic by the OP. Technology has changed since the old power robbing auto transmissions have been made. G and Z owners seen enough of dynos over the past years to know that the differences in loss between the two G transmissions when compared under the same conditions same day same dyno are insignificant and have negligible impact on the performance between them. Performance results both by magazines and by folks at the drag strip indicate no significant differences in performance between the two transmissions. In fact many tests have shown the AT with the advantage. Aftermarket vendors have done tests and have acknowledged the same.

 

I think we're talking about two different things here. The old 'power robbing' automatics are starting to get more gears (noted by the 7-speed auto in the G), which helps offset their inefficiencies versus a manual transmission (which only has 6 speeds in the G). Put 7 speeds (with identical ratios) in a manual transmission G and any gearing advantage the AT has will quickly disappear. Of course I'm assuming ultimate performance, not driver ability. With equal gearing, the true differences would become apparent.

But the fact remains that a conventional automatic transmission will always "rob" more of the engine's power than a manual transmission. Drivetrain losses start with the transmission and in the case of an automatic, the torque converter. No matter what, a fluid coupling will never be as efficient as a direct mechanical coupling. And the only way to accurately measure drivetrain losses on a dyno is via a coastdown test. Has anyone actually posted coastdown test data on the G37?

 

just to add to MSCA's post...automatics like the Zs are fully locked to prevent a lot of the drive train loss as well. so it's the gearing and this feature that make modern autos more efficient....but yes the ole' tq convertor is just that.

now if we're talking about DSGs...that's a different story.

 

I think that we are talking about the same thing- acceleration performance. My only point is that there have already been enough benchmarks to conclude that the two transmissions pretty much run neck and neck in these cars.
With regard to the coupe, from as far back at 2007 when this generation came out, 5ATs and 6MTs have posted posted track times, dynos, head-to-head track races/ dyno comparisons etc and the differences have been so marginal that it is apparently a drivers race. Magazine times have all indicated similar results. The 7AT appears to perform slightly better but even its slight improvement is marginal.

To answer your question about coast down, I'm not sure if anyone on the forums have performed such. But the relative differences between the power to the ground in the transmissions in these cars would typically shows up consistently in dyno comparisons- just like they always did in the previous generation G. Although I wouldn't mind seeing such results but I don't think we need them to prove anything with regard to performance- maybe for fine tuning mods.
What matters most is how the car performance on the track and on the street.

 

Well then I'd have to say that we are definitely not talking about the same thing. I've been talking about drivetrain losses as measured on a dyno and the best way to determine them. You are obviously talking about how each car accelerates (auto or man trans).

Numbers are numbers, nothing more, nothing less. Put the 3.7L engine on an engine dyno and there's nothing to even debate. But put the car on a set of rollers and all of a sudden there are differences due to parasitic losses through different drivetrains.

If you want to talk acceleration, tell me this: Do you think the 7AT has an advantage over the 5AT, all else equal?