Jsilvester81

Stumbled across this and old school still has some revalence.

M7's don't get credit for straight line performance as the A8 does.

Both trannies are great but this A great explanation for why after 60mph both car pull the same through the 1/4. Obviously the A8 wins bc of its superior launch.

Food for thought.

Jsilvester81

Very respectful partisan repsponse deleted????

Chonger

I would say the differences in aero packages have more impact on straight line acceleration than whether the car is an A8 or M7, especially at higher speeds.

BWFitz

That's like claiming the phase of the moon is also a factor. The Aero package doesn't come into play until you're well north of 100.

davepl

Automatics deliver less net HP to the rear wheels due to drivetrain losses. They still manage to out-accelerate the M7 due to (initially) torque multiplication at low RPM and (subsequently) much faster shifts at WOT.

I doubt the aero is much of a factor until fairly significant speeds, but top speed runs would almost certainly go to the M7. So it's not the "slow one" for top speeds.

Faster? M7
Quicker? A8

BooSSted

You'll start seeing a difference in stage 1 - 3 aero ~140 mph ...

Chonger

The aero package is still worth a couple MPH in the 1/4 mile which is noticeable. At that point your still only traveling around 126-130. It only increases at higher speeds.

If you race 2 cars all equal with different aero packages the stage 1 traps faster after the 1/4 mile.

The March 2016 R&T issue tested several high performance cars together. One was an A8 base aero and it did almost 133 in the 1/4 mile. They specifically talked about the aero package in the article. Same car, same day, same driver, same conditions, different aero package, the car would not have had the same trap speed.

dar02081961

I believe you are correct Sir. I am not sure where the drag starts to make an appreciable difference for the 2 cars. But folks say they have seen differences in gas mileage for the different stages at highway speeds. Folks also say they can tell the difference in down force between the stages at speeds as low as 80 mph. So I think a safe assumption would be the aero makes a difference at speeds above 80ish mph.

In the 1/4 mile you are looking at 6-8 seconds above 80 mph by the time you get to the 1/4 mile mark. Probably not enough time for a big difference to show. Or said another way, the difference may be so small that it is in the "statistical noise" of standard deviation.

I would guess the difference in a 1/4 mile trap for the stage 1 vs the stage 3 would be 1 mph maybe 2 mph max.

For longer runs 1/2 or 1 mile, well that's another entire discussion.

dar02081961

Dave here is a piece I wrote about 2 years ago when this discussion came up. I have since studied it further and broken down the percentages of time each transmission is at an advantage for the 50 mph to 170 mph run. Not included here. Anyway, it shows that where the race starts (0-170 mph) will determine which transmission will be at the advantage. Like anything else in life nobody wins all of the time.

"The A8 has advantages in certain areas of the acceleration curve. It also has the advantage of shifting a bit quicker.

However the A8 has the disadvantage of having a higher percentage of drive train loss.

The A8 is quicker in the 1/4 due to the gearing advantage in first which gets it off the line.

If you look at the gearing you will find the A8's only clear advantage is from a standstill. Or said another way there are periods during the acceleration curve where the A8 has less torque multiplication than a M7. For example when the A8 shifts to 2nd at 45mph (redline) the M7 is still in first. From 45 mph until about 68 mph the M7 has the gearing advantage. AND this advantage is greater because of less drive train loss for the M7.

Also the A8 makes 3 shifts from 0-125 mph while the M7 only needs 2. Yes the A8 shifts quicker but it shifts more often which takes time.
So from a roll in the real world (at the speeds a roll on is likely to happen) the A8 advantage may not be what many folk think it is. And above 125mph the M7 holds the advantage until about 150mph.
Then its A8 and back and forth until max speed.

From a 50 mph roll on the A8 would have the theoretical advantage because the M7 can’t go back to first. I say theoretical because it’s hard to quantify the momentum the M7 would gain from a no lift down shift to 2nd vs the A8 automatic down shift to 2nd. (Ok I could do it but my head already hurts)

Regardless the A8's advantage is short lived because the A8 shifts to 3rd at 71 mph while the M7 can hold second until 95 mph.

So the A8 pulls off from 50 until it shifts at 71 mph, where it losses time (however long it takes to shift), then it losses hp (gearing, 3rd vs 2nd) and it constantly losses hp due to drive train loss. So the M7 should close some if not all of the gap.

At 95 mph when the M7 shifts to 3rd the advantage may go back to the A8 until 102 mph (due to time for the M7 to shift and gearing). But there may not be time for it to show much because of power train loss and the short (7 mph) time span the advantage is applied.

At 102 mph the A8 losses time from the 3-4 shift. From 102 mph all the way to 126 mph the M7 has 2 advantages. Gearing, and less drive train loss. If there is any gap at this point the M7 will close it and likely begin to pull.

At 126 mph when they both shift, the A8 will my close for a split second due to the quicker shift vs the M7. However after the shift is completed the M7 continues the hp advantage it has held (gearing AND drivetrain loss) since 102 mph all the way to 155 mph when it shifts into an acceleration killing 5th. The A8 will arrest the pull and begin closing the gap until its forced to shift at 170 mph. Its doubtful the A8 will make up all of the gap the M7 has been creating since 102ish mph in the next 15 mph. I suppose it could but some of its gearing advantage from 155-170 is negated by drive train loss.
So as you can see after we get rolling, the A8 advantage aint always what it’s cracked up to be."

SnowyATX

Left side of the road, drag strip or another country? : )

Chonger

Yes........most races are not straight up 1/4 mile drag races. If racing from a roll or from a stop to 160 or so the difference would be really noticeable, probably 2-4 car lengths which goes back to my original comment about it being a big factor.

Sorry didn't mean to hijack the thread it was supposed to be about the A8 vs. M7.

3 Z06ZR1

The Auto wins the 60 ft from the 10.99 over all low gear vs the 7.83
over all low of the M7. 1/4 is all about the 60ft.
Rolling in 2nd up my money is on the M7.

Z0HS1CK

I don't know but what's up with the A8's 4-5 shift?

It falls flat on it's face. I forgot which video i watched and the test driver said the same thing. He said, "yeah right about here..........yup falls right on it's face"..

LOL i gotta find that video.

2017ZO6

Come on guys we all know the A8 is faster from a roll or stop. How many of us can shift like a pro. Slim amount.

2017ZO6

How many guys on Street Otlaws are running a manual. The answer is zero.

Z0HS1CK

Um who cares about that show?

Those are dedicated drag cars. I mean christ sometimes they trailer the car to the drag spot, race, then trailer it back home.

We all know auto is good for drag.

Isn't the Z amazing in corners? And the A8's are more prone to overheating at those types of racing?

No gracias.

Warp Factor

Yup.

Ltrain925

there was a member that tested a stage 3 step a8 z06 vs a stage 1 m7 z06, from 45mph roll or something to 160mph the stage 1 was ahead by 4-5 car lengths and the stage 1 was a m7. All cars were stock, there's a video of it. I can say for sure my stage 3 areo without the center wickerbill feels like a wind brake at 140mph when I shift into nutural and let it roll LOL.

BEZ06

My 2016 M7 accelerates nicely in 5th right up to the redline. You can see in the video that the M7 pulls strong until I need to brake down to turn into the infield.

I have shifted to 6th coming out of NASCAR Turn4 and it does continue to accelerate, but much less than when it's in 5th.

In the video I'm running Stage 1-1/2 aero - Stage 2 front splitter end plates, and Stage 1 rear spoiler extensions.

I've got full Stage 3 on it right now from running VIR last month. I'll be running Daytona again at the Performance Driving Group HPDE Oct 6-8, and I may leave the Stage 3 on for the first day just to see what difference there might be.

davepl

Someone "rolls up on" me and I'll wait for them at the next light. I don't roll race, because I'm not 14 or a trust fund baby. Not that you are, I didn't mean that. Unless you roll race ;-)