Here in Albuquerque, there are two guys that have gone 13.1 with 5-speeds, one car is close to stock, the other has bolt-ons including headers. They both have drag radials. Edit: the guy with headers I think recently went 13.0. My Scat Pack stock with drag radials went 12.7 and also traps 1-2 mph higher. They are both 2011s FWIW. Lots of other guys race their near-stock Challengers here, but they are all slower. Hope that helps.

 

From what I gather, the main reason for the large number of gears in these transmition is fuel economy not acceleration performance. It's part of the equation that lets high horsepower engines meet the government regulations.

For me, even the A5 in my wife's R/T has too many gears. At times, it stumbles a little while trying to decide what gear it wants to be in. I would never go higher if I don't have to.

Jeff

 

Have you driven a new 8spd yet? I took one on a test drive, and it had a much better shift schedule than my current 5spd. It seemed as if it were always in the correct gear. Plus with the 8spd mated to a 3.06 rear, it's geared lower than the previous 5spd with a 3.92 rear gear..win win all around in my book

 

Eric, what brand and size are your drag radials? and I thought the 8A improved everything by .5
Thanks
Moparized

 

I have Nitto 555r's 275/40, and it is very close to a half second, maybe a tenth less...based on my experience anyway.

 

I've had both the A5 and A8, but my A5 was in a 6.1 SRT and the A8 is in a 6.4 so I can't compare power directly. What I can do is tell you the three things where I see the A8 standing out from a performance standpoint. I won't mention better gas mileage due to a taller 8th gear since that's not performance based, but there's that too:

(1) The A8 delivers 30% more torque to the rear wheels in 1st gear (up to about 35 MPH). Notice I said to the rear wheels and not necessarily to the ground because you can't always put that much to the ground without spinning. But, on places like sticky dragstrips, you can get the tires planted by about 3000 RPM if you feather your takeoff on stock tires and when you can get it hooked, you'll have substantially better acceleration out of the hole (again, up to about 32 to 35 MPH).

(2) The A8 ratios keep the 392 in the sweet RPM range. With the A5, I found that there were speeds where mashing the throttle caused a slight bog because you were near the transition point between two gears: so it would pick the higher gear and you'd lose some acceleration. Doesn't happen with the A8 as it just doesn't have those "bog spots".

(3) Shift speed and efficiency: the A8 shifts much faster than the A5. The fact that the A8 can get from one gear to the next faster than the A5 makes up for the fact that there will be more shifts (say in the 1/4 mile) with the A8. In addition, it has been said by SRT engineers that the drivetrain loss on the A8 is closer to 12% compared to 15% to 17% with the A5. I don't know how accurate that number is, but it all goes to being able to have more gears and still be able to perform better than a transmission with fewer gears (and thus fewer shifts).

Now, I've done a lot of searching and browsing of 1/4 mile ET and MPH for 2011 to 2014 392's with the A5 versus the 2015's with the A8. Needless to say, the times and MPH are all over the place. But, one can get a general idea if you look hard enough. With the A5, a "good" 1/4 mile time and MPH was around 12.4 to 12.5 at about 111 to 112 MPH. With the A8, a "good" run seems to be about 12.2 to 12.3 at 113 to 114 MPH. So it appears the A8 (and possibly a few extra horses in the 2015 392) gives you a couple tenths and 1 to 2 MPH. I've seen a 12.1 to 12.2 at 113 or 114 hero run from a stock A5 on DR's. And I've seen an 11.9x at 114 to 115 hero run on the A8, stock save the drag radials. So the numbers seem to translate.

That's my 2 pennies worth.

Mike

 

The A8 would be even quicker if it finished the 1/4 mile in 4th gear.


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The A8 would be even quicker if it finished the 1/4 mile in 4th gear.
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You could always slap it into Manuel Mode when it hits 4th gear...

 

I dunno, I feel like 8 speeds is overkill for a big torquey engine like the 392. Yes the 8 speed offers a performance advantage over the old 5 speed, but it isnt much and it will be a complete drivers race between the two. The gobs of torque the 392 produces has no problem getting the 5 speed in the powerband. Also the 5 speed only has to shift 3 times in the 1/4 mile, while the 8 speed has to shift 5 times. The 8 speed is a great transmission and I'm not trying to bash it at all, it gets more mpg than the 5 speed could only ever hope for. It will also 'feel' more powerful due to an extremely short 1st gear. But from a real world performance standpoint it is only slightly better than the 5 speed in the 1/4 mile.

 

I don't know, I think .3-.4 and 1-2 mph is decent difference. When you are racing side by side and pull someone by a few car lengths over a 10 second span it is a decisive win.

 

I think the 8spd also does down shift rev matching and the 5spd doesn't. That said, I still love my old 5spd.

 

With the efficiency and shift speed of the A8, the performance gain is there, but I wouldn't argue about it not being a big difference in the 1/4 mile. By itself, I think it's a small gain in the 1/4 mile where you are winding out multiple gears. The thing I like most about it is just the way it drives and the extra MPG. I get about a 15% boost in fuel economy: always thought he A5 revved way too high at highway speeds for being married to a big motor.

Performance wise, I really like that it has more gears because it just doesn't matter what speed you mash it: you're gonna get pinned in your seat. The A5 did have some lulls at certain speeds due to the broader gearing. Unfortunately one of them was right where I usually wanted the power most: about 50 MPH when I'm doing 50 in a 60 behind a slow poke and want to pass. The A5 would only drop to the very bottom of 2nd gear in that instance and it took it a few seconds to get going. The A8 completely eliminates the bog zones.

And it also drives more like a stick: the torque converter is always locked up once you're moving. That actually takes some getting used to because when you change pedal positions, the car responds instantly: like it would if you were driving a manual in gear. You don't have that TC "slush" as a buffer like on the A5.

Mike

 

So now the 8 speed is 4 tenths faster than an A5. They just keep getting faster. Why buy a blower when you can change gearboxes.


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8speed has a different floor plan

 

Plus the averages don't show if it's an A5 or m6.Also some of the 12.2 a5 hero runs were on stock tires .
Dad's toy for one.Its not going to be several or a few car links as someone stated for sure.
If anyone's around Waco with a 15 let me know and we will find out.Prarie hill is a good track.

 

If you find some buddy to race I suggest you do it from a rolling star to eliminate the many variables that goes with dig racings

 

Well according to some here, the A8 is 0.4 faster than the A5. And some say the A5 is 0.5 faster than the M6. This means the best an M6 392 can run the quarter in is about 13.2. Problem with this scenario is the facts, and real track times. I think a lot of people hear are FOS. I think an A8 might be 0.1 sec faster than an A5, which might be 0.2 faster than an M6.


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And some say the A5 is 0.5 faster than the M6. This means the best an M6 392 can run the quarter in is about 13.2.

How do you figure? That means the fastest A8 would have to be 12.7. I believe the fastest 2015 M6 time so far has been 12.6 (Woz I believe). Fastest 2015 A8 time is 11.98, backed up by a 12.15 by another member. So the .5 second advantage for the A8 versus M6 seems pretty reasonable given the slips that have been posted.

Mike

 

I say let's have a stock shoutout with real cars and not Fagazine, I mean Magazine drivers. I want to see what the real world shows. I've seen a magazine shoot and test in person and I wouldn't trust anything you read about performance numbers till you see or feel it yourself!

 

I say yes for that.

 

There have been quite a few A5s that ran 12.2 bone stock down to the tires, I think one person even ran a 12.1 bone stock, mexi comes to mind when I think of it. With 1/4 mile times like that, I think the A5 could run 11.8-11.9 with DR.

Also consider the 2015 392 "supposedly" gained 15 hp, which may be part of the reason why the 2015s are running faster than the 2014s. So the A8 may be making less of a difference than people think. Personally, I don't see the A8 being more than .1-.2 tenths quicker than the A5.

 

I certainly couldn't find quite a few stock A5's in the low 12's. Fastest I found was Dads Toy at 12.28 @ 114.2. If you found any faster than that, I'd like to see the thread(s). And the inherent problem with picking out hero runs is you are comparing a 4 year sample size with the A5 versus maybe 8 months with the A8. The vast majority of people with the A8 that don't live in a subtropical climate have not even had the chance to run their cars in cool weather yet. So at this point, I do think it's more accurate to look at what people are commonly running versus trying to pick hero runs: one out of a set of a couple dozen and the other out of a set of hundreds.

Mike

 

I think I remember reading srt8tech got like a 12.23 in positive DA, it's somewhere on the forums. Tried finding it but its hard, lots of posts to go through. And I agree, it will be interesting to see what the A8 can pull off in the coming months and years. What I'm saying is the performance difference between the A8 and the A5 isn't night and day as some people are lead to believe. The A5 is a very good transmission in the 1/4 mile, it's hard to beat only 3 shifts. The main advantage the A8 has over the A5 is fuel economy.

 

Just a point of info...1st gear in either the A5 or A8 is essentially irrelevant on the v8 models. You can't dump full power in 1st and expect the tires will hook. So what you get out of 1st gear is strictly up to the tire capability, rather than the gearing value (assuming you had to feed-in carefully and feather the throttle to get the tires to hook under load). Gearing benefits don't show up until 2nd gear (where you can then put full power down).

Now if it was the v6 model, then you can expect the extra gearing on the A8 to really go to work, including the 1st gear.

Also, if it is really true that the A8 employs the torque convertor lockup clutch for every gear even at high throttle, then that changes the gearing advantages significantly (not necessarily in the A8's favor). Essentially, you would lose all of the convertor multiplication benefits. You would lose *a lot* at the launch in 1st (which may not really matter, since the gear is too aggressive for available traction, anyway...which raises another potential issue...if the tires aren't giving when you hammer it out of the gate, you can expect that that torque convertor clutch to wear out pretty darn soon with that kind of treatment ), and take a smaller hit across the board in the gears thereafter. The 3.08 axle on the A8 would be more like 2.86, compared to the 3.06 on the A5 (it's essentially like a 5-7% torque hit during higher rpm operation, if you aren't exploiting convertor multiplication).

 

Also, if it is really true that the A8 employs the torque convertor lockup clutch for every gear even at high throttle, then that changes the gearing advantages significantly (not necessarily in the A8's favor). Essentially, you would lose all of the convertor multiplication benefits.

I would respectfully disagree with that statement. Much of the advantage of TC multiplication is lost to coupling efficiency as you just can't transfer as much power through a fluid without losing quite a bit to turbulence. Both will have some TC multiplication off the line but with the A8's lower gearing, it can get to higher RPM faster, lock sooner, and be more efficient earlier with the lockup. Simply put, it's better to get your multiplication from gearing than TC slip.

Mike

 

With my old 2012 srt I used to feel that 3rd is too long.

 

I test drove a '14 SRT Core before settling on the '15 Scat. The feel of the A8 sealed the deal for me. The '14 was a great car, I just enjoy the feeling of having no deadspots.

 

Slip is what generates the torque multiplication effect. It's not like you get slip and nothing back. That's the biggest misconception to automatics...thinking the slip is just pure loss. There is a torque boost + you will be at a slightly higher operating point as far as actual hp production. It is essentially like a variable gear reduction stage.

In any event, if it is in direct mechanical drive all of the time, then the 3.08 axle is going to be too tall, just like 3.08 would be too tall an axle ratio for a manual Tremec gearbox. Lock-up makes sense for fuel economy benefits during low load operations. During high throttle for sheer performance...not so much. It's like engaging a taller axle ratio...which means less wheel torque for the gear and less engine hp for the road speed (since the rpm will be slightly lower).

If the clutch is engaging right in the middle of a high throttle event on every single gear, all you're going to end up with is a burnt out clutch over time.

 

Slip is what generates the torque multiplication effect. It's not like you get slip and nothing back. That's the biggest misconception to automatics...thinking the slip is just pure loss. There is a torque boost + you will be at a slightly higher operating point as far as actual hp production. It is essentially like a variable gear reduction stage.

True, but you are going to pay for that multiplication as well. Unlocked, a torque converter will lose between 5% and 10% due to slip even after the coupling point (maximum efficiency will be 90 to 95% at best). So one way to increase performance is to lower first gear, get yourself to higher RPM quicker, and lock the converter to regain that 5% to 10% loss. Letting (more) gears do the work allows the gears to do the multiplication rather than slipping the converter. The TC multiplication is very short anyway: you're not going to get much multiplication (again, 5% to 10%) beyond about 3000 RPM so once you're in gear and up into the shifting rev range, it doesn't make much sense to allow the converter to still slip. You're just losing power to parasitic loss of the fluid drive.

Mike

 

The A8 has a claimed shift time of 160ms. Not sure about the A5, but the average automatic shifts in 250ms.

Just simple math:

160ms x 4 shifts = 640ms

250ms x 2 shifts = 500ms

So, the A5 spends approx. 140ms less time shifting during the 1/4 mile.

However, the superior gear ratios and lower powertrain losses of the A8 prove to make it faster.

I think about 2-3 tenths on average is spot on.

The 2015 cars are still new and haven't seen the best air yet (fall).

If you think that we've see the "not to be beat" record time yet.... your crazy.

 

I'm not sure about your avg shift time for other brand cars but current A6 Mustangs are around 4-500 ms and many owners cannot wait for a tune...BUT, for whatever resson, it doesn't give any concensus shift quality and shift speed has shown better ET's.

Status on your next passes?

 

These are multi-clutch style transmissions. So the time it takes to complete a shift has less relevance than people think. The actual engine load is more or less interleaved from one gear to the next, so there is no point where the engine load to drivetrain drops to zero (which is when shift times would become a concern). If this were a single-clutch design (such as in a conventional manual gearbox), then the shift times would be more important. In that scenario, the amount of shift time is then the amount of time spent "coasting" instead of accelerating (hence, the reasoning to minimize that time).

The modern automatic is more akin to a hand-off from one runner to the next in a relay race...hence, the actual hand-off time (or even "number" of hand-offs) is not all that critical.

 

I'm thinking the TC lockup starts in 4th gear at WOT with these. Good for ET and mph.

 

Yes, upper rpm torque multiplication is less than stall torque multiplication, but mathematically it is still there. It is still having an effect. Plus, the slip means you are at an incrementally higher hp point (via rpm), going into the system. So it all works out in your favor, as if it was a mechanical gear reduction (rather than pure slip w/o any benefits). Parasitic loss in a fluid drive is more an issue during low load situations (that is why it is the best time to engage a lockup clutch). Losses when you are really hammering it...lesser understood. It's not like the turbine design inside modern fluid convertors have stood still in time, either.

It should also be noted that the operation of higher mechanical gear reduction (shorter gears) will also incur higher (but not necessarily "high") frictional losses. So you don't get to sidestep parasitic losses just by going one way instead of the other. In all likelihood, the comparative losses between fluid coupling vs shorter mechanical gearing are closer than you might think (probably a wash).

If you are starting from a baseline of direct mechanical connection, then add 5-7% torque benefit (from broadband convertor multiplication), then add a 7% hp benefit (from an incrementally higher rpm operation point via slip), those things can't be "hurting" when integrated over the course of the run. Nobody's gonna care if you used an extra tenth of a gallon of fuel to do it.

 

I wonder if those paddles

are as fast as letting it shift itself. I've used paddles before in a BMW. It was not the same to me.


When people ask if they can drive my car, I tell them its a manual. They lose interest.


If I was still drag racing, I'd consider the A8. I just don't have the time.

 

As far as gearing, torque converters, multiplication, etc. I agree it's all going to basically be a wash among comparisons, particularly once you reach the first gear shift. A little bit of TC multiplication might help (given the same gearing) before you shift, but it's also going to cause you to have to shift to the next gear sooner, which drops the torque multiplication significantly. It all comes out in the wash one way or another.

On the number of shifts in the 1/4 mile, you're going to reach the rev limiter in 4th before you can cross, so no point in putting it in manual mode when you hit 4th gear... you're just going to bounce off the limiter 100 feet or so before the finish. If you want to eliminate a shift, just take off in second gear in manual mode and once you reach about 4000 RPM, push the stick over to the right to auto mode and let it do 2-3, 3-4, and 4-5 automatically, giving you 3 total shifts in the 1/4 instead of 4.

Edit: Forgot to say... referencing a prior post, neither the A5 nor the A8 is dual clutch. The A8 shifts as fast as some dual clutch applications but if you look up our A8, it's not dual clutch.

Mike

 

Edit: Forgot to say... referencing a prior post, neither the A5 nor the A8 is dual clutch. The A8 shifts as fast as some dual clutch applications but if you look up our A8, it's not dual clutch.

Mike

I never said it was. It is, however, a multi-clutch pack design (as are probably all modern automatics). That is where the hand-off of shifts first came to reality. People think that is only something a dct can do, but that is only the first manual-style gearbox that people became aware of that strategy. Multi-clutch style automatics have been doing it all along. That is exactly what you want to take advantage of, when you have multiple (and independently-acting) clutch devices in the design (especially when you can precisely control/coordinate them with computerized controls and electric solenoids).

If you have any doubts, do some research on data logs showing road speed (and throttle) during shift events on automatics vs manuals. You'll see a very interesting difference (the distinction of interleaving engine load in a hand-off strategy vs steps that are handled more in a sequential manner).

 

I have always been curious on how the 8-spd would respond (positive or negative) to a 2nd gear launch. With the 3.08 axle, I suspect the gearing might be advantageous in that scenario. Of course, I had that thought based on the premise that torque multiplication in the convertor would be in-play. If it is not, then that goes out the window. If you have a bunch of low end torque (as in a HC engine, for example) and limited traction, seems like the 2nd gear ratio would be a good "1st gear" to launch, assuming the 8-spd and engine controls allows for those sorts of antics.

 

Would be interesting to get some TC lockup data but I don't think my DashHawk can read that parameter on a 2015. It's still unlocked on the line and up to a certain speed, but after a certain speed (say 15 MPH), I believe it stays locked based on my own experience and interviews I've seen where Tim Kuniskis basically said the same thing. If you're at the track and you're lucky enough to get it hooked and to the floor before about 3000 RPM in first gear (sometimes I can), you can actually feel it lock midway through first gear. Then when you're driving around, even at speeds of say 30 MPH, you can tell it's locked because you can put it in any gear at any RPM, mash it, and you can see that there's no "slack" in the RPM. You can also feel that it is a direct connection even when driving slowly through a parking lot.

Mike

 

Here is what I ran on Street tires with my 2013 Charger SRT8 A5. 12.04@117mph

 

I guess the A8's can run 11.64


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