ACR developers talk tech

[JPL]

Found this article from 2008, great read, sorry if it's a repost.

https://www.autoweek.com/news/a20344...ers-talk-tech/

[SA Heat]

Found this article from 2008, great read, sorry if it's a repost.

https://www.autoweek.com/news/a20344...ers-talk-tech/

Thanks for posting that....had never seen it until now. Lots of good info in there. One thing I've never seen specifically mentioned before was "The panel's actually three or four feet deep and the full width of the car, and there are seven different kick-ups that diffuse the air to help generate front downforce." Interesting.

[Cap'n Hook]

Nice read, thanks

[JonB ~ PartsRack]

Sticky-Worthy Indeed. Rare insights from Mike S.

[Steve M]

Before allowing a few hot laps on a cold December day at Willow Springs raceway, three key members of Dodge's SRT development team talked about the new Dodge Viper SRT10 American Club Racer. Their unscripted remarks have been slightly edited and condensed.

Herb Helbig, senior manager of SRT Vehicle Dynamics. He's also known as "the Grail Keeper of the Viper":

What you've got to understand is that Mike (Shinedling) and Matt (Bejnarowicz) and a couple other guys who aren't here, such as (Vehicle Dynamics Supervisor) Erich Heuschele, formed the nucleus of a skunkworks team within a skunkworks. It was these guys, along with Erich, who came up with the idea (of the ACR).

We've had so many people ask us, as soon as the '08 car came out, "When are you going to do an ACR version of it?" Because they had become accustomed to us doing that kind of thing.

Frankly we didn't really have an idea, very much, about doing an ACR as the '08 car was coming along. These guys came to me and said, "We need to do it."

I said, "OK, let's get the wish list together. Figure out what the purpose of the car is going to be and then let's get after it."

Matt did all the suspension development and handling development in conjunction with Mike, who did all of the aerodynamic and bodywork activity, as well as kind of managing the entire program. (They) figured out what roles needed to be done inside the team that was working on Caliber SRT4s and 300 SRT8s, and these guys took on the added responsibility to bring this car to life.

I think what's unique about it is these guys have such a passion for what they're doing, they understand what they want to do, and then you get out of their way because whatever it takes, it gets done, whether it's working on vacation or holidays or whatever. They do it because they know it needs to get done, to get the car to be just the way we want it.

(In a moment each will) talk about their areas of expertise. Matt's going to cover chassis, ride and handling and brakes; Mike's going to cover the body, the aerodynamics and why they work so well together. This car has fearsome downforce.

When they're done I'll come back to the purpose of the car, and why it doesn't have any more horsepower than it already has--of course, 600 is pretty significant when it comes to the horsepower scale.

Let me talk a little bit about the powertrain. The ACR has an identical powertrain to the base car, 'the 08 Viper. So it's got the brand new, variable valve timing, all-aluminum V10; 600 horsepower, 560 lb-ft of torque.

Because of the engine's brute force, we had to beef up the rest of the drivetrain (on all 2008 Vipers), so it goes like this: Stuck on the back of the motor, instead of the big, single-plate clutch, is now a smaller-diameter, dual-plate, dual-disc clutch that reduces our rotating inertia by about 18 percent. So throttle response is pretty damn good.

We backed that up with a modified and improved T6060 Tremec 6-speed manual transmission. It's a double-overdrive manual gearbox. What's unique about it is that we changed the synchronizers in first and second from a double cone to a triple cone synchronizer; it gives really nice first-second shift feel to the car.

The gears are cut wider to take the torque. They actually have a 10-percent wider gear face on 'em to manage the additional torque.

And then the axle is basically the same architecture, but it's got a brand new differential in it. We had what was called a Hydro-Lok in the previous generation car--which was the '06. We didn't have an '07 model year, we went from '06, ran that long and then we went to '08.

This car has what's called a Visco-Lok. What makes this really unique is that it has its own sump that it uses to generate the hydraulic pressure that brings the clutches to bear when the axle goes into differential activity. This is much more precise, it's much more progressive, and it allows you to put the power down much more easily coming out of the turns.

The older differential used the actual sump that was in the axle, and sometimes it would take a few milliseconds to prime--very short, but it was enough that you'd spin up the inside wheel and then when the clutch would come on it would upset the car, because it was a really abrupt engagement. The Visco-Lock is not like that, it's a real improvement.

So drivetrain's basically carryover from the '08 car.

We decided that we were not going to be able to do anything in the horsepower end for the ACR for the simple reason it would have meant recertification, and (that's) a big deal. If you added all the time and all the work and all the calibration activity that's required, it's probably in the millions of dollars in terms of resources for the company.

So with that, I want to hand it over to Matt, who is going to take you through ride, handling and the brakes on the car.

Matt Bejnarowicz, supervisor for Viper ACR chassis development:

I'll start with the tires and kind of work inboard. For '08 the Viper got new tires, Michelin Pilot Sport. It's an outstanding tire, but we wanted to figure out how to take it to the next level. The answer for us was to go to a street-legal race tire and that's why we have the Michelin Pilot Sport Cup tires standard on all ACRs.

We went larger in front, up to a 295 front tire (vs. 275), and the rear maintains its 345 width, mainly because that' s the largest that Michelin could possibly build us within their tooling restrictions.

So the grip is phenomenal. It's suited for the race track and of course it's street-legal, so you can drive it to the track and drive it back home.

The tires are mounted on a lightweight wheel. We call it the Sidewinder wheel. It's a forged aluminum, one-piece wheel. It's optimized for race stiffness as well as weight, and the wheels alone take 30 pounds out of the weight of the car. That's what we call a triple-header--it's vehicle mass, it's unsprung mass and it's rotating mass. So in terms of bang for your buck in taking weight out of the car, it's the absolute best place to take it.

The 2008 Vipers have phenomenal brakes, so how do you raise the bar up on that? Well, we've got two-piece brake rotors on these. We kind of searched around the field and looked for two-piece rotor technologies, and we went to StopTech rotors for one specific reason: They have a patented design on their cooling. It's a curved-fin rotor, and they're able to maintain our existing thermal requirements and take significant weight out of the rotor.

It's an aluminum hat with a curve-fin steel ring … and the rotors have six slots per face that also help reduce fade.

The result is another 30 pounds out of the vehicle and it's another triple-header--it's vehicle mass, unsprung mass and rotating inertia. So we're able to exceed the braking on our 2008 car and drop weight and still keep our thermal requirements.

The brake bias is electronically adjusted automatically. The car comes standard with electronic brake distribution as well as ABS, so it's constantly adjusted as you're in your stop so you get optimal grip with the tires.

So we've got great grip, less weight, great brakes. Mike'll get into the monster aerodynamics that we put in the car, but it all kind of comes together at the suspension, so you need a suspension that can make use of that grip, control the chassis and deal with the aerodynamics that are on the car.

For that we chose KW Suspension. We have a race level damper in the car. It's a double-adjustable monotube aluminum damper. It's compression- and rebound-adjustable as well as ride height-adjustable. It comes with a standard 60-mm race spring, so if the customer wanted to commit his car more to track use he could also swap that out.

The dampers have 14 positions, so you can dial it back for your soft setting when you're driving to the track, you crank up your dampers for your best time, and then bring it back home.

They're manual adjustments, just like all the race dampers. It depends on the ride height, you might have to jack up the car to raise the ride heights, but everything's got knobs, there are no tools involved. In the front you can just lie under the car and grab the knob and twist it. We wanted to make sure you could adjust the dampers without removing the wheels.

This suspension is going to be proprietary to us. When we went looking around for dampers that were suitable for the car, we didn't find one. We went to KW Suspension mostly because of their background and because of their abilities. They have multiple Nurburgring 24-hour victories in Vipers and they're very high-performance company, especially in Europe.

We went and looked at their facilities and their abilities and chose them as the damper supplier that could make a completely new damper for this car, and that's what they did. It was a long road, but they have come out with a phenomenal product.

Mopar might pick it up for the Viper aftermarket, but it's going to be proprietary to Chrysler.

As I said, it's got tons of grip and tons of aero, so the spring rates we wound up with on the car are more than double what a normal Viper comes with.

The car comes with a stiffer front anti-roll bar, about 20 to 30 percent stiffer. That was, again, to get the balance and to get the roll stiffness where we needed it. The sway bars are not adjustable and they're single-rate.

By the time you get everything set and done you've got a pretty stiff platform.

The car you're going to be driving today is set lower than the normal ride height [which is about 4 inches]. I dropped the front by 28 mm, so a little over an inch. The rear is lowered less, to put some rake in the car. We will recommend that a customer not go lower or you start getting too much jounce rubber contact.

We will supply a setup manual.

You know, every Viper on the assembly line goes through bump steer adjustment using what we call the Viper Alignment Machine. It cost $500,000. It clamps the frame in place, then it cycles the suspension through its full travel, measures toe patterns, also the rear caster, and tells the worker what shims to install.

Now Mike will talk about the aerodynamics.

Mike Shinedling, program manager for the Viper ACR:

For starters, when we were going through the '08 development, by that point we knew that we were going to do the ACR and we put a feature up front on the hood to help us out with our aerodynamic setup. We moved the louvers forward and increased the size, and that was to help us to generate a forward balance-shift in the aerodynamics.

Herb Helbig: Let me just interrupt for a sec. That was a big deal for us because we tried to do that in '06 and the design office, which was run by a different group in those days, fought us tooth and nail. That actually goes back to 2003. They thought the car looked better with the louvers at the rear of the hood. We fought real hard and lost the battle in that case to form vs. function.

So with guys like (design vice president) Ralph Gilles in our product design office, he gets what we're after. He understands how to make that special blend of getting the right look and getting the aerodynamics. We allowed the function now to lead the form of the car--and singularly, everybody thinks the car looks terrific with the new hood on it.

Mike Shinedling: When we started out our brainstorming session for the ACR, we knew we wanted to add an aerodynamic enhancement. The Viper starts out as a very good platform aerodynamically. It actually generates downforce. The base Viper Coupe generates about 100 pounds of downforce at 150 mph, which is a good benchmark for sports cars, many of which create lift at speed.

So we had a good starting point and we originally started talking about some small enhancements which maybe take that to 150 or 200 pounds. But we wanted something that would be a significant change on the race track, something that a driver would notice and would really enhance the grip. So we decided to add a rear wing to the car.

We knew that this was going to give us a big leap, so we set an aggressive downforce target, and that was 1000 pounds of downforce at 150 mph.

In doing that, we knew we didn't want to just lump all that 1000 pounds on the rear wing because that wouldn't be a good balance for the race track. We knew we needed a good harmony between the front and rear.

That meant having a splitter up front. What you see of the splitter is actually a small percentage of the whole panel. The panel's actually three or four feet deep and the full width of the car, and there are seven different kick-ups that diffuse the air to help generate front downforce.

The splitter and the wing are made out of autoclave carbon fiber. They use the latest technology in clear coat protection to limit UV degradation of the material.

When we got into the wind tunnel, we found that in order to meet our balance targets the splitter had to increase the front overhang of the car, and given the Federal bumper requirements we knew this was going to be a challenge.

So the car is delivered with a street-legal setup. We call it the "fanged geometry," since the splitter kind of looks like it has fangs. We scalloped the splitter's center to allow us to meet these bumper regulations, and it also helps the customer get over speed bumps and approach angles and it keeps the nose of the splitter away from the parking curbs.

The track extension (a removable center section of splitter) is included with the car. It looks like a small piece. It's about a 4-inch increase in overhang, but it actually increases the front downforce by a third.

After all of this work with the splitter, we still weren't quite at our 1000-pound target, so we took a lesson learned from the GTSR program (for ALMS and other racing) and we began working with dive plane geometry on the front fascia. These actually provide another 20 to 25 percent more front downforce.

It generates downforce in two ways. The surface itself is an aerodynamic plane which pushes down, but then the geometry of the dive plane creates a vortex behind it which helps extract air out of the front wheel well. That also helps brake cooling and helps push the car down at speed.

The rear wing is the most dramatic aero element on the car. It's also pre-preg autoclave carbon fiber, and it's seven-position adjustable. But it will come from the factory locked in a set position, and I think we would recommend that only the most serious customers would make any adjustments to that, since it is a pretty powerful aerodynamic element.

It's going to be locked with solid aluminum rivets; the test cars here all have adjustable fasteners because they're development vehicles.

The wing is set in the relatively high leading edge position. We wanted to have the other adjustable positions to be more on increasing the rear balance, because as you increase rear downforce you increase understeer, generally. We didn't want to have it set up to where the customer could make the car loose and increase the oversteer, we wanted it to be safe. Err on the side of safety.

It's set at a nice track balance, once the track extension is in place.

There are a couple positions up, and the rest of the positions are down. We're still toying with whether it's position two or three that we're going to ship the car at.

We're still doing the final aerodynamic tuning. We did play a little bit with that rear lip that you see on the rear edge, the Gurney lip. That will be a little bit different in production as well.

In a nutshell, what we wanted to do with the 2008 Viper ACR was to bring big aerodynamics to the sports car world--kind of in the same way that the original Viper brought big horsepower. It's really going to offer our customers a thrilling experience at the track, something that we think is unique to the factory sports car setup.

And a significant percentage of our customers do track their cars. We've had a lot of good feedback about the car. In fact we were blown away at the response for those track rats that have gasoline in their veins. They can't wait to get the car.

Matt Bejnarowicz: One more comment on the wing adjustment is that we're making our 1000-pound downforce target at the moderate angle. So if the customer were to drop his wing leading edge down you're going to gain even more downforce.

[Steve M]

Question: Would removing the radiator exit grilles increase front downforce?

Mike Shinedling: It actually does, a little bit. We toyed with doing that early on in the program because it's added weight as well. But it wasn't significant enough. It exposes so much underhood hardware. We didn't want people messing with the car, you know, in the parking lot. You can almost take the oil cap off the engine.

Herb Helbig: It wasn't a battle worth fighting. We got 98 percent of what we wanted by moving the louvers to the front. Taking the grilles out, we'll let customers do that on their own.

Mike Shinedling: The front splitter is supported at the leading edge by two stainless steel cables, and those actually have some adjustment capability as well. There's a turnbuckle feature so owners can drop the splitter down a little bit and that will give them more front downforce.

And all told, the aerodynamics that we added to the car were on a fairly efficient basis. The drag did of course increase, but we added downforce at a ratio of seven pounds of downforce for every one pound of drag. That's a pretty good number. Most professional racing teams are looking for a minimum of a 3:1 ratio.

As far as weight, we knew we wanted to take as much weight out of the car as possible, and Matt talked about the most significant change, which is the brake rotors and the wheels. But we went after every little piece we could. The foglamps are deleted on every ACR and replaced with an acrylic closeout panel.

In fact we got a little bit crazy--we actually deleted the side badges that say Viper and we replaced it with the ACR sticker.

Question: Did you measure the drag difference?

Mike Shinedling: No, it's more a symbolic change, I think.

Then we do offer a lot of options for the customer to individualize the car. The "driver's stripe" is kind of the signature paint scheme. (Editor's note: This consists of a paint band running up the hood on the driver's side and includes a similarly-colored section of the same width atop the steering wheel.)

But the car is going to be available in every color combination. We have a pretty good variety for our customers.

One of the options we call the Hard Core Package. This is for the serious track rat. It's basically getting every last bit of we can get out of the car. We get rid of the audio system, the amplifier, speakers, everything that goes along with that. We get rid of the trunk carpet, which is actually 13 pounds. We get rid of the tire inflator and a few other non-essential items for going around the track fast.

Those openings that are left by the speakers we plug with carbon fiber panels. That Hard Core Package takes another 40 pounds out of the car for a total of 80 pounds.

On the Hard Core Package we add back in a lap timer. The customer can go to the track, set up a beacon transmitter, which is included in the kit, and it'll log every lap. At the end of the day he can download that information into his computer and see how his lap times progressed through the day. This is for the extreme customer that is really single-minded.

With that, we'll turn it back over to Matt to talk about the performance results we got so far.

Matt Bejnarowicz: Any time you put a race-level tire on, you'll feel more grip right away. But the way the tires and the aerodynamics and the suspension work together, they all complement each other.

You can feel the aerodynamic influence on the car as low as 50 mph. In fact, early on in the development tuning I actually screwed up the car balance-wise and I thought it was totally suspension. I took off some of the aerodynamics and it completely changed every single corner.

A 50-mph corner is a hairpin, so the aerodynamics are influencing everywhere you go around the track.

The ACR is designed for the customer that wants a little more than the base car. He wants to take it to the track and he wants to have those little knobs to turn and adjust the car, but he doesn't want to commit that car to a full race car. We have that (2003) Competition Coupe out there if he wants to be in a full race-level mode. This car is supposed to bridge that gap. It's supposed to be, drive it on the street, drive it to the track, put on your splitter extension, dial up the dampers, run it all day long and then drive it back home on the same tires you came with.

From our initial reaction I think people are pretty excited.

Mike Shinedling: There were some earlier questions about skid pad numbers and how the aerodynamics affect that. Speeds are pretty low around a skid pad, and in order to affect the grip we had to go to a pretty good rake. In high-speed sweepers we've recorded g-forces at 1.5 g. Like this last turn here (Willow Springs' Turn 9, which has a 600-ft radius).

Matt Bejnarowicz: Yeah, if you're up in the 120-, 130-mph range in a high-speed sweeper you'll see those kind of g-levels. To tell you the truth, I don't have the guts to do it here!

Question: Does this car meet any existing SCCA or NASA racing classes?

Mike Shinedling: No, it doesn't. With cars like this, a lot of times they create the class. There is a Viper Racing League, and every time we've come out with a new car like this they've adjusted.

We'll see what happens with this.

Matt Bejnarowicz: If you look at our racing background, it's a pretty small percentage of customers that commit their Vipers to full-time racing. The large group is the weekend warriors that are really active in their local club. They want to go out and have fun, do their time trials, but they're not going to put a cage in the car and dedicate it to racing. That's where this car is supposed to fit.

Herb Helbig: This is actually the third-generation ACR package. We had one early-on in the '90s, we had one in 2000, which was the second-generation package. And of course this body style has only been out there since 2003, but this is the first ACR on that.

People ask why did you do an ACR? Well, the obvious answer is we could, number one. The second one was, we responded to what our customers wanted. You know, we're driven these days--especially with our new management--to having customer focus. You can have customer focus on folks that like minivans, and you can have customer focus on folks that like Vipers. Our Viper customers came to us and they indicated very clearly that they were all over having even a more dramatic car than an '08 base car, with the 600 hp.

So it was a natural kind of thing for us. We could do it and they wanted it.

And it gave us a chance to do what we love best. You know, our team is rife with racers and car fanatics, and when you have a chance to take it to yet another level--I mean it doesn't get any better than that for guys like us!

So it was more than natural, it was like we were destined to do that kind of thing.

The performance, 0-60 times are very similar. Quarter-mile times, we have some data that just was generated last week; the car is almost 130 mph in the traps and it's a mid- to low-11s street car.

When you step back and think about that, an 11-second street car that you can go down to the Burger King and scoff up a burger on your way to the track and run 11 seconds. For guys like me that grew up in the '60s, remembering what was a good car back then, this is absolutely measured on a different scale.

Question: I would think this would be a little slower than the base car, considering all the drag.

Herb Helbig: Actually, we thought the same thing, that's a good point. And actually drag doesn't evidence itself in the quarter-mile. It actually helps the car stick in the top end. And the 7:1 number that Mike was talking about does that.

Now, what we haven't done, and we know it will be affected, is the top speed of the car. The '08 car is a bona-fide 200-mph street car. This car will not go 200 mph. We're thinking it's probably going to lose 10 percent, be in the high 180s, maybe low 190s with all of the aerodynamics on it. But at that point it's going to be generating well over 1000 pounds. of downforce.

But this car isn't about top speed. We did this car so we could continue the legacy of raising the bar. Here are guys who said, we're going to make a car that's way faster than the '08 car on the track, and the '08 car is way faster than the '06 car on the track. This car, as a general kind of a benchmark, is a couple of seconds quicker around a race track than the base '08 car, which was a couple of seconds quicker than the '06 car.

We wanted to raise the bar. We wanted to show the rest of the guys that build cars like this that this car will take no prisoners when it's out on the race track. And that's what these guys did. That was the purpose for doing it, make it absolutely untouchable on a race track. dollar for dollar.

And if you look at the value equation, we always talk about bang for the buck when it comes to SRT. Here's a car that will run that hard, generate those kinds of numbers, for less than $100,000. There is no extra charge for the Hard Core option package.

Question: How many hours in the wind tunnel?

Herb Helbig: All of it in the middle of the night!

Mike Shinedling: Yeah, our tunnel has rules that you can't take it to the peak speed in the day because of high electric power draw, so we spent a lot of man-hours on the graveyard shift.

Herb alluded to this was kind of a skunkworks project in the skunkworks group, so when we started in the wind tunnel, over a year ago now, it was pretty quiet. We just started sneakin' in to every wind tunnel shift that opened up.

This project was top secret within company until recently. We used a code name, EM50, and didn't even mention ACR until it became public. When we had to take one of the test mules to several tracks around the country, the easiest way to hide it from attention was to make it look like a race car. That's why it's painted-up like that.

Question: The Corvette ZR1 at around 100 grand is the only competition for this, right?

Herb Helbig: Let's be honest: the race has always been between us and Corvette--and it's been a beautiful thing. I mean, when you think about the magic of competition between guys like the Corvette guys and the Viper guys, we're really the same guys under the skin. I feel for them, because they've got more bureaucracy and more suits in their deal, so that's an advantage for us.

But covertly or not, it's always been about the Corvette and us. I mean, think about why the ZO6 ever came to be born. Why do you think the Blue Devil was ever conceived of? Because Bob Lutz said, "I don't want you to get your ass kicked by those guys over at Viper. Oh, by the way, they've been kicking your ass!" It's always been about that.

The Blue Devil guys are going to have to bring some pretty serious stuff to compete with this. And it's more than just sticking a supercharger on.

But those guys are like us. They're guys just like Mike and Matt and myself back there twiddlin' away, trying to figure out how to one-up us. And, you know, it doesn't get any better than that these days!

We've got to consider this car is an urban weapon, is what I like to call it. This is a serious piece of machinery, this is not just a grocery-getter.

Question: Is the warranty voided if the car is used on-track?

Kathy Graham, public relations:

Not if they use the car as it comes, out-of-the-box. The warranty would be voided if they install race parts or modifications, such as a chip.

Question: Is the Viper's future secure?

Herb Helbig: We look at it very pragmatically. The halo that the Viper brings to the Dodge brand and the company secures its place within the company. We don't have to make a ton of money. I mean we all know, even though we're big enthusiasts, we can't afford to lose money. That just isn't in the cards.

And this car does not lose money. This car makes money. It just doesn't make as much as a minivan or a Caliber, perhaps, or something like that.

But very clearly our new management understands what not only Viper but SRT brings to the party, the halo of the special effect.

So I don't see any reason that we have any security issues with Viper in particular right now.

Kathy Graham: Viper has already outlived what it was originally intended to do. It was never intended to be here the number of years that it has been. Originally it was supposed to go away before Prowler went away. It is sustaining its own legacy [and] it makes money.

Question: Do you think there'll be another generation?

Herb Helbig: We never talk about future products, especially when the PR folks are standin' right next to me!

As long as there's a need for the car and a desire for the car, people want to buy the car, we'll continue to build what they want. We'll refine it as it needs to be refined to meet the customer satisfaction requirements. That's really what it's all about.

Question: How will the upcoming 35 mpg CAFE standard affect this car down the road?

Herb Helbig: I don't think Viper will be affected very much, because volumes are so low. You know, that's an average fuel economy.

Although I would tell you it is not all that bad for fuel economy, because if you stick it up in sixth gear, which is a point-five overdrive, you can get 26 mpg in a 600-hp car.

Kathy Graham: The '08 Viper actually gets a mile per gallon better city and highway than the '06; it's got 90 more hp and better fuel economy.

Herb Helbig: We reduced the gas guzzler tax with the '08 car. So it's significant in our world, but it doesn't have much of an impact on the CAFE.

[BlknBlu]

Awesome, thanks for sharing. Who will be the first to use EM50 as a license plate.


Bruce