2002 Chevrolet Corvette Z06: Dyno Tested

>>CommonSense01 says:
>>...that means the engine is putting out at least 40 more hp then advertised by chevy.

That's easy to believe if you've every driven one of these.

Why under-rate the power an engine makes? The most famous (infamous) current example that first comes to mind is the twin turbo inline six in the BMW 3 Series. EVERYONE knows it makes more power than advertised so why not state the real number?

This is impressive for an 8 year old car though any way you look at it.

So why do car companies underrate cars output?
So if someone actually puts it on a dyno and comes up with less they can't say the company is advertising fraudulently?

Wow - if that engine is all stock, that is MUCH more power than average. My '02 did 353 rwhp and about 345 rwtq when it was stock. Even after long tube headers, Vortex rammer intake, X-pipe, cat back, and a dyno tune, mine made 380 rwhp, which is still less than yours stock!

That's 450 crank hp, boys and girls. Far more than the advertised 405. You got a healthy one there. The previous owner must have at least had it dyno tuned to pick up that much hp. Most stock '02 Z06s dyno at 345-355 rwhp, on average.

Those numbers are more on par with a 430hp rated LS3 than a 405hp LS6.

LS2 = ~345 rwhp
LS3 = ~380 rwhp
LS7 = ~440 rwhp
LS9 = ~550 rwhp

@everyone did you people not read??? he said at the crank that's why the horsepower is underrated because manufactures measure horsepower at the crank and not the wheels!!!!!

"@everyone did you people not read??? he said at the crank that's why the horsepower is underrated because manufactures measure horsepower at the crank and not the wheels!!!!!"

Uh

@itm1221,

I don't even know where to begin my response.

Just read.

Everyone is commenting on how much REAR WHEEL HORSEPOWER the vehicle is making and how that translates to MORE CRANK HORSEPOWER. Everyone is talking about how the vehicle makes MORE horsepower than advertised and is asking why GM UNDERRATES it's engines.

Maybe you don't understand this, but vehicles make more horsepower at the CRANK than at the wheels. THINK about it. Power is lost overcoming friction and transferring power from the engine through the driveshaft to the transaxle to the wheels.

ugh.

First of all, that's a durn healthy 'vette you've got their. From any engine (well, perhaps lets limit it to car engines) 382/375 at the wheel is plenty of go. Plenty.

As for the folks above who can't seem to figure out which comes first the crank or the wheel - just do a bit of reading & reread/edit your comment before posting to make sure it holds water.

As for the intriguing question about why auto manufacturers underrate their engines - perhaps for insurance sake? Perhaps to show "We can run an XXX 1/4 mile with XXX hp/tq?"

Personally I think underrating something looks/feels/sounds cooler. "Oh, it's only running 300hp" and yet somehow you're always pulling away from the crowd. Compare that to "I'm running 300hp" and the crowd is always leaving you behind. Its much better to under promise - car guys love getting more than they "paid" for. Oh well... that Z06 rocks.

Well i heard that the reason a company will lie about the power one of their cars make is to evade gas guzzler taxes. It has been said that they did the same thing with the new Z06 but i heard this from a car sales men at Chevy. lol

Perhaps they underrated it as not to step on the feet of their new C6 LS2 that was in the pipeline?

sherief and 3ricchu

It says "Here's what we found at the WHEELS of our silver long-termer, as measured on a Dynojet 248 chassis dyno:"

385 hp at the wheels means that the engine is putting out much more than the factory claimed 405hp. If the vette had 405 hp at the crank, as claimed by chevy, considering drivetrain losses, the car would never put down such amazing numbers. whats the confusion?

Alright Edmunds: I've got a major beef I need to air and hopefully get a well informed response.

I believe your assumptions of underrating are fundamentally flawed.

The common discussion, by owners and marketing guys and dyno shops, is that there is a driveline parasitic loss as a percentage of the overall power.

Why?

Why do people expect a 200hp car to have a 10% drivetrain loss, and then when it's boosted to 400hp the drivetrain is still sapping 10% of that power? Does it take twice as much power to turn the U-joints and camshafts and flywheels? Do those parts weigh twice as much in the same car?

My understanding is that no, it doesn't. THE PARASITIC LOSS as a PERCENTAGE OF POWER decreases as POWER GOES UP.

Applying a parasitic loss factor to get true "engine HP" is crap when done like this. That is one of the reasons almost every modern car has been seen as under-rated time and time again.

Either take the engine out of the car and measure power at the flywheel/crank, or don't say it's hugely underrated.

Now, I'd love to hear someone prove my assertion wrong here. I'm not a mechanical engineer. But I've never seen an explanation of why parasitic loss would remain a static percentage of overall power, and I don't expect to see one now.

Joe

P.s. Please don't tell me that driveshafts weigh more in higher powered applications, etc.....I realize that stuff. It ignores alot of the fundamentals of inertia to say stuff like that.

@joefrompa - You answered your own question with your final line. More power means stronger and heavier components to handle that additional power. Think about, you will need a stronger clutch, stronger transmission, stronger rear end, stronger axles, stronger brakes and stronger rims to handle all the extra power. This is physics we're talking here, and you can't cheat the rules!!!

Now, going back to the subject of the LS6 in this Vette. 382rwhp is very, very strong. I am extremely impressed. I have never heard of another 'stock' LS6 Z06 making that much power.

Now....get to the track and lay down some numbers already!!! Sheesh!!!

Why understate power? Easy, anyone remember the 305 hp Mustang Cobra that never made it or Hyundai overstating power back in the day, all the lawsuits. Well the companies are trying to cover their asses.

Actually, the answer is easy, they didn't overrate the engine from the factory, in a car like that they would want to advertise it as high as possible. The answer is that Edmunds uses an optimistic dyno. Look at how high the dyno readings they got on the '11 mustang GT compared to Motor Trend. It was 20+ hp more. Also, they dynoed a GT500 awhile back and it made significantly more power than I've ever seen a GT500 make on my dyno. This Z06 made more than I've ever seen a C5 Z06 make on my dyno. It's just an optimistic dyno is all, easy as pie. Dynos are just tools anyway, used to assure that the changes made to a car are going in the right direction as far as performance is concerned. Who cares what the silly number says, as long as it's higher than where you started?

There must be a way to calibrate a dynamometer.

Aside from that, it's the intoxicating sound that is important. How about some more loud acceleration noise.

A technical question, since everyone is in that mode:

On the dyno test above, and on pretty much all the dyno tests on Edmunds, when you let off on the throttle at the end, there is a highpitched whine. My theory is that the drive gears go from drive side mesh to the coast side mesh, and that the coast side of gears is not as smooth as the drive side, hence the noise.

Anyone care to comment.

The reason parasitic losses is not a fixed value is not simply the weight of its parts or inertia. Its actually the polar moment of inertia. Just like a car it takes more power to accelerate a car faster, the same principal works on the driveline components, it takes more power to spin them up faster (or increase there rate of acceleration). The car works on a normal plane and the driveline is working on a polar plane.

To better understand think of riding a bicycle. When you first start off you have to use a large amount of power to get up to speed or accelerate. Once you are at speed it takes alot less power to maintain that speed. The additional power is needed to create a change in speed. If adding power did not create any increase parasitic losses than it would in turn not create any more heat, or friction, or wear.

Why do transmissions fail with more horsepower if components are not breaking under stress but because of heat? The only logical answer is that with more horsepower in a motor more of that power gets converted to heat and friction in the driveline.

Half_ton in the case of the BMW, some have said it was underated as not to get close to the M3. So its car politics.

Half_ton in the case of the BMW, some have said it was underated as not to get close to the M3. So its car politics.

ed124c: That's interesting, I always thought that whine was the rollers on the dyno spinning down.

Well, in any case, I think the whine has something to do with loose gears or dyno rollers during decel. Maybe both.

Thanks for your reply, Matt.

There are ways to calibrate dynos, but they aren't 100% accurate, and from the perspective of a shop that's trying to develop or install upgrades (which is why most buy dynos), it's the before and after that matter not the actual number itself.

For example, lets say that this dyno uses a heavier drum than another dyno. This means for a given output level it will make the car accelerate slower through a given RPM range, resulting in higher numbers because the flywheel effect is reduced. It's like pulling the car in a higher gear. There are many factors like this that just are impossible to always account for.

half_ton says,

The reason is because if the insurance company knew how much horsepower this really had, it would cost to much to insure. Unless you have the money to afford it. And its the same thing with other sports car.

Just for reference, the 2011 Mustang GT was dyno'd at the same place right? That made 365tq and 395hp; rated at 412 crank.

@half_ton The BMW 335 DID make more power than advertise, but to those who don't own one (My lease just ended and i had a 2007) a "software update" took all that power away. I noticed a marked drop in performance and if you read most reviews of the cars and looked at speeds they all dropped from the sub 5 second range to over 5 seconds.

Ironically the new 333is comes with about 330 hp...which is what early tuning had that engine at.

Manufacturers UNDERRATE for a very simple reason. To AVOID lawsuits of engines not making the power they produce. Ask Mazda and I think even Ford (Shelby?) had this issue. It's much better to have an over achieving engine than an underachiever.

Keep in mind it's not apples-to-apples to compare dyno results from the Z06 and '11 Mustang GT as the rear drivetrain is different. Corvette is independent with diff, axles, cv joints, while the Mustang is live axle. The live axle system has less drivetrain loss (more efficient) so it will alway have a closer whp result relative to crank. I think it's like 10-11% drivetrain loss for a live axle versus the 13-15% edmunds quoted for the Vette in this situation.

spdracerut said: "the 2011 Mustang GT was dyno'd at the same place right? That made 365tq and 395hp; rated at 412 crank."

ls series powered cars are known to make more power than advertised. and it's pretty much known amongst ths ls community that these motors make more after break in and as they age. gm designed a fantastic line of engines here. look at how many non gm ls powered engines swaps are out there. these engines will fit in everything from miata's, 240sx's, s2000's, 944's, 911's, 928's, volvos,... i mean anything. I LOVE 'EM!

that pic of the Z06 on the dyno is sic! i still love the c5 Z06. so menacing with the roof cut short.

I have been reading this blog with great interest, I really like my stock 2002 Electron Blue Z06 with only 11,000 miles.

I've bounced around corvette forum ever since i bought my c5 (310 rwhp stock/350 after cai, headers and tune). Typically a stock z will come in at 350. I agree with the poster who says your dyno is optimistic. I was beginning to think your numbers were consistently high.

Now i really feel bad for project miata. it has a long way to go!

I think the obvious thing to do here is listen to the guy who owns his own shop and dyno. He said this is an optimistic dyno, plain and simple. It's like radar guns. Some read faster than others. I've never seen an owner of a C5 Z06 post numbers like this on any of the forums I read.

As for the high pitched whine, it definitely comes from the dyno rollers. Have you ever heard a car do that when it's on the road? Yet, you hear it in every single dyno youtube video out there.

Joefrompa,

I agree with you. The Z06 will have less parasitic drivetrain loss than a regular Vette because it has more power with basically the same drivetrain. The same drivetrain with a more powerfull engine will equal less drivetrain loss. Just because an engine has 20% more power than a similar vehicle doesn't mean the drivetrain needs to be 20% heavier if the base vehicle was designed to handle more power than it produces.

A 10% drivetrain loss is a very genaric number. I guarantee that 10 different RWD vehicles would all have different amounts of drivetrain losses. A 10% drivetrain loss might be the average but each vehicle would have different amounts depending on how each vehicle was engineered.

I just want to say the reason the HP numbers have been so high is because they are using a Dynojet Dyno. Dynojet Dyno's tend to give rather optimistic WHP numbers. Those parasitic percentages would better suit a mustang dyno. Mustang dynos have more rolling resistance giving a more real world reading for the WHP. I have a 2003 z06 and pulled 379RWHP stock (which is close to what you guys have) when I was running on a Dynojet dyno. A year later I had it tested on a mustang dyno with a full intake, true long tube headers, no cats and X-pipe and I was pulling only 385 RWHP (similar temp and altitude to the year before). I don't know all the technical reasons the two dynos differ. Just something to think about when you see numbers that seem to good to be true (which most of the cars tested here have been). If you were to put these same cars on a mustang dyno I think you would find that these cars would be a lot closer to the manufacture claimed numbers. Besides auto companies have to have the engine dyno tests overseen by someone from the SAE (that was mandated after the 50's 60's and early 70's when car companies would do all sorts of tricks to get higher or lower HP ratings to what the engine could actually do).

First off lets clear a few things.

Radar guns DO NOT read high. They are tuned. We have a $2500 stalker radar system...and it's tuned.

Second. No engine EVER will have the same dyno reading. More so on different days, different times of day, different seconds. The engine's environment is constantly changing and therefore every run will be different and can even be 10-15hp less per run depending on temps/heat soak. Also who uses a 10% loss? It's typically 12-15%. Also the dyno CAN actually calculate drivetrain loss with a coast down run. I don't think most shops actually do it.

@chevy598 says: drivetrain loss is drivetain loss. A more powerful engine doesn't change physics. The Z06 will show more at the wheel simply because the engine is more powerful. It's simple math.

In the end it's what the engine puts to the ground that matters. If it makes 400hp at the crank but only gets 300 to the wheels what the engine produces alone is irrelevant.

The current SAE dyno numbers are much more strict than years ago and include all the accessories and other things that are fitted on the cars. So there is little "Fudging" that can happen.

beermagazine,

All you have to do is put heavy or lighter rims on the same vehicle to change its inertia. If you take this vette and put a different drive shaft made of some exotic metal and it will change the percentage of drivetrain loss. An aluminum drive shaft will result in less parasitic loss on the same vehicle with an old school iron driveshaft. Same thing will ball joints and every other part of the drivetrain. Again it's genaric to say that all RWD drivetrains have the same amount of drivetrain losses.

I wasn't specifically referring to IL's radar guns or your $2500 radar gun. I'm talking about radar guns in general that baseball scouts use and cops use. Sit behind two scouts with two different brands of radar guns and they'll have two different speed readings. I've heard about scouts getting out of speeding tickets by showing cops how differently radar guns can read. My point was just for comparison's sake. Maybe I should have used scales instead? My point is that instrumentation is not always accurate.

Secondly, I still stand by the opinion that this dyno reads high. I completely agree that RWHP is more important that factory claimed HP. But to me it is quite obvious that there are some dynos that are optimistic and and some that read lower. Again, its the guys who own these dynos and test dozens of vehicles on them that are saying so.

"The engine's environment is constantly changing and therefore every run will be different and can even be 10-15hp less per run depending on temps/heat soak. "

True, but that's what the correction factor is for. That's what surprised me about the 382 rwhp - they said that was the corrected number.

I do know the LS6 is quite sensitive to ambient intake air temperatures. The engine will make MUCH more power in colder weather. My car made 365 rwhp uncorrected, because it was a cool, low humidity day, about 60 F when the run was made. Corrected, it was 353 rwhp.

I wouldn't be surprised to see a 382 UNcorrected rwhp number at say 30-40F.

What was the uncorrected number from this run anyway?

Even if temps and humidity are the same it doesn't mean the fuel in the gas tank is the same. Gas bought at the same station and the same pump 2 months later isn't going to be exactly the same. In a perfect world 91 Octane should be the same but this isn't a perfect world. Getting 91 octane that was refined at a different refinery can make some difference. Even gas refined at the same refinery will have minute differences from one batch to another.

@c5z06er If they are sighting the same target they will be close to the same. Except that with radar if you're not at 90-degrees you have less speed. It's something like the COS of the angle to get the difference. So if you sit behind two scouts they are not at the same angle and will not read the same....if they even are picking up the same target. Radar doesn't just pick up the moving object but ALL moving objects. A

@chevy598 You changed the discussion. Yes you cannot use the same drivetrain loss for different cars. It's an estimate. But you can use it for the same model if all stock parts are used. But again, most software has a coast down to get the actual drivetrain friction.

@stingray454 correction factor is for weather conditions and not the heatsoak of the engine. As far as I've seen there is NO correction for intake temps. And that is to say that hot air doesn't have some strange affect on performance. That's why most will argue that dynos are slightly in accurate because you can't simulate air flow around the car that it would have while moving. But yes you can use either corrected or un-corrected HP numbers and very clearly see the difference in power from cold to hot air. Correction works in both ways. If they dyno'd out here in SOCAL it's been very cold lately...good for some extra power..

BUT that still means it made that power.

@c5zo6r Radar guns only show different speeds if they aren't calibrated & verified. The stories you've heard from scouts are pretty much BS as far as getting out of tickets. Every cop has been certified to use the radar & verifies the readings are correct before they use the radar unit each day & at the end of the shift & logs it (using the tuning forks certified for that unit). The police units are calibrated yearly by factory reps to be legally used. I hear all of the wives tales about radar & tickets & court, but in the last 10 yrs, none of us have lost a radar case. All of the get out of radar ticket tips from the websites are usually learned by the officers & taught during training. Every time I've heard a tale about beating the case in court, the records have showed otherwise or it had nothing to do with the radar. The units used in the civilian world show different readings because they aren't currently certified & calibrated. Laser works nicer & is much easier to use. The new radar units we have are pretty nice. They can switch back & forth between front/rear while on the move & can tell you the speed of people going the same direction, whether they're in front of or behind you.

@ Edmunds Let's see the track test.

All of the dynos can show higher numbers depending on whatever correction factor the operator uses.

m1tanker, I bet lots that even an "out of calibration" radar gun is within a 1-2mph. We've had two different radar guns. A speedtracker (which was about $900) and now have a Stalker ATS (about $2500) the Speedtrack one lasted years (i think it's what most police radar had or have) and it was never out of tune (calibration is using a tuning fork).

Our Stalker is known as one of the best period and it's even more accurate in targeting. laser just allows you to pinpoint a target. It's not really any more accurate in speed determination. The rest of the tracking is purely software (a little PC doing math).

The cheap Radar that's like $100 just get more interference, but i'm willing to be the cheap ones are pretty accurate too. IT's like thinking that there's no way we can have cell phones that cost $50 that can do all they can. :)

Computers and electronics are pretty accurate. The user isn't always. But even then software is just as, or even more amazing. I have dyno software and it's crazy what it can do....and we use all this stuff for RC car testing!

My neighbor had this car with a similar color combination. He also had an after market exhaust and some head work (ported, camshaft).... Long story short, he couldn't get traction till' about a 100 mph. The car was so fast that me being a speed lover would hold on for deer life as he'd row through the gears on that thing. Easily the fastest car I've ever been in. He recently upgraded to the new Z06 and is doing some work to that.

Most of the radars are pretty accurate. Lasers nice mostly for picking out people from the herd (& no tuning forks).

This discussion has kinda gone out of whack, but the dyno discussion is interesting. Different manufacturers of dynos set up their dynos in different ways, so it isn't often that two different types of dynos will read the same. Aside from that, even the same type of dyno, or even the exact same dyno, can read different by pretty wide margins. Roller dynos are the worst, as strap tension, tire pressure, and tire friction coefficient (traction) can all affect the output. That's why I use a dynapack, eliminates the variables, or at least the great majority of them. The dyno is tool, who cares what number it spits out?

And a special note, MANUFACTURERS do not have their own "special" way. Car companies actually use an ENGINE dyno. The reason why we use a wheel dyno is because most don't have the ability to take an engine out to test it's power. That is the ONLY reason why we came up with wheel hp.

"@stingray454 correction factor is for weather conditions and not the heatsoak of the engine. As far as I've seen there is NO correction for intake temps. And that is to say that hot air doesn't have some strange affect on performance. "

Yes, I know that. But heatsoak in a naturally aspirated engine such as the LS6 is minimal to none. You can see this is the case if you look at the dyno results of 3 or more consecutive pulls: the numbers don't change much, and actually they usually increase a bit in the 2nd and 3rd run. The opposite is true with most forced induction cars of course.

Geez, sorry I used radar guns as an example of instrumentation that can vary in their readings. I certainly won't do that again. My dad was a scout for a long time, and it was generally accepted knowledge that "Ray guns read slow and Jugs guns read fast" but perhaps that was wrong. Whatever, this wasn't supposed to be about radar guns.

Maybe I should have used kitchen timers instead?

I'm very familiar with the dynojet 248 and have had my 02 z06 on 4 different dynojet 248s in the Dallas area.. People seem to believe putting a car on a dyno is like weighing yourself on a scale.. 200lbs is 200 lbs right? Wrong.. In fact dynos are only as good as the dyno operator/technician.. There are various dyno settings that range from Density altitude uncorrecred or corrected.. temp,elevationand humidity are critical.. If you read the original post it says that a 1% Sae correction was done for weather.. What about elevation, humidity? Was 1% really enough of a correction? This is all up to the operator of the dyno... My z06 with a dynotune and Cold Air induction made between 358-380hp on 4 different dynojets with standard and corrected values among the same dynos,, The 358 was done on a hot humid day and the 380 was achieved on a cold dry day.. The 365 and 372 rwhp were done in normal 75 degree weather... Dynos all have a margin of error also.. So between that and the tech you will see numbers all over the place.. The purpose of a dyno is to see what gains modifications will give you.. Again stay with the same speed shop, dyno and dyno operator.. Everyone does things differently.. You can go to corvetteforums.com and do a search of stock dyno runs and find the numbers range from 345-380 on bone stock ls6 engines, using a dynojet 248.. Do you really think the variance would be that much from the factory?? I think not... I take a dyno reading with a grain of salt.. Just remember its not like getting on a scale 90% of people have this mentality..

This is a wonderful opinion. The things mentioned are unanimous and
needs to be appreciated by everyone.
--------
john
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Motor Caravan Insurance

@3ricchu

no shit.....

ugh..

Static Caravan Insurance UK

What is the elevation where this dyno was done. My Z06 has longtubes(catless), Magnaflow Exhaust, and CAI. Did 366 here in Alb, NM. It was 5300 ft above sea level here in Alb, NM, and 75 degrees. 380rwhp seems like a far stretch for a stock ls6.

Just my two cents.

What is the elevation where this dyno was done. My Z06 has LG longtubes(catless), Magnaflow Exhaust, and CAI. Did 366 here in Alb, NM. It was 5300 ft above sea level here in Alb, NM, and 75 degrees. 380rwhp seems like a far stretch for a stock ls6.

Just my two cents.