When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So .. as I see it there’s a lot of let’s say issues here. In the end more than likely ….. within a couple months we will see everything, You know .. it’s called transparency. Just that simple. Everything will be weeded out. Hopefully, there are no sheep
So .. as I see it there’s a lot of let’s say issues here. In the end more than likely ….. within a couple months we will see everything, You know .. it’s called transparency. Just that simple. Everything will be weeded out. Hopefully, there are no sheep
I don't understand. We now have three different dyno run groups on 3 different Z06, <600, 610 and 640. Where is the "Let's say issues"? We have been discussing why the big variances. I have no experience with C7s, but I know that 505 CHP LS7s were tested stock on Dynojet dynos and the variance was from just above 420 whp to 475 whp
I’ll start off with I have no experience with dynos other than going to a few dyno days etc.
how does the dyno discern the difference between transmission ratio and final drive ? If I dyno the same engine in direct in a manual with a a 3.42 diff and a 4.10 diff would that be somehow different than being in OD on the 4.10 car?
In my C5 I dynoed less with 4.10 gears than 3.42 and my understanding is the parasitic loss of the extra friction from the extra teeth of the steeper gear set creates the loss on the dyno, but of course the car wasn’t actually slower at the track from the extra torque multiplication. I believe it also lessens the load on the engine which makes the numbers slightly less as well. So gearing in the trans can vary the parasitic loss as well as load the engine, both of which can alter the outcome of dyno numbers.
dynoing in a lower gear will show higher torque but lower HP due to how a dyno calculates HP from torque and the relationship between the acceleration of the engine vs wheels on the dyno.
sometimes these numbers are just within a margin of error but I'd say that the closer you can get to a 1:1 trans ratio the more accurate it will be (holding steady tire height and rear gear ratio).
the problem with comparing dyno numbers is of course altitude and weather in different locations but also the settings inputted into the dyno itself for the car's setup/specs.
use a dyno as a tuning tool only. this conversation is as old as oil threads.
Thanks, makes perfect sense.
Originally Posted by dar02081961
Why shouldn't it be dynoed in 5th if 5th is in fact the gear closest to 1:1 ?
The goal is to get a reading with as little positive or negative torque multiplication as possible.
The closer you can get to 1:1 the more accurate your calculation of drive train loss will be.
Any gear ratio greater than 1:1 will mask or lessen drive train loss. Any gear less than 1:1 (overdrive) will increase drive train loss.
Many dynos don't like high wheel speeds (ie 170 mph) and this is often the reason folks say don't dyno in 5th or 6th or overdrive gears. But that's a dyno limitation/issue, not whats best scientifically.
Agree. Most accurate result is in 1:1. So, is it 4th or 5th gear? 4th is closest if we don't count the reduction gears. That is constant, just like the rear end ratio.
Originally Posted by Ramv
I’ll start off with I have no experience with dynos other than going to a few dyno days etc.
how does the dyno discern the difference between transmission ratio and final drive ? If I dyno the same engine in direct in a manual with a a 3.42 diff and a 4.10 diff would that be somehow different than being in OD on the 4.10 car?
That's the question. 1:1 has the least friction on the gears themselves and no torque multiplication. But it does not count the torque multiplication of the reduction gears and the rear end (which is another reduction gear).
Call me confused.
One thing I'm not confused about - something is strange with getting 640 whp on the dyno.
Agree. Most accurate result is in 1:1. So, is it 4th or 5th gear? 4th is closest if we don't count the reduction gears. That is constant, just like the rear end ratio.
That's the question. 1:1 has the least friction on the gears themselves and no torque multiplication. But it does not count the torque multiplication of the reduction gears and the rear end (which is another reduction gear).
Call me confused.
One thing I'm not confused about - something is strange with getting 640 whp on the dyno.
You can’t change the transfer gear ratio or the rearend gear ratio they are fixed, so it won’t alter the results from car to car. The biggest variables from car to car are going to be trans gear, CCB option and CF wheel option. Air psi and fluid temps could make slight differences as well as the weather will affect uncorrected numbers though dyno should correct for the weather if calibrated correctly. It’s best used as a tool to compare before and after differences as mentioned previously.
C8Z06 stock baseline 4th gear runs to all 4 wheels. Consistent just like previous Z06. More Z06s next week.
===============
carbon fiber wheels are significantly lighter and will result in significant power gains to the wheels since its all acceleration of the Dyno jets metal drums.
FYIW NASCAR drivers car consistently paid down 644hp last week bone stock at Fabspeed.
We ran car in 5th gear 1:1 and dyno did not lik it as car was over 170mph and got cautions. Went to 4th gear pulls and perhaps torque multiplication is +15hp to +20hp higher. Both Z06s consistent 4th gear chassis dyno data. If anyone is around cruise by and C8Z06 design development in full swing. Fabspeed dynojet state of the art updated non tamper automated weather station- temperature, humidity, air density automatically correlated. Therefore before & after results are the ONLY items that matter. More to come as race headers in 321SS under development.
Next up GT4RS and Ferrari 296GTB on the way by boat North Atlantic.
Regardless the Z06 engine accelerates great since its super lightweight internals and makes great power. And regardless of baseline readings the Objective is always improved sportscar sound and reliable increased power. Chevy built us “ Vette fans” a masterpiece. Going to ROLEX 24 January 28th to cheer them on ands watch new GTP cars. Joe@fabspeed.com president & founder
Sounds like your dyno methods are consistently wrong. It would’ve been more believable if Streetspeed just had a one off. That every car you’ve dynoed is off by 40RWHP points to an issue with your methods/dyno.
This is not something I would be proud of or advertising.
I thought dynos were only meant to measure differences of power on same car for before/after comparison after mods. I suggest that if we care to use dynos as the absolute measuring stick, then average them out. The more data points that are added the closer to the true number we will get.
I thought dynos were only meant to measure differences of power on same car for before/after comparison after mods. I suggest that if we care to use dynos as the absolute measuring stick, then average them out. The more data points that are added the closer to the true number we will get.
When you have multiple different dynos come within a few hp of one another (in this case 2) and then 1 dyno consistently much higher, the issue is most likely with the higher dyno. The owner of said dyno keeps insisting that the dyno can't be manipulated which we all know is not true, which further decreases the credibility of the results & operator.
I use equipment in my lab that has an attached weather station that inputs the conditions of my lab before every calibration and subsequent test I run. Another lab that uses the same equipment that I use and runs a test on the same subject under similar conditions should end up with results very similar to mine. Now I can manipulate the variables or the calibration to alter the results, and so could lab 2. Just averaging my results and lab 2 results does not get us closer to the true values.
My opinion, dynos can be manipulated, I've seen it with my own eyes.
I do believe the new C8 Z06 makes around 600 or so whp, not 640 or so, just my opinion based on what to me is common sense based on the SAE engine results.
I'm sure the carbon wheels/rotors may create a little benefit but nowhere near 40whp.
Again, just my opinion, until we see the same cars with different options on the dyno, which will take a few more months to get these cars into owners hands and then be properly broken in.
I do agree that we'll likely see a range of results as suggested by AzDave47 due to dyno differences.
Joe, I didn't start this thread to be the ultimate dyno comparo thread but since you waded in, do you really believe the C8 Z06 makes nearly 650 whp based on your dyno results and its 670hp SAE rating?
I don't.
I'm sure we'll see the a better representation of results once these cars start hitting the track as they will soon do....trap speeds don't lie.
In my C5 I dynoed less with 4.10 gears than 3.42 and my understanding is the parasitic loss of the extra friction from the extra teeth of the steeper gear set creates the loss on the dyno, but of course the car wasn’t actually slower at the track from the extra torque multiplication. I believe it also lessens the load on the engine which makes the numbers slightly less as well. So gearing in the trans can vary the parasitic loss as well as load the engine, both of which can alter the outcome of dyno numbers.
That makes sense and would explain why traditionally 1:1 is the right gear as it should have the least friction loss (since it's direct.) The reduced load on the engine is interesting, I can see how that could impact it as well.
I believe the reason that 1:1 was used was not because of torque multiplication, as that does not really matter(except for the friction of the gear interface) if you stay within the parameters of the equipment. If you have tire slippage due to too much torque to the tires, you will not get good readings. It is due to there being less gear interfaces involved, therefore less friction and drag. If you could just put in a clutch and a straight shaft you would have fewer losses. Also, transmission gear types make a difference. Are they helical cut (most), what angle? Straight cut? Planetary?
So the question is not is it 1 to 1, but which gear choice has the fewest gear interactions, and doesn't spin the tires on the drum.
You can’t change the transfer gear ratio or the rearend gear ratio they are fixed, so it won’t alter the results from car to car. The biggest variables from car to car are going to be trans gear, CCB option and CF wheel option. Air psi and fluid temps could make slight differences as well as the weather will affect uncorrected numbers though dyno should correct for the weather if calibrated correctly. It’s best used as a tool to compare before and after differences as mentioned previously.
Exactly. Tried to figure out if running the dyno in 5th instead of 4th could account for +40 whp. Clearly NOT. The difference would be minimal.
Originally Posted by Racer X
I believe the reason that 1:1 was used was not because of torque multiplication, as that does not really matter(except for the friction of the gear interface) if you stay within the parameters of the equipment. If you have tire slippage due to too much torque to the tires, you will not get good readings. It is due to there being less gear interfaces involved, therefore less friction and drag. If you could just put in a clutch and a straight shaft you would have fewer losses. Also, transmission gear types make a difference. Are they helical cut (most), what angle? Straight cut? Planetary?
So the question is not is it 1 to 1, but which gear choice has the fewest gear interactions, and doesn't spin the tires on the drum.
Understood. Too low gear, tire slippage. Too high gear, dyno can't handle (and accurately measure) at 200+ mph tire speed. Straight shaft - would be closer to the engine dyno removing the transmission from the equation. There would be still plenty of power loss due to the rear end and rotating mass of the wheels/tires...
This thread has been very educational in many ways.
If the engine makes 670hp SAE and you figure drivetrain loss is similar to a C8 at around 10-11% then it shouldn’t come as a surprise that it makes 600-610rwhp SAE. I asked Joe what a stock C8 makes for comparison though I don’t recall seeing a response.
There are a lot of inaccuracies and misunderstandings in this thread about a lot of different things, I'm only going to address the misunderstanding surrounding the 1:1 gear ratio and what's the best gear to dyno the C8 in.
I'll start with the reason 1:1 is the most efficient gear to dyno a car in and I'm sure it's going to shock a lot of people here based on what I've read above. All 4-7 speed manual transmission Corvettes have a 1:1 ratio for 4th gear. It's the most efficient gear to dyno those cars in because there are no ACTUAL gears for 4th gear, the input shaft and output shaft are locked together and power flows straight through the transmission without traveling through any gearsets. (It's the closest thing to having no transmission except for losses to bearings/seals (negligible) and oil churn.) All other gears have one set of gears transferring power from the input shaft to the countershaft and another set of gears transferring power from the countershaft to the output shaft. Each set of gears will lose 1-2% HP for a total of 2-4% HP loss in any other gear besides 4th. (The gear teeth are an involute helical design with zero sliding velocity at the pitch line, the most efficient gear tooth design other than involute spur gear teeth which is only slightly better.) The image below is the internals of a ZF-6 transmission used in the C4 (uploaded from the zfdoc.com website). The shift ring in the upper right is for 1st and 2nd gears, 5th and 6th shift ring is labeled, and the shift ring in the upper left is the 3rd/4th shift ring. You can clearly see how moving the 3rd/4th gear shift ring to the left engages the dogs on the input gear shaft thus locking the input/output shafts together...and zero HP flows through any gearsets.
If the ratio is anything other than exactly 1:1, HP is flowing through two gearsets and you're going to have the same HP loss through the transmission as a 2.97:1 gear ratio or a 0.75:1 gear ratio...even if it's 1.0001:1. Only 1:1 avoids HP loss to the gears in the transmission.
So what is the best gear ratio to dyno a C8 in? Relative to the transmission only, it doesn't matter since all gears go through two gearsets in the transmission. Since the HP flows through the same transfer ratio and differential gear ratio, HP loss won't change either. What will make a difference is an external factor, specifically the type of dyno. There are 3 types of chassis dynos: pure inertia, pure absorption, and combination inertia/absorption. The overwhelming majority of modern dynos are inertia/absorption. (I see a lot of time where someone refers to an absorption dyno as a load type dyno and an inertia dyno isn't...to be clear, ALL dynos load the engine, they just differ in how the load is achieved.) If it's an inertia/absorption or pure absorption, the dyno is capable of controlling the rate of engine RPM increase so it can replicate how the engine is tested on an engine dyno. If I remember correctly, the SAE J1349 test procedure uses a 250 RPM per second sweep rate. Obviously higher sweep rates (i.e. 500 RPM per second) will cause more HP loss due to increased inertia losses as all rotating components must spin up faster. The same will occur on a chassis dyno as the drivetrain components must spin up faster also. Using that same logic and keeping sweep rate the same but using different gears for the dyno run, higher number gears will have more loss to inertia as the wheels/tires increase rotational velocity more and it occurs at a higher rotational velocity. Keep in mind the formula for inertia squares rotational velocity (v²). A C8 Z06 dyno run (4000 RPM to 8500 RPM) in 5th gear will have ~1.9 times more loss to inertia than a dyno run in 4th gear for all components after the pinion gear. Fortunately, there's not a whole lot of loss to inertia for those components so we're not talking huge numbers. Tires are the biggest ticket item when talking losses to inertia of components after the pinion gear because their weight is farther from the radius of rotation than all other components with the tread being having the most weight. The halfshafts are almost nothing compared to the tires, a human could probably spin the halfshafts up to speed by legs (via bicycle) in the same time as the dyno run. The rotors are more than the halfshafts but still substantially less than the tires, that's why CCB equipped cars won't see any difference in HP (when considering the dyno error). Wheels are more than rotors but still less than the tire since the majority of the wheel's weight is at a radius less than the tires. There will be a HP difference with carbon fiber wheels but probably less than 5 HP.
Just to address chassis dyno accuracy, they can be very accurate as long as they're kept calibrated, operated correctly, and the cars are prepared properly. Tire pressure is critical to accuracy, people have no idea how much HP an under inflated tire can eat up. Look at how much difference tire pressure can make to fuel economy at 70 MPH, the sidewalls constantly flexing every revolution create a lot of friction/heat. Now think about a dyno run from 85 MPH to 178 MPH...
I'm very familiar with C6 Z06 chassis dyno results, the overwhelming majority of them were in the 445 +/-5 HP range. There were the high/low ones with the high ones proclaiming they had a "factory freak" and the low ones thinking they had a lemon...of course neither was true. The LS7 was the very first engine to have certified HP using the new SAE J2723 testing procedure. For those not familiar with J2723, it requires GM to submit 3 engines to an independent tester and all 3 engines have to dyno to within +/-1% of claimed HP. Furthermore, J2723 requires all production engines to be within +/-2% of advertised HP. So for anyone who owns a car with engine HP certified to SAE J2723 who claims GM underrated the HP or they have a "factory freak", they don't have a clue...what they have is a "happy" dyno.
My LS7 was run on a Dynojet SAE Smoothing 0 (? don't know why 0) at "472 rwhp - strong". I didn't care about the absolute number, just that after my build I had gained 133 rwhp on the same dyno. Since then all the dyno runs have been reported SAE Smoothing 5. I do have many of the files and the software to play around with STD, uncorrected, different smoothing etc and it is interesting what the changes are. All the dyno runs were on 3 separate dynojets down in the Phoenix valley so almost every run corrected "up" primarily due to the high ambient temperatures during the runs.
just want to see the difference on the same dyno between a Z07 with CCB’s and carbon fiber wheels and a base car without those to compare.
Dig around and you'll find a few legit back to back tests here on the CF. If I'm remembering correctly a 24lb reduction in rotating mass (12lbs per side) yielded an 11rwhp gain.
My opinion, dynos can be manipulated, I've seen it with my own eyes.
I do believe the new C8 Z06 makes around 600 or so whp, not 640 or so, just my opinion based on what to me is common sense based on the SAE engine results.
I'm sure the carbon wheels/rotors may create a little benefit but nowhere near 40whp.
Again, just my opinion, until we see the same cars with different options on the dyno, which will take a few more months to get these cars into owners hands and then be properly broken in.
I do agree that we'll likely see a range of results as suggested by AzDave47 due to dyno differences.
Joe, I didn't start this thread to be the ultimate dyno comparo thread but since you waded in, do you really believe the C8 Z06 makes nearly 650 whp based on your dyno results and its 670hp SAE rating?
I don't.
I'm sure we'll see the a better representation of results once these cars start hitting the track as they will soon do....trap speeds don't lie.
==================
we have the C8Z06 for a while. We will be on the dyno a lot more very soon as the Z06 will be retested with several new designs for headers and rear valvetronic exhaust .
The 2nd C8Z06 is the exact same build as Mike StreetSpeeds C8Z06 same color and Z07 package. Ill have my guys call dynojet and consult with them. Our dynojet is an all wheel drive system thats well maintained and 100% maintains equal front & rear wheel speeds so modern cars wheel speed sensors match and no front diff issues. Often on late model porsche, ferrari, lamborghini and mclaren cars you can NOT run the car in rear wheel/2 wheel modes. We DYNO run all late model cars in all wheel drive.
furthermore , regardless of the power reading we achieved at fabspeed we are observing consistent 640hp to all 4 wheels on the 2 z06 cars . The runs are consistent time after time with no drop off due to heat soak. GM Z06 gave the car plenty of cooling and she’s a beast and sounds fabulous. Think before you post ……….why would I want to deliberately post a higher than normal power baseline?
there are no advantages nor reasons to do this.
The 2 C8Z06 cars both have MIKE WARD engines and make great NA power . The only thing that truly matters is improving power and sports car sound with reliable German 200cell racing catalytic converters and USA hot-Rodding cad design. These engines simply want to breathe and exhale and thats what we accomplish at fabspeed Motorsports usa.
3rd Z06 due soon. If anyone wants to cruise by and assist and watch be my guest. These are magical times for ICE engines and C8Z06 is a pinnacle of NA engineering. JabCat i will fly you in and ZVrBad drive down from New Jersey! C8Z06 billet aluminum wing risers IMSA GTD PRO Lots of corvettes at fabspeed My C8Z06 spec ………
12-26-2022, 10:09 PM
