JerryU

Bit off the Thread subject but relates.

First, I understand that folks who spend a lot of time at the drag strip were upset that my posting 2.5 seconds 0 to 60 from GM Dash Test. Many work hard to gain a 0.1 better 60-foot time. That 2.5 seconds did not fit their data as GM test includes a 1 foot roll-out to match what Magazines publish! Understand and since I didn't care about the absolute value didn't appreciate their concern. I said I didn't care about GM subtracting 1 foot rollout as I was just using the relative change for "things" I was doing differently.

In fact, what prompted this Post is the significantly higher front rise on my E-Ray tests without using Launch Control. Much more than my C8. I expected the FWD traction to be the main benefit and did not think that would cause a higher front lift. It's similar to what I get with my 3000 lb street rod with a setback 8.2 Liter engine putting 53% of it's 3000 lbs on the 16.5 section width Mickey Thompsons. I also have the adjustable 4 bar link rear suspension set to provide and Instant Center a foot+ ahead of the front wheels. That causes extra front lift at launch. I have adjustable front shock coilovers on the Street Rod. There are 9 click setting and I use the softest for best launch, again helping front lift and rear weight transfer.

Not sure why the extra lift without Lauch Control on the E-Ray. With Launch Control set perhaps GM adjusts the front MRC to have a very soft rebound and high compression, like a Drag Shock (although never heard that stated.)

I recalled a situation that occurred in a Kinematics class (branch of mechanics concerned with the motion of objects) many years ago. Prof drew a free body diagram of a car and said when accelerating because of the high CG and rear springs handling the higher load and the rear squats. Several of us said not with a ~'50 Olds! We didn't prove why the suspension mechanics were different, but it has coil springs and long radius arms (see pic.) Is it possible the front E-Ray suspension reacting to the front tire torque the cause? Don't know. Will it be the same or perhaps more with Launch Control?

Nether Draggy using satellite position measurement or my G-Tech that uses an accelerometer (IMO as the GM Dash Test with 1 foot rollout subtracted) deals with the other factors. Such as amount of front lift, tire distortion etc. They all cause a difference however small in 60-foot times. As noted in the example I found shown below, 10/90 drag shocks gained 0.1 in 60-foot time.

Perhaps some folks have Jim Mero MRC Drag Shock software that allows adjusting to achieve the very low rebound and high compression of the front shocks (I assume.) Also, GM optimizes the Corvette suspension for road racing NOT drag racing. Are there adjustments/additions that can improve launch response. Don't know but worth looking into. Perhaps these issues have been considered and others.

Here are some pics;



Is the reason the E-Ray front lifts higher than my C8 Z51 with MRC, the way the front suspension interacts with torque applied to front wheels? Don't know.


Here are some references to consider.

CRUZ1NN

Jerry,
I was not upset about your numbers or your dashboard performance recorder posting. There is no doubt that the E-Ray is fast in the 0-60 and I do not doubt GM's claim.

My only point is that the Dash Performance Recorder is unquestionably inaccurate and does not represent the true 0-60 with a 1-ft rollout. It may try, but it is not accurate based on my analysis of many runs using Dragy and the PRD's mp4 data. The same is true about the 0-60 times that are presented in the PRD's Video Screen. The PDR's video display also seems to consistently differ to the the Dash's 0-60 numbers. The 0-30mph number seems off almost all the time. I am puzzled by how GM estimates each, especially since there is more accurate data stored in the PDR's MP4 file. Maybe GM's processors cannot analyze the mp4 file data fast enough in real time for presentation on the dashboard or PRD's Video display.

Drag strips also include the 1-ft rollout on the 1/4 mile times. The time slips do not normally reflect the 0-60mph time.

Getting past all of that... The rise in your front-end on an acceleration or launch that is more than your C8 is intriguing. I would be surprised that the MRC would be adjusted since it can be controlled by settings in Sport or Track mode. I assume you were in Track mode or the stiffest suspension settings.

JerryU

^^^
Good thoughts. Yep I used Z-Mode Power set to Track. I found that if I drive in Z-Mode the battery charges to 100%. Just saw that again today coming back from town. I switched to Z-Mode about 5 miles from where I turn into a 3/4-mile-long road near my home with mostly farm fields both sides. I had been in My Mode (set to Sport) and the battery was at its usual 80% charge. Within a few miles it was charged to 100%.

I agree without setting launch control the car would not know I was performing a launch so it could not set the MRC. In fact I had never heard they did that with Launch Control- just speculated they could. Jim Mero who helped developed the MRC tuning for GM is retired. He sells controls that allow MRC adjustment. He mentions Drag Racing but no details. It's a call me on his website. Expect some avid trackers may have that software for their MRC.

The easiest thing for GM to use is an accelerometer for the dash test. They use a matrix of accelerometers as input for the MRC control. Don't know their arrangement is with Cosworth, as it is their PDR system. Could be limited. Accelerometers are not involved with them. Don't know what GM is using for the roll-out number. I know Bear is planning tests with his measurement device we'll see what he gets!

I'll see when I have enough miles to use Launch control what I get. Just dusted off my 23-year-old G-Tech that only uses an accelerometer. Will see if it is the same!

RedLS6

Load transfer doesn't care which end of the car is driven - if you add more torque at either the front or rear, the load distribution changes with the increased acceleration and the front rises more - the only way around this would be to place the Cg at the road surface.

The anti-sway reacts to dA/dT (the derivative of acceleration) initially, and then to total steady-state acceleration .... , so during that initial hit off the line, as acceleration changes rapidly, the anti-sway reacts and either provides for, or negates, rotation speed. At steady state, when acceleration = constant, the load transfer stabilizes and the front end rotation settles into a spot dictated by the Cg height, wheelbase, and total acceleration. That's why some slower drag cars with a 4-link set up to transfer rotation pop the front wheels off the ground for a couple of feet then immediately drop back down, while the faster cars carry the front wheels past the 60' mark.

JerryU

^^^^
Excellent point! Just as that Kinematics Prof was showing ~60 years ago, with the free body diagram! Acceleration acting on the CG will cause more rear tire load less front! Doesn't care where the acceleration is being produced!

I was looking for a non existent, complex A frame load or something!

I do remember the issue with the 49 to 51 Olds! Unlike most cars of the era with rear leaf springs that in addition to the higher spring loads they would bend, wrap due to rear end housing torque! Made the squat even more. Perhaps the Old's was more the difference from what was expected!

RedLS6

We all ran slapper bars back in the day - I had them on my Mustang back in high school, we called them traction bars and I knew I needed traction. Unfortunately my issue was that I had spent all of my $ on the engine and none on tires.

WRT the 0-60 timer; I'd also rather have precision over accuracy if I can't have both. My main issue is that the timer is so far off of other measurement methods, and that GM never bothered to explain how or why. If you're a TierX supplier to GM, you'll be subject to multiple engineering reviews until GM know exactly how every part performs, how it works including its patents or trade secrets, and where the margins of reliability are. When you as a customer buy their car, it's a long drawn out process to glean explanations of the tech that you've paid $$ for. For a simple user feature like the timer, it would be nice to have some basic info to at least have confidence in the measurement.

JerryU

^^^
Agee, GM won't say what rollout time reduction they use or how it's triggered. We'll see what Bear gets for a comparison with his instrumentation.

Ordered my S10 Step Side with every HD option GM offered. Quick Steering ratio, HD springs shocks, HD sway bars, Posi. It included a 5th shock, called a "hop shock" mounted on the right rear spring such that it reduced spring wrap-up. It came lowered ~3" with aluminum wheels and wider tires. It was a 5 speed V6 with an advertised ~20 more hp than the similar stripped 5 speed V6 S-10 I bought when we were building our current home. We're 30 miles from town and had to haul "stuff' the 9months it took to build. That turned out to be an issue!

SIDEBAR
That ~20 hp sounded good BUT when I left the stop sign at the end of our rural road to merge into traffic on 4 lane divided highway had to use a lot of throttle and slip the clutch as I accelerated. Did ot have to do that with the stripped prior S-10. Brought it to the dealer and the service manage took it for a ride. Came back and said yep, they changed the cam and increased hp but it occurs at a higher rpm. Not an issue with automatics but can see it is with a standard shift. He was a drag racer and had this advice. If I were you I'd buy a Hypertech Programmer.

I did and used their highest hp recommended setting. That suggested using 160 degree thermostat and required 93 octane. Worked great! It advanced the timing and probably richened the mixture when accelerating (like adding a larger accelerator pump as I did on the Holley on my street rod!) I had a Flowmaster and duals added. Had the shop modify the crossover pipe that GM had flattened as it went under the engine, probably to match a Ford ground clearance spec! Modified the intake for a cold air with K&N and added an MSD ignition. Installed a B&M short shifter, and Polyurethane bushings for the sway bar. Added an amp for a fabricated subwoofer enclosure I built to fit behind the console between the bucket seats! After it hydroplaned on the highway dumped the OEM wider tires that came with the truck for quality radials. Bought a body colored fiberglass bed cover.
Loved that Truck!

jafo1970

I was actually wondering why my battery level showed almost 100% yesterday as I was driving. I was setting up my Z mode and had left it on for awhile. I was wondering if I had an issue going on as I never tried the charge+ button but this confirms it. I set up the Z mode to activate launch mode with 2 clicks of the Z mode for faster activation. I'm only at 625 miles so far and haven't done it. Have yet to have a decent time to run it here. I did one quick 0-60 on cold tires at 58F with the dragy with just a foot launch and was surprised how much all 4 tires spun. I was just in sport mode and traction control kicked in pretty good. PDR said 2.6 and dragy said 3.1 which is still much better than my C7z every did stock or even after it was modded to 654rwhp on the street here. Our roads here are pretty slick. No doubt with warmer tires, 100% battery and launch control should be around 2.7 or better on the draggy. Going to try a full run with draggy hopefully this weekend when it hits higher 70s here.

JerryU

^^^
Yep I was surprised when with just over 500 miles I had promised the local branch bank manager I would take her for a ride. It was about 65F and just a quick manual launch the rear tires spun and I had to lift. Was surprised those 345s slipped as IMO my 2020 C8 Z51 under those conditions would not! And I have the ZER Option.

But later that day when it was about 75/78 I ran the test with 1st heating the tires. Did that by driving in Z-Mode where battery quickly gets to 100%. Then accelerated at WOT from ~30 mph to about 110 (which it get too quickly.) That put some heat in the tires. Then applied the brakes aggressively, probably ~0.8 g. That added to the tire heat and charged the battery also putting more heat in the front tires. Once stopped set the Dash Test and achieved my first Dash 2.5.

Would not surprise me if GM used 0.5 second subtraction for 1 foot rollout. We'll see what others get and should be able to define the value.

vipervetteguy

How do you set Z mode up so that 2 clicks activate launch control?

jafo1970

In drive modes under Z make sure suspension is set to track and choose a track pdm.

CRUZ1NN

About tire slippage... I found that roads with visible smooth tar levels on the surface produced tire slippage. A rough surface with no tar visible produced the best traction. Even at temps in the mid 40's to low 60's my Stock 4S All Seasons do not slip most of the time if the rear tires have been warmed up to at least 66 deg F. On unprepped surfaces, some believe that setting the suspension to Sport mode instead of Track mode will allow the car to hunch down more over the rear tires to prevent slippage. This may not be necessary on a prepped dragway. I personally need to do more testing on the dragway.

On the topic of 0-60mph Dash Timer vs. PDR Video Displayed, vs. PI Toolbox calculated times based on PDR data, vs. Dragy... I analyzed 10 runs with the average difference shown below in my heavier C8 HTC. Times were collected over many days over 1-month period under different road conditions, air temperatures, fuel levels, number of passengers, etc. My point is to show the average difference to the Dragy number. As you can see, my calculations analyzing the PDR's mp4 file's data in the PI Toolbox software came the closest to Dragy. The Data in the PRD mp4 file shows data every 1/100th of a second.

0-60mph time comparisons between Dragy, PI Tool Box, Dash Timer, and PDR Video Timer.

JerryU

^^^
Interesting data. Thanks.

Understand there are questions re the GM 2.5 seconds 0 to 60 mph number for the E-Ray. But for me Car & Drivers published E-Ray review showed they achieved 2.5 seconds in their test. They use V-Box. Like other magazines they subtract 0.3 seconds for rollout in their published 0 to 60 numbers. I'm sure we'll get other magazine data. Be good if one could show compared their data with the Dash Test! That should be possible.

BTW, the Jason Camissa MC'd video where they performed 1/4-mile tests with a Ferrari and Lambo and showed 2.4 seconds on an unprepared track.

SIDEBAR
Car and Driver uses a V-Box to measure a car's acceleration. Their logger records at 20 times per second and is accurate to six hundredths of a mile per hour. The V-box is used for straight-line testing. Like other magazine reporting they use a 1-foot rollout and subtract 0.3 seconds for their published value.




Be good if GM would say what they use to trigger their Dash Test and really good (since they have the data) that test accuracy and repeatability. Doubt that will happen..

CRUZ1NN

Car and Driver's Specs show 0.2 seconds for the 1-foot rollout on their site for the Corvette: https://www.caranddriver.com/chevrolet/corvette
They discuss the Rollout here in a little more detail: https://www.caranddriver.com/feature...hange-rollout/

Interesting enough, my average calculations for the 1-ft rollout vs. no rollout when analyzing PDR data with the PI Toolbox comes to 0.212s. This is averaging 10 separate runs.

gatorfl

I wonder when they are going to release the 2nd part of that video. I'm guessing GM is having the say as to what is allowed and when. Kind of like why they didn't do a Z06 vs E-ray race off the bat. Its not like people would fight about it. (sarcasm). Who even knows if the Tune is the same and what if any tweaks the GM engineers did.

We have yet to see that video of the E-ray with cup2r's. Looks like Boost district put those on the rear and nittos in the front for a race next week, but the turbos will not help get stock numbers. As time goes by we will see more and more.

JerryU

Yep they are actually using the true 1 foot rollout depending on car, how hard it launches etc.
"Here's how our change affects the C8 Corvette. The C8 accelerates to 3 mph in 0.1 second, but the one-foot time is 0.2 second, at which point the Corvette is going 6 mph. In general, acceleration times for most cars will improve by about 0.1 second with the new procedure. In the interest of full disclosure, we'll be publishing the one-foot-rollout time of every tested vehicle so you can add it to the acceleration times to arrive at true zero-to-X measurements. We also will be recalculating times for past vehicles, so that any comparisons we make today are apples to apples. Unfortunately, it is impossible to recrunch pre-VBox test results. We will generate estimates in those rare instances."

That is car and many other variables dependent. Does vary. Doudt the GM subtraction is that sophisticated, nor need it be. Hope they are starting with a simple accelerometer.

Found this: "A one foot rollout can affect the final run time of an AA/Fuel Dragster by up to 0.3 of a second. The industry standard for acceleration testing is to include a one foot rollout before the clock starts, which means that the clock doesn't start when the vehicle starts rolling. This first foot of movement is subtracted from the final run time to ensure that the run time captured by the GPS data logger is as close as possible to the official drag strip time"

GM, is probably subtracting a fixed number. That is all that matters to me when I compare my "time" without Lauch Control to those I have achieved without. Also how it feels, front rise etc, which is subjective! My 23-year-old G-Tech just started the timing with an accelerometer. That is all I needed to set up my suspension and holly carb etc.

As Einstein would say, "It's All Relative."

yell03

Thanks for getting a real Dragy #.
With Launch control and warm weather you should easily do mid 2s
Was the 3.1 with rollout factored in or just the straight number?
Launch control is definitely going to reduce that time.
The main thing is, you can see how inaccurate the in car timer is.

My C8Z in 58 degree weather on summer tires would not hook at all, best I could do was a 3.09 with rollout factored in using the auto launch control in Sport mode.
I know in warm weather in Track Mode using a 4000-4500rpm launch and 10% slip dialed in I should easily crack in to the 2.9s or better.
I will use PTM Sport which will hold me back a bit, but I want the nannies on in case of a slick spot on the unprepped road.

With the Eray, just as with my AWD Porsche, you can just launch with no TC and let her hit hard, I would be surprised and anything over 2.7-2.8s.
Even on hard all-season radials the Porsche does 2.6s with 1.61 60' times.

vipervetteguy

What I still don't get is: If I click the Z button twice, it goes to Z mode and then back to MyMode. (2024 E)

Ragtop 99

Do you have Z mode configured to use PTM? As I understand it for my 2023, the second click is to confirm the driver wanted PTM. If PTM wasn't configured, then pressing the button just cycles between modes. I don't have PTM configured in Z mode and will sometimes click it off then on again to bring up the menu to change a Z mode setting. I'm guessing your e-ray is similar.

jafo1970

This.
It will ask you to confirm the pdm as it changes you to track mode.