Very successful day at Thunderhill 2 mile course last weekend

I'm posting this to get get some help interpreting the data from more knowledgeable forum members. I'll explain what I know as well as I can.

Highlights
No powersteering overheating
No engine overhating (max coolant temperature 243*)
Closed the gap on the fastest car at the event, a Radical SR4
Running all time best lap times 1:23.xx
All that in 95* ambient, 100* showing on the display





The list of mods:
GM second radiator
GM powersteering cooling duct
C&R racing radiator
80/20 water/coolant mix
Girodisc iron rotor brakes replacing CCBs

Description
About a year ago I tried to drive on this track stock in 85* ambients. The powersteering overheated, engine overheated, and I melted an engine harness taking me off the track. I only timed a few laps given all the problems, ran 1:28 with limp mode kicking in on the straight before the finish line. This year the car ran the entire time, and I turned much faster times in 10* hotter ambient. The mods are working.

This track is just under 2 miles long. It does not place a large load on the engine but it does place a large load on the power steering. If the car didn't overheat the powersteering here it won't anywhere else for me. The GM cooling scoop under the car works!

The engine is not loaded as much because it's a short technical track. I used only 2nd and 3rd gears, about 70% of the time in 3rd. MPG was 4.5 miles/gallon compared to under 3 mpg I get on other tracks. This is likely the reason I overheated the engine in 10 minutes in the same ambient on the sister track 3 mile, but not here on the 2 mile track.

I did my best to run the same time as the Radical. It ran a best of 1:21.xx in the morning. I couldn't match that, but I ran the same times in the afternoon when it got hot as I got a handle on the track. I ran with 200 lbs additional weight (car stereo, 50 lbs additional rotating mass in iron rotors, and passenger). If I were to drive a stock Z07 with no passenger in the morning I think I can turn a 1:21.xx. The car is substantially slower in 95* ambients, 6 mph down on the straight, and the Cup 2s get greasy after about 10 minutes of run time.

The C7 Z finally shows its strengths! It ran without breaking down in a tough climate and only second to a pure breed race car. As usual no TC no AH and the roof off, so the fun factor was high driving a manual car in this era white knuckled.

Other fun facts

I promised to check trans temperature. The most I saw was 280* indicated. The Z06 appears to cool down the M7 much better than the Z51 then. It's running hot, at the beginning of the red zone, but I think it's unlikely I'll run 325* and overheat it anytime soon.

I started with 30 psi cold in the tires. At the end of the 20 minute session one of the tires, front passenger side, was running 46 psi!! Holly Xhit, I never heard anyone building 16 psi in a tire before. Is this a record? I can call the Guiness book of world records to the track next time if so. I knew I was best at something!

How fast was I going?

My best time was 1:23.97. I scored that twice in the same session. The consistency was there too, doing 1:24.5 laps plus minus half a second. See below:



Since this may not mean anything for someone that hasn't driven on that track, here are the SCCA time trial records:

http://www.renoscca.org/documents/Tr...0TH%20West.pdf

Some entries:
"CTA" Danny Hart, 2016 Porsche GT3" Laptime 01:24.054 Date:04/23/2016

"FC" Richard Stock, 1997 Van Diemen F2000 Laptime 01:22.729 Date:04/23/2016

"SM" Schuyler Van BusKirk, Mazda Miata Laptime 01:31.448 Date:03/22/2015

"TTA" Chris McMillan, 2008 Chevrolet Corvette Laptime 01:23.304 Date:03/24/2015


Next post, I'm showing the data.

 

I'm picking session 4 to show data, since there was the least traffic. Fastest lap 1:24 dead.

Coolant got up to 243* max. Ambient 95*, showing 100* on the car screen. Well below overheating!



This I need some interpretation for. Where is the intake air tempererature sensor? In the intake? Looks like it gets really heatsoaked sitting at the grid but it's fine afterwards.


Is this how well our stock air filter flows? Is it good?


Don't know what to make of this one either.


Same here.


The fuel sensor seems to be all over the place.


Here is one graph from session 5. I was stuck behind a C6 Z06 for a few laps until I gave up trying to pass him. Slowed down to build some room and went at it. That's when I got my best time. I guess hot tires but low coolant temp is best.

 

Some data from Thunderill 3 mile this weekend.

Session 5, max transmission temp 273*, max engine coolant 237*, max engine oil 295*. Notice that the trans temps still don't stabilize by the end of 20 minutes.


There is almost a 20* difference between intake air temps and ambient. Max ambient 86* but notice it's 81* for almost the whole time. It must be the ambient sensor gets heatsoaked about 5 degrees when pulling in. No IAT2 recording which is sort of what I wanted. Figured out how to make it work but forgot to log it. Sigh.



Air fuel mix is between 10.88 and 14.7 the whole time.


Timing advance, I'll let someone more knowledgeable tackle this one


Compare with timing advance in the morning, 9 degrees cooler (running a mix of 100 octane and 91 both times):


Fun facts:
Wore out the cup 2s to the cords, only 3 track days out of this set...

 

Outstanding information and congrats on your record lap time.

Understand you had extra weight and the shorter track kept top speed down. With so many folks saying drag is an issue with the Z06, I cant help but wonder how much time having the top off cost you?

I know a great deal of air is deflected around the car due to its shape but with the Targa top off the car is "scooping" and trapping tons of air into the hatch area and acting like a parachute. The drag coefficient of the car in this configuration is horrible.

I am willing to bet if you ran with the top on without the passenger and extra weight you would save an appreciable amount of time. You may even see a "1:22" if you (the driver) don't over heat and pass out first.

 

Also the data parameters you logged are great. However it is very hard to interpret and analyze from a mechanical point of view.

Those of us that could help analyze this data need to plot it (any of your chosen parameters) against engine RPM and throttle opening......ie manifold absolute pressure (MAP) or Cylinder mass (grams of air/per second).

That is the only way for us to stratify the data. Hard to explain.
But if you asked me what was your timing at 4400 RPM at wide open throttle I couldn't tell you...no one could from this information.

For example your timing graph has advance plotted every second (or some interval of time) with no relationship to engine speed or throttle opening. So all we see is advance plotted over time and no way to "connect the dots". We have no clue based on the info provided whether you were accelerating or decelerating, and what RPM the engine is turning. And consequently no way of verifying if any area or setting is "off" or where improvements can be made.

I know you have seen this before, the example shows how your data would look if it were posted in a base line graph.
Now if you asked me what was your timing doing at full throttle at 4400 rpm? I could say "28* right were it should have been".

 

I thought the same thing. I couldn't go faster than 132 mph on the straight on the 3 mile track. Put the roof back on...133 mph. To me it's not a big performance loss. Negligible, but I do feel the car slides more in the fast sweepers which probably means the rear flap is not creating as much downforce.

How about if I plot only the data at full throttle in a narrow range like 5800 rpm to 6300 rpm? If I get every session in the same graph we can see how much timing it's pulling as it gets hotter. I can make any plot or calculation if I know what I should be looking for.

 

In for the info.....

 

That's a pretty low end of straight speed. My c6z (stock) was commonly between 141-144 on good laps with cup 1 and cup 2 tires. You think it'd due to downforce? What's your back straight speed like before T14 braking?

 

Yeah it is slow. Another C7 Z06 Z07 was running 140 mph that same day but 7 seconds slower laptimes. Mine also ran 140 mph here the first track day I ran it. It's not a fresh chicken anymore. Not sure what to make of it. I also lost 6mph down the straight at the West course. The rotors are heavier but come on...

T14 I top out third, 124* mph I think.

 

Yeah, that's quite a bit down on the c6z. Also a decent drop from your first time until now also. Certainly an area worth investigating, I'd say. With 650hp, it shouldn't be that much of a drop. My 3 mile over the top times were :55-:57 for reference. Rich's speeds are in the mid to high 150 I believe and his HP is probably close to yours. and aero similar also and I think he's down in the 52-54 range now. Not that laptimes are end all but for similar cars with similar HP and close enough laptimes, there should be similarity to speeds at the end of straights.

Makes you wonder how much time you're leaving on the table by the car just not pulling strong enough as it should with those specs.

 

Sometimes it runs a mean first lap or two but performance drops pretty fast. It might just be in my head but it's usually the first session where it runs a few first laps very fast and it's pretty bland for the rest of the day. I mean it's still a fast car, but compared to what it is in ideal conditions...ugh. In the morning I have to really respect it coming out of hairpins. Once it gets hot I can pretty much plant my foot at 40mph and it hooks. 650hp/650tq should demolish any tire in second gear at 40 mph.

I once entered the straight at 90mph and was flooring it down the straight. Rich and another modded C6 Z flew by me on the straight like I was standing still! I got flanked on both sides and off they went.

Taking the car in to get all the air out of the intercooler circuit next. Overall I'm pretty happy since the car runs the whole time. Only 1/15 sessions I overheated with my mods. I'd say that's acceptable.

 

That makes sense as it's fast at the beginning of the day. Less ambient temp and the car is building up it's temps but after that as it doesn't have enough time to fully cool down (retaining heat) and the ambient temp is getting higher. Thus both things working against you.

Glad to see you are able to run the car for an extended period of time though. Once you're certain, hopefully you can get it perform at a high level throughout.

 

Currently traveling but I plan to throw in my $.02 when I get stationary.

 

SBC,

Lining your data up in a table format may help highlight trends on what the ECU is doing during your sessions. Below is some data I recorded during my last event at VIR.

About the Data:

• Data recorded using Torque App with OBDii reader @ 2.5Hz refresh rate
• Day 1 I had an instructor, Day 2 I ran solo
• Snapshot of 4th gear pull going up VIR's back straight.
• Still working through the data.

Day 1 Session 3 - Ambient high-90's



Day 2 Session 3 - Ambient mid-80's

 

Thanks for posting your data and I'm glad the car is starting to perform better for you in the cooling regard.

Definitely interested to see any future data with IAT2 like you mentioned you figured out how to display. Also, I've heard it said on the forum that manifold temperature is the appropriate place to look for post blower temps, and not IAT2. Not sure of the validity of that, or what that makes the IAT2 reading then, but figured I'd mention it in the interest of getting as much data as possible.

 

Not only taking out the roof affects the airflow but also it lowers the chassis rigidity so the handling is not as sharp or precise.

 

Our C7Z is typically 138-139 in the morning sessions and 132-136 in the afternoon sessions. The yellow car is 150+ at any given time and the highest I've seen was 156 MPH, but it's also about 6-7 seconds faster per lap than the C7 without dropping off when temps get a little hotter.

 

Hitting 1.6 MAP, maybe 8.7 psi and about 540 lb/min out of the MAF are both lower than expected and I attribute this to the weather.

It is also possible your throttle isn't opening all the way, which does happen bone stock from about 2500 - 3500 RPMs.

Your AFR also is bottoming out in the high 10s, which is indicative of CatOverTemp Protection being active the whole time, which is expected (and unfortunate) on this car. Removing the cats and disabling COT will make a huge improvement in power but also a large noise penalty (and emissions).

 

That looks like my data in raw format. I was thinking of summarizing it in a way that we can answer some questions such as how much timing it pulls in ideal conditions versus at the end of a hot session or ideally how much power it loses.

Is your method based on comparing raw data at full throttle in a small section of the track? That can work too I think, basically eliminating all the variables we're not interested in.

BTW if you figure out new PIDs for the Torque app let me know. I'm very interested in logging more than the default PIDs.

I'll take a look to see if I have any options for logging that.

Sure does but I can't tell a difference. I love open air motoring.

Any plans on making a C7 yellow?

 

Can you feel it? I've driven my convertible and I've driven Z07 coupes (not back to back unfortunately) at the track and didn't find them significantly different.

It'd be useless trying to mentally compare overall grip, but I felt the Z07 Coupe was looser in the rear than the Z06 Convertible. Sort of the opposite of what you'd expect from chassis flex.

I don't want to randomize this thread, I can start a new one if warranted, but I'm just curious as to what extent the roof panel actually helps handling, as the chassis seems very rigid. I get that more is better. I'm just wondering if anyone can feel the difference between roof in and roof out.

Impressive lap times from SB+S up top... funny how the brain works, I first read the quoted line as "a Stock 1997 Van". Not likely!