NSC5

I have a feeling just adding a scoop to the existing ducting and cooler (referring to owner modded C7/Z51 and not the upcoming Z06) won't help very much. Airflow is going to be very restricted by the size of the stock duct and cooler so the scoop will end up creating more air pressure but not as much additional flow as you would like. When I saw the two different Z06 fan setups I wondered if they are quantifying cooling based upon a larger fan (better cooling at low speed) versus a smaller fan and more open area which will provide better cooling at speed.

Hope they get this one right and that it will be well tested before release. A lot of GM's truck buyers were very upset when Chevy/GMC released the second generation Duramax diesel pickups that would overheat too easily under load and go into protective limp mode; this wasn't resolved until the third generation of the Duramax engine. A couple of companies sold an auxiliary radiator but the problem wasn't addressed by GM until the next redesign.

kp

Honestly, I have been building racing auto transmissions for over 30 years, even with the bigger core and scoops I doubt that will be enough - especially on the Z06.

Torque converter autos are huge heat generators, lots of moving parts plus disengaged clutch packs slipping and the torque converter itself churning away. Unless GM really comes up with one heck of a cooler, increases fluid capacity and keeps the converter locked most of the time, that trans temp gauge is going to keep climbing on a road course on hot days. I'm not into that type of events but I'm sure if GM can keep it out of protection mode for the average length on a tough track that will be a 'win' for them.

CeeSeven

You may be right. It's all about BTU's, gained and lost. Increased air flow IS a pretty big factor, though, as long as it can get to and through that cooler. They don't make fans for nothing. Also, those little louvers on the shroud allow forced air to go over the cooling fins outside the fan area. Theoretically, with enough air, heat loss could be 100% from intake side of the cooler to the output side. Practical limitations, though are air flow and thermal efficiency of the cooling fins.

I'm guessing the air pressure at the air duct intakes on the fenders is possibly quite inadequately low. They designed the car for low drag. To create a high pressure point right in that spot was almost certainly not on their drawing board. If they claim a 50% increase in air flow for the Z06 with that little dinky air deflector they added on the vent intakes then a big, ugly, honky, home made one (for track) might just increase it 2 or 3 times on track. If so, that has got to dissipate a whole bunch more BTU's at speed.

Enough speculation. I'm going to take a break from this thread until I get some solid info and test results. I'll be back. Try not to get off topic.

kp

I agree, of course airflow is a major factor and where that cooler is not the best place. Fans can only do so much and if you have a lot of airflow at speed they will limit the the air going through the core, thats why the shutters are there.

If you look at those small ducts going to the cooler I cant imagine them getting anywhere near the airflow of a front mounted cooler. Not to mention the exit area has to be there too. Its possible the Z06 with its wider fenders will have room for larger ducting in and out also.

Any word on damage from the dealer?

Hopefully nothing was damaged on your last outing and you will back on the road soon, cant imagine what was clanking around in there if the cae was still moving, torque converter clutch maybe.

Shaka

Nice post. Without electronics, it can't be done of course. The TC has some interesting patents which will reduce it's duty cycles in track mode. The DCTs and autos in class 8 trucks protect those clutch packs vigorously electronically. They just wont work at high temps. The lock up clutches will work more like a regular wet clutch in the Vette.

The friction in the mesh of the epicyclic gear trains is less than that of constant mesh gearboxes and especially DCTs depending on how they are cut. The quiter, the weaker. This is not where the heat is produced, much.
Problem with the LT1 engines is that they have much enertia so there is a lot of heat generation when rev matching is forced at open throttle shifts. The Torque converter does a lot to reduce impact loads on the gears. Also there is less engine braking with a regular torque converter so a lock up in coast is in order but with the initial fluid couple in reverse, the load transfer will be less harsh and won't upset turn in transitions.

The F70 shifts much slower than the 458 and electronics tries to match RPMs as best as possible with fuel cut offs. If you are in the habit of fast launches, goodbye DCT clutches. Ask any F458 owner.

The multi disc clutch pack within the torque converter at these high energy shift events must engage sooner in track mode. The fluid in the TC will absorb most of this energy before the lock up which is most of the heat generation. The duties of the TC can be reduced in track mode.
The faster all hydrahlic chambers, brakes and clutches, can be pressurized and depressurized within the gearbox, the better. Also the faster the TC locks in up in up and down shifts, the better. The tuning between street and track will surely be interesting. It will make your work more interesting.

http://www.thetruthaboutcars.com/201...n/#more-805018

NSC5

Well stated and one of the programming tricks used to reduce heat buildup in other applications won't work for the road course guys. Every shift creates a little heat spike in the clutch packs involved for that shift thus the "shift stabilization" program used in vehicles used for towing that greatly reduces the number of up and down shifts. But on some of the road courses there is going to be frequent repetitive shifting and if the torque converter gets unlocked for these then there is a huge heat load to be dissipated.

In previous generations I don't believe the dry sump engine was available with auto because the auto wasn't suited for repetitive high G cornering which causes fluid pickup problems resulting in air entrained in the fluid which greatly increases heat buildup. I wonder how much of the excessive heating reported in the current generation is due to this problem? Hopefully this was fully addressed in the coming 8L series.

kp

True, but it all adds up

Yep, delicate balance between line/passage/chamber size, pressure and pump size. I know the C7 A6 is a punching bag for a lot of people but its really not a bad trans, I assume the A8 will be a good upgrade as well.

Wont make my work much more interesting, I'm a drag race guy. But after working with 1200hp+ true street cars that have to go 20 miles in stop and go traffic and then make three back to back passes with no cool down I'm pretty familiar keeping things cool (locking up the converter when possible) and getting rid of a lot of heat as quick as possible.

Possibly, never really thought about why GM didnt offer the dry sump with GS automatic cars. Not sure how much of the heat on the C7 is coming from getting air picked up, but thats something that can be fixed fairly easy, looks like more room for a deeper pan. If the A8 is as good as the hype GM will be forced to look into cooling more and more, since more and more people will try to track the auto. I'm surprised the C7 A6 doesnt do a little better, the Z51 thing kind of implies 'track ready' even with the auto.

CeeSeven

Just heard from the dealer with good news - I think.... That loud clanking in the back end at idle that I thought was the tranny tearing itself apart was actually the exhaust valve on one side. I could only speculate as to what was going on inside it. But it's hard for me to believe that thing could make that much noise!

So I'm back to trying to figure out how to cool this A6 off.

You guys bring up some interesting stuff with the entrained air in the fluid. That makes a lot of sense in my case because when it got to 275° and started to up-shift on its own it also was shifting like an old worn out auto trans -- namely gaining RPM between shifts even with little load. I guess that was its inability to develop pressure because of air??

Also, regarding the TC heat from frequent shift changes. Am I understanding correctly that less shifting = more lock-up time and therefore less heat production? Will the TC stay locked up regardless of engine demand (pedal position) as long as a gear change is not made? And, hand in hand, is less air entrained as a result of lower RPM or less shifting or both?

NSC5

That is good news about the noise source!

I am not familiar with how the TC lockup is managed in this transmission but my guess is it doesn't stay locked all of the time in-between shifts and will unlock both with hard acceleration and with rapid throttle closing. You can watch the tach with the transmission in manual shift mode or preferably use a scan tool (with a passenger to watch the tool or use data logging) to see when it is locked/unlocked.

Most automotive transmission torque converter clutches weren't designed to stand the stress of running locked under all conditions and the first vehicle I owned which did allow lockup at all times including during shifts was a 2001 GMC 2500HD pickup with the diesel engine and Allison automatic. Set for heavy duty personality mode the torque converter clutch would lock with the shift to second and remain locked until the vehicle slowed enough to force a shift back into first regardless of pedal position. This was also my first experience with clutch to clutch architecture which is now used in most if not all GM automatics and it depends upon precise computer control to apply one clutch pack while releasing another without slipping the clutches or having "tie up" with two gears selected simultaneously. I was impressed with how well this technology works with the lockup converter and it gives the automatic a very solid feel without the "slush/slip" feeling, I hope the upcoming 8L90 provides this same feel.

The downside of the Allison is it is very large and heavy and isn't designed for lightning fast shifting so it isn't a sports car transmission. Hopefully they can fit a very sturdy converter clutch into the 8L90 housing. My current 2006 GMC has the same Allison setup except it is a 6 speed unlike the original 5 speed and I well remember the first time I pulled out to pass on a 2 lane road during planting season when I was stuck behind a slow vehicle. At 50 MPH it is in 6th (second overdrive) and the downshift from 6th to 4th doesn't take that long but it seems like it when you are exposed in the passing lane

CeeSeven

Got the car back and did a first effort mod on the air intake for the trans and diff. Here's the trans air scoop before sealing up the air leak at the inside rear. 1st opportunity to test it is next Sat and not a good one with a small track (.75 mile) at CAC and short lap count. Better test at Inde a week from Sat.

There's a closeup pic of some stuff from 3M I used to hold the scoop in place for sheer strength called Dual Lock® in case you're unfamiliar with it. It's a pretty high strength material for removable attachments - like Velcro only better holding strength and a LOT better adhesive: UV and heat stable, clean removal and won't peal properly applied paint. I've been using it for all sorts of stuff since it came on the market about 15 years ago. Source for it is : www.itapestore.com

The Dual Lock will provide great sheer strength, but for safety against lifting up I included a bracket attachment around which I ran a Velcro tie to the existing louvers and screen below.

dcbingaman

Very cool. Let us know how it works ! I have some CFD wizards working for me - I may have them do some analysis on a true pitot type intake that would completely cover the vent top and increase airflow and ram pressure recovery well down into the duct.

If you want lots of airflow - check out the Bugatti Veyron ducting. If you want max airflow on the Stingray you need an inlet area normal to the flow at least 100% of the vent projected area, (about 36 sq. in.) Think a B727 center engine inlet about 7 inches in diameter that turns 90 degrees to cover the entire vent entrance. You also need a small 1" tall diverter between the bottom of the inlet and the door top so you pick up good air. It may look goofy, but it will work at lot better than stock.

If this doesn't work, then you may need to increase the transport ducting size inside the fender to the cooler location, again, at least a cross-section area of 36 sq. in. Finally, rather than buying a Z06 cooler, it may make sense just to add a second Z51 cooler in parallel with the first one. Finally, a water/oil cooler in place of the air/oil cooler should keep the ATF below 220 degrees, using the water jacket and the front radiator. Lot's of plumbing but it should work...

CeeSeven

Lot's of good info. Thanks. Hope it doesn't come to drastic measures, but I'm not averse to increasing the scoop size and design. Don't much care what it looks like on track (within reason) as long as it works. If the temp goes down ANY due to this scoop then that tells us something -- a starting place. Thanks again for the know-how.

kp

Make sure the air exit is large enough as well, air has to flow through the core, the more air that can be pushed out the better.

NSC5

Great point! I remember looking at some forced air cooling studies of large transmitting tubes that are equipped with finned external coolers and reducing the restriction on the outlet side provided far greater gains than greater cooling pressure on the inlet side. Less turbulence at the cooler was the primary advantage of reducing the exhaust side pressure.

With enough airflow at speed the fan itself will become restrictive negating the benefit of bigger scoops. At that point you will need a better fan or one with flap type valves on the shroud/housing that open under positive pressure.

kp

Yep, the stock trans cooler fan has the flaps, so does the radiator shroud on these.

You generally cant move more air through the fan then the CFM rating of the fan when its running. A well designed system should be able to use no fans at speed, most late model cars shut the fan(s) off at highway speeds. Low speed and sitting still is when the fans come into play.

NSC5

kp,

Good info, thanks!

If someone gets close with a larger cooler but still falls a little short I would use a couple of sensors to check the aluminum frame temperature in that area to see how much heat it gains during a hard run. Aluminum has good thermal conductivity and the new frame might be useful in managing the transmission fluid heat. A fluid pass through thermal block bonded to the frame might prove quite useful in dumping some of the heat to the frame before it passes to the main cooler.

Good2me

Very interesting thread. As a novice to the car tracking thing, a dumb question, is it best to shift with the paddles, or let the auto tran do the work, to help with the heat issue? I have a non Z-51 coupe, that came with the performance exhaust. Will be doing a weekend in early June.

CeeSeven

Got some results from the dealer regarding the exhaust actuators and nothing about the overheating transmission and both are disappointing.

Because I disconnected one of the exhaust actuator connectors momentarily to see the effect on the code throwing and then reconnected it [and stupidly told the service rep about it] he called today and said I might have to pay for the actuator repair because I "tampered with the car." A load of crap, obviously, but it let's me know the mindset of the dealer - deny and look for a way not to fix it. I called my attorney today and he said ignore him and tell him to present his evidence to HIM [the lawyer] that "disconnecting and reconnecting the connector had or still has any ongoing effect on the performance of the actuator." Also, I found others on forums with [momentarily sticking] actuator problems like mine. I can clear the code and the first time I start it it's back. The code appears to be thrown at engine start when the actuator encounters resistance then opens (or closes). Some guys even lube them with temporary results. Most problems in very cold or very hot weather. So even replacing actuators (which one??? of four??) - and the front ones are a nightmare to get to - might only be temporary.

As far as the trans overheating issue it appears the dealer has done nothing and intends to do nothing. When questioned the service advisor simply said, "Well, it did not throw any codes so we have nothing to go on but your word." That's nice, huh? My word [and that of others having the same problem] isn't worth anything at all. So I am going to bring my data recorder (Trinity) and laptop to the track next weekend and get some temperature data with timestamps on it. Also, nothing from the GM rep. Ignored so far.

For those of you experiencing the same transmission overheating problems that I am, please weigh in here with details of the conditions/temps, etc when it overheats. There is possible clout in #'s. Also, my attorney said this would be clearly covered under the Arizona lemon laws if they fail to rectify it after 3 attempts or 30days at the dealer within 2 years of taking delivery of the car.

One further thing the dealer attitude indicates: that ANY alterations to the car -- even bigger coolers at our expense, or changing the TC lock points, etc would be grounds for warranty voiding even if it helped the situation. A buddy with a BMW said their attitude is similar.

slief

So let me get this straight. Your attorney is advising you that if your dealer can't keep your cars automatic tranny from overheating on the track it would be covered under lemon law???? I hope your not paying for this advice.

Good luck with that one!

Snorman

I'm happy to weigh in, but not sure if it will help.
The trans in my car overheated twice during two session at Daytona-Rolex approximately 11-12 minutes into each session. Both times, the "Transmission Temperature High, Idle Engine" warning was followed by a limp mode where the car would automatically shift at a lower rpm. Both times I basically pitted in and let the car cool, so I experienced no odd noises or lingering problems.
Temps were in the 80's for each session.
S.