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Old 11-15-2018, 04:28 PM
  #81  
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Default Oil life monitor calibration same for dry and wet sump?

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Patman asked:
I'm curious if the algorithm is exactly the same for the oil life monitor on the dry sump equipped cars as it is for the wet sump equipped cars? With the extra 3 quarts of oil in the dry sump (30% more oil), in theory the oil should last longer between changes and therefore I wonder if the OLM allows for that extra mileage possibility? Also, how does the OLM take into account both the time factor and the mileage factor?


Tadge answered:
Great question, Patman. This is one I bet a lot of people are curious about. Obviously, maintaining the quantity and quality of the oil in your engine is paramount for long term durability and performance. There are many things that work to deteriorate the quality of your oil and we make the oil life monitor (OLM) as accurate as we can to predict oil life in consideration of all of those variables. The simplest variable is the length of time the oil is in the engine. As you surmise in your question, this is an important variable. Oil ages sitting inside your engine differently than in a sealed container. It is exposed to more oxygen, humidity, various sealants and a variety of metals in your engine. Also, time causes things you might not expect to have an influence such as oxidation of your oil filter. To account for this variable there is an OLM clock that begins a year-long count down every time it is reset. So that is the best you can do…. Change your oil and filter once a year.

You also surmise that mileage should be a factor. We could use mileage, but it is more accurate to actually count combustion events. Every time the fuel and oxygen ignite in the cylinder a tiny quantity of contaminants slip past the piston rings and gets into your oil. Over time, these contaminants build up and hurt the oil’s lubrication capability. You can see this effect as the oil darkens over time.

OK, but all combustion events are not created equal, right? There is a big difference between cruising down the highway under light load and tearing it up on the track. On the highway, the coolant and oil stay relatively cool and there is little stress on the engine. On the track, when oil temps are high, oil molecules actually fracture and that hurts lubrication performance. We handle that buy adding a multiplier that compounds the number of combustion events that occur at higher temperatures. The hotter the oil, the more heavily we weight those events and the shorter the life prediction. On the other hand, running your engine at low temperatures stresses the oil as well. So we also have a multiplier that over-weights combustion events when it is cold. People who drive in cold climates and take relatively short trips are going to find they have shorter oil life. The display in the cluster is regularly updated to the lesser of the time-based or use-based metrics.

Lastly, to get to the first part of your question: No, the dry-sump cars do not use the same algorithm as the wet-sump. As you theorize, having more oil dilutes contamination and distributes thermal stress across a greater quantity of oil. Those are both true and, even though you get some life extension, it is not in direct proportion to the total quantity of oil in the system. Why not? Well the time-based degradation is very insensitive to oil quantity. And don’t forget the oil in dry-sump cars get more exposure to air and system metals (and other materials) because of the tank and plumbing. The extra oil quantity helps roughly in proportion to volume for contamination, but not quite in proportion when it comes to thermal stress. Since dry-sump cars are more likely to see track duty or hard street driving we tend to be a little conservative to make sure oil is changed before it falls below a performance level needed to assure perfect operation of your engine. Bottom line is that, depending how you use your car, the dry sump will have at least the life of wet sump, and probably somewhat more.
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Old 12-17-2018, 06:19 PM
  #82  
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Default Effects of front tire deflector on downforce

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Poor-sha asked:
In the past you have answered questions about the center rubber deflector that is only present on C7 base and Z06 cars without the stage 2 or 3 aero. However, what is the aerodynamic effect of the smaller side deflectors that hang under the splitter in front of the front tires (seen below)? They have been described on the Camaro as there to increase front downforce but it appears as though on the C7 ZR1 these are only present on non-ZTK cars. Do the deflectors increase or decrease downforce and can they be used to tune front aero grip? Also, is there a likely aero benefit to using helicopter tape or an equivalent to cover over gaps in the front underwing like the recessed bolts and the radiator supports? As always, thanks!


Tadge answered:
The ZR1 has, by far, the most downforce of any Corvette we have ever built. Getting that much downforce on a street car is very challenging and it is quite rare in the auto industry. Some auto makers talk about the downforce of their aerodynamics aids as independent features. They say things like “this spoiler generates XXX lbs of down force”. The entire vehicle may actually generate lift, but the impression is left that the car has true down force. When we talk about the ZR1 ZTK package generating 950 lbs of down force, we are talking about the whole car as a system. The most visible part, the big wing, is only part of the story. Sometimes that subtlety gets lost in some of the descriptions of the car.

When we start designing an aerodynamic package for Corvettes, we start with the front of the car. Down force on the nose is is the toughest to get. We developed a structural under wing similar to what the C7.R uses and tuned it to get maximum performance. Then we tuned the rear wing size, height and shape to precisely balance the car. We shoot for a pitch moment (think of the relative power of the front and rear aero aids) that keep the car stable and easy to drive all the way up to top speed. Too much down force on the rear relative to the front makes the car understeer and vice versa makes it oversteer at speed. This is obviously a gross simplification since we are simultaneously working driveline and brake cooling as the surfaces develop. We generally start with the max down force configuration (ZTK in this case) because it is easier to de-power aero aids than find more performance once they are designed. The image below on the left shows the underwing pressure distribution on the ZTK package. The blue color indicates low pressure or downforce. On the right you see a very different looking pressure distribution created by the tire deflectors, or air dams. Despite being relatively small, those features de-power the underwing by disturbing the flow pretty dramatically. High pressure in front of the dams causes the effect, but because they keep air from impinging on the front face of the tire, the net effect is actually a drag reduction. We can then pair the de-powered underwing with a smaller wing at the back of the car to yield a package that trades some downforce for drag reduction. This is why the standard ZR1 has the highest top speed.



As to the question on taping gaps…. You are right that creating smoother transitions will help drag and downforce performance. The effect is very small, but because it is more likely to improve front performance, it is in the less conservative direction for pitch moment – it will tend to make the car oversteer. We optimize the car for the real construction coming from the factory, so we don’t recommend additional sealing. Also, since we don’t test with those gaps completely sealed you may cause other problems. For example, hot soak issues where we count on convection drawing cool air from below the car after it stops moving or splash drainage when you drive on wet roads.
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Old 01-18-2019, 06:40 PM
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Default C7, c7zo6 and c7zr1 manual tranmission and axles

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black_c7 asked:

In previous thread tadge answered Fyreant that all c7 manual cars have the same axles, but I found that base c7 have a different axles parts number (20977316 left side + 20977317 right side ), for c7zo6 and c7zr1 (23301162 left side +23301163 right side), pricing is different from both part numbers.

My question is why there is different part numbers and different pricing if they are the same axles?

Also: is the transmission in c7zo6 is the same as the c7zr1 for manual trans?


Tadge answered:

In reviewing my answer to Fyreant on ZR1 hardware upgrades, what I said was: “The half shafts and prop shaft assembly are carry over from Z06”. That was and still is true. There are a number of part numbers in our service catalog because left and right half shafts are different in diameter and there have been continuous improvements over time. We traditionally use half shafts of different stiffness’s on either side of the car to help with power hop. Power hop occurs when spinning the rear tires on surfaces with friction characteristics that create a stick/slip condition. The stick/slip phenomena alternately winds and unwinds the driveline like a big spring preventing smooth acceleration and creating quite a disturbance in the car. Having a very stiff half shaft on one side will break that tire loose sooner than the one on the other side, creating an asynchrony that helps dampen the resonance of the system. The part numbers you quote for the base C7 are in fact parts that were released for the 2014 model year Stingray. They have a unique interface and so can not be replaced with the newer part numbers. All manual transmission Corvette since the 2015 model year use the 62/63 part numbers. You do see some minor price changes between the older and newer part as our suppliers change the price to us, but the big difference is left to right. As I describe above, the stiffer half shaft is designed with a larger diameter. There is more material and a more complicated construction, that is why the right side parts cost more than the left.

The answer to your final question is, yes, the manual transmission assembly number is the same for Z06 and ZR1, we build both cars with the same trans.
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