I’ve been reading the info dump and other links regarding heat soak and everyone’s attempt to prevent/reduce HS. However, as a newbie, I’m not clear on the exact problem.
Is it just an issue for guys who want to take their car to a drag strip and experience temporary reduced hp because of heat soak?
Or is heat soak causing permanent damage to components on the car? If so, is it just happening when racing or does it happen under normal driving conditions?
It typically refers to a temporary loss of power due to a higher temperature intake charge (lower density, higher pre-detonation propensity)
Yes, heat soak is a condition where the car is irreparably heated to the point it’s down on power for quite a while.
Kind of a point of no return. That’s what I’ve always considered it.
Great question
Ill add some more, and let the experts correct me if Im wrong about anything…
Heat soak can lead to earlier detonation (detected by the knock sensors). To decrease detonation, the ECU on the S6 will start pulling timing. This decreases power.
While detonation could potential cause severe issues, I dont think it necessarily does in the S6 due to heak soak, because the engine will just keep pulling the timing, and decreasing power, until there is little to no detonation being detected.
Here is an article on detonation (not Audi specific) and mention of heat soak
http://www.autospeed.com/cms/article.html?&title=Dodging-Detonation-Part-One&A=111608
Some vehicles are also very sensitive to driving conditions. If the car is idling around in traffic for extended periods, the resulting heat-soak in the intake manifold, induction system and under-bonnet heat can lead to detonation when you resume driving.
Part longevity issues due to heat soak - I have been trying to see if there is a link between the really hot engine bay in the S6, and the premature failure of plastic parts (e.g. intake manifold pieces, water pump housing, etc). At this time, I dont think there is enough evidence of part failure due to heat soak. The plastic parts inside the intake manifold are prone to failure, at a level much higher then I am aware other Audis that I am familiar with. However, this could be due to a design issue, and it would be very hard to link it to heat soak, without doing extensive testing.
There are two cats right behind the engine that, like all cats, get extremely hot. It would be interesting to see if the cylinders that flow into those cats, have greater amount of detonation, cylinder wear, carbon on the back of the valves, etc.
On the other Audis I have worked on (C5 v8 4.2 with S8 heads, modified exhaust), some cylinders seem to ‘knock’ earlier than others. This can be due to how the exhaust flows differently out of certain cylinders.
But, from what I understand, you can’t necessarily determine the level of actually detonation on each cylinder, with the factory knock sensors. Experts, please correct this if wrong. The knock sensors will pick up the ‘knock’ more from the cylinders that they are closer to. I am not sure if this is the case on the v10.
These are my timeslips from a 1/4 mile run. What is interesting, is that they are VERY consistent
http://ep1.pinkbike.org/p4pb11847770/p4pb11847770.jpg
My friend who performed the testing did his best to keep the engine bay cool in between runs by leaving the hood open, and provide cool down between runs. The day was a warm day in mid summer (IIRC)
Considering of the consistency of the performance results, there are a few possible scenarios:
The S6 engine bay gets very hot, very fast, and is never really running at optimum power levels due to timing pull. This could explain where car magazines and Audi, report much better 1/4 runs, that seem impossible to duplicate under normal conditions.
Maybe the car is designed to run ‘hot’ and the factory tune is set conservative. Further logging and testing of a stock car could confirm this. Ill have to talk to my Tuner and see if he logged more data during the stock runs.
The stock ECU (and most tunes) adjust the timing as the ECU learns how close to optimum it can go without detonation. So, even if the car runs at the base level of the factory tune, it doesnt mean it is running at optimum power levels. You would have to look at the tune, establish the baseline, and then see how far it was willing to adjust. Then do some logging of a healthy stock car, and see how far the timing is actually advanced (or pulled) during normal spirited driving, after the car has had sufficient time to adjust to the octane gas being used, and other environmental factors.
This is another possibility. Further testing would be needed to confirm.
With the stock v10 S6, there is only so much investigation that can be done, unless someone really has a lot of time to log the stock car under different conditions, and figure out exactly how the heat soak effects performance.
What we have done instead with the project car, is make the assumption that the v10 will operate, and respond to modifications, much the same way the B6/B7 S4, v8 S5, B6/B7 RS4, etc, have reacted. In those cars, repeated hard runs would cause heat soak, and then the engine subsequently pulls timing, decreasing power. Products like the JHM intake spacers allow cooler IAT temps for a prolonged period, before heat soak becomes an issue.
Thanks guys… good info.
Everyone kinda nailed it. To add a few points. The motor already runs hot and heat soak will reduce power for a few reasons.
Heat soak really is effecting the in coming air. The quality and quantity of that air will effect how much power the car car make. When air gets hot it gets thinner with less mass. Cold thick air makes big power because it contains more oxygen. The more oxygen you can pack into a motor the more power you can make. The manufacturer actually wants the air to be hot so they don’t go out of there way to cool it off too much. You can see one of the ways the manufacturer heats the air by looking at your coolant line running through most of the audi throttle body units. I don’t think the S6 has this but lots of other more fuel efficient Audi have them. My 4.2 s4 had it. Anyways less thick air less fuel used. But also less power.
So less thick hot air tends to not be optimal for big power and as the car acceleration picks up so will the heat. The quality of the air will effect the power by how it’s disturbed the burning. It’s thin and causes less full burn cycles. Some people say this leads to , ore carbon knock and obviously less power.