04-25-2015, 01:54 PM | #23 |
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Drives: 2014. 640 ix Vert
Join Date: Nov 2013
Location: NYC
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Wow, amazing and highly educational.
Thanks for a great piece. |
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04-25-2015, 04:12 PM | #24 |
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Your welcome. It was my pleasure. In case you couldn't tell I really love this stuff.
Most of that post was based on work done from back in the 30's to around the 70's - not mine of course. A lot of it comes from high speed photography of the combustion process - that alone was pretty fascinating to see. Seeing the actual pictures of combustion really helped make it very easy to understand the basics of it. As I alluded to, the turbulence of the mixture plays a big part. That the air enters through the intake valve(s) on one side of the chamber causes some. The piston coming up on the compression stroke causes some more. The shape of the chamber also has a huge affect all of that. Then there is the location of the spark plug - wherever the engine designer managed to fit it in after getting the intake and exhaust valves in there. When the electrical arc occurs across the spark plug gap the mixture is flowing past it so quickly that the flame sort of makes a swirl at first. But that changes rather quickly. Although there are some variations between cycles, the photo sequences I saw seemed to show that the end gas would most often occur in roughly the same area of the chamber. Often it was near the exhaust valve(s) - they tend to be particularly hot spots since some of the burning is still going on when they open. It all has to go past that valve(s) on the way out and there is not much to cool it. The exhaust valves on the S63TU motor are hollow and filled with sodium to facilitate some cooling. I think they are on most engines but don't count on that - I'm not a mechanical guy (electronics and control systems are my forte). But that valve and the area around it present hot spots that can help raise the tendency for self ignition or detonation in any of the end gas that happens to be around them. The intake valves get a fresh shot of relatively much cooler air every time they open so that side of the chamber stays a bit cooler. Detonation is also far more likely when you raise the pressure of the mixture (in other words go into boost) and the temperature. The temperature of the intake air is also boost related. When the boost is really high the inefficiencies of compression can easily raise the intake air temperature by a couple of hundred degrees or more. Back when I was involved in this stuff running a bar of boost was really pushing it. Most kit makers and manufacturers were running 8-10 psi. Temperature increases were around 150-200 over ambient - on a 90 degree F day that would mean air temps of 240-290 degrees F. At a bar (14.7 psi) you could easily see 250-350 degree F increases over ambient. Getting the temperature down is why intercoolers are such a big deal. The really high air temperature is why they can use engine coolant (already at around 200 degrees F) as the cooling medium. It is also why injection of some water or a water/methanol mixture helps. The heat of vaporization reduces the temperature and the temperatures are so high that adding water does not hurt the power output at all. This cooling effect is also present when you run a fuel with alcohol in it (ethanol or methanol). The trick to making power is getting air in the engine. You can get more into the combustion chamber if it is colder. I hope the OP and others can understand why it is important not to fool around with this stuff. Although I have not used their products, from what I have seen BMS and the others making similar systems have tried to work this out to provide a reasonable increase in performance without jeopardizing longevity very much. You can easily spoil those efforts by ignoring their recommendations. Although it could, it most likely won't go boom the very first time - you are more likely to see a gradual fatiguing of something before a catastrophic failure. How quickly that happens depends a lot on how hard you push it. It also does not help to drive it really hard all the time. If you do you might want to think about doing other things that would help mitigate the effects of demanding that kind of performance out of your engine. Fortunately BMW tends to design things to last. That and the way they drive are the main reasons I love driving them. If you are going to push it, I'd suggest you pick components from people you trust are good at doing this and then listen to them. If you want to push it further, do it the right way. I think BMS recommends (has maps for) using race gas and octane booster and meth injection. You can usually get away with it for a while. But if it fails, your car is going to be down for a while. Even if you opt to just put another stock motor back in there, these engines are not just lying around everywhere. It'll take some time to get shipped to you and then a little more to get it installed. Just something to think about before you push it too hard. Last edited by chask; 04-25-2015 at 05:40 PM.. |
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04-26-2015, 07:07 AM | #25 | |
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Quote:
Regarding the quote above, one interesting note about the S63Tu is that it uses a completely independent cooling system with 3 radiators for the intercoolers and DMEs. This just reinforces the point how important it is to keep the charge air temperature down. |
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04-27-2015, 07:35 AM | #26 | ||
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Quote:
It's a brand new car, so all components should be able to handle it for a bit since I don't do any hgwy driving during the week, and my commute to work is only 4miles. However, I don't want to take the chances of blowing the engine, so I will keep it on map 5 instead. My car is a lease, and I won't buy it at the end of the lease. I am waiting for the 2017 M6 to come out and have a high power car from stock. |
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