4.2 Biturbo and cooling issues with mods and high temps, etc.

[SteveKen]

OK, I've been thinking about this and the recent discussion of removing the aux radiators garners a separate discussion.

So the big question is how does extra HP affect the stock cooling system?

I'm hoping Mr. Balsen can chime in here, as I've seen him write that the limiting factor is cooling with the biturbo. Although, I've never seen any evidence of overheating at all, I also haven't seen anyone making gobs of HP over the stock amount.

If cooling isn't an issue, or doesn't seem to be one, then why hood vents and modifications to the belly pan? Could it be safe to say that underhood temperatures have no affect on the cooling and strictly affect IAT's?

I'm wondering if anyone knows at which HP mark does the cooling tradeoff occur? Improve IATs and IC efficiency by removing the aux rads and get more HP, but at what point will the stock cooling system be affected?

As, many of you know, I'm embarking on a manual conversion. This is somewhat related to this issue on a few fronts.

#1. The smaller transmission can free up space for bigger turbos.
#2. The manual trans can get away without being cooled, which is less taxing to the oil and water cooling.

Initial thoughts I had were to replace the stock radiator with one that doesn't have a trans cooling circuit. I don't think that running water through the trans circuit will help with water cooling as it would be too restrictive to the water pump.

Another thought was to run the trans cooling portion of the oil cooler in series with the oil lines to improve oil cooling. Basically making the entire unit a singe oil cooler.

FYI, my 4.2 S6 has an aux radiator and so do the 4.2 B6/7 S4s.

Also, the coolant after run pump. I've seen it removed on the 2.7T without any issues. With due diligence, could the same be done on the 4.2 biturbo?

Anyone have any thoughts or evidence that can lend to the discussion?

[hahnmgh63]

Part of the deal is how hard and how long do you drive your car. It doesn't matter if it is a Bugatti Veyron if you only drive it at 40mph you won't need the 10 radiators it has as you will be using less than 100bhp so it won't be producing the heat. If you track your RS6 or run it cross country at sustained higher speeds you will see the temp climb as you are producing more heat and producing it for a longer period as you are producing more BHP. And as many know, don't believe the temp gauge in the car, hook up Vagcom and you will see the temp vary by 5'C without the needle moving off of that centerpoint. The temp gauge is controlled by a chip in the cluster and it will normally center before full temp and keep center even if you run it a little hard. If you track the car or do that long high speed sustained run you might see the needle nudge a little past center but with Vagcom you will see that your temps may be pushing 100'C or greater. Just doing some 2500rpm to Redline Vagcom pulls for logging will get your water temp up a couple of degrees Centigrade in one run, and once again, the needle won't show it, but Vagcom or the climate control cluster in the diagnostic mode will show it.

[Brav]

I really want to throw mine out as well. One thing I plan on doing as the mods come on, is install a permanent mechanical boost gauge and one of these:

http://www.plxdevices.com/multigauges.html

Or maybe 2 of these and no mechanical boost gauge. It will read OBDII info in any combo you please. I will show IAT, AFR, Water temp, Trans temp (if possible?), and probably Ignition advance. I'm working out 1 of 2 ways to mount these 2 gauges. This will give us a lot of easy, useable real time data that can detect a problem.