Theory behind turbo limits and heat

[phunny]

I wad recently talking to a friend about my IAT's at the end of a run and he informed me that its because I'm pushing the turbo to its limits. I had to leave before I could ask so I'll ask it hear, what's the theory behind this?

Just FYI it's a FPred running at 66+lbs/min

 

[BoostedBeaver]

The theory behind this could very well be compressor efficiency. If you can find a compressor map of your particular turbo this would be easily spotted.

At some point your compressor is most efficient. Every point past that and the compressor becomes less and less efficient. This means that the compressor is spinning faster and chopping the air charge more and more. This means that the air is being heated up more and your overall compressor efficiency has decreased which will in turn increase your IAT's.

The rest of your system plays a part too. The HX35 Compressor at its most efficient point is 76% efficient. This means the intercooler needs to come up with the 24% to bring the temps back down to ambient.

With this being said Yes, you could be pushing the turbo to the point where it is pushing very hot air and your intercooler (good or not) can not keep up. You could also be in a good efficiency range with a poor intercooler and experience the same issues. Hope this helps.

Robert

 

[donniekak]

Air heats as it compresses. A centrifugal compressor never operates at 100% efficiency. Some of the drive energy extracted from the exhaust doesn't compress the air, it heats it. Those are the efficiency islands on a compressor map. As you get further away from the maximum efficiency range of the turbo, high boost, high flow, and even lower flow at a certain boost, the compressor is less efficient, and heats the air more than at its optimal range.

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[silvreclips]

Heres a good read for you that should help you understand the theory behind it

How To Read A Compressor Map - Turbo Magazine

 

[5150DSM]

I'm going to guess that you're running 30-35 psi, which would put your pressure ratio upward of 3-3.3:1. As the others stated compressor efficiency is a product of PR, the higher the PR the lower the overall efficiency. Without a map it's hard to say exactly but I would bet that the Red is less than 70% efficient at that PR and approaching choke flow. At that point you're going to generate a lot of additional heat due to shear forces inside the compressor and friction from airspeed. I don't know what kind of I/C you're running but it also may be having trouble keeping up with the extra heat generated by pushing the compressor that far. As far as choices: you could back off the boost a few psi and see if that reduces your IAT's, replace your cooler with a more efficient unit or add water/meth after the compressor. My .02, hope it was helpful.