Here is something about how much an intercooler gives in a turbodiesel.
My Peugeot 307 has two versions with a 1.6 turdodiesel engine: 90hp and 110hp. There are also 407's with the same two engines and 307 with 2.0 liter, 90hp and 110 hp engines. I have the 110hp engine and was wondering about differences between it and the weaker version. I found this
thread on the Peugeot-Klub Polska forum, and in it two links:
http://tdi.pl and
http://www.psc.com.pl. It's all in Polish, but the last link is supposed to have some charts (my browser doesn't like them).
It turns out that the 90hp version doesn't have an intercooler. Someone took a stock intercooler from the 110hp version and installed it in the weaker one. This gave about 9hp. The increase was in the mid range of rpm's, at lower and higher rpm's the power and torque were the same or slightly lower. Nothing else was changed. If the compression ratio was increased to compensate for the extra drag in the air supply, then you should get the 110hp engine.
Unfortunately, neither turbos, nor intercoolers, help much in the 1500rpm range where my engine is usually at
