Quote:
Originally Posted by nicks90
2) EGT can be reduced by lowering the boost pressure in the inlet due to restrictive intercooler.
correct. Most diesel turbos have a wastegate to control the amount of boost they deliver. this is usually situated right after the compressor.
Adding restrictions to the inlet after this point will rob the intake manifold of pressure - because the wastegate doesnt care where the final restriction is, it just knows its hitting 15psi and opens!
This loss of boost at the cylinder can be offset by the greater density/lower temps - therefore producing simillar overall power and hence why some people notice no power increase or decrease when running an i/c
solution!!! - the wastegate is usually operated by bleeding pressure from the compressor side via a small tube. relocate this tube onto a tapped hole on the intake manifold, This will ensure the boost pressure at the cylinder will be 15psi irrespective of what restrictions are between the compressor and inlet manifold. As long as the restrictions are sooooo massive as to exceed the possible boost deliverable by the turbo (very very unlikely) then it works very well.
this is standard practice on tdi defenders when fitted with full width intercoolers. Boost would normally drop by 1psi - simply relocate the pipe and you regain the boost.
Downside of an i/c - increased turbo lag
1) you are pressurising an increased volume of air between the compressor and the cylinder. Takes longer
2) if the i/c is causing significant restrictions to air flow - add some extra lag to the above.
all this arse about mapping turbos has already been done - by TOYOTA! They mapped the appropriate turbo characteristics to the appropriate engine. Adding an intercooler into the mix makes no difference to the volumetric capabilities of the engine (you aint changing head design or valve sizes or displacement) and the volumetric capabilities of the turbo supplying it.
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On point 2. That increases boost, doesn't decrease it. The extra air reduces egt's.
And your last point about volume flow.
Intercooling increases the volume of air that a turbo and engine has to move.
Where do you think those extra air molecules you're cramming into the cyilnders come from?