LPT (low pressure turbo) systems are very popular in europe, Saab, PSA Volvo etc..
Generally the engine retains a high compression ratio that a similar NA engine
would have,
the turbo's are small, and the boost is low ~5psi.
this beafs up and flattens the torque curve which is available from around 1500rpm.
My supra runs the factory compression ratio of 10:1 and I run large T3/T4 turbo's which
are on song at around 3500rpm with 7.5psi.
it is somewhat annoying but I built the system with engine mods in mind,
namely decompressing the engine and adding more boost, which the 10:1 compression would not tolerate.
My intention is to twin turbo a 1UZ with small T25's or sim so that boost response is immediate as it will be going into a landcruiser.
Lag is ok in the supra, its has a 4L v8 with enough power off boost, and a close ratio gearbox that keeps the engine above the magical 3500rpm when I'm thrashing the pants off it.
But in a 4x4 you dont want to be waiting for turbo's to spool.
In a factory Silvia with a SR20DET the small turbo boosts quickly, you have pressure around 2000rpm but you are limited to ~250hp with the small turbo. to much boost over-speeds the turbo and also goes beyond its most efficient operating range.
The result of this is heat. everywhere. and most likely a broken turbo will also result or engine, if your tune is average or det becomes uncontrollable due to the extra heat in the intake air.
Put tiny turbo's on your engine, but be prepared to have the engine choked at high rpm.
Put oversized turbos on your engine, but be prepared to wait for the boost/power.
research folks, corky bells book maximum boost is a good read.
a fluff around on:
http://www.turboneticsinc.com/choose_turbocharger
http://www.turbobygarrett.com/turbobygarrett/
http://www.turbofast.com.au/
http://www.bankspower.com/
I must warn against reading forums to find out important details, manufacturer's publications are really the best place to find info, as they are require to provide accurate info to their customers.
I can write anything i like on a forum, but who is going to hold me to account if the information i provide is erroneous?? nobody.
Ok, thats enough ramblings from me for today.
