[stillsearching]

I was curious who else is familiar with this, and whether tests show the theory to be valid and work or not. I'd think if it worked great everyone else would do it unless it was locked in patent/trademark type protection.

Basically the point of the Saab Low Pressure Turbo is a combination of turbo boost at low rpm and steep gearing. The turbo is sized to have full boost by 1500rpm or so if I remember right (or at least to be coming on significantly by then), there is zero turbo lag, it's basically undersized for the engine - top end HP improves almost not at all. A stock engine producing 125hp before, after the LPT might put out 140-150hp at max. What the turbo does is radically improve the torque curve especially at low rpm typically 30% or more. This makes the inline 4 have more like V6 types of torque so they do not have to rev up.

High compression ratios are maintained - the boost is light (no more than 5psi) so high compression for efficiency can still be used.

This is combined with steep gearing. The turbo almost acts like "displacement on demand" since whenever the engine gets loaded to where it would normally start to slow down in top gear, like due to aerodynamic load or going up a minor hill, the boost will come on. Thus you are allowed to use an engine that would normally be undersized for running at that rpm.


The problem is that cars that use this technology do not seem to show spectacular mileage. (they are not posting better mileage figures than other compacts, the LPT turbo numbers seem to be worse mileage than say other small 4cyl cars which may be comparable power levels even without boost) So i'm wondering if a 4cyl on boost at 1500rpm honestly has any advantage over a bigger engine at part throttle flowing about the same level of fuel...

I like the theory - to me it seems like a good strategy to try on any engine but maybe doesn't work in reality. Yet I was hoping someone here might know more..