Light turbo vs. high-pressure turbo

[philosophicaldreamer]

I have a stupid question: Can someone succinctly explain to me the differences between a light turbo and any other turbo? :confused: Is there a difference in the way one should drive a high-pressure-turbo car and my XC, for instance?

Thanks.
Ta-ta, janusz

[skibo]

I believe it simply means that the 'light pressure' version limits the maximum boost pressure to a lower value than the 'high pressure' version. In general, higher boost pressures increase power output, but also lead to higher loads on the engine, with the potential of increasing wear and risk of failure.

I would guess that a light pressure turbo would be less prone to turbo lag, and would be more transparant to the driver.

[eraas]

I would guess that a light pressure turbo would be less prone to turbo lag, and would be more transparant to the driver.

This is consistent with the marketing literature I've seen and my experiences driving 'Turbo' and 'GLT' 850's (the GLT came with light-pressure turbo in latter years - the older GLT's had no turbo; the 'Turbo' badged 850's came with the high-pressure turbo).

The 'Turbo's' I've driven feel slightly anemic out of a dead stop but you get that 'pushed back into the seat' acceleration if you hit the gas at 50km/hr. Volvo's early marketing of the LPT made much of the minimal (as in practically nonexistent) turbo lag, which I certainly found to be the case. The LPT car has good torque from a dead stop or at low RPM's. I find this to be more useful for everyday driving... the XC70 is based on a newer version of the LPT engine.

The HPT's had a smaller engine displacement, I believe this was in order to have thicker cylinder walls.

[philosophicaldreamer]

Thanks for your explanations.

Ta-ta, janusz :)

[dlr97]

Light pressure turbo superchargers are smaller and spin up at lower gas flows, i.e. lighter throttle and lower RPM. They produce torque across a wide RPM range, but less peak torque than a high pressure unit. Tend to have less throttle lag than higher pressure units.

The XC70, T5, and R motors are examples of light, medium, and high pressure turbo applications.

[philosophicaldreamer]

dlr97,

Thanks for your explanation.

Ta-ta, janusz

[CrazyTiger]

Light pressure turbo superchargers are smaller and spin up at lower gas flows, i.e. lighter throttle and lower RPM. They produce torque across a wide RPM range, but less peak torque than a high pressure unit. Tend to have less throttle lag than higher pressure units.

The XC70, T5, and R motors are examples of light, medium, and high pressure turbo applications.

I thought the R is a twin turbo (from what the volvo sales guy told me..)
Is twin turbo same as High pressure turbo or maybe it means 2 high pressure turbo in the engine as it is called Twin Turbo. :confused:

[TrueBlue]

Ummmmm,

The R is a 2.5l 5 cylinder engine isn't it. That means 2 and a half cylinders per turbo?? Bit of an engineering feat if so....

The twin turbo is on the T6 (as fitted to the XC90), so perhaps the salesman fell asleep during his training session....

'Course I could be wrong.

[Willy]

Hi,
I think that the wide powerband of Volvo's light pressure turbo is not as much a result of the moderate pressure, but more of the design of the turbo itself. The turbo has fins around the rotor (of the compressor) which are "displaced" in function of the engine load (vacuum I believe) to make the volume variable. The result is a small volume, fast acting turbo at lower revs. and a larger volume turbo at higher revs (which is needed to keep up the good work since at higher revs more air must be delivered).
See the nice drawing!
Willy

[Palisandr]

ECU upgrades... Don't they increase the turbo pressure to increase power/torque?

[dlr97]

Hi,
The result is a small volume, fast acting turbo at lower revs. and a larger volume turbo at higher revs (which is needed to keep up the good work since at higher revs more air must be delivered).
See the nice drawing!
Willy

That is really cool! The picture says this variable nozzle turbine is for the diesel. Do they use it on the gasoline motors also?

[Filibuster]

That is really cool! The picture says this variable nozzle turbine is for the diesel. Do they use it on the gasoline motors also?

No, as far as I know, there are no gasoline engines with a variable geometry turbine using variable vanes on the market today. However I can bet that the manufacturers of turbochargers or working on it. I think that the higher exhuast temperatures poses a problem in developing this typ of turbine for gasoline engines.

[Willy]

Take a look at this: http://www.honeywell.com/sites/ts/tt/PassengerCars_LightTruks.htm
http://www.honeywell.com/sites/ts/tt/turbo_feature.htm
Willy

[tmaxa]

just thought i would let you know that there is a variable vained turbo for gas engines aerocharger makes it i have one on my the harley i built

[asperez]

Yes - ECU upgrades increase boost pressure which directly affects power output. The IPD/TME upgrade increases stock 9lbs boost to 14lbs. This is tsill a "conservative" level of increase.