What is a soft turbo?

[alpha33]

hello...is there anyone who can tell me what s soft turbo?
Is it a turbo charged system, but working at lower boost hence a lower power rating?

i am wondering, if i can put a turbo propelling air directly into my manifold without a intercooler.
looking forward for a low boost for city driving,not for racing use. Say like, 0.3 bar max.

can this be achieve?

 

[pgarner]

hey and welcome to the site
if your wanting it for town driving look more for superchargers instead. these wont have any lag issues like you would get even with a small turbo.

you dont really need a intercooler but it is advisable as the lower temps will help aid power and prevent knocking

 

[alpha33]

thanks for the advice.
due to several reasons, a supercharger is not very easy to work on unlike turbo...

if i do insist on a turbo without intercooler and other blings blings to go on, do you think its possible to achieve what i am looking for?

 

[HDi fun]

Light Pressure Turbocharging is used extensively by Saab and Volvo in their petrol models. Intercoolers are definitely not blings, you will always get better results with an intercooler but if you're only looking at mild boost pressures then you can manage without one.

The important thing is to get a turbo of the correct size for your application as you want it to work all the time the engine is under load and right down to almost idle speed. So, basically as small as you can get away with so long as it doesn't choke off the engine at higher revs and throttle openings otherwise any efficiency gains will be negated.

You will also need to re-align the fuelling curve to account for the extra air the engine is drawing in.

It's a nice way to flatten out the torque curve on a peaky engine.

 

[obi_waynne]

Have you thought of a remote turbo?

 

[HDi fun]

Does remote turbocharging really work? I imagine the lag must be horrendous.

 

[pgarner]

seems to in some cars especially in engine bays where room is tight.
shame most of the kits seem to be for GM V8 engines.
dont see how a supercharger is harder to work on than the turbo ? surely the supercharger setup is easier to plumb in rather than having to get a manifold and down pipe made up along with the intake pipework

 

[HDi fun]

I'm slightly confused by that as well. Both need careful consideration but I cannot see the benefit of fitting a turbocharger eight feet from both manifolds. The spool up time could well be into several seconds for enough back pressure to develop to start driving the turbine.

 

[obi_waynne]

It does give lower boost than a standard turbo but that is actually the benefit. You won't need to lower the compression ratio and do much to the engine to make it work.

If you add a turbo in the conventional position you will have to either run pitifully low boost or rebuild the engine for a lower compression ratio.

 

[claymore]

I'm slightly confused by that as well. Both need careful consideration but I cannot see the benefit of fitting a turbocharger eight feet from both manifolds. The spool up time could well be into several seconds for enough back pressure to develop to start driving the turbine.

Generally a remote turbo would be fitted to a car which already has good power, something like a Peugeot gti for example, so you would have good power then more power.

 

[HDi fun]

SO what we'd be doing is making the engine operate as if the prevailing atmospheric pressure is a few percent higher.

 

[pgarner]

pretty much. if you look at the original post he was thinking 0.3 bar which is only around 4 psi.

 

[alpha33]

yeapz..
was just thinking about running very low boost without modifying/changing alot of things in the engine.

or maybe can i do this?I would lower the compression,install a full turbo...BUT running at low boost. Will this be more easier to achieve?


on my first thought:
1 turbo propelled by only 2 exhaust cylinder,(mine is a 4 cylinder engine) pushing the air directly into intake manifold.At low boost of course...

 

[pgarner]

if you lower the compression you will start to lose low end torque which is what you want when town driving.
not sure how running 2 cylinders would work as it would be more pulsing the turbine rather than a steady flow.

still think youd be better with a supercharger have a look at this thread by another member of his old car
http://www.torquecars.com/forums/f111/marea-volumex-2596/
used a supercharger from a new mini cooper
now these can be picked up cheaply on the bay along with some pipework to plumb it through and could be done in a weekend possible rather than having to see where the turbo fits getting 2 manifolds made up, going with your idea, downpipe and all the induction pipe work

 

[alpha33]

hm.....most of u all do recommend supercharger....
with super charger, how do i control the total of air that goes in?
aint it being control with another throttle body which is controlled electronicly?

i do have an old compressor from a merc W203.But i dun think that will fit. i'll have to find another one tho.

 

[HDi fun]

A mechanically driven supercharger does require a mechanical connection to the engine. Superchargers are alomst always belt driven. This means that you have to be able to fit it so that belt drive can be applied.

A turbocharger (turbo-supercharger to give it it's full name) is driven by exhaust gases. The positioning is not as critical as for a supercharger but proximity to both sets of manifolds is of prime importance.

All superchargers serve to increase the mass of air fed to the engine. This means that more fuel can be injected and thus more torque is generated.

Often people think that turbos give 'free' extra power. Not totally true.

Diesel engines are perfect candidates for turbocharging, there is no throttle to get in the way and volumetric efficiency is massively increased.

 

[pgarner]

the amount of air is still controlled the boost pressure this is decided on by the size of whell that is used to turn the compressor.
the merc one could be the same as the mini and eton 230 iirc

 

[HDi fun]

the amount of air is still controlled the boost pressure this is decided on by the size of whell that is used to turn the compressor.
the merc one could be the same as the mini and eton 230 iirc

Yes, it is. But a diesel engine's torque and power output is determined and controlled by fuel delivery only. They basically operate on excess air (of which over 19% is oxygen) under 95% of the operating conditions. That's why it's much simpler to design a turbo-diesel engine and associated control systems.

 

[pgarner]

sorry hdi i was replying to

hm.....most of u all do recommend supercharger....
with super charger, how do i control the total of air that goes in

 

[HDi fun]

"with super charger, how do i control the total of air that goes in "

In the case of a throttled engine it's with the accelerator pedal.

With a diesel engine, which has no throttle, you control it with the fuel delivery, which is governed by the accelerator pedal. Within the design envelope the more fuel administered, the more air the engine will draw according to revs.

 

[alpha33]

ah....
thanks to all the comments and advice.

I think i will be doing a full turbo setup with a lowered compression. But not running on a high boost either. Around 0.3- 0.4 only...since i will not be replacing or upgrading the pistons materials.

Maybe its time to seek the "How to DIY a turbo" thread instead..
any helpers?