Conference terri::cars_uk

    With regard to Volvo - no.
    
    Saab do a low pressure turbo, also termed EcoPower and a full turbo. It
    depends how much boost the turbo gives. Whether it is pressure or
    volume I don't know. What I do know is that one ends up with three
    options on Saab 9000:-
    
    2.0l non turbo. Absolutely useless.
    2.0 LPT or Eco Much improved performance. Adequate for normal use.
    Full turbo, maybe only on 2.3 but I think on 2.0. Whoosh.
    
    My wife lets me drive hers at times, LPT that is.
    
    Andrew

  Typically a LPT would be used on an engine with a close to normal
  compression ratio, and designed to be in use most of the time.  A
  'normal' turbo would mean the compression ratio of the engine is lowered,
  which means less power before the turbo kicks in.  It would also result
  in a larger power surge once the turbo spins up.
  
  The LPT is designed to add more power (but not gobs of power) over a
  broader rev range.  It would also not spin as fast, so should last longer
  than a normal turbo.
  
  Dave 

    If remember right, pressure goes up to only 0.4psi and works from
    almost idle speed. This is SAAB's case, I didn't know Volvo had it.
    
    mn
    

Would that be 0.4 bar instead of 0.4 psi?  0.4 bar would be about 6psi... What 
does a typical turbo run at?

Dave

    It's  "BAR" not psi, my mistake.
    I knew something didn't look right when I was typing.
    
    Normal turbo(SAAB's case again) would be at 0.75 bar to 1.0 bar
    depend on temperaure and octane. 
    
    mn
    
    

Shoudln't that be 1.4 bar?  Seems odd that a turbo would provide lower than 
atmospheric pressure...

Chris.

    The man did say "goes up by".
    
    Just blowing in the wind.
    
    Andrew

    No, he said "goes up to only.."
    
    TonyI$pedantic  8*)

    Oh yes.
    
    Andrew

    	>>Shoudln't that be 1.4 bar?  Seems odd that a turbo would
    	>>provide lower than atmospheric pressure...
    
    Well, end result boost pressure will be 1.4 bar, contribution from the
    LPT is 0.4 bar that what I meant.
    
    mn
    
    
    

>    Well, end result boost pressure will be 1.4 bar, contribution from the
>    LPT is 0.4 bar that what I meant.
    
ah, right.  Although I was being largely pedantic (as usual :), there was a 
hint of curiosity.

Hmm, I wonder what sort of pressures the F1 cars used to run at when turbos 
were in vogue (if anyone does know, could they make it clear if the pressure 
they're referring to is boost or absolute!)

Chris.

    Don't know the answer to .11 but the pressures involved must have been 
    humungus because the engines were only about 1.3litres if I remember
    correctly.
    
    
    
    
    B.T.W.	What does a dump valve do ?
    
    		I've heard various people recomending one as a good
   		aftermarket addition to turbo'd cars
    
    
    
    Cheers
    
    Rory...

    
    Don't quote me on this (please !) but I think F1 cars were up higher
    than 6 bar at one point - I seem to remember legislation to restrict power
    by introducing a max boost of 6 bar, then down to 4 bar a year later.
    
    Then again, it could have been 1.6 and 1,4 ?
    
    Graham
    
    BTW, I'll ask in F1 - that should get a definitive answer (or three)

    And the Turbo F1 cars were 1500cc not 1300cc. 6 bar sounds right.

>    And the Turbo F1 cars were 1500cc not 1300cc. 6 bar sounds right.

that's right.  Didn't someone manage to (very briefly) get almost 1bhp per CC 
out of one of these things?

Chris.

The Brabham BMW 4 cylinders used in qualifying were producing between 1200 and 
1300 bhp, or so someone claimed...  I believe the race engines of that era 
were producing 'only' 700-800 bhp.

Let's see, in qualifying trim, that means my Isetta should be able to put out 
about 250bhp.  Not bad!

Dave

    In mid 80s when Porche, BMW, Honda engines were still in F1 race,
    engine size was 1.5L for turbos.(most of them were V6, BMW was IL4)
    Honda's qualify engine boost was up to 5.0 bar and produced over
    1100hp+
    Later FIA ruled to have popoff valve installed and limited turbo
    pressure down to 4.0 bar, then again down to 2.5 bar.
    At very end of turbo era, Honda managed to squeeze 1500hp+ out of
    1500cc engine with help of Shell's special petrol.
    
    Back to Volvo 940,
    Volvo 940 SE(normal turbo?):  The TOWCAR OF THE YEAR in '92 by British
    			          Camper Assosiation.
    
    mn
    

    
    Yes, I've checked in the F1 conf. and it was definitely 6 bar or there
    abouts, later restricted to 4 bar and then 2.5 before banning Turbo's
    altogether.
    
    G.

    Re .16
    
    	An Issetta with 250BHP?  That would be lethal!!!!!!
    
    				Malcolm.

    
>    B.T.W.      What does a dump valve do ?
>   
>               I've heard various people recomending one as a good
>               aftermarket addition to turbo'd cars
	
	
	A dump valve keeps the turbo spinning when you let off the throttle.
	
	The turbo forces air into the chamber when the throttle is open.
	When you close the throttle (IE during gear changes) the turbo has 
	nowhere to blow the air so it slows down dramatically. When the throttle
	is re-opened, the turbo has to spin up to speed again to start forcing
	the air into the chamber.   The dump valve is a release valve on the side
	of the impeller housing which is designed to let the air out and so keep the
	turbo spinning at full operational speed.  This reduces the amount of lag
	once on the move.

	If you ever listen to the Grp A rally cars at full speed, between gear 
	changes they emit a high pitch squeek or chirp, this is the dump valve
	working.

	Hope it makes sense

	Graham_S 

    
    is that the same thing as a WasteGate then ? or is the Wastegate their
    to limit the pressure ?
    
    G.

>    is that the same thing as a WasteGate then ? or is the Wastegate their
>    to limit the pressure ?
    
the wastegate is a boost limiter, if I understand correctly...

Chris.

    Okay I get the bit about the dump valve but I always thought the
    wastgate opened when reving up to the boost point to let the turbo spin
    up to working revs not to stop it going to fast...
    
    
    
    						...but then I'm not sure.
    
    
    Rory...

    re 2515.23
    
    The wastegate simply has a spring of a set strength governing when it
    opens. When the  boost pressure hits a certain point it opens enough to
    let out excess boost thus ensuring that your engine does not self
    destruct. It doesn't stop the turbo from spinning as fast as it wants
    it just dumps the excess pressure it produces from doing this. People
    who modify turbo charged cars on the cheap - usually make the wastegate
    open at a higher pressure.
    
    Dump valves are necessary on very highly boosted cars since the back
    pressure caused by lifting off the accelerator can actually destroy the
    rotors on the turbo. It was also discovered that it helped reduce turbo
    lag whilst changing gears.
    
    Rick
    
    

    
    
    
      
    
    What you say makes sense but if the wastegate is simply governed by a
    spring then what is the air operated actuater (the piston goes onto a
    lever on top of my turbo) for ? I notice that my fathers turbo diesel
    does not have the auctuator.	
    				Of couse this actuater may be leading us up
    another lengthy garden path but I did have a few problems with mine
    sticking causing the engine to shut down.The was when normally you'd just
    start feeling the boost as you go up though the rev range (aprox.
    5000rpm).
    
    
    Confused of Ayrshire
    ^^
    and its geting worse.
     
    
    

I think that the wastegate is operated by a valve in the inlet manifold (or 
the corresponding bit of the turbo), so if the boost pressure gets too high, 
some of the exhaust gases are released, reducing the compression.  Or 
something like that (it's been too long since I knew about this sort of 
stuff!)

Chris.

    On older (simpler)turbo systems there is a little (usually rubber) hose
    connected at one end to a Diaphagm unit (On top of the turbocharger)
    and at the other end connnected directly to the inlet manifold. Inside
    the diaphragm unit there is a spring. When the air pressure in the
    inlet manifold rises to the point that it overcomes the spring
    pressure, the diaphragm moves and via a connecting rod and lever, opens
    a valve within the exhaust side of the turbo enabling some of the
    exhaust gasses to be vented past the exhaust turbine, thus limiting the
    inlet manifold pressure. More modern (complex) systems do this by using
    a weaker spring within the diaphragm but having an electronic control
    unit (APC in Saab terminology) to detect the boost state and then
    operate an electric control valve to open the airline from the manifold
    to the diaphragm and hence open the wastegate more quickly. This gives
    more accurate and quicker control over boost pressure. It can also be
    used (as on the current Saab 900 Turbo) to reduce boost pressure in the
    lower gears to reduce the possibility of wheelspin. (In the Saab 900
    this occurs in first and second and reduces the boost from .95 bar down
    to approx .70 bar (or as near as I can tell from my boost gauge!))
    On the early (NOT GTTi) charades it was possible to fit an external
    spring to the wastegate to improve the boost from (a very sad) 4psi to
    approx 7psi. This gave a terrific boost to performance (25%) for no real
    cost. There is always however a cost in reliability for any increase in
    power. More modern systems such as Saabs Trionic or APC and Daihatsu in
    the GTTi require a remapping of the 'black box'. This can give
    significant improvements also, as you can have the boost pressure
    progressively increase as revs increase. This is acceptable because to
    get the same internal CYLINDER pressures as revs increase requires more
    boost because the valve opening times are reduced, therefore there is
    less time available to get the same volume of gas into the combustion
    chamber. An example of a dramatic improvement possible: BBR do a kit
    which transforms a standard Volvo 440 Turbo from 120 bhp to 210 bhp.
    The kit comprises no more than a new actuator (diaphragm unit) and a
    new 'blac box'.  The GTTi rally car I was involved with 8 years ago (in
    NZ) was 'chipped' from 99 bhp to 170 bhp.... and we still claimed it
    was standard group 'N' (showroom class!).