Turbo; JH or PL?

[jdbubb at verizon.net (Dan Bubb)]

I agree, we should agree to disagree.
That doesn't mean I can't say what I believe.

I'll make the point again that your statement "just turn up the boost" and not bother with traditional performance enhancements can be true depending on how much boost you're running.
If you're at 5 psi then it's easy to turn up the boost and make more power. Most turbos have a maximum efficiency around a pressure ratio of 2, i.e. 15 psi boost. So, turning up the boost actually increases the compressor's efficiency and doesn't incur any huge additional heat load due to turbo inefficiencies although, of course, the more you compress air the hotter it gets even with 100% efficiency.

If you're running 15psi, then turning up the boost not only increases the heat just from compression, but you're also getting into an area where the turbo is less efficient so the heat also increases due to that, not to mention the greater restriction from ports, cam timing and exhaust systems sized for half the flow. The gain you will see from an incremental increase in boost will be less than the gain you will see from that same increment if you're starting at 5 psi.

At some point, turning up the boost simply produces more heat and no more power. The turbo compressor's efficiency continues to drop and it heats the air much more, the IC, presuming you have one, will not be able to cool the incoming charge sufficiently and as a result although the pressure in the cylinder is high it's density is low due to it's high heat so you're actually getting less mass of air into the cylinder. Hotter charge air is more susceptible to detonation, so you need to retard the ignition more costing power. And at some point, if your exhaust system hasn't been sized for the additional flow it'll simply choke the turbine and the limit the amount of boost the turbo can make.

One example that comes to mind is the Formula 1 McLaren Porsche turbo of 1985. Obviously an extreme example since these were 1.5L engines running in the 45 psi boost range and making ~900 Hp. In those days boost was not limited during qualifying and they were simply removing the wastegates for maximum boost. Porsche tried this, yet when they ran without wastegates the cars were no faster. Which just illustrates my point that "just turning up the boost" has it's limits even for an out-and-out race engine. (Reference The 1000 BHP Grand Prix Car by Ian Bamsey)

So, when you say just turn up the boost and not bother with other performance enhancements I think you need to be specific about the boost levels where this is actually true and be aware of the fact that the lack of other performance enhancements will limit the boost attainable to a lower level than if you treat the engine as a system and size all the components appropriately.
I am most curious how much boost and power a Scirocco would make with a dead stock exhaust system. I know it wasn't much on a 1979 Scirocco!

I'm sorry if you feel this is a personal attack. It's not intended that way. I just think that your theory is true only to a limited extent and that extent ought to be addressed.
And irritating or not, there are a number of people on the list that have turbos are or contemplating turbos and as such it would be nice to have data on the various engines and how well they perform.
I've detailed the work and results on my nephew's engine here:
http://forums.vwvortex.com/zerothread?id=2766838
and here:
http://forums.vwvortex.com/zerothread?id=2196997
And one of these days when I finally get my 84 turbo running I'll detail the results from that also.
my .02
Dan


From: "LEF" <rocco16@sbcglobal.net>
Sent: Sunday, January 07, 2007 9:45 PM
Subject: Re: Turbo; JH or PL?


Dan,
 You are getting further and further away from the subject of our discussion and closing in on personal attacks.
I've told you, repeatedly, what my theories are on the benefits of the usual NA  power modifications as applied to a turbo motor, and why I feel that way.

You don't agree, and that's okay; you don't have to.  But you seem determined to try to prove me "wrong" in every statement I make, which is getting slightly irritating.

As I said earlier, let's just agree to disagree.  To continue in this manner is fruitless.

larry
sandiego16v
  ----- Original Message ----- 
  From: Dan Bubb 
  To: LEF ; scirocco-l@scirocco.org 
  Sent: Sunday, January 07, 2007 10:42 AM
  Subject: Re: Turbo; JH or PL?


  Start cranking the boost up on your son's engine. Watch the diminishing returns. Watch the engine melt down at a low power level because of all the heat and resultant detonation you'll get from a restricted normally aspirated lump with minimal adaptation to FI.
  You haven't produced any data for the list relative to this project at all other than it exists.
  Why don't you let us all know the specs and the performance?
  And what's wrong with responding to this on the list?

    ----- Original Message ----- 
    From: LEF 
    To: Dan Bubb 
    Sent: Sunday, January 07, 2007 10:51 AM
    Subject: Re: Turbo; JH or PL?



    Dan,
    You are correct in your last statement; the power increase that a turbo provides does not come without a negative power effect; that effect is additional exhuaust restriction.  Like the hp required to drive a supercharger, that hp loss is more than offset by the hp gain provided by the device that is absorbing the energy. There is no free lunch (this has been my favorite saying for all the years I've been on this list).
     A turbo is driven by waste energy, but it does impart its own price tag (even though that price tag is not parasitic drag). To me, the price of the turbo lunch is additional heat in the engine compartment (with its affect on rubber and plastic parts and electrical components), lag, exhaust fabrication, the moving/modifying of engine compartment components to make room for large amounts of tubing and intercooler, etc., not the fact that the turbo absorbs 5hp worth of exhuast flow in order to make 45 additional hp; in the end, what we see is a net 40hp increase, which is all we are concerned with in our quest for additional power.

    You aren't going to convince me that I was wrong when I said "More power can be had by simply increasing boost... normal go-fast methods of big cams, free-flowing intakes and exhausts, porting and polishing(part of those free-flowing items), higher compression, etc. are not only uneccessary but, in some cases, counterproductive to the turbo engine.

    I also realize that I am not going to convince you that I am right.  What say we agree to disagree?

    larry
    sandiego16v

    I guess if your theory that the turbo was driven only by waste energy was correct then none of this would be true. Unfortunately, the engine does have to work to drive the turbo. There is no free lunch.
      Dan