Turbo; JH or PL?

[pb3vr6 at yahoo.com (Tonee Northam)]

I really don't mean to interupt, Dan and Larry, but have you guys ever ridden in Scott Kraus's yellow mk2?
   
  No turbo, and was crazy fast.
   
  My point being, If I have one really, what can you do to the engine to get it to produce great hp/tq numbers without a turbo?
   
  What are the alternatives?
   
  Thanks Guys,
   
  Tonee

LEF <rocco16@sbcglobal.net> wrote:
  

Dan sez:
If you're running 15psi, ......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.

Larry sez:
Agree. Let's take it to extremes to illustrate your point: if you are running 1psi and increase it by 1psi (to two psi), you have increased your boost by 100%. If you are running 100psi and increase it by that same 1psi, you have increased your boost by only 1%. However, this doesn't necessarily mean the engine is making less hp by going from 100psi to 101psi....just that the percentage of increase is less.

At some point, turning up the boost simply produces more heat and no more power..... 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. 

You're saying that at some point, the more air I put into a given volumn (increase the pressure), the less air I'm putting in?
Hmmmmmmmmmmm...I need to chew on that one for awhile. :)

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. 

This begs the question of whether the failure to drop lap times had more to do with too much power rather than no net increase in power. You CAN absolutely reach a point where more power gains no net improvement in lap times. But we aren't talking about dropping lap times, we are talking about increasing power.
BTW, if more boost is counterproductive, why did the F1 cars turn up the boost for qualifying????? That statement above doesn't support your theory, it supports mine....."turn up the boost!!!" :)



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.
The F1 guys apparently believed that just "turning up the boost" was the path to more hp, and I doubt they changed cams, ported & polished, put different exhausts on, etc. for those qualifiying runs. Were they just guessing?

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.
Didn't say it was a personal attack, did I? I said it was getting close to it. :)
Fair enough, as I think the same of your theory. We're even.




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