(I am killing time waiting for an ebay auction the end... I have 44 minutes, so sit back, sip some hot chocolate and enjoy)
When the */c is sucking in atmosperic pressure, it has to overcome any/all restrictions in the intake tract - the MAF, the throttle blade, the upturn in the blower entrance, the flattening-widening of the roof of the blower - then, the air at atmospheric pressure gets pulled
into the rotors and sqeezed out below. All of this work is done by the crankshaft via the belt and pulleys.
With a turbo providing pressurized air into the blower, the blower
doesn;t have to work
as hard to pull
the air in. AND
actual pumping losses inherent in a */c are reduced to nearly nothing due to the turbo "pushing" the rotors.
Here'* an example everyone can understand:
As a kid, I remember playing with a pinwheel, you know, the colorful plastic wheel on the end of a plastic stick. In the house, or on a still day, the only way to get that thing to spin (*/c) was to flick the end of the blades with your finger. The thing would spin about three turns and stop (let'* face it, the tolerances on that thing were like .062" on both sides... they had a butt-load of runout!). If you could flick thatthing over and over you could get it going pretty fast, but as soon as you stopped flicking it, it would go another three turns and stop. This is the */c. As soon as the crank stops turning, the */c stops, too.
, something really cool would happen if you started running thru the house holding that pinwheel out in front of you - the dad-blamed thing would start spinning on it'* own!
When you introduced moving air
in front of the wheel, it would spin all on it'* own! And the faster you went, the faster it would spin. You could never get it spinning that fast just by flicking it with your finger (nor would it accelerate as fast).
I anticipate, and expect to demonstrate, that a turbo feeding a */c as little as 1psi above atmospheric pressure will show significantly more power gain than 1psi boost would normally provide, based almost entirely on the reduction of pumping losses in the */c.
What does this mean in the engine? A roots-type */c is one of the LEAST effective power adders, taking away a huge percent of power.
At average boost levels, the M90 can use as much as 50hp. Some very knowledgeable folks in the 3800 market claim that at extremely high boost (25-up), the M90 can siphon off as much as 150hp just to turn it!
Ever hear about the draft? Not WWII, Korea, or Vietnam, but NASCAR! The car in the front uses less power to stay there b/c the car behind him is pushing
him! (the car behind also has the added benefit of reduction in wind drag across the front of his car!)
So, what does thismean in the engine? Since the */c is not working as hard, it does not produce as much heat
. That'* good. And since it is squeezing air that is already squeezed, it doesn't just add
boost, it multiplies
Ex: 10psi turbo pressure and 10psi */c prssure DOES NOT EQUAL 20psi. It goes like this:
10psi turbo = 1.67 pressure ratio (p/r) is 14.7psi atmosperic pressure + 10psi boost pressure = 24.7psi total pressure. Divide that by 14.7psi atmoshperic pressure to getthe p/r = 1.666666 or 1.67. Now, take that and increase it by ianother
1.67 p/r and you get this:
1.67 * 1.67 = 2.79 * 14.7 (atmospheric pressure) = 41psi total pressure - 14.7psi atmospheric = 26.3psi boost pressure.
10 + 10 doesn't equal 20, it equals 26.3! LOL!!!!!!!!!!!!
(31 minutes and 12 secs left)
The reason not too many people try this is b/c it is way too easy to make insane amounts of boost! If the turbo is not carefully controlled, it can get crazy.
At shown on the chart above and quoted from some bright guys, at 26psi on all */c, you'd be losing 150+hp in pumping losses! And producing insane amounts of heat! If you had a turbo doing all that work by it
self, the same thing would happen - you wouldn't have the extreme power loss, but you would have an insane amount of heat requiring a huge air-air intercooler and it'* long charge air piping, or expensive an liquid-air intercooler with it'* plumbing, coolant pump, heat exchanger, and all the necessary hardware. Not to mention a turbo getting to 26psi would take a day and a half! That'* some serious lag.
I can;t wait to start experimenting with this. There is alot more than I have typed about here. Like turbo size and */c speed. Oh, well, time to go bid on the turbo in question!
Hope you enjoyed this (or at least, I didn;t bore you to tears, but then if it was that bad, you probably didn;t read it all anyway and certainly didn;t get to this sentence, so no apologies necessary. All right then....)