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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 11-29-2007, 05:51 PM   #101
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It isn't conjecture when you have the data to support it, in this case the two lines denoting boost.

Your definition of spool is limited.

Nothing of what you posit is likely as the only change made to the car is the addition of our DV.

Whichever type of back pressure you were talking about... it has nothing to do with it.
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Old 11-30-2007, 06:27 AM   #102
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my definition was only limited by your imagination.

target at 3k = 130kpa, target at 4k = 170kpa, target at 5k = 220kpa etc.

the main one being the final value of boost, and at what rpm that is reached.

that being what most people care about, and what the word is commonly understood to mean.

i'm not saying that having more boost below it is not important, on the contrary, its a very good thing indeed. however, if the extra pressure was present from increased spool AKA turbine/compressor RPM then the curve would merge in from the side, not from below.

given that the wastegate is firmly closed through most of that lower rpm region, there is a fixed amount of energy and gas flow available to push it around. given that its being pushed around with the same energy, it can only add that same energy back into the inlet. if it is spinning at say 30000rpm, then it is moving a certain amount of air. then it is down to the restriction to flow, leaks reduce restriction, sealed forge bovs increase restriction, restriction creates higher pressure.

obviously there is more exhaust flow because of the higher pressure on the intake, but rpm will be aproximately the same, just pressure in the exhaust (what i am calling back pressure) will be higher to match the higher intake pressure with the same net flow, just more of it going into the engine than out of the leak.

besides all that, obviously a valve that seals is far prefferable to a valve thats leaking like a sieve.

in short, the data strongly supports my theory of what is going on in that engine.

i have had some sleep now, and thought about the valve discussion some more, and rather than totally wrong, i was half right. i'm going to draw a diagram some time later to illustrate my point such that it can not be missed.

i'll post that rather poor diagram a bit later after i have done other more important things.

fred.
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Old 11-30-2007, 10:14 AM   #103
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So then by your definition (as you restated it) it does help spool. At every point before ~3800.

I like how you keep editing your posts. At this point I'm just scanning them... but I will stop even that as I can't imagine ever being bored enough to continue this discussion.
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Old 11-30-2007, 10:28 AM   #104
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Quote:
Originally Posted by PAT! View Post
So then by your definition (as you restated it) it does help spool. At every point before ~3800.

I like how you keep editing your posts. At this point I'm just scanning them... but I will stop even that as I can't imagine ever being bored enough to continue this discussion.
from 11 posts in this thread, i have edited precisely ONE, and the ONLY change that i made to that post was to add the word "one" where i had intended it to be in the first place, and i stated that in the following post. "keep editing" is not the truth is it Pat??

as for twisting spool in that way, the precise rpm where wastegate set boost was attained was exactly the same on the two runs. as much as i agree that there is an improvement in all areas, i for one rarely let rpms fall below 5k when WOT in my vehicles. so in terms of performance on a drag strip or road course, not significant really.

I've installed and configured and tested a full secure web dav served subversion server this morning, and fairly soon, i'll crack out kolourpaint and whip up some diagrams for the benefit of anyone that cares to understand these devices in detail. I'll get it right this time.
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