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Thread: How important is boost source?

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Posts: 11-20 of 37
2012-04-13 22:01:15
#11
gomba I'm pretty sure all stock throttle bodies have vacuum sources on them, or at least one, that is before the throttle plate. Look for that one and use that. Or you could "T" into the other tiny stock line that goes to the intake boot. These both exist on my lowport, and no reason I see why they wouldn't on highports and others.

Vadim, I edited that post to include a link to the thread where I posted more info. Also... People talk about pressure drops across their charge pipe system and I never understood why a big pressure drop was a bad thing. IMO if you have an intercooler that's doing it's job, you're going to have a huge pressure drop. If you test in controlled conditions with a supply of ambient temp air and the IC at ambient temp and everything at ambient temp then if you get a pressure drop I can understand that being bad. But if the IC is cooling worth a damn, you should have a really big pressure drop, and you want that.
2012-04-14 00:21:12
#12
Originally Posted by BenFenner
gomba I'm pretty sure all stock throttle bodies have vacuum sources on them, or at least one, that is before the throttle plate. Look for that one and use that. Or you could "T" into the other tiny stock line that goes to the intake boot. These both exist on my lowport, and no reason I see why they wouldn't on highports and others.


But I need a boost source, without vacuum. Are we talking about the same thing? Probably a semantic thing but just checking. I'll have to check my throttle body to see if I have a boost source before the plate.

-G
2012-04-14 00:52:38
#13
A good thread on the subject - Boost sag? No, you don't need EBC. - Miata Turbo Forum - Home to the Turbo Miata

C
2012-04-14 01:03:40
#14
Originally Posted by Chriscar
A good thread on the subject - Boost sag? No, you don't need EBC. - Miata Turbo Forum - Home to the Turbo Miata

C


Very nice. Too bad he never mentions anything about what happens if you get a boost source from point 'C'

-G
2012-04-14 01:26:24
#15
The way Vadim has his (and mine as well) is for low lag, low boost. If you have a boost controller/adjustable wastegate that the best route to go. If stock turbo, then low lag, low boost. My w11 puts out 5-7 psi but no lag
2012-04-14 01:29:49
#16
Originally Posted by gomba
But I need a boost source, without vacuum. Are we talking about the same thing? Probably a semantic thing but just checking. I'll have to check my throttle body to see if I have a boost source before the plate.

-G
Yah, when I said that I should have said "boost source". You're right about the semantics. Sorry...
2012-04-14 04:34:38
#17
Originally Posted by Chriscar
A good thread on the subject - Boost sag? No, you don't need EBC. - Miata Turbo Forum - Home to the Turbo Miata

C


Awesome thread, it explains it well and with pretty pictures ontop of that.

Originally Posted by zacward
The way Vadim has his (and mine as well) is for low lag, low boost. If you have a boost controller/adjustable wastegate that the best route to go. If stock turbo, then low lag, low boost. My w11 puts out 5-7 psi but no lag


Now I've heard of this plenty, am personally running it like that at the moment, but it really makes me wonder why people saw that.


We have the wastegate door, when the door is closed all of the exhaust is going to the turbine. When we start building pressure, the wastegate diaphragm starts to expand and meets the spring tension, once it overcomes that tension it starts pushing the wastegate arm out, when this happens the wastegate door starts opening.

The door is now starting to open, thus you are now bypassing the turbine, which means you are building boost slower. Once we hit the peak pressure that the wastegate spring is designed for, the door is completely open and is bypassing enough exhaust not to build any more pressure above that.

Now about the pressure reference point, we can agree that the compressor outlet sees pressure way before the throttle body sees pressure right? That means compressor outlet will start opening the wastegate a lot earlier then the port before the throttle body.

If we think about the process as described earlier, that means compressor outlet would actually increase boost lag. Thus it doesn't make logical sense on why having it closer to the compressor outlet will decrease the lag.


Originally Posted by BenFenner
Vadim, the GTi-R wastegate spring is 8 psi I'm almost positive. Yes, they have a boost controller that takes it up to 10.5 psi.

Vadim I know we talked about the diaphragm wear issue. It may have been exactly what killed my wastegate diaphragm, or it could have been age. That issue was not enough for me to reroute my vacuum lines.

I had a conversation with someone who pointed out the bigger issue (to me) with having the wastegate see vacuum. And now that I'm going to a piston wastegate, I'm still going to route boost only to the wastegate because of this issue.

I'll describe the issue in the appropriate thread and link it in a second. The issue may no longer exist depending on which boost control method you're using.

Edit: I described the problem here in post #15.


What about partial throttle, there is vacuum past throttle body. It might not be as high as manifold vacuum with throttle closed, but vacuum still goes into the piping. I guess it's so minor that it shouldn't do any damage to the wastegate. So having it further away from the throttle plate should help limit this too.
2012-04-14 21:27:15
#18
Shorter vacuum line= less lag.
2012-04-14 21:34:35
#19
That doesn't make any sense at all zac.
2012-04-14 23:52:48
#20
Ok did some testing today. First tested with the WG hooked up to the compressor housing, then tested with to WG hooked up before the throttle body.

Boost building was tested in 4th gear. WHP was tested in 2nd gear using Virtual Dyno.

WasteGate on Compressor Housing
Starts building boost: 1900 rpm
Full boost (7psi): 3600 rpm
WHP: 223

WasteGate Before ThrottleBody
Starts building boost: 1900 rpm
Full Boost (8psi): 3300 rpm
WHP: 228

Wastegate Before ThrottleBody, with MBC
Starts building boost: 1900 rpm
Full Boost (11 psi): 3600 rpm.
WHP: 257



WG connected to comp housing:


WG connected right before TB:


Last edited by Vadim on 2012-04-15 at 03-42-29.
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