Wormhole

Why did Porsche run the vacuum line for the cycling valve off the intercooler pipe and not the intake manifold? Wouldn’t a measurement from the manifold be more accurate? All other lines are measured from there.

I’m thinking about teeing a line from the manifold to run to my manual boost controller/dual port wastegate, instead of the intercooler. I’m hoping this will flatten the boost curve, by having my boost gauge and controller reading from the same location. Right now I’m getting small spikes.

Anyone have any opinions?

Chris Cervelli

This is a great question.

Let's see if anyone comes up with the right answer!

Chris Cervelli
Technodyne Inc.

David Floyd

The stock location is right at the turbo exit most likley the highest pressure area and before any pressure drop from travel thru pipes, intercooler and monifold.

The spikes are from a weak wastegate ?

Thats my guess

Wormhole

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The spikes are from a weak wastegate ?
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The wastegate is a new 35mm Tail with one bar spring.

David Floyd

Same wastegate setup I have, nice unit

roadrunner

Chris,

The location at the intercooler pipe usually sees very little vacuum. Would vacuum cause a problem for the cycling valve?

special tool

Compressor outlet signals promote quiker response time and allow control of the charge throughout the rest of the intake tract.
Manifold signals will provide more exact control, but will allow spiking of boost and heat to momentarily hit the intercooler and the rest of the plumbing.

Wormhole

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"> Compressor outlet signals promote quiker response time </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">I agree and understand boost pressure development as a linear progression from the compressor outlet forward. Are we saying then the boost lag to the control devise (cycling valve, or in my case manual boost controller) would cause spikes if it were measure from the manifold? And Porsche put it closer to the compressor outlet to account for the delay in pressure development and wastage control.

Chris, the suspense is killing me. What’s your take?

Thanks

krickmann

I would think that one would want the pressure source that opens the wastegate to be closest to the turbo - the highest pressure.
The wastegate opening signal should be the most representative of the final inlet pressure sources. It should therefore come from the manifold, or one (possibly insignificant) step prior like the intercooler pipe feeding the intake.

DanaT

I dont think that you need to control boost from the manifold. Set the boost from the manifold. Control it from near the turbo.

I can't tell all my little secrets, but i got a MUCH faster reacting wastegate with a simple modification. Think of rapid manufacturing processes that use pnuematic pressure. You have to have air go in fast to activate the device and then air to exit fast to de-activate the device.

I ws able to get a wastegate that was MUCH faster reacting by redesigning the wastegate control system without using electronics. It has to do with air control.

I can hold whatever boost you aske with no spikes.

-Dana

jimbo1111

Let's see if anyone comes up with the right answer!
Your spoolup time would be affected because vacuum would open your wastegate buy reducing the spring rate.

Chris Cervelli

You guys are thinking a little too hard!! Some of those ideas sound pretty good though.

Porsche stated that they do it that way so the wastegate will be open during conditions when the mainfold is under vacuum and the charge air pipes are under slight boost. If you were cruising at say 100mph there would be enough load that the turbo would be making boost even though the engine makes enough power to maintain 100mph at say .7 bar absolute pressure (slight vacuum in other words). By having the wastegate control line on the pressure pipe the wastegate can potentially be open under these conditions if the cycling valve wants it to be.

For efficiency you want the wastegate open at all times, except of course when you are trying to build boost. Having the wastegate open reduces exhaust pressure, which reduces the pumping losses from pumping exhaust.

I think that with a non-electronically controlled wastegate, plumbing it to the manifold would probably give better performance.

One other thing to consider when thinking about wastegates:

There is only one means of keeping the wastegate shut which is the spring in the top part of the wastegate.

There are two mechanisms by which the wastegate can open. One is the obvious pressure line, which acts on the diaphragm to overcome the spring force. The other mechanism is the pressure of the exhaust acting on the surface area of the valve. The exhaust pressure can easily be 15 psi (or much more) and the valve usually has an area of say 1.25 square inches. That's 18.75 pounds trying to open the gate which is significant.

This is the reason why 951 wastegates can't really hold boost over 1.0 bar to redline. The exhaust pressure gets high enough to open it even if the pressure line is not connected.

Chris Cervelli
Technodyne Inc.

silicondigital

Better for your turbo-at the intercooler duct. Better for a little more power at part throttle- at the manifold. The factory location controlls what the turbo is really putting out at its outlet, you adjust around the restriction after the turbo to get it where you want by the time its at the manifold. It might be a little less air going through the throttle body at some points at part throttle becase of this. If you controll it with the manifold pressure, the turbo will be constantly working against your throttle body. Say when your at WOT makeing full boost, you back off the throttle, the pressure before the throttle body goes up and normally your turbo sees this and backs off too. bot when the controll line is at the manifold it wil try to make as much pressure as possable to still fource your max set boost past your part closed throttle body into the manifold. Also that would make most recircualation or blow off valves open at least partly, bleeding some if not most of that extra boost off and makeing the turbo work even harder. This would make a little more power at part throttle conditions but should make the same boost at WOT whichever way you have it run.

silicondigital

also "spool up" would be the same when at wide open throttle with either setup, when pressure is pretty much the same everywhere in the tract anyway. The only time the wastegate would be more closed then normal when hooked up to the manifold would be when you were at part throttle, when spool up dosent matter. IF you were cruiseing along at part throttle and "stomped it" it might spool from there a little bit faster because of the already added stress on the turbo described in my last post under part throttle conditions.

nine-44

We re routed the W/G line on my friend's Supra to a place right before the TB, it was at the housing. Significant decrease in lag and 3psi more boost with no boost controller installed(factory setup).