sicklyscott

iTrader: (1)

My turbo install is almost complete. I've been doing a lot of reading here about where to take the vacuum source for the wastegate and bov off of and have plumbed mine as follows, I'd like your input on this.

Leg 1
Off IM right behind TB -> T-fitting feeding 50mm TIAL BOV and do-dads on pass fender

Leg 2
Off IM right behind TB -> T-fitting feeding internal WG actuator and MS (line for the MS also feeds boost guage)

Do you think putting the WG in line with the MS and boost guage is too much seeing as how I'm dependant on the WG to not blow my motor up?

I originally wanted to tap into the brake booster line but couldn't find the right T's for it.

Jeff_Ciesielski

iTrader: (10)

Wrong. You're going to murder your turbo that way and get a shitty map signal to your MS. The source for the WG needs to be before the throttle body to avoid the turbo trying to make INFINITY boost against the throttle plate. General consensus is that a fitting pre-TB and post-intercooler is best to minimize boost falling off in the upper RPMs.

For the megasquirt, try T-ing into the FPR.

Techsalvager

I suggest the wastegate line either at turbo compressor housing or intake pipe\piping right after the turbo compressor housing outlet.

sicklyscott

iTrader: (1)

I do have a hole in the compressor housing with a plug in it. I removed the plug but it doesn't look like it's threads would line up with any fittings at the hardware store. Is there a standard size for these fittings? It's a GT2554r.

Joe Perez

iTrader: (8)

The wastegate reference on a street-driven car signal shall be taken from a point in the system which is after the compressor but before the throttle body. Fittings installed upon the compressor housing itself by the manufacturer of the turbo qualify as being "after" the compressor, as they are located on the discharge side of the scroll.

Where an intercooler is present, the signal is ideally taken from a point after the intercooler. If the signal is taken from a point before the intercooler (including the compressor housing) then you will experience boost sag (manifold pressure will decrease as RPM increases) owing to the pressure drop across the intercooler, which is not a constant, but increases with the square of the flowrate across the restriction. Taking the wastegate reference after the intercooler will cause pressure measured at the compressor outlet to increase in response to the pressure differential across the intercooler, and thus, pressure as measured within the intake manifold (or at least, between the intercooler and the throttle) will remain constant.

If the wastegate signal is taken from a point after the throttle, then whenever you are in boost but are using the throttle to modulate boost to a level below the setpoint, the wastegate will remain completely closed, as the turbo will be attempting to produce an infinite pressure ratio across the compressor, in order to achieve the setpoint at a point in the system at which it cannot be achieved. This reduces efficiency, makes a lot of heat, and is just generall a Bad Thing™. This is also the reason why TPS is a critical input when EBC is being implemented inside the main ECU, using the main MAP sensor. The system must know to reduce the setpoint when the throttle is not fully open, as the MAP sensor is not seeing the true compressor pressure.



The signal to the BOV, however, should be taken after the throttle plate.

sicklyscott

iTrader: (1)

Thanks for the help, I think I figured this out. I had a fitting on an old turbo I was able to get threaded into the turbo that's on the car, I'll use that for the WG. BOV will be off the first nipple behind the TB, MS will be fed from a T fitting in the FPR line and the boost guage will be fed from the second nipple behind the TB that also feeds the evap canister.

Sparetire

It would be cool to log boost before and after the throttle plate with a WG signal taken off the intake manifold.

miatauser884

iTrader: (11)

There is also another thread by Joe which includes where to pull the MAP signal. Joe knows vac signals

proughj

iTrader: (2)

is there a link to said thread

Sparetire

https://www.miataturbo.net/search.php

dgmorr

iTrader: (4)

Thanks, I did not know this. I'm gonna change mine tonight.

Blaize

Ditto for me , I am only a week into boost but I have found 8.5 psi at 4k and 6 at redline. Off to find a way to add a vac hose port to my charge pipes.

greenday3437

iTrader: (2)

JKav

iTrader: (1)

Never do this. Internal wastegate actuators that use pressure to open the gate (that describes about 99.999% of aftermarket gates) are not designed to handle vacuum.

Over time, what happens is the diaphragm inside the actuator will pull out of the crimp that is holding it in place. And then there is nothing to open the wastegate. Well, except for the exhaust manifold pressure acting on the face of the valve itself. But you will have long since overboosted.

So don't hook your gate up to manifold vacuum, kids.

Sparetire

^ Now that aspect of an internal actuator I had never considered, and it makes total sense. Gee, I wonder if thats why I had to go eternal on my last setup.

There is not a facepalm emoticon large anough for me right now. This will have to do:

proughj

iTrader: (2)

off topic but how close does the bov need to be to the throttle body to be effective? or does it matter

mekaw

iTrader: (1)

^ there are both ups and downs of bov placement closer to TB vs turbo.

but generally, to make your life easier, closer to tb the better. but doesnt have to be super close like literally an inch from TB, now thats just ridiculious.

mine currently sits about not sure a foot? or less from TB roughly around mid way down the rad on cold side

Sparetire

https://www.miataturbo.net/search.php?searchid=1232326

3rd one down.

musanovic

iTrader: (2)

anywhere between the trubo and the TB.