Too much boost/wastegate not effective/Precision states to port exhaust "hole"

[racerxrick]

Just about have this car ready to fine tune and hit the track but we couldn't seem to get the boost down. (6768 w/39mm external wastegate on 3" DP of unkown brand).

15psi spring netted 28psi QUICKLY before I backed out of the throttle. 9psi spring still 26psi, 5psi spring and the turbo was very lazy but still hit 24psi.

Checked for obstructions etc. then spoke with Precision. after sending photos and measurements they want me to port the exhaust opening to match the DP. (current exhaust opening is .91 and wastegate is 1.36).

Any issues with this as I do plan to run 26-28psi once dialed in? However I'd like to be able to dial back to 18psi and carefully tune from there.

Any feedback from experience is appreciated!

 

[TurboBuRick]

That is the biggest problem with eternal gate pipes. You will need to port and contour the housing.

 

[V6sleeper]

You could be over powering the 39mm pte wg, you should look into a Turbosmart 45mm hyper-gate.

 

[tsm3089]

with a 38 mm gate i can get down to 5 psi with a 3 psi spring. c02 controlled after that.

 

[racerxrick]

That is the biggest problem with eternal gate pipes. You will need to port and contour the housing.

yes after searching last night I see that's pretty common. I am curious if I need to port match (per precision's instruction) or perhaps go a little smaller? The again the 39mm wastegate isn't that big regardless.

 

[racerxrick]

You could be over powering the 39mm pte wg, you should look into a Turbosmart 45mm hyper-gate.

thanks for the reply, initially that was our concern and assumption. However because of the small (.91) diameter exhaust port it would appear the current wastegate isn't being given a chance.

 

[racerxrick]

with a 38 mm gate i can get down to 5 psi with a 3 psi spring. c02 controlled after that.View attachment 264420

good to know...thanks

 

[TurboBuRick]

For the most control I would match port and smooth the turn toward the header flange. It's a fairly easy task with a carbide burr and a die grinder.

 

[Reggie West]

Its not your wastegate that is causing the restriction, it is the size of the stock hole on the turbine housing. Once you match it to the diameter of the wastegate tube you will be able to control the turbo like you should. Notice you have that circular pattern on the housing around the wastegate hole? There is your pattern to do the port work.

This is a common problem running bigger turbos, you can't dump enough exhaust gas out of that little hole to control the turbo.

 

[Chuck Leeper]

Also, if that's a wb, it is too close to the exh hsg...

 

[racerxrick]

Also, if that's a wb, it is too close to the exh hsg...

Where is the preferred location? (This is a build I bought that i am getting back on the road/track for the first time in ten+ years)

 

[Reggie West]

At least 12 inches past the turbine housing.

 

[fastblackracing]

Just about have this car ready to fine tune and hit the track but we couldn't seem to get the boost down. (6768 w/39mm external wastegate on 3" DP of unkown brand).

15psi spring netted 28psi QUICKLY before I backed out of the throttle. 9psi spring still 26psi, 5psi spring and the turbo was very lazy but still hit 24psi.

Checked for obstructions etc. then spoke with Precision. after sending photos and measurements they want me to port the exhaust opening to match the DP. (current exhaust opening is .91 and wastegate is 1.36).

Any issues with this as I do plan to run 26-28psi once dialed in? However I'd like to be able to dial back to 18psi and carefully tune from there.
View attachment 264405 View attachment 264406 View attachment 264407 View attachment 264408
Any feedback from experience is appreciated!

I would go up in size in increments, go to 1.00 then 1.100 etc....you will reach a point where the boost will start to fall of fast, just going from .910 to 1.00 and radiusing the turn inside the housing dropped mine by 6#. Also a shop vac can catch most of the grindings if you have a helper.

 

[racerxrick]

At least 12 inches past the turbine housing.

thanks

 

[racerxrick]

I would go up in size in increments, go to 1.00 then 1.100 etc....you will reach a point where the boost will start to fall of fast, just going from .910 to 1.00 and radiusing the turn inside the housing dropped mine by 6#. Also a shop vac can catch most of the grindings if you have a helper.

I appreciate the response and personal experience. BTW along with the wastegate we now have a Turbosmart EBoost 2 controller wired in. Of course we are most tempted to just port match to the carbon marks and let her rip...however if there is a benefit to a smaller opening??

 

[Chuck Leeper]

however if there is a benefit to a smaller opening??

Already answered: you will reach a point where the boost will start to fall off fast,

 

[racerxrick]

Already answered: you will reach a point where the boost will start to fall off fast,

point taken...guess I just want to have my cake and eat it too.

 

[Reggie West]

Well if the boost builds up and falls off faster that is a good thing in my book. I kind of like it when my right foot has much better control over the turbo.

 

[Mike Licht]

The boost will not fall off with an external gate, only with a flapper valve

 

[TR Custom Parts]

Verify that the hole where the bypass pipe rejoins the downpipe is fully opened up.