I recently had my car tuned. In the wastegate I have the red spring which is a 12 psi spring. No boost controller. I'm running a TC78. 3" exhaust into a hooker catback. My tuner said the car is only making 8 psi. I'm wondering what can cause this? Possible red spring is not a 12 psi spring? Exhaust too restrictive? Any input is appreciated.

 

Could be a boost leak, but most likely is just the spring being soft. Why not hook up a boost controller? A ball and spring is cheap and reliable.

It also depends where you have the boost source for the wastegate coming from. If you're running it from the compressor housing - you're going to see some boost drop from there to the intake manifold. If you run that line from the intake manifold, you will see more actual pressure because it is post intercooler, piping, etc. (no boost drop)

 

So its smarter to run it from the intake manifold more so than the compressor housing?

 

It doesn't matter all that much if you have a boost controller. But since he's just trying to run the wastegate off of a boost source, placement will matter.

For example: My friend had a little single cam Honda with a T3/T4 turbo setup, running no boost controller. He had the boost line coming from the compressor housing, to the wastegate and he was getting 6 psi at the manifold. I told him to cap the nipple on the compressor housing and run the wastegate line straight to the intake manifold if he wants to run 1-2 more psi. Sure enough, he was at 8 psi just by moving the hose to the intake manifold which means he had 2 psi of pressure drop between the compressor outlet and the intake manifold.

 

Thanks for explaining

 

The compressor housing will almost ALWAYS see more boost pressure than the intake manifold will (Mostly because of intercooler pressure drop). So with that being said, it will open your wastegate sooner, which in result would cause your intake manifold pressure to be lower than if you referenced the manifold.

 

Also... A "12 psi Spring" is misleading. Assuming you have a actual 12 psi spring (usually accurate with name brand gates not china knock off's) that means the cracking pressure of the gate uninstalled is 12psi. You can verify this by testing it with regulated shop air.

Once installed, you have to account for WG placement,WG size,Drive pressure and a few other variables. A "12 psi spring" could open at many different boost pressures. Personally I wouldn't worry about it. Install a heavier spring, shim the one you have, or use a boost controller to set your desired boost.

 

The wastegate is where my exhaust pipes meet before they enter in turbo. I do plan on getting a boost controller. I was just curious if my exhaust system is too restrictive or if it was other problems. Thanks for the info guys.

 

As stated above the intake psi will be lower than piping pressure. Gauge off the intake and try to run the wastegate off intake pressure (or just adjust the wastegate till the desired manifold pressure is met)

 

Yeah as others have said you can expect a pressure drop if referencing off of the intake manifold. I believe once referenced after the intercooler such as at the intake manifold like most of us do the pressure drops as the intercooler cools the intake charge. You could reference off of the compressor housing and it may show that 12psi that your spring reflects but in reality your intake is going to still see that 8-9psi so you might as well reference off of the intake to get the most accurate reading of what the motor is receiving.