The wastegate hose on most owners cars has probably been replaced a few times over the years. The replacement part was gray and as I recall, those were identical to the TTA spec with the smaller hole in the orifice. I think they were the only ones available from GM for the last several years and, typical GM, crossed the parts over to the available ones.
That's where the confusion set in. To get the proper boost control, the restrictor needs to be 0.050".
Going from memory here....
Good memory, John. in addition, several years ago there were a few factory wastegate hose asseblies floating around with restrictor orfices that were drilled too small causing over-boost conditions on some cars. Here's the contents of a letter we wrote to GM at the time explaining the problem. So, if you have a factory assembly, it's worth checking to make sure the restrictor hole is .050 as John as said.
Holler Oldsmobile
1970 N. Semoran Blvd.
Winter Park, Florida 32792
Attention: Tom Moon, Parts Manager
Subject: Part Discrepancy, P/N 25525576
Dear Tom,
This letter describes a problem that has occurred with a number of new Wastegate Hose Assemblies, P/N 25525576. This part is installed on 1986/87 Buick Regals with the LC1 Turbocharged 3.8 Liter V6 engine. (VIN code 7). This problem has been reported to us from other areas of the country as well as here in Orlando.
The following is a description of the function of the part, the problem it causes, and the apparent reason for the problem:
The Wastegate hose assembly consists of three vacuum hoses connected by a “T” fitting. It connects the turbocharger compressor housing with both the Wastegate actuator and the Wastegate solenoid. Its function is to route boost to the Wastegate actuator in order to overcome the actuator spring, allowing the wastegate to open, bypassing exhaust gasses around the turbine wheel. This process limits the amount of boost in the intake system to a specified level.
Several individuals have reported that when installing a brand new hose assembly the engine began to experience an over boost condition, resulting in severe spark knock. Upon examining the ECM data it was found that ignition timing was being retarded as a result of the severe knock. The problem could be cured by installing another “known good” Wastegate hose assembly.
Upon close examination of the suspect hose assembly the reason for the over boost problem was found to be in the “T” fitting. The fitting contains an orifice in that portion of the fitting, which goes to the turbocharger compressor housing. The diameter of the orifice in a properly operating assembly is about .050 inch. The orifice in the defective hose measured less than .035 inch. When the .035 hole was drilled out to .050 and the assembly reinstalled, the problem was cured. The smaller diameter orifice was not allowing sufficient boost signal to overcome the spring pressure of the Wastegate actuator, causing the over boost condition.
We have talked with a number of individuals on several Buick bulletin boards on the Internet who have experienced similar problems and feel that it may have contributed to an occasional blown head gasket. We have asked that anyone having a “suspect” hose assembly measure the orifice or send the hose to us to measure. We ask that GM take a look at samples of your inventory nationwide to see if there are any of these bad hose assemblies still in the system. Please keep us informed of your progress.
Respectfully,
Ray F. Kammer
Chuck McClellan
Central Florida GN/TType Club
. If you find a real GM one, double check the new orifice size before you install it so you don't have a boost surprise. If you can't find one, go buy some plain tees and find one the right size to press your old orifice into, and presto, new restrictor tee. You may need to slightly ream the inside of a tee to get the orifice to fit, that's actually good, just stop drilling before the branch to leave a step to keep the orifice from being able to blow all the way through. Make sure the orifice is facing the same way as before when you press it in, and install the tee with the orifice connected to the turbo compressor outlet hose.
