I have been working on sorting out some stuff on the car to get it ready for my next track day. I had to replace the tires as they were showing signs of some dry rot. I wound up purchasing some new Toyo R888R’s.
While doing some shake down runs, I discovered a new issue with the car. The car developed an issue controlling boost in upper RPMs. The gate would open around 18 psi at around 4500 rpm. From there it would creep up to +/-22 psi at 6000, than skyrocket to 30 by 6500 RPM. At that boost level, the motor developed a misfire which I think was a spark plug gap issue.
In previous posts, I documented how I had to re-work the downpipe to clear the V8 style bellhousing. The previous configuration of the downpipe had the wastegate dumping back into the downpipe. The reworked downpipe has the 38mm gate dumping to atmosphere. This change along with the 3” straight piped mandrel exhaust must have eliminate back pressure after the turbo. By doing so, this has affected the wastegates ability to divert gasses away from the turbine wheel as there maybe less restriction for the gasses to go straight through the turbo and bypass the internal wastegate port.
I will update this in a later post.
Here are some photos of the downpipe.
Before:
After:
These configurations package well but I don’t think that I would recommend this layout to folks running a straight 3” downpipe and exhaust. To make this setup work, I had to open up the internal wastegate port significantly. You can see this in the photos below:
Before: mild porting of stock internal wastegate port - ran with both downpipe configurations. Worked okay when the gate dumped back into the downpipe. Major fail when vented to atmosphere.
After: opened up to 1-3/8” diameter. Preliminary testing indicates this porting fixed my boost control issues
Hopefully someone learns something from my failures.