Dejon Tools Upper Y Pipe

One of the more problematic of the OEM engine parts is the upper "Y" pipe - so-called because it merges the outflow of the two separate turbochargers into a single connection to the throttle body.

The OEM Y pipe is a thermo plastic - strong and very light. It does, however, have a serious flaw in it. The connection to the throttle body is a female socket that fits over the male bung on the throttle body inlet. Plastic does not function well in a direct compression fitting like this, so a rubber adaptor sleeve is used to provide a sealing interface between the plastic pipe and the metal bung.

This rubber sleeve couplers wants to tear, bunch up, and generally not function in the manner desired. Every time the connection between the Y-pipe and the throttle body must be separated (which is fairly regularly as access to the rear head requires the upper portion of the intake manifold to come off) the mechanic can look forward to a fun session of trying to slip the sleeve over the bung and the pipe over the sleeve. Depending on luck and skill, this can take hours.

The most cursed part on a Stealth

Accordingly, there are a number of aftermarket replacement pipes that eliminate the troublesome coupler by replacing the intermediate sleeve with a more conventional female coupler. (male Y-pipe, female coupler, male TB bung)

The one I selected was the Dejon Tools version, provided by 3SX

The Dejon Tools Y-pipe is made of fairly heavy gauge mild steel, powdercoated any of a number of colors. It comes with either an OEM-style BOV coupler bung, or am aftermarket BOV flange. Mine was ordered with a GReddy BOV flange, and came with a Chinese knock-off of a GReddy Type RS BOV.

The Y-pipe is a solid and heavy affair. The welds are more workmanlike than pretty, and there were some minor blemishes in the powdercoat. This is not a racing piece, nor is it a show car piece, as it is neither light nor pretty.

My version did NOT come with a nipple for the wastegate boost source line, but the steel was thick enough to allow drilling and tapping a brass hose nipple.

Fitment, however, is pretty good. Everything lined up, and after loosening off all the connectors to the "intake bubble" hose and wiggling everything around, the OEM air filter housing closed up and there was plenty of room between the BOV and both the battery and the MAS airflow sensor.

Fitting the BOV did require the fabrication of a return hose, which was made from a section of radiator hose with a suitable bend, and a PVC pipe elbow. The location of the BOV pressure line also had to be clocked "forward" rather than "upward" (as originally provided) by removing the spring cap from the BOV and rotating it clockwise.

BOV recirculation hose detail

With the new parts in place, I then fitted an intake pressure tester adaptor and went hunting for boost leaks. The intake pressure adaptor is another 3SX part, and this one is worth its weight in gold. Using it, I tracked down no less than four separate boost leaks.

Pressure testing the intake tract

This pressure test revealed a possible problem with the BOV. The lower nipple on a GReddy Type RS is supposed to be open to atmosphere. It can be connected to a before-the-throttle boost source to help keep the BOV closed under very high boost conditions, but normally it is left unconnected. When working properly, it is only connected to the volume of space behind the main diaphragm, but mine is connected to the intake tract - meaning there is an internal leak inside this brand-new BOV.

GReddy no longer makes the Type RS, and I suspect that problems sealing the internals is the primary reason why. I will replace this knock-off with a proper TurboXS BOV sometime in the future. In the meantime, I capped off the leaky nipple.

Pipe install completed

Review Summary

Dejon Tools Y-Pipe

  • Pros:
    • Good fitment, with no shenanigans required to line up connections and plenty of battery and MAS sensor clearance
    • Properly seals off troublesome throttle body connector
    • Allows use of aftermarket BOVs
  • Cons:
    • No nipple for wastegate boost source line (at least on mine)
    • Not very pretty
    • Not very light
    • No BOV recirculation hose provided (at least as provided by 3SX)

Overall, a workmanlike part that does the job.