ARD has been offering Billet compressor wheels for the TD04 line of turbos for a few weeks now and the questions have been pouring in faster than I can answer them! So to help clarify the benefits and features of these compressor wheels, this weeks article will cover upgrading turbo components across the board, including billet wheels.
There are a number of upgrades available for TD04 turbochargers that are found on the majority of Volvo turbocharged engines and weíll outline the most popular ones and cover the benefits of each.
Compressor bypass valve:
The compressor bypass valve, or CBV, is a built into the compressor housing of the turbo and acts a pressure relief valve that protects the bearings in the turbo cartridge from excess side loading. This pressure venting occurs anytime the engine has been in boost and the throttle is suddenly closed. Since the compressor wheel is still spinning at a high rate of speed, the turbo is still pumping out a considerable volume of air. If the throttle blade is closed, then this air has nowhere to go and will end up backing up (also called turbo stack) against the compressor wheel which side loads it and puts strain on the bearings. The CBV vents the pressurized air back into the intake of the turbo and prevents this side loading from occurring. The CBV consists of a diaphragm and spring, the spring holds the diaphragm closed until the pressure difference between the turbo outlet and intake manifold is great enough to lift the diaphragm against the spring tension. When turbo stack occurs, the pressure at the turbo outlet is high, while the intake manifold is low (in vacuum). This differential is what allows the CBV to open and vent the excess pressure during turbo stack. The stronger the CBV spring, the harder it holds the CBV closed. During early boost development if there is a great enough difference in outlet pressure from the turbo, vs. intake manifold boost pressure the CBV can leak, this is undesirable as it slows boost development. In most cases this is not a common issue but with higher than stock boost levels the factory intercooler can cause enough boost pressure drop to create pressure differential that, in some cases, can cause the CBV to leak. Not sure with CBV upgrade is right for you, ask you tuner for recommendations. Whether CBV or BOV (blow off valve) itís important that yours is in good shape and adjusted correctly to provide the greatest performance and longevity!
Last week we took a closer look at wastegate actuators and while bigger might seem better itís certainly not the case. Keeping a proper balance of wastegate pretension and TCV operation is critical to precise boost control. A wastegate that is too tight can cause boost surging and overshoot which can be damaging. A wastegate that is set too loose can cause lethargic boost development and reduced performance. Typically a maximum wastegate starting pressure I recommend is 0.4 bar or 5.8 psi. ultimately it depends on your setup so do your homework before you lay down any hard earned dollars. Anytime you adjust your wastegate setting to higher than factory spec, especially if you are at higher than factory boost levels itís a good idea to consider a high precision TCV. While they are not necessarily a required upgrade, itís a good idea to help keep boost pressure where itís supposed to be!
Factory compressor wheels are made from cast aluminum and while they tend to do the job quite well in stock form, thereís still some considerable room for improvement as it relates to the performance enthusiast. Cast compressor wheels are simply not as strong as billet aluminum compressor wheels so they tend to be heavier and therefore spool more slowly. Billet aluminum compressor wheels are inherently stronger and consequently are lighter. This comes from a smaller center barrel and thinner overall design. Additionally, Improved flow from an 11 blade primary design vs. the 6+6 primary/secondary blade design allows for higher total horsepower and torque. So billet wheels allow for higher flow and quicker spooling, both of which are considerable benefits when it comes to engine performance!
Turbo quick change:
Looking for an inexpensive way to make a small turbo into a larger one? Fortunately the turbine side (exhaust side) of the TD04 turbos are all identical in terms of the blade and scroll design. Many folks are finding that they can take their smaller 13T, 15G, 16T, or 18T and convert it into the larger 19T by installing a billet compressor wheel and matching compressor housing. This allows for a 100% bolt in turbo that can provide up to 340bhp. Itís ultimately advisable to do a full rebuild on the turbo you might be contemplating this for however Iíve been surprised to see more than a few folks out there simply install these two parts to their turbo and have as much as 10K on the odometer without issue! Time will tell if thatís a good idea or not but either way itís a cost effective way to get into a larger turbo that is easy to install.
Robert Lucky Arnold