Contrary to popular belief, work has been progressing across all of my projects. I'll update each thread accordingly, starting with this one. I'll attempt to post more frequently from now on (my work life has been absolutely mental of late, hence my lack of forum posts!).
An unusual serial number revealed little about the history of my Cavalier’s new turbocharger, but after much in the way of head-scratching, I'm able to confirm that the unit was originally built for a heavily modified Ford Sapphire Cosworth competition car owned by Racing Technologies Norfolk (RTN). I'm pretty sure that RTN was the company owned by former Formula One driver, Jonathan Palmer (father of current Formula One pilot, Jolyon Palmer), that went on to become Motorsport Vision (MSV), the owner of Brands Hatch, Oulton Park, Cadwell Park, Snetterton and Bedford Aerodrome. Palmer Snr is the majority shareholder in MSV. I literally bumped into him at the Goodwood Festival of Speed last weekend. If I'd have thought about it in time, I could have asked him about the Cavalier's new bhp booster. "Oi, did I buy your Cossie's turbo?!"
The turbo had been upgraded with a 360° thrust bearing and a .48 A/R turbine housing for a faster response. The engineering firm that carried out the work told me that RTN wanted a punchy turbocharger that could deliver between 340bhp and 380bhp at 1.6bar boost. It’s claimed that the turbo had been serviced prior to being put into storage. Even if that’s true, I'll be introducing the unit to an entirely new engine operating environment. In short, without dismantling my new Garrett, there is no sure-fire way of being able to check that it is in sound working order.
Keen to avoid any nasty surprises (and hopeful of extracting more power out of the part), I contacted the hybrid turbo heroes at Turbo Dynamics and requested a strip and rebuild of my Cavalier's new bhp booster to a custom specification. The firm has what is thought to be largest catalogue of hybrid turbos in the world!
Most people know that a 'hybrid turbocharger' is the name given a turbo that features aftermarket or modified components. These parts are usually introduced to increase the power and/or reliability of the turbo in question, either as a consequence of accompanying engine modifications or turbo failure. What most people don't know, however, is the amount of work that goes into building a hybrid bhp booster, or what can be done to bring an old turbocharger up to modern standards. I hope the following build diary will shed some light on the matter!
To begin with, the turbocharger is fully stripped before each of its parts are checked and measured for wear. The turbine shaft surface, thrust bearing face, thrust collar and journal bearings are all checked for signs of heat damage,
material transfer or scoring. Reclaimable parts are put to one side.
The blades of the compressor and turbine wheels are examined in order to identify any foreign object damage or contact with their respective housings. The housings themselves are also looked at in detail. Here we can see scoring and material transfer on the turbine shaft.
Although many original parts are no longer fit for purpose, some can be reused. Reclaimable items (including our turbo’s half-moon clamp plates) are chemically cleaned, hot washed and media blasted in order to remove and dirt, grease, carbon deposits and/or corrosion.
Equipment that has been heavily affected by oil residue and carbon build-up – such as the compressor cover and turbine housing – is exposed to a high-temperature propane burner. This treatment eradicates any stubborn contaminants. The parts are then put through a heavy duty media blaster.
A high-performance compressor wheel is selected for use in my turbo. A device known as a clock gauge is called upon to ensure that the new part is held correctly before any machine work begins. The compass-like instrument consists of an extendable arm, a fine point and a ball tip. The ball is rested on the hub of the compressor wheel. The wheel then spins, and the clock gauge lets the operator know whether or not the new part needs to be re-seated.
Despite its age, my turbocharger can be equipped with thoroughly modern parts. This picture shows the very latest in compressor wheel design, chosen for its lightweight, billet construction and a performance rating of 450bhp. This compressor wheel is 20% lighter and much stronger than cast equivalents.
Because the guys at Turbo Dynamics are building my Garrett to a custom spec, the centre bore of the new compressor wheel needs to be modified to match the diameter of the turbine shaft that will be inserted into it. If the shaft being used was smaller than the core, however, the core could be sleeved to suit.
The modified compressor wheel is test-fitted to the new ‘turbine shaft and wheel’. The new shaft is designed to accommodate staggered gap oil seal rings that prevent leaks even when exhaust back pressure is reduced through the use of a decat pipe or an exhaust system with an enlarged bore.
The shaft is a perfect fit. The turbine wheel can now be worked on. Its blades are cut to a specific angle so that back pressure at high rpm is reduced. A large grinding wheel is used to make the change (a mod that greatly improves top-end performance by allowing the turbine to flow air beyond its usual limit).
The modified turbine wheel. Look at any dyno graph and you’ll see that linear power tends to drop suddenly when a turbocharger reaches its limit. Cut-back blades allow for greater performance in the upper rev range, enabling the turbo to continue producing power long after it would ordinarily be able to do so.
Turbos get hot. Red hot. Any metal surface can be affected by heat, but it is vitally important that a turbocharger flange face is perfectly flat so that exhaust gas leaks are avoided. This is especially important if you’re planning to attach a used turbo to a new or replacement exhaust manifold.
More to follow...
