Services

Custom turbo builds for drag, track and fast road

Some cars need more than a standard upgrade. GP Turbos specifies and builds hybrid and custom-specification turbos around the engine, the fuel, the way the car is used and the rest of the build, from a Scunthorpe workshop run by Grant Parker, who has drag raced his own turbocharged Golf.

Discuss your build Call 07795 165355

A custom turbo build starts from the job the turbo has to do. A drag car, a track car that has to survive long sessions and a fast road car that still needs to pull cleanly at low engine speed each ask something different of the turbo. GP Turbos has described its hybrid work as designing and building turbos to each customer’s requirements, and many of its past upgrades were made to order for the engine in question.

A custom specification takes that further. The compressor wheel, compressor cover, turbine trim, bearings, seals and actuator are chosen for your build rather than taken from a standard stage. If a hybrid turbo on the original housings will do the job, we will say so.

Grant Parker’s racing background

Grant Parker has been tuning cars since the early 1990s. By his account, his own Volkswagen Golfs have included:

a 2.0 16-valve Mk1 Golf GTI running motorcycle carburettors and nitrous, which finished in the top ten at the GTI International quarter-mile sprints;
a Mk2 Golf GTI from the late 1990s with a 1.9 TDI Pumpe-Düse diesel engine, which took the quickest-diesel title at GTI International with a 13.40-second run;
a Mk1 Golf built around 2000 with Audi quattro four-wheel drive and a five-cylinder turbo engine, which won the 0–60 mph challenge with a best time of 2.47 seconds.

In 2021 the motoring website Engine Swap Depot featured Grant’s four-wheel-drive Mk1 Golf, running a GP Turbos billet turbocharger on an Audi 20-valve five-cylinder engine, and reported a 10.65-second pass at 128 mph at Santa Pod Raceway. By his account, he has also helped drag racers, rallycross drivers and owners of fast road cars with turbos and tuning advice.

What goes into the specification

Compressor side

The compressor wheel sets how much air the turbo can move, and the cover around it has to match.

Billet compressor wheel, often with extended tips
Cover machined or re-profiled to suit the wheel
Area-to-radius (A/R) ratio changed where needed

Turbine side

The turbine wheel and housing are matched to the bigger compressor, and the actuator to the boost the build needs.

Turbine wheel trimmed or cut back
Turbine housing re-profiled where needed
Uprated actuator and spring to suit the boost target

Bearings, seals and balance

Higher boost means more thrust load and higher shaft speeds, so the bearings, seals and balance all matter more.

360° thrust bearing and uprated collar
Uprated journal bearings
Step-gap oil seals
Reverse-thread shaft nut
Rotating assembly balanced to a motorsport tolerance

Twin-turbo engines

On a twin-turbo engine, both turbos have to be specified together. GP Turbos’ past listings included upgraded pairs for the Audi RS6 4.2 V8, the Porsche 993-generation GT2 and X50 engines and the Range Rover 4.4 SDV8 diesel, and both turbos of BMW’s twin-turbo 3.0 diesel in the 335d, 535d and 635d.

Matching the turbo to the engine

The compressor has to suit the engine’s airflow, which is read from its compressor map. Past the choke line on Garrett’s maps, efficiency falls away and turbo speed climbs very quickly, and Garrett says overspeed is then very likely; when an engine needs flow beyond that point, Garrett’s answer is a larger compressor. Garrett also recommends a shaft speed sensor for performance use, and MAHLE notes that major damage can follow within seconds once a turbo exceeds its permitted speed.

A billet compressor wheel is about strength. Garrett tested machined and cast wheels of the same design and found no noticeable difference in performance; the benefit of a machined wheel is fatigue life under repeated load cycles, which BorgWarner puts down to the refined grain of a forged and milled wheel. That is relevant to any turbo taken to full boost again and again.

Whatever the specification, the result depends on supporting modifications and a matching calibration: fuelling, boost control, intercooling and exhaust. Tell us who is calibrating the car so the turbo and the calibration are planned together. The turbo overspeed guide covers compressor maps and wheel fatigue in more detail.

How a custom build works

STEP 01

Describe the build

The engine, fuel, gearbox and drivetrain, how the car is used, the current turbo part number and the modifications already done or planned.

STEP 02

Agree the specification

Wheel sizes, housings, bearings and actuator, whether a hybrid on the original housings will do or a custom specification is needed, and the price.

STEP 03

The build

The turbo, or the pair, is built to the agreed specification.

STEP 04

Fit and calibrate

Fit it with clean oil lines and a primed oil feed, then calibrate the engine to suit the new turbo before using full boost.

Custom turbo build questions

Do I need a custom turbo or will a hybrid do?

If what you want from the car fits within what the original housings can flow, a hybrid is usually the simpler route and keeps the standard mountings. When it does not, a custom specification is the next step. Tell us about the car and how it is used, and we will advise which fits.

Why are there no power figures on this page?

Power depends on the whole engine: its internals, the fuel, the supporting modifications and the calibration. A turbo on its own does not set it, so we do not quote power figures for a turbo in isolation. Ask about your build and we can talk it through.

Does a billet compressor wheel make more power than a cast one?

Not by itself. Garrett found no noticeable performance difference between machined and cast wheels of the same design. The advantage of billet is strength and fatigue life; extra airflow comes from the size and shape of the wheel and a cover matched to it.

Do I need to tell my insurer?

Yes. Insurers expect performance modifications, including an upgraded turbo, to be declared. Emissions equipment matters too: government guidance is that a diesel with its particulate filter removed is illegal to use on the road and fails the MOT.

Planning a drag, track or fast-road build? Tell us the engine, the use and what else it has.

Contact GP Turbos Call 07795 165355

Discuss your build

07795 165355 sales@gpturbos.com

Monday – Friday: 9am – 5pm
Saturday: 9am – 1pm
Sunday: Closed

Welbeck House · Holme Lane · Scunthorpe · DN16 3RF