There are limited Honeywell OE Motorsports turbochargers that are not qualified to contain a wheel burst; however, these are not available to the general public. For top-level professional racing series such as Le Mans and the World Rally Championship, OE vehicle manufacturers cannot accept the weight penalty associated with thicker housings that would be necessary for burst containment.
The OE customer assumes full responsibility to include secondary containment measures on the racing vehicle and assumes all liability in the event of a wheel burst. Again, these turbochargers are not available to purchase unless the customer is a large OE vehicle manufacturer and is willing to accept the associated risks and liability. The average independent racing team cannot realistically assume such risk because of limited resources, and this is exactly the reason that commonly available Garrett® turbochargers are qualified to successfully contain.
Guidelines for Designing a Burst-Safe Turbo System
Testing and qualification from the turbo manufacturer is just the first step to building a system that will withstand the worst possible failures. In order to maximize the safety of a turbo system, start with a true burst containment qualified turbocharger, and do not modify the housings in such a way that would compromise their strength. Do not drill holes in the housings or weld on tabs for mounting, and do not remove any material from the housing to reduce weight.
A Garrett® burst containment qualified turbocharger comprises an exact, unique combination of wheels, housings, and compressor backplate, so do not swap wheels, housings or backplates with parts from another turbocharger or from another manufacturer. Regardless of the turbo being used, consider the consequences of a wheel burst and the chain of events that could take place. Are there any fuel or oil lines near the vicinity of the turbocharger? Any fuel or oil tanks that would be in the path of a hot escaping wheel or fragment?
A non-qualified turbocharger could eject shrapnel towards these flammable liquids, causing a leak and potentially a fire. Garrett® by Honeywell qualifies turbocharger housings to contain radial bursts, but cannot prevent the turbine wheel from escaping through the turbine housing outlet because of the need for the efficient discharge of turbine flow. In the case of an aftermarket turbo build, the vehicle owner must assume responsibility to prevent the unsafe escape of the turbine wheel, should the shaft or weld joint fail.
Even if a containment qualified turbo is used, reasonable care must be taken when designing the downpipe and/or post-turbo exhaust system. Aluminum is used by many drag racers as a downpipe material due to its light weight; however, it will pose little to no resistance to an escaping turbine wheel or wheel fragment.
As safety should be the priority, 1020 steel is the best material to use for downpipes and post-turbo exhaust tubing because it has an extremely high capacity to absorb ballistic energy; the combination of high strength and high ductility allow a thick enough piece of 1020 steel to “catch” the wheel or fragments without shattering apart as a more brittle material would.
Also consider that even though a straight-shot downpipe will be the least restrictive to turbine flow and therefore the best for power production, it will also be the least restrictive to impeding a detached turbine wheel from exiting the vehicle and shooting away as a projectile. A bend can help slow the wheel down, and crossed bolts installed in the downpipe or a thick steel grating in the tube can help to catch a wheel and absorb a good deal of its energy.
Consider a turbine housing with a straight downpipe and no means of slowing down an escaping wheel. If the wheel-to-shaft weld joint or hub fails, or if the shaft breaks allowing the turbine wheel to detach, angular momentum is conserved and the wheel can exit the outlet of the turbine housing with a tremendous amount of energy due to the high rotational speed.
Even an unburst intact turbine wheel skipping down a racetrack at rotational tip speeds of 2000 ft/s (1360 mph) can have the potential to damage anything that it contacts until this energy is absorbed and/or the wheel speed slows down due to air resistance.
Turbochargers are generally reliable, but even the highest quality turbo may fail when subjected to excessive abuse. A wheel burst is the extreme example of turbo failure but is a contingency that must be planned for with utmost care. Using a non-burst containment qualified turbocharger presents a very real risk to the end user and their surroundings, especially in motorsports, spirited enthusiast driving and racing situations.
Garrett performance aftermarket, replacement aftermarket, and original equipment turbochargers are well qualified to contain a wheel burst, as long as the combination of Garrett wheels and housings remains unaltered.