More about FIA Turbo restrictors - facts and stories
Following the extinction of the GroupB
rally cars, FIA
introduced devices known as turbo restrictors in order to limit the maximum output of turbocharged engines. These are to be applied to all GroupA
vehicles taking part in FIA
explains the introduction of turbo restrictors with safety reasons. Like many other FIA
decisions this an unfortunate one. Most rally drivers are complaining that the cars are less easy to drive with these devices fitted since the chassis handling capacity is under-exploited. Most of the negative effects of turbo restrictors are efficiently addressed by electronic engine management systems.
A turbo restrictor is essentially a tube fitted directly on the turbocharger's air intake. We will not go into very technical (bureaucratic) details on their geometry but their main purpose is to reduce the turbine's air intake flow and, consequently, its output. The internal diameter of the restrictor is being continually reduced by FIA regulations from 38mm (1992) to 36mm (1994) to 34mm (1995) and now 32mm on GroupN cars (the 34mm restrictor still applies to GroupA cars). Turbo restrictors also increase the turbo's lag time but most teams overcome this effect by fitting anti-lag systems.
The turbo restrictor's effect is mostly noticed in high engine RPM (above 5000). In this region of operation, the engine's output is very dependent on air flow. This is why engine heads are ported and air intake channels are polished to optimize air flow. The restrictor's effect on engine torque is beneficial. Peak torque values are obtained in medium engine rotational speeds. The presence of the restrictor, which actually accelerates the gases flowing through it and directs the air flow to the center of the turbocharger's compressor wheel, essentially increases the engine torque. We can roughly estimate the drop in engine power to be as high as 40% whereas the engine torque can be increased, through appropriate engine management, by around 20%.
The use of the restrictor not only has negative effects on the engine's output but also introduces other side effects. For instance the technology research applied to the mechanical parts racing engines is now almost pointless. Engineers try to find ways to optimize the engine's output by optimizing its electronic management rather than the engine internals. Rally car racing engines are less sophisticated, mechanically, than they might have been if the FIA didn't impose the use of restrictors. Since most rally cars are based on commercial vehicles the latter are available with engines that are also less interesting mechanically. Excerpt from www.rallycars.com
RallySport, December 1995 - Toyota story
Toyota Team Europe has been banned from competition for the next 12months, and the points already gained in the 1995 World Rally Championship have been taken away by the FIA.
"It's the most ingenious thing I have seen in 30 years of motorsport." admitted FIA President Max Mosley after an extraordinary meeting of the FIA's World Council convened following technical reports on Toyota from the Catalunya Rally.
The offending illegally modified turbo restrictors which banished Toyota from the WRC.
The cause of complaint was that Toyota had fitted turbo restrictor’s which were modified in three ways:
The restrictor was not sealed so it was possible to move it without touching the seals.
It was possible for airto enter the engine without passing through the restrictor.
The position of the restrictor could be moved so it was further away from the turbine than the50 mm limit permitted.
It was discovered that these irregularities were made possible by a flange which had a special hidden bypass device which was held open against a very strong spring. The hose which connected the restrictor to the turbo had a metal casing inside, and attached to this casing were catches which could secretly force open the by-pass flange to the extent of 5 mm.
Max Mosley explained: "When the system was dismantled, the flange would automatically close itself and remove evidence that extra air could have entered engine. This system not only allowed extra air which did not pass through the restrictor to enter the engine, but also the restrictor itself could illegally be moved further from the turbo.
"The hose was fixed to the restrictor by a jubilee clip. A special tool was then applied to open the device and then the device then gripped in the open position by a second clip. Both of these clips had to be undone for a scrutineer to check the restrictor and in the process of opening those clips the device snapped shut.
"Inside it was beautifully made. The springs inside the hose had been polished and machined so not to impede the air which passed through. To force the springs open without the special tool would require substantial force. It is the most sophisticated and ingenious device either I or the FIA's technical experts have seen for a long-time. It was so well made that there was no gap apparent to suggest there was any means of opening it."
The FIA estimates that 25 per cent more air was allowed into the engine than permitted although admits it's difficult to estimate how much more power that would achieve. An expert put it as high as an extra 50 bhp—a considerable advantage when the cars are supposedly limited to 300 BHP.
TTE did not claim the device was legal but was represented by lawyers who entered a plea in mitigation. Mosley went on to say that the points Toyota and their drivers, Juha Kankkunen, Didier Auriol and Armin Schwarz had gained in 1995 would simply be taken away but others would not move up to fill the gaps.
The team would also be banned from contesting the 1995 Network Q RAC Rally and the 1996 World Rally Championship. He also stated that the FIA would not allow the team to get around the restrictions by entering under another guise and went on to say that there was however, nothing to suggest that the drivers were aware of anything going on.
According to Toyota the device had been devised at a "certain level" and the management knew nothing about it. The FIA dismissed this claim, saying that as a team they were responsible for all their actions.
He went on to say that there were indications that this type of thing was not happening with in other teams and praised those who were concerned with discovering the irregularity. TTE has announced that it is planning to appeal against the ban extending through 1996.
The absence of the team would weaken an already frail championship and leave it to a fight between Subaru, Mitsubishi and Ford with Subaru being the obvious favourites.