Souping up your vehicle's engine and exhaust illegally could land you in the soup.
From next month, owners caught modifying these parts more than once will have to send their vehicles for official inspections more often.
Those caught a second time will have to send their vehicles for an inspection every six months, over a period of two years, said the Land Transport Authority (LTA). Those caught a third or subsequent time will have to do this every three months over a two-year period.
Inspections are usually required every year or two, depending on a car's age and type.
The tougher measures are in addition to existing penalties of a fine of up to $2,000 or jail of up to three months for first-time offenders.
Existing penalties also apply to other illegal modifications made, such as overly tinted windows or installing after-market high-intensity discharge lamps.
LTA said it takes a "serious view" of illegal modifications made to engines and exhaust systems because they posed a safety and environmental hazard.
"Once a vehicle's engine or exhaust system is modified without due certification and approval, the existing vehicle components may not be able to handle the increased power or speed," it said. "Such modifications may also affect the durability and reliability of a vehicle."
Those who flout the tougher inspection regime can be fined up to $1,000 or jailed for up to three months. The maximum penalty will be doubled for repeated convictions.
Under LTA's guidelines, after-market exhaust systems can be legally installed if they are certified to be suitable for the vehicle's make and model. These exhaust systems also have to be tested by the vehicle manufacturer or laboratories, to ensure compliance with international standards relating to emissions, noise and component quality.
According to the LTA, 1,384 motorists were caught for illegally modifying their engines or exhaust systems last year. Among them, 15 per cent were repeat offenders.
In 2013, there were 3,575 motorists caught, with repeat offenders making up 10 per cent. The year before, repeat offenders made up 9 per cent of the 4,316 caught.
Overall, the total number of cases of illegal modifications has been on the rise. Last year, there was an average of 1,835 cases every month, a jump of 26 per cent compared to the year before. In 2013, 1,457 cases were registered every month, a 53 per cent increase from the 955 cases a month in 2012. However, up to August this year, an average of 1,764 cases was registered each month, 3.9 per cent fewer than the monthly average for last year.
A 54-year-old car workshop owner, who requested anonymity, said: "As the law is quite strict, most car workshops here are only offering to do legal modifications. However, motorists are still going to Johor Baru, where the costs are cheaper - almost dollar-for-dollar."