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Beware of raising car's RPM levels

TO Morgan,

I want to increase the rpm limit on my car so that I can get extra power from the motor. If I increase it from 5500rpm to 7000rpm what difference in power will I get? I'm also thinking of adding a performance chip. Thanks. - Darryl Eaton, Howick

Morgan's advice:

Hi Darryl,

Be very careful before raising the rpm limit because you can damage the engine as the rotating parts are pushed beyond their designed specification. The rpm limit is usually controlled by the engine management system, cutting fuel or spark delivery to the engine. By raising the rev limit you are not guaranteed extra performance. At higher rpm factors such as inertia loads, friction, heat and volumetric efficiency overcome an engine's ability to produce energy play a major role.

To get the maximum output from setting a higher rev limit one needs to modify the cylinder head with stronger valve springs, bigger valves, a flowed head and a sporty camshaft set.

Once this is done the rpm limit can be changed by modifying the setting on the engine management, usually with after-market software.

My advice is to begin with these modifications before changing the rpm limit to avoid an expensive repair bill.

'The car began to shudder and ran out of fuel'

Hi Morgan,

Please help me, I think I might have damaged my car. I was driving back from my parents and the petrol light came on but I couldn't find a petrol station on the highway. I kept driving and the car began to shudder and ran out of fuel. When someone came to help he said it is bad to drive when the tank is nearly empty. The car seems to be working fine now but do you think I should take it for a service? Noxolo, Mpumalanga

Morgan replies:

Dear Noxolo,

If this is the first time you've driven on a low fuel level your car will be fine, but it's not something you should continue to do. The bottom of a fuel tank is filled with tiny dirt particles, many of them deposited by the fuel.

By driving on an empty tank this dirt can be picked up by the fuel pump and create a blockage, affecting the car's power and even preventing the car from running. Small filters in the fuel pump and line prevent these from entering the engine and are changed regularly during service. If the car is running well I would not worry about taking it for an unscheduled service.

BATTERY LOOKS NEW BUT CAR WONT START

Dear Morgan,

Howzit man, perhaps you can help me because my car is driving me crazy. I bought it second hand and the salesperson told me that it is in perfect condition. It ran for the first few weeks but when I tried to drive it the other day it wouldn't start. None of the lights came on and the central locking didn't work so I charged the battery and it started. I drove it some more and the same problem happened. The battery looks new and I don't know what else it could be. - Matteo, Fordsburg

Morgan says:

Hi Matteo,

Used cars which have been standing on the floor for some time often suffer from battery problems because they are not regularly started. Some batteries require attention to the level of water inside each of the caps. It could also be that the alternator is not charging the battery properly.

This can be modified inexpensively.

Take the car to an auto electrician and he will detect if there is an unusual current drain caused by the radio, an old tracking device, immobiliser or loose wiring. A healthy battery reads around 14 volts. Be sure to have the correct sized battery for your type of car.