This is something that i have slapped together on another website
alot of it has relavence here
This next post will be dedicated to the "Road Less Travelled" in modifications, Natural Aspiration (NA).
One of the most noticed improvements of an NA engine is the response it gives. Put the throttle down, and the power (even though it might not be much) is felt immediatly. There is no turbo lag. One of the other main changes is most NA mods look factory, and go un-noticed by the untrained eye. I mean, how does average joe officer know that you have aftermarket cams, or a larger throttle body? Read on.
(1) Engine Conversion
Lets face it, if you want to chase some serious power in the NA game, you must look towards a conversion to a larger capacity engine. Be warned, as simple as it sounds, research is the key to a painless conversion. Also this can be an expensive step, and one definatly left to professionals, not a couple of mates, a slab of beer, and a rainy weekend. Many gremlins can surface and in some most cases, custom parts are required.
No matter what your mates say, you aren't going to be able to fit that 351 Big-Block into your X3 accent, no matter what angle it you put it.
(2) Exhaust Systems
A larger exhaust will be of benefit, however don't fall into the trap of "bigger is better" commonly seen in turbocharged engines. Getting the exhaust gas to move quickly is the idea, but you need to maintain backpressure. If you don't maintian appropriate backpressure, it can interfere with engine recompression, and engine tourqe can be lost. General rule of thumb is for a (1.5L) engine, no larger than a 2" system. for a (2-2.5 L) engine, 2 1-2" system, and above that (3-4-5L) 3" systems.
(3) Air Filters & Intake
Another basic step for performance is a free flowing aftermarket air filter. Beware however of pod filters, yes they generally have better airflow than standard filters, but having an unshielded pod in an engine bay can lead to dramas. Ducting more air into a factory air box, and replacing the filter with a high flow aftermarket item, can often provide the best improvement. Face it, by using the factory airbox you aren't drawing any hot air from the engine bay, or debris from the road (if the pod is too low in the engine) and due to the "factory" look of the intake, can often go un-noticed by the Authorities.
(4) Throttle Bodies
For better airflow, often the next step is upgrading your throttle body to a bigger bore or multiple item. The main noticable difference in doing this is throttle response. Your ride will react quicker to even slight changes in acceleration, across the entire rev-range.
However if one chooses the path of multiple throttle bodies, you must be aware that the engine may now run "leaner" and can be prone to detonation without additional aftermarket tuning.
(5) Aftermarket Cams & Cam Gears
If you are chasing the big power numbers, you can't look past aftermarket cams & Adjustable cam gears. By using these items you can dial in the amount of exhaust & inlet degrees, and tune the engine to suit specific power bands. With NA engines, the best power is often seen at high revs, top end. However, the larger cams you go, and further you adjust the timing, the more low end power and idle will suffer. A Lumpy idle & stalling at low revs is not uncommon on a worked NA Engine.
(6) Engine Management
With cams comes management to control the ignition and fuel delivery. depending on what you have to spend, dictates whether you go full standalone systems, piggy back, or ECU remaps. Management becomes essential once cams are introduced, and can also be utilised before this stage if your engine runs too lean after throttle body upgrades.
(7) Port / Polish
A port polish is a technique that increases airflow across the top of the engine by smoothing the cylinder heads. Porting will increase the heads potential to flow more air die to the increased area for the air to move in and out of. This is often an expensive upgrade, as the engine must be pulled apart and worked on, often using a flow bench to measure results.
(8 ) Ignition & Fuel Systems
Well, if we are chasing every last drop of power, some more simple improvements are; Thicker ignition wires, aftermarket coil packs & colder plugs wont hurt. This ensures no loss of spark when it is needed.
With fuels, most stock fuel systems are up to the mark, due to the fact that NA engines not make that great deal of power as apposed to a turbocharged engine. With some bolt on turbo systems, upping the boost and advancing timing, sees the fuel system suffer, thefore requiring larger fuel pumps and injectors to supply the demand. In an NA engine, this is not the case. Most fuel issues, if at all, can be fixed with aftermarket tuning, rather than additional components.
Even higher octane or race fuels can be added in the hopes of extra power, be aware, some fuels will require tuning.
(9) Pulleys, Flywheels, Cooling & Extras
Finally comes the other bolt ons that aren't neccesarly NA orientated, but wont harm the goal of a quicker ride.
Lighter Flywheels and engine pulleys add to a more responsive revvy engine. Aftermarket radiators and engine & transmission oil coolers, although not adding any power, will often help in the overall performance package, by offering better protection to your components.
(10) Weight Loss
Weight loss adds to perfomance, lets face it, if you can shed 50 kilos of stereo gear, you engine dosent have to haul that weight along. Again, this will help with fuel economy. Additional ways to lose weight is lighter rims & carbon fibre panels, even removing the aircon system, will not only remove weight, but lessen the strain on the engine pulley system. some horses could be saved there.
Conclusion
Realisticaly there is more ways out there to make your ride go quicker, this has covered only some of the simple NA upgrades for more power and a quicker ride. It may not be as quick or powerful as forced induction, but it can be equally as fun to drive. With the way the laws are headed with young drives, commonly seen NA monsters may not be too far off.
Extracts from various Car Tuning Magazines & personal research. Enjoy and please add more improvements you are aware of or have done yourselves.
Jacko
