Improving Speed on a Four-Cylinder Engine

There's performance parts, adding a turbo/supercharger, and there's shaving the cylinders themselves (or shaving something inside the engine anyway, I saw it on my Wyotech DVD). What else can one do to improve the speed of a Four-Cylinder Engine in detail?

If by speed you mean power, there are virtually limitless ways one can modify an engine to create more. The fact that the engine is a four cylinder hardly matters, as one could perform just about any modification possible on a larger motor, on the four cylinder one.
As for methods of improving power, one must remember that to create power, one must burn fuel. So any modification that allows the motor to burn more fuel efficiently will also increase power. The key to these types of modification is to make sure any added fuel is burned efficiently, otherwise one may actually lose power. This is the purpose of forced induction, enlarged displacement, nitrous oxide, high flow manifolds and "headers", aggressive camshafts, etc.; so that the motor will be able to burn more fuel and do it effectively.
Then there are the types of modifications that don't actually create more power, but merely free more up by reducing power losses to friction and parasitic loss; this includes underdrive pulleys, engine blueprinting, rollerized engine components, etc.
I gave a few examples, but I won't write a list because it would take too long. There are virtually limitless methods of improving your engine's output, but most of these methods either allow more fuel to be burnt, allow the fuel to be burnt more efficiently, or reduce lost power.

You could buy lower restriction exaust system(can add up to 25hp), bigger exaust, super/turbo charger, add N2O(Not street legal everywhere), get better spark plugs(I heard you can add more than 30hp), better suspension, lighten the car by removing useless accesories, etc. Is this car for racing or street and do you want it as powerful as it can be or just make it more fun to drive?

A newer, fast-flowing exhaust will not free up 25HP unless you have had extensive work done, or the engine is already at a high state of tune and it's the exhaust that's choking it.

An exhaust system with larger pipe diameter will tend to slow down the exhaust gases if the engine is not making large amounts of power. Smaller diameters usually are better, say 2.5" ID for up to 275HP, or 3" to 350HP.

You could buy lower restriction exaust system(can add up to 25hp), bigger exaust, super/turbo charger, add N2O(Not street legal everywhere), get better spark plugs(I heard you can add more than 30hp), better suspension, lighten the car by removing useless accesories, etc. Is this car for racing or street and do you want it as powerful as it can be or just make it more fun to drive?


No offesne, but i sugest you stay away from that "honda math". You cant put definite numbers to different mods. All cars, and engines are different and respond differently to mods. The only way to know for sure is to dyno the car.

w/e i've seen cars get up to 25hp from better exaust. i'm not necessarily saying it will give that on this vehicle. notice the "up to" that means not always, maybe less. the spark plugs, i dunno where i saw it but i think they were nology hot wires that did it. anyway these are just suggestions that he can look into.

Power = torque x revs

The simple equation to getting more power is to improve the breathing ability of an engine.


You can increase the breathing ability and ability of the engine to produce power at high rpm by:

- Improvements to intake and exhaust - this may be as simple as have a less restrictive filter to altering the intake and exhaust manifolds, changes to the ports, heads etc
- Changes to cam duration, timing and grind (ie breathe deeper, longer)
- Increasing the density of the intake charge eg Forced induction such as using a supercharger or turbocharger or simply keeping the intake on a NA engine cooler
- Increasing the compression ratio (so that the intake charge is squeezed harder to maximise expansion)
- Increasing displacement (ie making the engine bigger)
- Reducing frictional losses eg lighter pistons, different rings, removing unnecessary ancillaries eg air conditioning, power steering etc
- Optimising ignition, engine management for improved combustion and tune
- Improving fuel enrichment (more air, requires more fuel especially for turbo/super charged applications or using an oxidant) or improved fuel

The only thing is there is a trade off with all of these options - eg using a wild cam can mean idle speeds of 3000 rpm and no flexibility below 4500 rpm.

As an example, the 100cc two-stroke engines we used on karts produced around 16-17hp and revved up to 11,500 rpm but would be lucky to last a season of racing before a rebuild and constantly were fettled to maintain power including adjusting air/fuel ratio while racing. They made no power below 6,000 rpm.

In comparison, the 6 Hp Johnson 2 stroke outboard we use on the inflatable is 164cc and maxes at 5000 rpm and we expect it to work with little maintenance and run for years.

Every gain has its cost...