4G93 Modification From Mild to Extreme

For those 4G93 engine (first generation) owners who wish to modify their engine to on path with the Honda B18C, let's continue to read t...

For those 4G93 engine (first generation) owners who wish to modify their engine to on path with the Honda B18C, let's continue to read this post. All these information of this post were gathered from the net. Thus, I would like to thank all the author of these informative articles.

In any engine, the only way to make more power is by adding more air and fuel. This is why Turbocharger and Supercharger came in mind in the early decade. For Normally Aspirated (NA), we can try to increase the breathing performance and efficiency. There are several ways to increase the breathing efficiency and here are some of those things that help to improve the performance of the engine.

1. Increase the port shape and size so that more air flows in without losing the velocity.

2. Increase the cam duration and lift. The longer the valves are opened and lifted the more the air can flow in. However for a NA engine, the bigger cam duration and lifts are still depends on the vacuum to suck the air in and this area is compromise.

Having the ports open sooner and more valve lift is the equivalent to increasing the air and the engine will lose the velocity. However, this problem is not an issue once there's an increase in revs and the efficiency of the engine is enough to match the camshaft characteristics.

There are many ways to open and close the cams and most road engines usually use a mechanism called a hydraulic lifter or followers. The advantage of this mechanism is its quiet and doesn't need frequent and labor intensive adjustment like a solid lifter engine. However, there is a downside to the hydraulic lifter where it can't have a long duration and lift.

Let's talk about how to modify the 4G93. Here are some of the things you may do:-

1. Increase the compression ratio of the engine.

- When using a bigger cam profiles, normally we will lose the dynamic compression. But as we know that the theory shows that every 1 point of compression increase in the engine, there will be approximately 3 or 4% increase in performance. So by increase the compression ratio to 11:1 according to Honda VTEC B series engine specification or the 11.5:1 of the Toyota VVTL-i engine, we can gain an impression increase of performance for the 4G93. FYI, the compression ratio of 4G93 is around10:1.

2. Good port shapes and flow of the engine.

- The B18C straight out of the box flows an amazing 141+ cfm with no loss when the throttle body and inlet manifold are fitted compared to the 4G93 at around 120+cfm. As long as you able to find a mechanic with good knowledge, skill and experience of porting the engine, there will not be a problem of losing the velocity.

3. Increase cam duration and lift.

- A stock 4G93 is having approximately 256 degree and at 8++mm of lift. Try to change the cam to mild cam (288 degree) and with an inlet valve lift at 11.5mm and 10.5mm for exhaust valve. This is just a reference from me because mild cam is more daily driving friendly. If you wish to have a higher cam profile, you may try to increase to 300++ degree but bare in mind that you will suffer bad idling at lower rpm. 

For first generation 4G91 and 4G92 (non MIVEC) engines owners who wish to maintain NA path and modify their engines to on path with Honda B series engines, you may have this information as reference.