Basic of POWER (3)

The fun part of engine tuning is to play around with the engine powerband. And what the heck is powerband?

In simple term, it is the power output across various rpm. There are just too many powerbands in real world. I categorize them into 3 types:


stock powerband

usually stock engine has loads of torque at low-mid rpm to ease cruising, and crippled mid-high to top rpm power to limit exhaust emission.

racing powerband

usually racing engine has loads of horsepower from mid-high to top rpm, as horsepower = (torque x rpm)/5252. Theoretically, the higher rpm we go, the more horsepower we can get. However, we need to sacrifice low to mid range torque to increase top end power. A torque-less engine is hard to drive on street.

Balance powerband

This is what I defined as street racing power band. You got enough torque from low to mid range for cruising, and increased horsepower from mid-high to top rpm for some street racing. It's especially good for mountain passes. This engine rev very smoothly from low to high rpm.


If you still don't get what are they, here's an easy real world indication --> engaged your 3rd gear and start accelerating from 30kph to 120kph. Now you can feel the engine power band across all rpm.


Stock:
30..40..50..60..70...80....90.....100......110.........120

Racing:
30.....40....50....60....70...80...90...100..110..120

Balance:
30...40...50...60...70...80...90...100...110....120

Basic Of POWER (2)

A golden rule in reading engine specification - do not totally mesmerized by the high horsepower and torque figure! A bike which has bigger horsepower and torque at the same CC, does not mean it is better in overall performance. The most important aspect of an engine is a smooth power output from low to high rpm, where you can feel the torque from low to mid, and some good power at high rpm. You can cruise, and you can run! However, the problem of standard 135LC is, we can cruise, but we can't run away too far. Goshh.

Nevermind, put that aside first. Let's move on......

How do we know the power output characteristic of an engine? Read the power curve in dyno chart.

Below is the dyno chart extracted from B.R.T. website. It described power curve of standard 135LC engine, before and after installing its product.

The blue color curve is standard setting. See? The power goes up smoothly up to 7k rpm only (mid-high range). At high rpm, the power not only sux, but unstable. It goes up a bit, then go down again, up again and down again. The feel on our buttock will be like, wanna go ... dowan to go... wanna go.... dowan to go. It is really shit, especially we want to play top speed with people on straight road, or accelerating up a steep hill.

After changing the CDI, the ripple effect at high rpm is still there. Although power figure increased slightly, you will still feel the stupid wanna go... dowan go... wanna go ... dowan go feeling.

This problem usually is caused by bad airflow from exhaust system at high rpm. As you know, we have some rules and regulations on exhaust gas emission. Manufacturers have to comply to these, so they have no choice but to seal the best part!

Don't worry, I already know how to break this seal and will share out in upcoming articles.

Stay tuned !

Basic of POWER (1)

When you guys read the specification sheet of 135LC, I am sure you went through the horsepower and torque figure.

Standard 135LC has a maximum of 11.33 BHP at 8500rpm and 11.65Nm at 5500rpm. Have you ever wondered what are all these means.

To calculate the BHP at 5500rpm,

First, you need to convert the torque from Nm to lb/ft:
11.65Nm x 0.7375 = 8.59 lb/ft torque

Then, use this formula: BHP = (torque x rpm)/5252
8.59 x 5500 / 5252 = 9 BHP

A simple question to you guys: Why do I calculate the BHP at maximum torque rpm?

Make a guess ......




and here's the answer:

I am able to find out how good is the engine at mid range and top rpm. From the result, 135LC standard engine already has 80% of horsepower at mid range rpm. This is very good for cruising and mileage, but it is bad for top speed.

The reason is that, I rev so hard from 5500rpm to 8500rpm and gain 20% BHP only =.="

The worst thing is, the rpm limiter kicks in at 9500rpm, but max power is just at 8500rpm. From 8500rpm -> 9500rpm, we have a drop in power. This is why many people can get 120kph with 3rd gear when going downhill, but on straight road, it takes yearrssss to reach 120kph. How about uphill? Oh gosh, I am damn happy if I got 100kph at full throttle.

So, I started to study on engine performance tuning, just to make the engine revs happier from mid to high rpm.

Oh no, I am the one who gets happiness only. The engine definitely feels sad because he has to do more work.