I didn't wanna get into the compression ratio discussion cos it is rather lengthy, but you've mentioned out a good point that prompted me to share a little bit on this topic.
2.0 Mitsu engine? By looking at our market in the past 10 years, not many cars came factory fitted with Mitsu's 2.0 petrol engine on the road. Either Proton Perdana, or Mitsubishi Airtrek (correct me if I'm wrong). And if it is indeed the Perdana with 4G63 l4, then the compression ratio is 9.0:1, which is rather low compared to our CamPro's 10:1. The lower the compression ratio is, the lower RON you can pump for the car to still run as usual. If it is the Perdana V6 with 6A12 engine, I'm not at all surprised that it ran without any problem as the compression ratio is the same as our CamPro, which is 10:1. Most CamPro users will tell you that their cars can run on RON 95 without any knocking issues (me being one of them), but a fair share of CamPro-ers also said that their engines are facing it. So probably you're one of the lot. But let me explain further to enlight you on this matter.
To understand what compression ratio is in the first place, imagine a piston in a cylinder while it is at the bottom of its' stroke. The volume of air in the space between the piston and the top end of the cylinder is 900 cubic centimetres, while the volume of air in the combustion chamber on top of the cylinder is 100 cubic centimetres. Total it up, you'll get 1000 cubic centimetres, or 1000 cc. When this piston moves up and reaches the end of the cylinder, the volume of air left in the combustion chamber is 100 cubic centimetres (piston moves up, reducing volume of air left in the cylinder until it reaches the top of the cylinder, and what's left is the air in the combustion chamber, which is 100 cc at all times). As such, the compression ratio is calculated as 1000 (total of 900cc in cylinder + 100cc in combustion chamber) to 100 (the volume in combustion chamber), or 1000:100. Primary school maths, fraction reduction and you'll get 10.0:1.
And then.. I'll have to get into the part how does an engine with high compression ratio works, but I rather get to the point right away as to why there is knocking in an engine when you use low RON petrol in a high compression engine.
In high compression engines, higher RON petrol is recommended for a more complete burning. When you're using a low RON petrol in a high compression engine, there might be chances that the fuel could not burn properly. Now picture a spark plug firing and the piston goes down and reach the bottom of the stroke. When it comes back up, there should not be any large volume of air left in the cylinder; there should only be air in the combustion chamber. But then, our cylinders may have imperfections on the surface, causing there to be small air pockets on top of the piston. Because of the heat and pressure from the incomplete fuel burning in the combustion chamber, these air pockets 'burn' and 'exploded', causing the knocking sound that you hear.
What causes knocking? Many reasons.
1. First of all as you mentioned, usage of low RON/octane fuel causes knocking in our high compression CamPro engines. Solution? Pump RON 97. But then our engines are tuned to run on lower RON as well to comply with manufacturing standards, and so that the export units may also run well at countries which does not offer petrol with RON higher than 95. So proceed to reason & solution #2 & #3 as this is less likely to be the issue here.
2. Second, your ECU may have been tuned to run too lean, which means there are more air than fuel in any single time during combustion. As I've mentioned just now, knocking happens when there are air in excess in the cylinder. If this is indeed your problem, a quick tune by the guys at CoSE to switch your air to fuel ratio (or AFR) to slightly richer (more fuel, slightly less air) will solve it.
3. Third, most, if not all of the cars that are manufactured today are tuned to run on low octanes (including our CamPro). And as such, these cars are often equipped with knock sensors to detect knocking in the cylinder. When knocking is detected, the ECU will retard the ignition timing to eliminate it. This is usually what is done to allow cars with high compression ratio to run on low RONs. It is less likely for the ECU or ignition timing to fail in this case (as you wouldn't be able to operate/start your car at all if it does), so the culprit here is a failed knock sensor.
If you're facing a very bad knocking issue with your car while running on 95 (which you shouldn't), then have the 2 items mentioned above checked (AFR and knock sensor). It is a must, as knocking may cause detrimental damage to the engine pistons, which in turn may require a engine rebuild at the end of the day. Unless, of course, you want to (and can afford to) run on 97 all the time.
I hope this clarifies thing a little bit for you.
Wow. Xandras expert giler ni.
Last time dyno my car with some light performance upgrade part & our continental ecu air/fuel ratio very good from low to high.
Added on October 31, 2011, 2:20 amHaiz. Nothing to do, and since haven't sleep yet.. Answer your question lah.
Basic mods? Depends on what you're expecting from your car. If you want better FC & slightly improved throttle response & horsepower, then may I suggest you to replace your spark plugs to Denso Iridiums and Simota/Works Performance air filter. Total cost less than RM 300.
If you don't mind about the slight increase in exhaust noise, then go for a set of exhaust system (might set you back close to RM 1k, but well worth the money). With a proper set of exhaust setup, expect around 8-12 WHP extra over your current engine output, and also better fuel efficiency of up to 15% (varies, some claims that the FC reduced more than that, some complain FC goes up, but usually because they're addicted to the extra oomph & noise after the installation).
Hope this helps!
If affordable, go for stainless steel mandrel bend exhaust system with tuned length header will be good. Cost around 1.3-1.6k include resonator & rear muffler. Pay few hundred more to mandrel bent are worth it.
Oct 20 2011, 03:10 AM
Quote
if I'm not mistaken, Saga 1.3 is using 16 bit Siemens ECU. Correct me if I'm wrong, but the Continental ECU is offered only starting from Persona Elegance and Exora. Maybe I was wrong, maybe Saga 1.3 indeed is using Continental ECU..
0.0204sec
0.87
7 queries
GZIP Disabled