Choon

standard gasoline would have compression ration between 8-12.. 14:1 normally are for HCCI engines, they are the intermediate between gasoline and diesel engine. HCCI (homogeneous charge compression ignition) compresses gasoline-air mixture until it reaches its ignition point, almost similar to diesel. Diesel engine compression ratio ranges from 16:1 to 20+:1 :)

     

CarroTT

i dunno lar, but on my bike ,
if my calculation is right,
give or take the head gasket, coz i din measure the thickness the second time when i dissambled it n change to another gasket.
is about 12.5 - 12.8
but i m sure its minimum 12.5
so its always knocking if i m pushing up a hill when the engine is not on the powerband with std petrol

honestly, this NX arr, although i say it works, but arr consider the RM38 per bottle and 1 botol for 1 tank of fuel . . . . .not worth at all using on car lar.
but on kapcai no problem lar, 1 botol will last me long time coz i oni put 4ml per tank.
so 4ml to 4 liter tank is 1:1000 ratio, already enough to eliminate all the knocking



wat jinkl said is true, the problem with over tuned engines with too high compression oni most of the time happen when u suddenly have to drive up a hill. Ur engine dun ping on flat road, but once going up a hill, the extra load will make it ping.
So our normal safe comp ratio around 7 to 11:1 is because the engine will not ping even when the engine load becomes much higher, to be on safe side.
I discussing the problem in general oni lar, leaving out the boring details lar.

So u see some cars nowadays tat runs at 13-14:1 comp ratios, these cars are fitted with knock sensors.
When on normal flat road its no problem wan, no knocking
Oni when suddenly got higher engine load (i.e. going up a very steep hill), den the knock sensor will retard the ignition timing.
This will give advantage in getting better fuel mileage without having to conform to the usual 7 to 11:1 ratio.

I tink all cars shud have this kind of veli high compression ratio + knock sensor configuration lar, rather than putting the fancy vtec n vvt n mivec's system into cars.
higher comp give much more advantages in terms of power n fuel saving.

I was even told by my fren, there was once that SAAB made a car with variable compression ratio engine. It cud change its combustion volume. Interesting things engineers can do.

i dunno y direct injection system r not used on gasoline cars . . . .anyone can discuss y ?

     

papagoines

VW got it.. FSI am I correct?

     

Choon

got ad direct injection, they call it GDI, gasoline direct injection.. i think mitsu is the pioneer..

     

CarroTT

but dunno y its not widely used

probabli i dunno the mechanism behind direct injection well enough to understand y its not well suited for gasoline cars . . . .

     

papagoines

found one...

http://volvospeed.com/Reviews/octane_boosters.html

yup, better spend the money on maintenance and tuning...

yeah.... forgot to mention... here's the resource for more reading
http://en.wikipedia.org/wiki/Gasoline_direct_injection