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Old 21st April 2006, 11:12   #1
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Default Compression ratio of Zen carb.

I tried searching the forum but could not find the information I require.
I need to know the compression ratio of carb zen. My zen has covered around 1,15000 km, shows compression ratio of 10.5-11 with each cylinder, any clues of how much more kms of engine life is expected ?
With rising fuel costs , I plan to convert this to cng however with an investment of 40000/- I am not pretty sure if I could break even with this car. Else, I am thinking to sell this off and buy a second hand esteem / baleno with decent mileage and have a cng kit installed. Pls advise.

Tarun.

P.S. Anyone has information of compression ratio of cars in India. May be a compilation and we post it in tech section with Red, yellow, green indicators as alarming, average and healthy engine indicators against each cars.
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Old 21st April 2006, 11:43   #2
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Quote:
Originally Posted by Tarun
My zen has covered around 1,15000 km, shows compression ratio of 10.5-11 with each cylinder,


Tarun,

Are you talking about after you ran a compression test on your zen??
The results should be in PSI, and about 8-12 times higher than what you stated.

Compression ratio as such is fixed on an engine. (in theory)

cya
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Old 21st April 2006, 13:47   #3
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Quote:
Originally Posted by Rehaan


Tarun,

Are you talking about after you ran a compression test on your zen??

Yeps, Iíll explain :
I took it to a dealer, he removed the spark plugs , put the gauge ( assuming the one to measure CR) in of the cylinders and then cranked the car. The max. pressure (as per the no.s indicated on gauge) it could reach was in between 10.5 to 11 (outer most reading in gauge).
I did not notice the unit of the measurement but thatís what I observed and he also concluded. This was done with two dealers and both of them notifying similar values with each cylinder. The other thing they mentioned that when the values hit below 8.5, engine is losing its breath. Any idea whatís the unit they could have mentioned ?

thx
Tarun.
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Old 21st April 2006, 13:51   #4
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the measuring unit, in all probabilty, could be bar.
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Old 22nd April 2006, 02:55   #5
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The compression ratio will be 10.5:1 or 11:1. That means that the fuel and air mixture in the compression stroke is compressed to 1/11th or 1/10.5 th of its original volume.
Normally in gasoline based cars, it never goes above 14:1. In diesels it can be anywhere between 17-18 to 27-28 as there is no spark plug and the fuel mixture has to be compressed a lot more to be ignited.
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Old 22nd April 2006, 03:51   #6
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Ask the dealer how much a new Zen shows. Based on what he said, it seems like you engine is still in good health. Of course you can always put in new rings if it drops too low.
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Old 22nd April 2006, 10:47   #7
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Quote:
Originally Posted by Tarun
I took it to a dealer, he removed the spark plugs , put the gauge ( assuming the one to measure CR) in of the cylinders and then cranked the car.
Hey Tarun,

As i said, this is a compression test. (Not compression ratio which is a FIXED ratio in your engine as well as every other stock car with the same engine)


Quote:
Originally Posted by veyron1
the measuring unit, in all probabilty, could be bar.
Thats what i thought too, but didnt include it in my reply earlier as i thought that 10.5-11 bar for a car that had run 1,15000 km was off the scale, but in actuality it is right in the good range.

Quote:
Originally Posted by Tarun
The other thing they mentioned that when the values hit below 8.5, engine is losing its breath. Any idea what’s the unit they could have mentioned ?
Okay, so that just confirms that it is in bar.
(fyi 1 bar = 14.5psi)

As Mpower suggested, ask the dealer what a new zen shows and then compare (or post here

cya
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Old 23rd April 2006, 17:31   #8
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Quote:
Originally Posted by Rehaan


Tarun,

Are you talking about after you ran a compression test on your zen??
The results should be in PSI, and about 8-12 times higher than what you stated.

Compression ratio as such is fixed on an engine. (in theory)

cya
R
He meant the compression pressure,by the values i fell they are in Kg/Sq cm or BARS.That is abt 155 psi,he is right in seeking the standerd comp pressure on a good ZEN.
cheers
engine hacker

Last edited by venugopal : 23rd April 2006 at 17:33.
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Old 24th April 2006, 00:21   #9
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Guys..What he is talkin about is the compression test..it is carried out as he said by removin the spark plug..nd insertin the compression testing gauge inside the cylinder..the compression pressure should be 12 or more than 12....for a good runnin engine...where as his engine is showin 11 ..which is a little less...its measured in bar..
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