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Old 25th December 2005, 10:46   #1
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Smile Is it possible to increase the compression ratio

hello guys,
is it possible by any way to increase the compression ratio of an engine...
please reply

Pratheesh Prakash

Last edited by Domnic : 25th December 2005 at 11:28.
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Old 25th December 2005, 14:36   #2
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Yes, it is. The easiest way would be to shave the head off, thus decreasing the height. This would, in turn, increase compression.
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Old 25th December 2005, 19:32   #3
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I think its best not to do that, cuz the new cars here already have a high compression ratio but we don't have the high octane fuel to match.
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Old 25th December 2005, 20:30   #4
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The metros already have hi-octane petrol available.

All Indian cars are tuned for 87/85 octane, so if you are ready to spend 60bucks on Speed 97, then go ahead and bump up the compression.

In fact, I am thinking of doing this for our OHC.

Last edited by Mpower : 25th December 2005 at 20:31.
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Old 25th December 2005, 22:38   #5
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Quote:
Originally Posted by v1p3r
Yes, it is. The easiest way would be to shave the head off, thus decreasing the height. This would, in turn, increase compression.
i agree with v1p3r and thats what i have done in my esteem.. as far as fuel is concerned i fill up shell's super unleaded...
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Old 25th December 2005, 22:41   #6
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Hey Godfather, where did you get this done. Do you know how exactly how much the compression is right now. Any problems with knocking? Shell is still 87 octane right?
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Old 25th December 2005, 22:53   #7
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shell unleaded is 87 super unleaded is 90 above.. not sure..Raj did the car There is no knocking.. and the car is pretty quick.. will let you know the compression ratio..
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Old 26th December 2005, 02:38   #8
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Get the job done by a pro who's been there and done that. If the job is bad, u might have to replace the head.
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Old 26th December 2005, 02:42   #9
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If you screw up and take too much metal off, then you can use double gasket to get the compression back up.
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Old 26th December 2005, 03:07   #10
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Quote:
Originally Posted by Mpower
If you screw up and take too much metal off, then you can use double gasket to get the compression back up.
Agreed, but generally not recomended.
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Old 9th May 2006, 18:14   #11
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I always thought the compression ratio could be altered with a software remap. Isn't this possible?
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Old 9th May 2006, 19:09   #12
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There is a limit how far you can go. For example, diesel engines have more compression ratio compared to petrol engines because of its inherent design.
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Old 9th May 2006, 21:08   #13
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Quote:
Originally Posted by Boom Shiva
I always thought the compression ratio could be altered with a software remap. Isn't this possible?
No. Compression ratio is a hard quantity, beyond the control of software in the ECU.

Boom Shiva, consider one cylinder of a running engine.
The piston oscillates back and forth between
BDC (Bottom Dead Centre) when that cylinder's crank on the crankshaft is at bottom position,
to TDC (Top Dead Centre) when the crank is at its topmost position.
In doing so, the piston sweeps a volume equal to the bore area of the piston, multiplied by its swept stroke.

Compression ratio is the ratio of the swept volume of the cylinder plus combustion chamber volume, to the combustion chamber volume (at full compression).

For example, each cylinder of a 4-cylinder Maruti Esteem engine has a bore of 74 mm and a stroke of 75.5 mm.
The volume of the combustion chamber (at full compression (includes head gasket thickness)) is 40.6 cc.

So the compression ratio is


= (((pi()*7.4*7.4/4)*7.55)+40.6)/40.6

= 9.00 : 1

There are several ways to increase the compression ratio of an engine
  1. domed pistons,
  2. increased stroke,
  3. changing to a head with a smaller combustion chamber,
  4. Shaving the head or block of an engine,
Shaving beyond a limit, can get the valves bent if they violently collide with the pistons. That said, higher compression ratio generally puts more stress on pistons, connecting rods and bearings. We can't just assume that they will take the extra load, but must be very careful to build up the rest of the engine as needed.

Sometimes, just going with a thinner head gasket (if available) is a poor man's way to increase compression.

Last edited by Ram : 9th May 2006 at 21:17.
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Old 10th May 2006, 00:08   #14
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[SIZE=2]Thanks Ram, that was very informative.[/SIZE]
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Old 12th May 2006, 09:34   #15
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Default May soung stupid but this can be done.

Well the compression can be increased in a number of ways as discused.
Another way is to shave the head and then veld it to the cylender block (remove the packing).
Hade done it on my Suzuki Shogun a couple of years back. I did get the block re-bored after that never had to remove the head. Doing the same will be difficult on a car as a 4 stroke engine has valves and a car has 3-4 cylenders unless you beleave in replacine the cylender kit itself instead of reboaring or even changing the valves.
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