Is it possible to increase the compression ratio

pratheesh · 25th December 2005, 10:46

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

Pratheesh Prakash

v1p3r · 25th December 2005, 14:36

Yes, it is. The easiest way would be to shave the head off, thus decreasing the height. This would, in turn, increase compression.

karthik247 · 25th December 2005, 19:32

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.

Mpower · 25th December 2005, 20:30

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.

Godfather · 25th December 2005, 22:38

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...

Mpower · 25th December 2005, 22:41

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?

Godfather · 25th December 2005, 22:53

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..

nitrous · 26th December 2005, 02:38

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.

Mpower · 26th December 2005, 02:42

If you screw up and take too much metal off, then you can use double gasket to get the compression back up.

Sideways · 26th December 2005, 03:07

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.

Boom Shiva · 9th May 2006, 18:14

I always thought the compression ratio could be altered with a software remap. Isn't this possible?

sbasak · 9th May 2006, 19:09

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.

Ram · 9th May 2006, 21:08

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

domed pistons,
increased stroke,
changing to a head with a smaller combustion chamber,
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.

Boom Shiva · 10th May 2006, 00:08

[SIZE=2]Thanks Ram, that was very informative.[/SIZE]

bhogalrajnish · 12th May 2006, 09:34

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.

25th December 2005, 10:46	#1
pratheesh BHPian Join Date: Dec 2005 Location: Omnipresent Posts: 49 Thanked: 0 Times	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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25th December 2005, 14:36	#2
v1p3r Senior - BHPian Join Date: Feb 2005 Location: BLR / DXB / LON Posts: 5,365 Thanked: 7,507 Times View My Garage Infractions: 0/1 (7)	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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25th December 2005, 19:32	#3
karthik247 Senior - BHPian Join Date: Feb 2005 Location: BLR, HYD Posts: 2,710 Thanked: 30 Times	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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25th December 2005, 20:30	#4
Mpower Senior - BHPian Join Date: Mar 2005 Location: Bangalore Posts: 10,397 Thanked: 1,735 Times View My Garage	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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25th December 2005, 22:41	#6
Mpower Senior - BHPian Join Date: Mar 2005 Location: Bangalore Posts: 10,397 Thanked: 1,735 Times View My Garage	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?
	() Thanks

25th December 2005, 22:53	#7
Godfather Senior - BHPian Join Date: Dec 2005 Location: Bangalore / Atlanta Posts: 1,387 Thanked: 71 Times View My Garage	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..
	() Thanks

26th December 2005, 02:38	#8
nitrous Senior - BHPian Join Date: May 2004 Location: UAE/Lon/Madras Posts: 6,964 Thanked: 333 Times View My Garage	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.
	() Thanks

26th December 2005, 02:42	#9
Mpower Senior - BHPian Join Date: Mar 2005 Location: Bangalore Posts: 10,397 Thanked: 1,735 Times View My Garage	If you screw up and take too much metal off, then you can use double gasket to get the compression back up.
	() Thanks

9th May 2006, 18:14	#11
Boom Shiva BANNED Join Date: Feb 2005 Location: Mumbai Posts: 1,044 Thanked: 19 Times	I always thought the compression ratio could be altered with a software remap. Isn't this possible?
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9th May 2006, 19:09	#12
sbasak BHPian Join Date: Nov 2005 Location: CCU-LTN Posts: 607 Thanked: 16 Times	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.
	() Thanks

10th May 2006, 00:08	#14
Boom Shiva BANNED Join Date: Feb 2005 Location: Mumbai Posts: 1,044 Thanked: 19 Times	[SIZE=2]Thanks Ram, that was very informative.[/SIZE]
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12th May 2006, 09:34	#15
bhogalrajnish BHPian Join Date: Jan 2006 Location: Gurgaon Posts: 215 Thanked: 67 Times	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.
	() Thanks