How much displacement = compression?

[4cyl h2]

How much bigger piston would it take to equal a higher compression ratio? Like would. A 1325 10.5 to 1 equal a 1260 13.5??? What's been you experience?

 

[GS1150Pilot]

See post #14

http://www.zcar.com/forum/10-70-83-...er-compression-vs-greater-displacement-2.html

 

[rapidray]

The compression comes from the top of the piston. The bore size will only increase compression if all the pistons are flat top or have the same dome volume. A flat top 1166 is 10.25-10.5 to 1. A flat top 1327 is about 11.5 to 1. A flat top 1500 is about 12.5-12.7 to 1. You put a bigger bore piston into the same size combustion chamber, the larger bore will have more compression compared to other like pistons. That's why the street pistons get dished tops as the bore sizes go bigger to maintain around 10.25 to 1 compression. The bigger the bore, the more CCs the dish in the piston has to be to stay in same compression range. I hope this helps.
Ray.

 

[Guest]

In my experience I would say your close a 1325 at 10.5 to 1 would be about hp as the 1260 at 13.5 to 1. but the 1260 would not produce the torque that the 1325 would and the higher compression 1260 will produce more heat. Making the 1325 more dependable. If it was me I would go with the old saying " No replacement for displacement "

 

[4cyl h2]

The compression comes from the top of the piston. The bore size will only increase compression if all the pistons are flat top or have the same dome volume. A flat top 1166 is 10.25-10.5 to 1. A flat top 1327 is about 11.5 to 1. A flat top 1500 is about 12.5-12.7 to 1. You put a bigger bore piston into the same size combustion chamber, the larger bore will have more compression compared to other like pistons. That's why the street pistons get dished tops as the bore sizes go bigger to maintain around 10.25 to 1 compression. The bigger the bore, the more CCs the dish in the piston has to be to stay in same compression range. I hope this helps.
Ray.

sorry for the misleading wording on the question i did mean power output any more thoughts??

 

[rapidray]

An 1166 street engine with 10 to 1 compression will make 140 at the rear wheel with a street port head, .348 cams & 36 RSs. Make the pistons 13 to 1 & the HP is 160 or more. This becomes the difference between a 9.20 quarter mile & 8.90s. More compression is more power when used with the correct cams & head work. More compression will make more torque also but with more heat. Heat is not good for an air cooled street engine. More torque without excessive engine heat is from more displacement. A 10.5 to 1 compression, 1260 to 1400 cc, street engine is a BLAST & the bigger the engine the more torque it makes. Torque is what gets the bike moving, horsepower is how fast it will go. On the street I will take torque over HP every time. Does this help?
Ray.

 

[4cyl h2]

An 1166 street engine with 10 to 1 compression will make 140 at the rear wheel with a street port head, .348 cams & 36 RSs. Make the pistons 13 to 1 & the HP is 160 or more. This becomes the difference between a 9.20 quarter mile & 8.90s. More compression is more power when used with the correct cams & head work. More compression will make more torque also but with more heat. Heat is not good for an air cooled street engine. More torque without excessive engine heat is from more displacement. A 10.5 to 1 compression, 1260 to 1400 cc, street engine is a BLAST & the bigger the engine the more torque it makes. Torque is what gets the bike moving, horsepower is how fast it will go. On the street I will take torque over HP every time. Does this help?
Ray.

yes it is very helpfull info but what i would like to know is how much displacement would it take to make up the power difference of i want the power of a 1260 13.5to 1 in a 10.5 ratio how much displacement do i need to build and i realize engines need to be built to get the most of what they are but if there is a just in general answer

 

[rapidray]

This is too general a question with too may variables to answer correctly. I can make a 1260 over 225 hp with compression, the right cams & head work. A 1400, REALISTICALLY, will do 180-190 if it is to be a STREET engine. That is reliable hp but it costs money. You HAVE to build the crank & go straight cut gears.
Ray.