Valin Posted October 3, 2009 Report Share Posted October 3, 2009 (edited) ho do u find/ figure out your compression ratio ? Compression ratio is a calculation based on bore/stroke, and volume of the cylinder head. The head volume must be measured on the motor, with the piston at TDC. For those of you who don't know, here's how you would do it: -Get yourself some 10cc syringes (without the needle). -Get yourself a small piece of hose (6" is fine) that you can attach to the nipple on the syringe. You will use this hose later on to suck the oil back out of the cylinder before you pull off the head to clean it thoroughly. -You are going to need some oil. Injector oil is fine......whatever you've got. -Ensure your cylinders are sitting level. You might have to jack up the front of somehow to ensure this. If it is on an angle, you won't get a true head volume. -Choose a cylinder to measure. -Remove the spark plug. -Bring the piston to TDC. I use a caliper and measure down inside the spark plug hole and bring it up until it is at the highest point. -Fill the head up with oil, keeping track of how many cc's you put in there (1 ml = 1cc) . You will stop filling when you get to the bottom of the spark plug hole. -Write this number down. You are going to end up with a volume in the 17-23cc range. -Put the hose on the end of the nipple on the syringe, and suck out as much oil as you can. -You are then going to lower that piston in the cylinder roughly 10mm. Do this again with something to measure through the spark plug hole. We lower the piston so that the remaining oil does not go into the water jacket, which it will do if you leave your piston at TDC and remove the head. -Remove the cylinder head, and clean up the remaining oil. -Repeat the procedure again to ensure you got the correct volume the first time. Then, it's just mathematics........... Here's the forula [(0.7854*(bore^2)*stroke) + Head Displacement] / Head Displacement Bore = cylinder bore diameter (in centimeters) Stroke = stroke (in centimeters) The number you receive will be your compression ratio in (your number):1. Edited October 3, 2009 by Valin Quote Link to comment Share on other sites More sharing options...
SAVAGE420 Posted October 3, 2009 Report Share Posted October 3, 2009 Nice informative write up Ryan. Quote Link to comment Share on other sites More sharing options...
Valin Posted October 3, 2009 Report Share Posted October 3, 2009 Thanks Chris. I tried to make it as understanding as possible. Quote Link to comment Share on other sites More sharing options...
blowit Posted October 3, 2009 Report Share Posted October 3, 2009 "[(0.7854*(bore^2)*stroke) + Head Displacement] / Head Displacement Bore = cylinder bore diameter (in centimeters) Stroke = stroke (in centimeters)" I am just a little confused. You indicate all linear measurements are in (cm), but the bore and stroke is typically measured in (mm), so does the equation account for this? Also, what are the units for volume? (cc)? Just trying to help clear that up. Typically an equation will be broke down with units attached in a situation like this. That might clear up any confusion. Also, you are calculating the UCCR or swept CR with this? B Quote Link to comment Share on other sites More sharing options...
Valin Posted October 3, 2009 Report Share Posted October 3, 2009 "[(0.7854*(bore^2)*stroke) + Head Displacement] / Head Displacement Bore = cylinder bore diameter (in centimeters) Stroke = stroke (in centimeters)" I am just a little confused. You indicate all linear measurements are in (cm), but the bore and stroke is typically measured in (mm), so does the equation account for this? Also, what are the units for volume? (cc)? Just trying to help clear that up. Typically an equation will be broke down with units attached in a situation like this. That might clear up any confusion. Also, you are calculating the UCCR or swept CR with this? B Yes, the bore and stroke are usually listed in mm, but you need to convert them to centimeters if you are dealing with cc's for heads. I'm sure nobody wants to deal with cubic millimeters when measuring head volume. The units for head volume are in CC's, which is mentioned above. 1ml is equal to 1cc in volume. The syringes will be listed in ml, so, put in 20ml, that is equal to 20cc. This is uncorrected compression ratio, which is also known as Swept CR. Corrected or Trapped CR is more accurate, yes, but most ppl and tuners go by Uncorrected, for whatever reason. Corrected is just as simple to calculate. Instead of using the entire stroke of the motor, you are calculating the volume trapped when the ports are closed. So, the stroke that you would enter is the distance from the top of the exhaust port to the deck of the cylinder. Quote Link to comment Share on other sites More sharing options...
flyRTby Posted October 6, 2009 Author Report Share Posted October 6, 2009 (edited) 60 HP Banshee - Toomey T6 Rev Edited October 6, 2009 by flyRTby Quote Link to comment Share on other sites More sharing options...
donkeypuncher Posted October 6, 2009 Report Share Posted October 6, 2009 60 HP Banshee - Toomey T6 Rev dayum, nice results man!!! so you gained 13 hp just by advancing the timing 6 degrees? wow! Quote Link to comment Share on other sites More sharing options...
flyRTby Posted October 6, 2009 Author Report Share Posted October 6, 2009 ya, something like that. shes way underpowered too.. if i was to throw some bigger carbs and switch up the pipes.. id easily be in the mid 60's Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted October 6, 2009 Report Share Posted October 6, 2009 thats a great result man!! Quote Link to comment Share on other sites More sharing options...
Coupelx Posted October 6, 2009 Report Share Posted October 6, 2009 the stoic number for race gas is 14.7, same as pump gas. so idk how it would richen it. Quote Link to comment Share on other sites More sharing options...
flyRTby Posted October 7, 2009 Author Report Share Posted October 7, 2009 @ what compression ratio would you say its safe to run race fuel? Quote Link to comment Share on other sites More sharing options...
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