- Sat Apr 14, 2018 11:52 pm
#75776
Hi Guys---- yes, spot-on there Barry......The two things not yet mentioned are a}--- These are long stroke engines and develop their power via an increase of Torque rather than higher engine speed, and b}--- The quality of commercially available fuel at the pumps is changing ---- and not necessarily for the better...
I think that Bullet Whisperer's idea of altering the inlet cam by 1 tooth is the best, no-cost idea yet !!!......has anybody got one of Performance Classics oversized Bullets ??.....Any idea what CR he runs them at ??..........Just for interest I had a look for long stroke engines and in particular Harley Davidson Tech. Specs and found this}----------http://hdhistory.com/most-popular-harle ... son-chart/ ---------- Notice how Comp. Ratios have gone up from 6 to 8.5 --or-- 9.0 and then settled there ??......
If you want to increase the Clearance Volume (CV) by another method then you can always have some metal removed from inside the head.............The length of the inlet tract can help torque development..For example}-----A long tract helps torque lower down the rev range whilst a short tract helps with top-end torque.............Have another look at that BSA Gold Star photo and notice that the carb is bolted direct onto the Cyl.head to help with the top-end torque as the engine reached it's max rpm........On my 250 Grass Tracker I made up several different tract lengths to try out...............Incidentally when we say a base gasket of 0.5mm then that's a metallic one, not a paper or card....We don't want it collapsing, do we ??
Using basic maths we can transpose the CR formula around such that the Clearance Volume (CV) can be calculated if we know what CR we'd like to be using..( Remember that point about poor quality fuels ??)...................So we now have this}---CV = SW + CR divided by CR.....If we want an 8:1 comp.ratio on an engine of 500cc swept vol. we get}------ CV = 500 + 8 divided by 8 which gives}--- 63.5cc.......and for an 8.5CR we get 59.8cc............and for 9:1CR we get 56.5cc..........and for the Bullet production CR of 6 we get 84.3cc..............Just for information 1mm = 0.0394" ( 40 thou if rounded up ) so half a mm = 20 thou. or just over 1/64"...
I think that Bullet Whisperer's idea of altering the inlet cam by 1 tooth is the best, no-cost idea yet !!!......has anybody got one of Performance Classics oversized Bullets ??.....Any idea what CR he runs them at ??..........Just for interest I had a look for long stroke engines and in particular Harley Davidson Tech. Specs and found this}----------http://hdhistory.com/most-popular-harle ... son-chart/ ---------- Notice how Comp. Ratios have gone up from 6 to 8.5 --or-- 9.0 and then settled there ??......
If you want to increase the Clearance Volume (CV) by another method then you can always have some metal removed from inside the head.............The length of the inlet tract can help torque development..For example}-----A long tract helps torque lower down the rev range whilst a short tract helps with top-end torque.............Have another look at that BSA Gold Star photo and notice that the carb is bolted direct onto the Cyl.head to help with the top-end torque as the engine reached it's max rpm........On my 250 Grass Tracker I made up several different tract lengths to try out...............Incidentally when we say a base gasket of 0.5mm then that's a metallic one, not a paper or card....We don't want it collapsing, do we ??
Using basic maths we can transpose the CR formula around such that the Clearance Volume (CV) can be calculated if we know what CR we'd like to be using..( Remember that point about poor quality fuels ??)...................So we now have this}---CV = SW + CR divided by CR.....If we want an 8:1 comp.ratio on an engine of 500cc swept vol. we get}------ CV = 500 + 8 divided by 8 which gives}--- 63.5cc.......and for an 8.5CR we get 59.8cc............and for 9:1CR we get 56.5cc..........and for the Bullet production CR of 6 we get 84.3cc..............Just for information 1mm = 0.0394" ( 40 thou if rounded up ) so half a mm = 20 thou. or just over 1/64"...