6 replies to this topic

[frostie]

hi,
how do u determine what CR you should have? is it just a case of asking a reputed engine tuner as to what they advise with your chosen cam? or is there a certain way to calculate??

thanx, Frostie

[TimS]

if your building a serious engine then you need consider cam and compression ratio. Details of this are in some tuning books, but im afraid i dont know the details of the top of my head(and my books in sheffield:( you can have a cam ground espeically to suit the CR but its more likely that a CR will be suited to the cam profile. Most engine builders produce kits which has a good cam range available for a cirtain kit. It is probably worth ringing a few and getting their opinions

[Guess-Works.com]

Also with Higher CR comes the requirement to use Higher octane fuel...

[TimS]

and to retard the timing slightly!

[frostie]

thanx guys! it wasn't a question before i do it.....it was a general "dont know what it means" lol

i've bin on that howstuffworks.co.uk that a guy from minifinity reccomended, now i actually understand an engine!!lol

[TimS]

ah, if your just understanding engines figuring the cam profile and compression ratios is alot more advanced! iv been trying to understand engien for around 2 years now(since i was 16) and im still stuck on alot of things espeically with injection. There are some good books out there to read. I got David Vizard A series tuning book, and that is like a bible to most people. It explains things very clearly. Im also reading 4 stroke Performance tuning but iv left it at uni in sheffield. both of these have taught me alot

[AlexF2003]

if you need a cr calulator...

http://www.afracing.com/cr.xls

Alex