what size carby for my motor?

[seb402]

ok awesome , thanks leigh

LMAO... camshafts do come in boxes...because thats what i was talking about

 

[ari666]

lol, ok. you find it yet?

 

[Immortality]

LOL.

there is a simple formula to work it out.

CFM = (CID x RPM x CF) / (2 x 1728)

CFM = cubic feet per minute
CID = displacmente
RPM = well if you don't know this one you may as well go to a different site
CF = correction factor. this is based on the VE% (volumetric efficiency) of the engine. i have a nice chart here for that in relation to cam duration but for stock heads and cams in the 240-250 duration @ .050 use .9

these numbers are all based on the standard 1.5" pressure drop across the carby. this is the part where it gets interesting because it doesn't take a lot of effort to get a decent intake to have less then 1.5" drop which changes the CFM rating of the carb.

there is however a formula for that too.

CFM / square root of( old pressure drop/ new pressure drop)

or 800cfm / sqaure root of 1.5/.5

= 800/1.732

= 462 CFM so a 800cfm carb (measured at 1.5" drop) only flows 462CFM @ .5" drop

i'd also go for a vac secondary carb for street use, this way you can also get a slightly larger carb without the problems associated with large DP style carbs i.e. it won't suck gas as much

 

[ari666]

LOL.

there is a simple formula to work it out.

CFM = (CID x RPM x CF) / (2 x 1728)

CFM = cubic feet per minute
CID = displacmente
RPM = well if you don't know this one you may as well go to a different site
CF = correction factor. this is based on the VE% (volumetric efficiency) of the engine. i have a nice chart here for that in relation to cam duration but for stock heads and cams in the 240-250 duration @ .050 use .9

these numbers are all based on the standard 1.5" pressure drop across the carby. this is the part where it gets interesting because it doesn't take a lot of effort to get a decent intake to have less then 1.5" drop which changes the CFM rating of the carb.

there is however a formula for that too.

CFM / square root of( old pressure drop/ new pressure drop)

or 800cfm / sqaure root of 1.5/.5

= 800/1.732

= 462 CFM so a 800cfm carb (measured at 1.5" drop) only flows 462CFM @ .5" drop

i'd also go for a vac secondary carb for street use, this way you can also get a slightly larger carb without the problems associated with large DP style carbs i.e. it won't suck gas as much

this post has now been saved to my desktop

 

[Immortality]

this post has now been saved to my desktop

LOL. i love the carby look but prefer efi. thats why i run a TBI setup on the VH. which means my above post means stuff all to me