How to pick a Cam FAQ
Posted: March 13th, 2008, 9:34 pm
We need some one that know Cam spec way better then i.........but i will pass on my thought and opinion on the subject.
When looking at a cam spec you need to know basically what each means so that you can take 10,000 cams and narrow then down to a hand full and then you have to decide which cam manufacture you want to use...........Now your down to a couple of cams.....
Some have cam spec "@.050".......and some use "Seat to seat". A cam that give you both spec, the @.050 will always be lower. Example of a 206* my be equal to 260* Seat to Seat.
NOTE: a different cam manufacturers same 206* may be rated at 240*.........confused??????? the speed in which the lifter raised off of the cam(or the ramp angle of the cam lobe) will decide how many degrees has past before the cam lobe has raise the lifter .050"
Every thing that i talk about will be Seat to Seat, as i think this will tell the most true about a cams design!
LIFT. .400" would be considered a stock to RV cam................... .450"= Power and with a well ported head .500'+ may work well(As a valve open, velocity or air speed increased up to to point of the ports efficiency............any more valve lift past this point will gain vary little more in volume........Just some food for thought)
DURATION. This is the time in with the valve is open(intake or exhaust)......240* good bottom end torque...........280*
Loss on bottom end (not a rock crowler cam!) but make up for it in the top end HP(Eng will rev higher and still make power)
OVER LAP. This is the time were the exhaust valve is closing, and the intake valve is starting to open. the smaller the number here, the more bottom end torque you will have......on the other side of the coin the higher the number gos the more bottom end Torque you will loose in order to gain top rpm power.........The higher the #### the more the eng will want to lop at a idle and the less over lap you have the smoother the eng will idle............ also the eng Vacuum at idle will go down.......If you choose a cam with enough over lap you vacuum brake boost will not be able to work properly(usually in the 60 degrees and up.....Torque cams, you would be wanting to look in the high 30* to 40*s)Advancing the cam 2* to 4* for a cam that is to big for the eng or intended us, Will get some of the vacuum back, but will lower the top rpm of power.
IVC (Intake Valve Close) Is always go info and this will give you a good idea as to what kind of compression you will need to get a good DCR (Dynamic Compression Ratio)
Make Sense????
Let me know were i lost yeah at and i will try and make it clearer.
Here is a beter, and more accurate discription that i found.
EDIT:....EDIT OK, it has taken a while but if you click on this image it will come in full and CLEAR.
Injoy....
Flash
When looking at a cam spec you need to know basically what each means so that you can take 10,000 cams and narrow then down to a hand full and then you have to decide which cam manufacture you want to use...........Now your down to a couple of cams.....
Some have cam spec "@.050".......and some use "Seat to seat". A cam that give you both spec, the @.050 will always be lower. Example of a 206* my be equal to 260* Seat to Seat.
NOTE: a different cam manufacturers same 206* may be rated at 240*.........confused??????? the speed in which the lifter raised off of the cam(or the ramp angle of the cam lobe) will decide how many degrees has past before the cam lobe has raise the lifter .050"
Every thing that i talk about will be Seat to Seat, as i think this will tell the most true about a cams design!
LIFT. .400" would be considered a stock to RV cam................... .450"= Power and with a well ported head .500'+ may work well(As a valve open, velocity or air speed increased up to to point of the ports efficiency............any more valve lift past this point will gain vary little more in volume........Just some food for thought)
DURATION. This is the time in with the valve is open(intake or exhaust)......240* good bottom end torque...........280*
Loss on bottom end (not a rock crowler cam!) but make up for it in the top end HP(Eng will rev higher and still make power)
OVER LAP. This is the time were the exhaust valve is closing, and the intake valve is starting to open. the smaller the number here, the more bottom end torque you will have......on the other side of the coin the higher the number gos the more bottom end Torque you will loose in order to gain top rpm power.........The higher the #### the more the eng will want to lop at a idle and the less over lap you have the smoother the eng will idle............ also the eng Vacuum at idle will go down.......If you choose a cam with enough over lap you vacuum brake boost will not be able to work properly(usually in the 60 degrees and up.....Torque cams, you would be wanting to look in the high 30* to 40*s)Advancing the cam 2* to 4* for a cam that is to big for the eng or intended us, Will get some of the vacuum back, but will lower the top rpm of power.
IVC (Intake Valve Close) Is always go info and this will give you a good idea as to what kind of compression you will need to get a good DCR (Dynamic Compression Ratio)
Make Sense????
Let me know were i lost yeah at and i will try and make it clearer.
Here is a beter, and more accurate discription that i found.
EDIT:....EDIT OK, it has taken a while but if you click on this image it will come in full and CLEAR.
Injoy....
Flash