can someone please explain cam numbering? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

s13rookie · 01-20-2003, 12:01 AM

im just wondering about the numbers for cams, like 248/11.0, okay i know they are for duration/lift. but what does that actually mean and how do i use those numbers to pick the cams that are best suited for my needs? thanks to anyone for their help, i just dont want to buy the recommended cams, i want to know how and why, im trying to learn as much as i can, thanks, matt

*DSC* · 01-20-2003, 12:55 AM

you mean like the measurements or whatever? Like they are open for 248 somethings (mili-seconds?) and open a max of 11 (feet, inches, milimeters?) something else?

I read this somewhere a while back but unfortionately don't remember...doh

I'm curious too

*Jeff240sx* · 01-20-2003, 01:06 AM

The first number (if it's a whole number) like 232 or 248 (s14 and s13 cams, respectively) is the degrees that the cam will hold the valve open at least .050". The remainder of the 360* of the circle is the valve closing, closed, then opening.
There is also a number. It's not a whole number, and it sure as hell isn't 11. That is the ammount of valve lift in inches. It usually reads (JWT cams) as .390". That is the max lift of the cam.
JWT cams will read out .390/275.
Also.. when I say valve lift... I really mean valve drop.. but that just sounds funny.
-Jeff

s13rookie · 01-20-2003, 01:30 AM

i have been looking on jspec to try to find the figures i was using, but to no avail, any way the numbers were, i think 248/11.0mm if that makes more sense

uiuc240 · 01-20-2003, 01:37 AM

yeah, Jeff, he's talking lift in millimeters

so, your 248/11.0 cams are 248 degrees duration, 11.0mm max lift.

make sense? The cam is egg shaped, and the valves stay open for a rather large portion of the revolution...this is where overlap comes in to play. If you have a longer duration, this will inherently give more overlap, seeing as how the valves will be open longer (more time at the same time).

overlap = good for NA, not so important for turbo.

Eric

s13rookie · 01-20-2003, 01:47 AM

so if picking cams for a nasty turbo vehicle, would i want to lower or raise the amount of (valve, im assuming) overlap, or would i want none at all?

*Jeff240sx* · 01-20-2003, 10:44 AM

You'd want no (or very little) valve overlap in a turbo car. The reason for this is so you don't lose all your boost thru the exhaust valves.
-Jeff

s13rookie · 01-20-2003, 08:03 PM

ok great, thanks for the help, im starting to understand now. probably going to head to borders this weekend and try to find an engine book, to explain some other things im an idiot on

01-20-2003, 12:01 AM	#1
s13rookie Zilvia FREAK! Join Date: Mar 2002 Location: connecticut Age: 44 Posts: 1,129 Trader Rating: (0) Feedback Score: 0 reviews	can someone please explain cam numbering? im just wondering about the numbers for cams, like 248/11.0, okay i know they are for duration/lift. but what does that actually mean and how do i use those numbers to pick the cams that are best suited for my needs? thanks to anyone for their help, i just dont want to buy the recommended cams, i want to know how and why, im trying to learn as much as i can, thanks, matt __________________ Ive spent most of my money on cars and women...the rest i wasted

01-20-2003, 12:55 AM	#2
DSC New Title Join Date: Aug 2001 Location: VA Posts: 3,454 Trader Rating: (0) Feedback Score: 0 reviews	you mean like the measurements or whatever? Like they are open for 248 somethings (mili-seconds?) and open a max of 11 (feet, inches, milimeters?) something else? I read this somewhere a while back but unfortionately don't remember...doh I'm curious too __________________

01-20-2003, 01:06 AM	#3
Jeff240sx I hate you too... Join Date: Jul 2001 Location: Tampa, FL Age: 42 Posts: 5,828 Trader Rating: (0) Rides Gallery: Jeff240sx Feedback Score: 0 reviews	The first number (if it's a whole number) like 232 or 248 (s14 and s13 cams, respectively) is the degrees that the cam will hold the valve open at least .050". The remainder of the 360* of the circle is the valve closing, closed, then opening. There is also a number. It's not a whole number, and it sure as hell isn't 11. That is the ammount of valve lift in inches. It usually reads (JWT cams) as .390". That is the max lift of the cam. JWT cams will read out .390/275. Also.. when I say valve lift... I really mean valve drop.. but that just sounds funny. -Jeff __________________ Whatup?

01-20-2003, 01:30 AM	#4
s13rookie Zilvia FREAK! Join Date: Mar 2002 Location: connecticut Age: 44 Posts: 1,129 Trader Rating: (0) Feedback Score: 0 reviews	i have been looking on jspec to try to find the figures i was using, but to no avail, any way the numbers were, i think 248/11.0mm if that makes more sense __________________ Ive spent most of my money on cars and women...the rest i wasted

01-20-2003, 01:37 AM	#5
uiuc240 Nissanaholic! Join Date: Apr 2002 Location: Naperville, IL Age: 46 Posts: 2,093 Trader Rating: (0) Feedback Score: 0 reviews	yeah, Jeff, he's talking lift in millimeters so, your 248/11.0 cams are 248 degrees duration, 11.0mm max lift. make sense? The cam is egg shaped, and the valves stay open for a rather large portion of the revolution...this is where overlap comes in to play. If you have a longer duration, this will inherently give more overlap, seeing as how the valves will be open longer (more time at the same time). overlap = good for NA, not so important for turbo. Eric __________________ 2002 Mazda Protege5 1989 S13 w/SR20DET (sold)

01-20-2003, 01:47 AM	#6
s13rookie Zilvia FREAK! Join Date: Mar 2002 Location: connecticut Age: 44 Posts: 1,129 Trader Rating: (0) Feedback Score: 0 reviews	so if picking cams for a nasty turbo vehicle, would i want to lower or raise the amount of (valve, im assuming) overlap, or would i want none at all? __________________ Ive spent most of my money on cars and women...the rest i wasted

01-20-2003, 10:44 AM	#7
Jeff240sx I hate you too... Join Date: Jul 2001 Location: Tampa, FL Age: 42 Posts: 5,828 Trader Rating: (0) Rides Gallery: Jeff240sx Feedback Score: 0 reviews	You'd want no (or very little) valve overlap in a turbo car. The reason for this is so you don't lose all your boost thru the exhaust valves. -Jeff __________________ Whatup?

01-20-2003, 08:03 PM	#8
s13rookie Zilvia FREAK! Join Date: Mar 2002 Location: connecticut Age: 44 Posts: 1,129 Trader Rating: (0) Feedback Score: 0 reviews	ok great, thanks for the help, im starting to understand now. probably going to head to borders this weekend and try to find an engine book, to explain some other things im an idiot on __________________ Ive spent most of my money on cars and women...the rest i wasted