question about camshafts

Hello, just hoping i could get some help with some information
regarding camshafts. Ive read alot of different explainantions on the
net so im not too sure about things. What im wondering about firstly
is the advertised duration and duration measured at .050" lift. Alot
of sites say to totally ignore advertised duration and some say its
still important. The cam i currently have has 214deg at .050 and
290deg advertised (measured at .006" lift) Now if i was to change the
cam to one with the same specs but a much shorter advertised duration
like 260deg would it make any difference at all ? The reason im
curious is i want to upgrade my cam to get a bit more top range and
have been recommended one at 222deg @ 0.50 but the advertised duration
is 274. Thing is when using programs like desktop dyno if you use the
advertised duration like they reccomend, the newer cam actually leaves
me with less top end power than my current cam. But of course if you
use 0.050 figures then the newer 222deg cam is better. So i dont
really know what to do and how much faith can be put in simulation
software. SO does the advertise duration have much of an effect on
things?
Actual specs of the two cams are 214deg 290advertised .470lift and 112
seperation and the other is 222deg 274adv .493lift 110deg seperation

And another question is about lobe seperation. If you take the same
cam but one has 112deg seperation and one 110deg would you notice the
difference between the two. And also which is better for top end
power, a narrow or wide seperation ?

"james" > wrote in message
...
> Hello, just hoping i could get some help with some information
> regarding camshafts. Ive read alot of different explainantions on the
> net so im not too sure about things. What im wondering about firstly
> is the advertised duration and duration measured at .050" lift. Alot
> of sites say to totally ignore advertised duration and some say its
> still important. The cam i currently have has 214deg at .050 and
> 290deg advertised (measured at .006" lift) Now if i was to change the
> cam to one with the same specs but a much shorter advertised duration
> like 260deg would it make any difference at all ? The reason im
> curious is i want to upgrade my cam to get a bit more top range and
> have been recommended one at 222deg @ 0.50 but the advertised duration
> is 274. Thing is when using programs like desktop dyno if you use the
> advertised duration like they reccomend, the newer cam actually leaves
> me with less top end power than my current cam. But of course if you
> use 0.050 figures then the newer 222deg cam is better. So i dont
> really know what to do and how much faith can be put in simulation
> software. SO does the advertise duration have much of an effect on
> things?
> Actual specs of the two cams are 214deg 290advertised .470lift and 112
> seperation and the other is 222deg 274adv .493lift 110deg seperation
>
> And another question is about lobe seperation. If you take the same
> cam but one has 112deg seperation and one 110deg would you notice the
> difference between the two. And also which is better for top end
> power, a narrow or wide seperation ?

The reason that most cam manufacturers use a duration measurement at 0.050"
lift is that it's not accurate to measure the duration at a lower lift. It
truly depends on the lobe design as to what measurement should be used.

As far as lobe separation it's relevant to the cams duration as well. If two
given cams have the same specifications with the exception of the lobe
separation, the cam with the higher lobe separation will have less valve
opening overlap. This will give you more bottom end. But keep in mind the
lobe separation must get wider as the duration increases to keep the overlap
at a reasonable figure. As well a cam with a lot of duration and more over
lap will reduce the engines static compression, but that's when the intake
lobe is generally degreed to open sooner so the cylinder gets a good fill of
fuel / air mixture. But that cause the exhaust to open early so the lobe
separation may be to narrow for the given duration to perform well.

Camshaft science isn't a simple thing, every change in the specification
effects another specification. Also on your demo software, if the cam you
selected shows less power you may then need more compression to take
advantage of it. Air flow through the heads can effect this drastically as
well.

As a rule of thumb most people over cam a street machine. After all do you
drive around all day at 4500 to 6500 RPM?

Brian

On Sat, 8 Jan 2005, el Diablo wrote:


<a bunch of good info on cams>

> As a rule of thumb most people over cam a street machine.

Yep. And over-carb it, too. Then wonder why they have trouble starting it,
an idle that shakes them off the seat, get 7 mpg, have no power at all
below 4000 rpm and flunk emissions so badly the inspector actually laughs
at them.

I'm trying my best to help a guy in Arizona who put a 264/264/46 cam and a
Holley 5200 carb off a mid-'70s Pinto in his Slant-6 Dart. I'm not sure
there's much that can be done short of scraping off one or the other or
both and starting all over again.

james > wrote in
:

> Hello, just hoping i could get some help with some information
> regarding camshafts. Ive read alot of different explainantions on the
> net so im not too sure about things. What im wondering about firstly
> is the advertised duration and duration measured at .050" lift. Alot
> of sites say to totally ignore advertised duration and some say its
> still important. The cam i currently have has 214deg at .050 and
> 290deg advertised (measured at .006" lift) Now if i was to change the
> cam to one with the same specs but a much shorter advertised duration
> like 260deg would it make any difference at all ? The reason im
> curious is i want to upgrade my cam to get a bit more top range and
> have been recommended one at 222deg @ 0.50 but the advertised duration
> is 274. Thing is when using programs like desktop dyno if you use the
> advertised duration like they reccomend, the newer cam actually leaves
> me with less top end power than my current cam. But of course if you
> use 0.050 figures then the newer 222deg cam is better. So i dont
> really know what to do and how much faith can be put in simulation
> software. SO does the advertise duration have much of an effect on
> things?
> Actual specs of the two cams are 214deg 290advertised .470lift and 112
> seperation and the other is 222deg 274adv .493lift 110deg seperation
>
> And another question is about lobe seperation. If you take the same
> cam but one has 112deg seperation and one 110deg would you notice the
> difference between the two. And also which is better for top end
> power, a narrow or wide seperation ?
>

The duration @0.006 and the duration @0.05 give you the 'ramp rate' of
the lobe. (slope)
A steep slope pops the valves open sooner, and slams them closed faster,
but leaves your valve open at an effective distance longer. But it costs
you some in frictional hp and can have a dramatic effect on spring life.
It can also help promote valve float, if the springs can't keep the
lifter on the cam because the slope is too steep on closing. This is
where roller cams have an advantage, you can generally have a little
steeper slope and get away without any of the other bad things.

The angle of separation determines how much overlap you have, (time when
both the intake and exhaust valves are open. For high-rpm operation,
overlap is desired, as the exiting gasses create a vaccum that helps to
pull in the fresh air/fuel. IIRC, the narrower the separation angle, the
more overlap, and thus helps higher rpm power.

Check your valve guide boss to retainer clearances when installing a
higher lift cam. Tis not good to beat the top of the valve guide with the
retainers...

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

"Daniel J. Stern" > wrote in
n.umich.edu:

>
>

What the heck???????? did he say why he used the 5200 carb. it is smaller
than the 1 barrel that came off it. KB (I used it on several hot pinto
2300s years ago, but the 390 cfm holley worked much better.)

--
ThunderSnake #9 Warn once, shoot twice
460 in the pkup, 460 on the stand for another pkup
and one in the shed for a fun project to yet be decided on

i'm not an authority on cams.
the reason for stating duration at .050" is that .first, the quieting ramps
on the cam have been factored out by this.
second, theres little flow before the .050" opening so the EFFECTIVE
duration is more accurately stated.

a close lobe separation generally gives more valve overlap.
this may give a poorer idle, raise the torque peak, and sometimes the MAX
HP.
since there's no free lunch, the increased specs may make the engine more
"peaky" and give shabby low speed performance.

may i suggest you subscribe to carcraft magazine or other hotrod builder's
type. the technical articles dwell very much on exactly your question
good luck, sammmmm




"james" > wrote in message
...
> Hello, just hoping i could get some help with some information
> regarding camshafts. Ive read alot of different explainantions on the
> net so im not too sure about things. What im wondering about firstly
> is the advertised duration and duration measured at .050" lift. Alot
> of sites say to totally ignore advertised duration and some say its
> still important. The cam i currently have has 214deg at .050 and
> 290deg advertised (measured at .006" lift) Now if i was to change the
> cam to one with the same specs but a much shorter advertised duration
> like 260deg would it make any difference at all ? The reason im
> curious is i want to upgrade my cam to get a bit more top range and
> have been recommended one at 222deg @ 0.50 but the advertised duration
> is 274. Thing is when using programs like desktop dyno if you use the
> advertised duration like they reccomend, the newer cam actually leaves
> me with less top end power than my current cam. But of course if you
> use 0.050 figures then the newer 222deg cam is better. So i dont
> really know what to do and how much faith can be put in simulation
> software. SO does the advertise duration have much of an effect on
> things?
> Actual specs of the two cams are 214deg 290advertised .470lift and 112
> seperation and the other is 222deg 274adv .493lift 110deg seperation
>
> And another question is about lobe seperation. If you take the same
> cam but one has 112deg seperation and one 110deg would you notice the
> difference between the two. And also which is better for top end
> power, a narrow or wide seperation ?

On Sun, 9 Jan 2005, Kevin Bottorff wrote:

>> I'm trying my best to help a guy in Arizona who put a 264/264/46 cam
>> and a Holley 5200 carb off a mid-'70s Pinto in his Slant-6 Dart. I'm
>> not sure there's much that can be done short of scraping off one or the
>> other or both and starting all over again.

> What the heck???????? did he say why he used the 5200 carb. it is
> smaller than the 1 barrel that came off it. KB (I used it on several
> hot pinto 2300s years ago, but the 390 cfm holley worked much better.)

Yeah, I know it. His answer to that one amounted to more or less "It
seemed like a good idea at the time". Now that he's trying to pass AZ smog
with this gross mismatch in equipment, you'd think it wouldn't seem like
such a good idea any more, but he's pretty insistent on keeping the setup.
Problem is, he's getting really ugly smog test results, 1429 ppm HC on a
limit of 400 ppm, 9.1% CO on a limit of 5.0%. He's had all kinds of jokers
making "helpful" suggestions for how to pass the test: Add ten bottles of
alcohol to the gas, temporarily install a catalytic converter, stupid
stuff like that.

Of course, the problem is he's got a generic too-big camshaft in his
engine (he says "It's staying in there!"), and he picked the wrong carb.

As for the Holley 390, I don't look very fondly on it (I prefer Carters
and Stromburgs, myself) but I agree it's considerably less worse than the
5200!

"Daniel J. Stern" > wrote in
. umich.edu:

> On Sun, 9 Jan 2005, Kevin Bottorff wrote:
>
>>> I'm trying my best to help a guy in Arizona who put a 264/264/46 cam
>>> and a Holley 5200 carb off a mid-'70s Pinto in his Slant-6 Dart. I'm
>>> not sure there's much that can be done short of scraping off one or
>>> the other or both and starting all over again.
>
>> What the heck???????? did he say why he used the 5200 carb. it is
>> smaller than the 1 barrel that came off it. KB (I used it on several
>> hot pinto 2300s years ago, but the 390 cfm holley worked much
>> better.)
>
> Yeah, I know it. His answer to that one amounted to more or less "It
> seemed like a good idea at the time". Now that he's trying to pass AZ
> smog with this gross mismatch in equipment, you'd think it wouldn't
> seem like such a good idea any more, but he's pretty insistent on
> keeping the setup. Problem is, he's getting really ugly smog test
> results, 1429 ppm HC on a limit of 400 ppm, 9.1% CO on a limit of
> 5.0%. He's had all kinds of jokers making "helpful" suggestions for
> how to pass the test: Add ten bottles of alcohol to the gas,
> temporarily install a catalytic converter, stupid stuff like that.
>
> Of course, the problem is he's got a generic too-big camshaft in his
> engine (he says "It's staying in there!"), and he picked the wrong
> carb.
>
> As for the Holley 390, I don't look very fondly on it (I prefer
> Carters and Stromburgs, myself) but I agree it's considerably less
> worse than the 5200!
>

I guess I like the holley just because I can get em to do what ever I
want. It would probly be the same with any other carb I had years of exp.
playing with. (I have years of playing with the 5200 also and really like
them but not on that kind of miss match) KB

--
ThunderSnake #9 Warn once, shoot twice
460 in the pkup, 460 on the stand for another pkup
and one in the shed for a fun project to yet be decided on