Cam design basics ?

[caddycarlo]

I don't think these guys are here to give away cam specs so the average
member can run off and grind their own cam, or buy from someone else.

I'm sure if the same questions were asked in their shop with money in
hand, the end user would get much more information and a camshaft
they required.

When I read posts from the cam design members, I take away something
new each time, however I don't expect them to hold my hand and give
away secrets, or do all the work for me without a dime to their name.

Try this experiment:

Walk into a speed shop empty handed and start asking questions about
a product.

Observe response.

Do the same thing with a few $100.00 bills in hand.

Observe response.

Having said that, when I read through this post I can make better judgement
on LSA and some timing events for the application.

Unless we're willing to spend hours on a dyno/track to test these
tips, we have nobody to blame but ourselves for accepting the info.

Hopefully nobody here is expecting an internet cam recommendation
to be 100% optimized for their motor?

if I ran a store this way I would not make much money .............

I have been in retail most of my life and never did I ask someone to show me money before I would talk to them nor did I treat the guy off the street any worse then the full time racer .............

You talk to them and help the best you can and let the chips fall where they my ...........

More then once a guy that I thought had no hope of buying the parts I showed him would pull a roll of bills out and take it all ......... You just never know...... So you are nice to everyone and after a while they know where to come ................


In the case of a cam just becouse you know the specs at 50 and the lift does not mean you can go to someone else and get the same cam there is a lot more to it then that ........

[Whitewater Racer]

so as far as you are concerned someone should call and talk to to so you can help them out ..............


what info do they need to have on hand for your formula to work ?

Mr. Jones has posted this list a couple of times before, maybe it will help....

I need,

Bore:
Stroke:
Rod length:
Comp Ratio:
Max HP RPM:
Max engine RPM:
Launch RPM:
Rocker Ratio:
Carb CFM:
Intake Port flow CFM @ .400", .500", 600":
Exhaust Port flow CFM @ .400", .500", 600":
Lift where port flow turns around:
_________________
Mike Jones
Jones Cam Designs
Denver, NC
www.jonescams.com
(704)489-2449

[CamKing]

so as far as you are concerned someone should call and talk to to so you can help them out ..............


what info do they need to have on hand for your formula to work ?

They can call whomever they trust.
They can also do a little research.
I've got one customer that has mocked up every cam he's ever bought and measured them at about 10 different valve lift durations.
He becoming pretty good at picking cams without my help.

For the average application I need,
Bore:
Stroke:
Rod length:
Comp Ratio:
Rocker Ratio:
Intake and Exhaust flow CFM:
Tappet type and size:
Intake Manifold:
Carb size:
Exhaust type and size:
Desired peak HP RPM:
Max engine RPM:
Stall Speed(or corner RPM):
Application:

[digger]

I don't think these guys are here to give away cam specs so the average
member can run off and grind their own cam, or buy from someone else.

I'm sure if the same questions were asked in their shop with money in
hand, the end user would get much more information and a camshaft
they required.

I don't think people expect that they'll get a specific set of specs to use on a cam, more that they get knowledge that will enable a better selection of cam either from a selection of aftermarket cams or a custom one. Similarly if they currently have a cam with a specific set of characteristics and want different characteristics what do they need to alter.

Take my example: I have a cam 32-84-80-28 looking at those #’s it is a late closing IV with relatively small overlap and lift during overlap (small duration compared to the valve closing angle and small lift compared to stock) so how do i get more low end torque (which is seriously lacking) without reducing top end (and even possibly increase top end)?

The cam timing events are nothing like what I have seen in the off the shelf type cam for my particular engine, now that doesn’t make it bad but I have found that engines with these cams have a reputation for not making the power expected.

My thoughts are as follows since the reversion of exhaust gas when intake is valve open would seem to be small given the lift at overlap and degrees overlap are relatively small, so the reversion in my case must be from the intake closing very late. The intake closing is well past the dwell point at BDC and every degree now has a big effect on piston position (going from 50*ABDC to 55* would have less effect than going from 80-85).

So should I look to close the intake valve earlier (something like 76*) to gain some extra charge at low speed and suffer some top end loss because of lost inertia filling (it’s a street car that will see the track occasionally so low end and midrange are equally important)? But to counter the lost inertia filling maybe I could introduce some more overlap to help midrange and top end.

I have advanced the cam 6* and it made a good improvement to low end with a loss in top end but I think its possible to improve both.

I am still a bit unsure what to do given that while I may need to reduce/increase things I don’t realistically know by how much.

[MaxFlow]

Digger,

If you have an engine peaking at 6000, why would you run 84* Intake closing? I sure hope this closing is @.006 or advertised......If that's an .050 closing # I don't think she would run well at all?

Just asking.

[UDHarold]

Digger,

Your cam with the 32-84-80-28 specs is a 296/288 straight up on a 116 LSA. These specs are probably more for emissions-control than for power. The numbers are probably at the SAE's .004" cam lift, and are probably very short at .050" cam lift.
For low-RPM power, exhaust closing seems to be the most disruptive, and intake closing the most help.
Advancing your cam would shorten both those points, and should help the bottom end, and mid-range torque.
A slightly tighter LSA would also help. An 116 LSA is extremely wide.

UDHarold

BTW, I do not make cams for most foreign cars. Only the pushrod engines........

[David Redszus]

I'll park my truck right next to Harold on this one. He is absolutely right in his analysis and suggestion.

We can examine valve curtain area during overlap and their time areas and calculate inlet valve reversionary pressure at your late IVC, but we would end up exactly like Harold said.

And let's hope those are .004" events and not .050".

[digger]

Digger,

If you have an engine peaking at 6000, why would you run 84* Intake closing? I sure hope this closing is @.006 or advertised......If that's an .050 closing # I don't think she would run well at all?

Just asking.

thats at the seat (which i just discovered) and this was unknown to me until starting find out why the performance is what it is.

[digger]

Digger,

Your cam with the 32-84-80-28 specs is a 296/288 straight up on a 116 LSA. These specs are probably more for emissions-control than for power. The numbers are probably at the SAE's .004" cam lift, and are probably very short at .050" cam lift.
For low-RPM power, exhaust closing seems to be the most disruptive, and intake closing the most help.
Advancing your cam would shorten both those points, and should help the bottom end, and mid-range torque.
A slightly tighter LSA would also help. An 116 LSA is extremely wide.

UDHarold

BTW, I do not make cams for most foreign cars. Only the pushrod engines........

The engine begins to come on cam at 3250rpm before this its very flat, it is strongest between 5000-5500rpm and ones peak power at 6k is reached is hits the wall a bit.

Why do you say the exhaust closing is most disruptive given it doesn’t appear to be overly late closing also bearing in mind that there is only 1mm lift during overlap which is much less than a factory cam so wouldn’t the overlap be less significant since the head won’t flow much during any overlap? For this reason i don't think i am getting many benefits or downsides of the header exhaust pulses at any rpm.

Smack bang on about the emissions…….it is a 286/272 @ 0.011” those are probably 0.004” numbers like you said giving 296/288 at this lift value. I suppose converting to 0.011” my cam would be 26-78-74-20?

The same 32-84-80-28 cam on a 112 LSA might look something like 36-80-76-32 this has helped the intake closing but the later exhaust closing exhaust may counter this somewhat?

The same 32-84-80-28 cam advanced 4 degrees would be 36-80-84-24 straight up this has helped intake closing and exhaust closing as you said.

The 112 LSA option is likely to have more mid and high rpm power isn’t it because of the overlap?

Cheers

[Procision-Auto]

CaddyCarlo, don't misunderstand my position. We all know that you can't
just push someone out of your shop because they are inquiring. Everyone
can relate to those certain customer(s) that call, or visit to fish out info.

so how do i get more low end torque (which is seriously lacking) without reducing top end (and even possibly increase top end)?

Digger, aside from what has already been suggested for the low end #'s,
as well as some upper RPM power try messing with pre-load (assuming this is a hyd. setup?) to a tighter setting.

If the valve train/springs allow, you might also try increasing the rocker
ratio. That will wake up the overlap for upper RPM.

Have you played with the timing curve at all?

It's all fairly routine stuff, but it's a start...and fairly inexpensive.

Back to the original topic...

[caddycarlo]

Ok if you have some real flow numbers now would be a good time to post them ........................................


just to see more what sort of cam we are looking at if I make a guess at ramp speed it is 246/237 at .050 on a 116 lc ........ if you can test it you could give us better numbers then these to work with


that puts the intake open at 7 closed at 59 and ex open at 54.5 and closed at 2.5 so overlap is under 10 degrees at .050 .......

if I was to make a "guess" at this the problem is the intake is not open soon enough to a lift that will help flow ......... if advancing the cam helped low end you could increase the intake duration and go to a tighter lobe center by fixing the closeing point where it is and moving the extra duration to the opening point ........

Alright cam gods now is you chance to tear me up.........................


real flow and real duration would help a lot but look at it from a theory standpoint

[RW TECH]

I can clearly see the cam guy's point when it comes to giving away a lot of indepth information to design and select cams. Why would they?

There are a LOT of people out there that will take every piece of information given to them and go on to claim it as their own discovery. If a person is asking deep enough questions & the cam guy doesn't know them, there's a definite threat that the person who they're speaking to is either a current or a potential future competitor. Not a good business practice at all.

As far as "guessing", there has to be a level of this once things get to a certain point. In other words, getting into the ballpark can easily be done with an accumulation of past experience combined with good judgement, or it can be done with simulation software that most people can afford.

Beyond that, there are too many variations of the same thing out there to say you can nail it first time with calculations, simulations, or whatever.

An example would be a SBF with Edelbrock Victor Glidden heads. Compare out of the box fully CNC'ed from Edelbrock to a set developed & ported by a different source that may have similar flow numbers & measured average cross-sectional areas in the intake ports.

One configuration may yield better power with more valve open timing than the other, where the weaker of the two combinations will do nothing but loose low end torque with no high-speed gains because in a dynamic state the engine cannot breath at those speeds.

Also, there's no reason to trust results from some of the simulation programs that cost a lot of money (i.e.-Mandy Opticam) for an application like the restrictor plate Cup engine. The simulation results I've seen are a billion miles off the mark from what works in reality.

[SchmidtMotorWorks]

As far as "guessing", there has to be a level of this once things get to a certain point. In other words, getting into the ballpark can easily be done with an accumulation of past experience combined with good judgement, or it can be done with simulation software that most people can afford.

I have made an attempt at doing that. It is basically a combination of formulas that I have collected over years and compared with each other merged the ones that agree the most.

Over last Xmas holidays I needed to learn VB.net so I thought I would do two things at once and combine all the stuff I had collected into an application.

You can download it for free. I would be interested to know from peoples experience how close the results of these formula are.

[digger]

CaddyCarlo, don't misunderstand my position. We all know that you can't
just push someone out of your shop because they are inquiring. Everyone
can relate to those certain customer(s) that call, or visit to fish out info.

so how do i get more low end torque (which is seriously lacking) without reducing top end (and even possibly increase top end)?

Digger, aside from what has already been suggested for the low end #'s,
as well as some upper RPM power try messing with pre-load (assuming this is a hyd. setup?) to a tighter setting.

If the valve train/springs allow, you might also try increasing the rocker
ratio. That will wake up the overlap for upper RPM.

Have you played with the timing curve at all?

It's all fairly routine stuff, but it's a start...and fairly inexpensive.

Back to the original topic...

With 6 degrees advance (not retuned for fuel or spark) according to a chassis dyno

Up to 4200 no change
4200 to 5500 1-2% loss
5500 to 5800 no change
5800 to 6200 3% average gain

part throttle was a lot better but at WOT low end was unchanged whatsoever.

There are no alternate rocker ratios available

[digger]

Ok if you have some real flow numbers now would be a good time to post them ........................................

just to see more what sort of cam we are looking at if I make a guess at ramp speed it is 246/237 at .050 on a 116 lc ........ if you can test it you could give us better numbers then these to work with

that puts the intake open at 7 closed at 59 and ex open at 54.5 and closed at 2.5 so overlap is under 10 degrees at .050 .......

if I was to make a "guess" at this the problem is the intake is not open soon enough to a lift that will help flow ......... if advancing the cam helped low end you could increase the intake duration and go to a tighter lobe center by fixing the closeing point where it is and moving the extra duration to the opening point ........

Alright cam gods now is you chance to tear me up.........................

real flow and real duration would help a lot but look at it from a theory standpoint

i have found the following data cam data

0.011” 286 272
0.015” 274 260
0.020” 264 250
0.050” 238 226
0.100” 208 202
0.200” 170 166
0.300” 132 126
0.400” 84 80

Lift off seat during overlap 0.038”
lift 11.75mm (0.4626”) both intake and exhaust

Intake port flow 25” H20 super flow 600 bench (no exhaust data)

0.10” 81.00
0.15” 103.5
0.20” 121.5
0.25” 142.5
0.30” 159.0
0.35” 172.5
0.40” 183.0
0.45” 186.0
0.50” 189.0