On a board to which I suscribe a guy said his ideal cam was 220/230, .600/.600 with a 112 LSA with 1.5 rockers. How would one expect to use this cam? What kind of advertised duration would be good to keep this cam barely in the smog legal range? Could this cam work as a flat tappet grind?

Does it matter if a cam has the exact same specs if it is a roller or flat, hyrdraulic or solid?

Instead of more duration on the exhaust valve could you use more lift? Can you use more lift in general since the exhaust valve is typically smaller?

What controls picking the right size valves? Is there a minimum/maximum ratio difference between intake and exhaust valves?

Is it a safe assumption that larger valves require a larger chamber? Is there a way to quantify the intake runner to chamber ratio? Would it matter?

What dimensions are required to determine the maximum lift you can get out of a cylinder head? How would a head/cam work if the cam was set to give you maximum lift up to about 3500 rpm and tapered down to about 75% of that lift by 6000 rpm? Would you need a big or small intake runner? The lift couldn't be bigger at the end than the beginning could it?

Does a lower head angle (23, 20, 18, 15) work better towards a larger or smaller bore? Does the lower head angle allow for higher or lower lift?

If the intake velocity is as important as the flow, how does one compute it? How do you determine how much flow and at what velocity you need it to accomplish x horsepower or torque?

At 100% volumetric effiency are you getting all of the flow you can out of a head, getting as much flow as the velocity will allow, both or neither?

How do you match the intake manifold to the head to get the right flow/velocity?

wow, some very in-depth questions, and sorry to say but you wont find anyone here that will answer them, try aiming these questions to oldbogie on the chevy high performance board

Well, as far as the cam is concerned, I would need to know the displacement of the engine in question, but 214 degrees duration @.050" lift is about the max on smog engines to keep legal. As far as the other things, head angle depends on your purpose, no it doesn't change the valve size needs. What you are going to need this engine to do will determine all of these answers. A street driven daily driver would be best with smaller ports with medium size valves. a weekend warrior that you race and dont care for drivability, could use larger ports and valves. The intake is the same way. Street, dual plane-strip single plane. Since I am an automotive tech( of 21 years) and an engine builder( 15 years) I can answer these questions for you if you would like. E mail me with any questions you may have at min301@comcast.net  

From what I understand there are two ways to choose engine parts. You can start with the displacement and work your way inward, or start with the cam and work your way outward. I'm trying to gain some understanding from approach number 2.

In another post (I think on this board) I have a 400 block that I am trying to fill out to pass the sniffer in an '85 Camaro that will be mated to a stickshift car (No stall, just clutch as you  would understand). My goal with it is to have an all purpose fun car that I can get plates for. Since it is not a daily driver I can surrender some torque relative to the 305 it cam with for the sounds of a high revving mid displacement engine. I'd like to shift it at 6000 or higher, but I'm told it would be a dog at low revs. Since I have never driven a sports car so to speak I don't have a frame of reference with which to quantify dogs at low revs.

The purpose of this post was for me to understand more of the interelations of the cam, heads,valves,and all of that. My first question was if there was an application in which this cam would work what would it be. From there is was free association of questions in relation to the topic.

I understand some of the basics - bigger holes mean higher rpms means 30 mph sucks gas - but in the in between how does it all relate. Can you make the system progressive with cam selection, timing, and advance? 214 degrees duration at what lift, at what LSA, and for what displacement engine? How does the advertised duration relate? Does it tell you more about the ramp rate of the cam? How does a small valve with high live compare to a big valve with low lift? Without having to refer to application how do the pieces relate? With as many dual plane inakes out there as there are how does one determine which one is the best choice for the application?

What sorts or power and torque trade offs can one expect in the progressions from smaller to bigger? How does the trade offs relate to gearing, especially when the gearing can be configured to match the engine?

I am trying to understand how to make the choices more than ask for part recommendations. Essentially from radiator to exhaust tip is going to change. I want to understand how to make the cohesive changes that all the magazines say you must do, but don't discuss.

Speaking of smog how does the cam size change the smog numbers? What happens when you keep all of the  smog accesory devices? Can they be made more efficient? Wouldn't higher volumetric efficiency make for lower emissions? How much of the smog issue is the basic mass of air/fuel burned as opposed to the specifice mixture or timing of the burn? Since the sniffer test are done at part throttle and most part selection is done for full throttle applications how does one bridge the gap.

The premise of just picking the small performance stuff and you'll be okay is fine if you only want to name names. The big cams cost just as muh as the small ones. The big heads are only so much more than the small ones. And all over the place somebody somewhere is having fun with a stupidly fast car, and still has legit plates on it. It is in the details, and that is what I'm after.

Jason

What your asking would take too long to discuss. I said 214 degrees @.050". If you use a 400 small block, you will have considerably more torque than the 305. Large ports with small valves creates issues such as reversion, and fuel suspension. All things must be matched or performance will suffer. If you want to talk about specific things and not a blanket of why's I would be happy to answer them.  

I would like to make a matched combination that accomplishes three things:

Passes the sniffer numbers below:
          HC   CO    NOx
Standards: 2.00 30.00 3.00
Readings:  1.72 19.50 0.77
Results:   PASS PASS  N/A

Has a power range that makes shifting at 6500 ideal.

Is fast enough to make $5-6000 worth the price of admission.

I apologize that my questons appear to be vague. It seems difficult to get the understanding about the relationship of the various pieces without being told get these parts, not those parts. On top of that there's the group of naysayers that say it can't be done because they haven't done it.

For a higher revving street car what sort of balancing act must the cam, valves, and heads do to meet the emissions requirements? (Is this more in line with the type of question you feel answerable?)

Jason

You will want to snag one of the late model specific cams, could even go with a retro-fit hyd-roller. You'll want to keep the lda somewhere around 108-110 degrees. As far as your questions concerning the balancing act, a high rise higher rpm intake is ideal( unless you have tpi-then youl want a larger throttle body and runners+injectors. Like I said, the parts must be well matched, so keep the valve sizes @ 1.94int-1.60exh with around a 180cc Intake port. AFR 180's would be perfect and have enough material for later mods for more power. Contact your favorite cam tech line and ask for the best recomendation for a camshaft that fits with your needs. Again if you would like, I would be happy to build you a motor. Contact me @min301@comcast.net and we can put together a plan.  

Here are some  discussion we had on this.  Several custom cam grinders like Ed Curtis and Chris Straub participated along with some good cylinder head folks.

Camshaft discussion pt II

http://www.ls1tech.com/forums/showthread.php?t=101100

Camshaft discussion pt III

http://www.ls1tech.com/forums/showthread.php?t=158394

Camshaft discussion Pt III.5 and David Vizard

http://www.ls1tech.com/forums/showthread.php?t=254976

Here is some math to help you figure some of htis out courtesy of Larry Meaux @ Meax Cylinder heads and MAx Race software, along with Erik Koenig @ SAM.

you can ghetto figure it as (346/2)CID*6800RPM/1728 CID per one Cubic Foot= air engine takes in at that RPM at 100 % VE or 680 CFM.

Now we see there are 8 cylinders so 680/8 = 85 CFM per cylinder ***

The cylinder is only open say in a heads cam car for 224 out of the 720 degrees of the 4 cycle engine so it's only open .311111 of the cycle or roughly 31 % of the time in this case.

The actual airflow therefore has to occur during the short time the piston is traveling DOWN the bore and the little extra time it has before velocity is overcome by rising cylinder pressure from the upward motion of the rising piston in the bore.

85/.311111=273cfm average during this shorter but real period of intake port flow.

I could run MORE cam and slow the air down by running a longer duration cam but at some point the cam will both open too early on the exhaust stroke and close too late on the intake stroke so yes there are limits. Cams over 280 are getting more and more rare in racing as heads have gotten better and better.

Flow_@28" = ( CID * RPM * .000978474 ) / Number_of_Cylinders
this Formula calcultes the "most" Flow needed @ 28" on a FlowBench ,
in order to have a chance at making up to 127.5 % Ve

the Formula should instead be =>

Flow = ( CID * RPM * .000978474 * Ve% ) / ( Cylinders * 127.5 )

where
Cylinders = Number of Cylinders
127.5 % Ve = theoretical VE possible at .60 Mach or 699-700 fps
Note=> that 127.5 theoretical Ve is also dependent upon piston speed
and that at lower piston speeds even if there is .60 Mach, its not possible to achieve 127.5 %, but much less

Example=
250.8 CFM @ 28" = ( 362.6 * 7200 * .000978474 * 100 ) / ( 8 * 127.5 )

this shows that the "minimum" amount of Flow @ 28" needed to attain
a Peak HP RPM point at 7200 RPM = 250.8 CFM at 100.0 % Ve

then again you could view that Formula the other way, that is, what's the required Flow @ 28" in order to achieve theoretical 127.5 % Percent Ve
at 7200 rpm ??

319.3 CFM @ 28" = ( 362.6 * 7200 * .000978474 * 127.5 ) / ( 8 * 127.5 )

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