Camshaft calculator opinions

[joe_rocket45]

After reading the Vizard article on cam selection and finding it wholly inadequate IMHO I decided to write a simple calculator that should get a person pretty close to the best cam. It's turned out to be a little harder than I expected to find the best LSA and ICL but i'm working on it and have my future scripts coming together. In the meantime let's see if the first half (intake side) of it's working well for everybody.
I need to note that the ideal lift may seem a little high to some but they should be in the neighborhood for the best power, but will probably take a roller with high ratio rockers to achieve in most circumstances. This is more about predicting the best RPM and durations for your particular head flow, CI and stroke.

http://www.bid2race.com/beta_cam_selector.html

let's hear some feedback!!

BTW, if you need your heads flow numbers:

http://users.erols.com/srweiss/tablehdc.htm

[joe_rocket45]

Re: Camshaft calculator opinions

K..? well I'm surprised that the forum can unanimously select one cam over another with just a couple of degrees difference but no feedback on this ... at all?

I did notice something strange myself, the duration figure is only supplied by the stroke and RPM, the RPM is supplied by the CI and the head flow. Sounds good right? ( The duration formula came from a guy who designs race cams and has won MANY championships including the Baja 500 and the Brickyard from what I understood from what he said?).

Soo... here's what I found very strange. If ONLY the stroke is changed the RPM changes but the camshaft durations DO NOT change? Further if the BORE is changed the suggested duration DOES change. And to add to that if the bore AND headflow is changed to match the RPM w/o changing the stroke the cam durations suggested are exactly the same...

Anybody wanna shed some insight? If anybody wants to see the formulas I can write them where they can be read and studied.

[revolutionary]

Re: Camshaft calculator opinions

OK I might be wrong but it seems odd that the program suggests a 245@ .050 cam for every stroke from 3" to 5". Probably need to make some alterations there.

For me the individual bore or stroke are not as important as the overall cubic inches and the desired peak torque or peak HP RPM. I would suggest asking for a desired peak HP rpm, cubic inches and compression ratio and go from there.

[joe_rocket45]

Re: Camshaft calculator opinions

OK I might be wrong but it seems odd that the program suggests a 245@ .050 cam for every stroke from 3" to 5". Probably need to make some alterations there.

Yea, and what's odd is that the duration formula only has 2 variables, the stroke and RPM!!
it's basically (sq/rt (stroke * rpm / constant_1) )* constant_2 = duration

I'm calculating the RPM from the CI and head flow.
this is the simple rpm formula I found:
cfm / ci per cyl * 1111
and I'm taking it that 1111 is the speed of sound (which would be dry so I modified that variable to 1145 for a hot intake with fuel).

For me the individual bore or stroke are not as important as the overall cubic inches and the desired peak torque or peak HP RPM. I would suggest asking for a desired peak HP rpm, cubic inches and compression ratio and go from there.

Same here, along with flow of the head.
My thinking is that if XXX flow will peak at XXXX rpm then the cam should also peak at that rpm, correct? Right now I'm leaving the compression/cyl pressure/exhaust out and just working on rpm/duration, intake side.

I'm pretty sure both formulas are correct, just showing STRANGE results...and might teach us something here, maybe. RPM wise it's been very close on the dyno sheets I've compared it to, on motors that ran good the cam was pretty close too.
Anybody want to compare it to a real dyno sheet with a pro spec'ed cam?

[BillBallinger Sr]

Re: Camshaft calculator opinions

Actually,I found it pretty close to what I came up with for choosing the cam for my 390. If you vary your lift and flow the duration will change. The rpm ranges were good too. I tried three different scenarios and the duration followed the flow and lift as closely as the stroke. I think it is pretty good.

[JeffMcKC]

Re: Camshaft calculator opinions

So if you have great 400-500-600 #'s and your peak flow is at 700 then it will give you the same cam as if its not got good low flow?

the better the flow on the heads as long as the heads have "proper flow not just a big hole the less cam you would need, I would say its a good start but needs more inputs

[Falcon67]

Re: Camshaft calculator opinions

For a 351C, I don't find it the least bit useful. It comes up a bit closer to what I would pick for a 302 similar to what's in the shop.

[ItBurnzWenIPee]

Re: Camshaft calculator opinions

right on dude that is pretty cool. it came really close to what i have.

[revolutionary]

Re: Camshaft calculator opinions

I just spent a while on Engine Analyzer running through a bunch of cams in various engine configurations. What I saw was pretty much what I figured in my head but what I didn't realize were the factors I was using that made the most changes.

First, runner size per cubic inch is a limiting factor. AS long as there is enough runner volume to support an increase in airflow, the peak HP RPM tends to rise about 200 rpm for every six degrees of intake duration increase. Once you reach the limits of your head volume and airflow, the rpm will only increase about 100rpm or less per six degree increment.

Second, lobe separation is not as important a factor as intake centerline for determining peak HP RPM.

Third, bore or stroke by themselves are not as important as total cubic inches. In a 383 example with a 242/248 @ .050 hyd flat tapet cam, moving from a 4.200 bore x 3.45 stroke to a 3.875 bore x 4.06 stroke only decreased the peak hp RPM by an estimated 100rpm.

Fourth, an increase in compression does not necessarily show a significant change in peak hp rpm as long as the correct fuel is used.

Those are some things to think about for now. I've not used the Comp Cams software but I've found the Performance Trends has been pretty well on the ball for getting really close to the cams I want.

[joe_rocket45]

Re: Camshaft calculator opinions

Great post and thanks for the info. I got "called in" today and just got but before I left I had made some additions to the calc, haven't checked it against and dyno sheets soo...it could be way off but hopefully it's getting closer.

http://www.bid2race.com/beta_cam_selector.html

[JeffMcKC]

Re: Camshaft calculator opinions

Peak power should be a input, and I think the comp. math is off

[TC]

Re: Camshaft calculator opinions

Interesting calculator, It's pretty close to the cam I picked, it says I should have 301 adv. duration, and my cam has 303/312, it says I should have .679 lift my cam has .675 using 1.6 rockers. Now it is a little off on the .050 duration as it recommends 255 degrees of duration and my cam has 270/278. And got to love the estimated peak HP at 668hp. Not bad for a weepy 406. ;)

And hey it doesn't give you a LSA value, it'd be interesting to see what it'd recommend, since my cam's on a 103.

[JeffMcKC]

Re: Camshaft calculator opinions

Sorry man, I know you are trying, but this is not how you pick a cam or lobe. Do you use the same lobe on a heavy car as a light one? What if its a two speed, insted of a three, you will have to have a lobe with less duration. Everything I have plugged in has to much duration for me, and thats saying something.

[joe_rocket45]

Re: Camshaft calculator opinions

in the smaller motors it seems pretty good but when the head flow gets up there it's getting some BIG duration numbers for me also. I got the duration formula from Camking. It's going to take some work.

The Ezdyno was primarily made up formulas by me, these are accepted formulas I made this with so..?Also the EZdyno is saying with the current motor we're building that power starts to drop with a cam over 276@050 and this is calling for a 291@050. I also noticed that as it starts calling for the bigger cams the peak Hp is dropping off substantially, it's a "beta" and I've got some feedback, give me a week or two to work on it, it's some pretty heavy math for somebody that hasn't even completed a semester of college or done much math since HS :P

[BillBallinger Sr]

Re: Camshaft calculator opinions

The DCR calculation seems a little high :-\ You might want to look at it. The dependent variables can cause a tolerance stack up that can lead off in the wrong direction when it loses its contextual range.

An example would be an IF equation: @IF ((cell, lets call it weight) > 3500,"93"(which is a boolean 1 or true),"91"(which is a boolean false or 0) What you are saying is that any number over 3500 will return the value 93, if not then 91. If this is nested with a number of other general IF conditions then weight can lose its context to octane by a condition downstream that nullifies the original context of weight to octane. It won't be a circular reference, but if the car weighs equal to 3500 and the cam duration condition is based on the intake closing point to static CR with a reference to octane it could give you a borderline false 91. Both parts of that reference need to be joined to say @IF (weight)=>3500,or (DCR)=>8.2:1,"93"(true), "91"(false)) Then you have created a compound reference to weight and DCR that can be an independent variable to other calculations that can't be nullified by references down stream. It is an octane recommendation based on weight and DCR with an equal to or greater than threshold of 3500 and 8.2:1 DCR regardless of weight. Both carry equal relevance but only at those thresholds.

An even better solution is to create a LOOKUP chart that will plot weight thresholds and DCRs based on ranges in your form inputs. I am rusty on this, but you essentially reference the values in a LOOKUP equation that sets the data ranges to the chart with a vertical lookup in one like weight, and horizontal for the other DCR and where they meet on the chart will be your return value. This allows an infinite number of possibilities from any number of LOOKUP charts you want to refer to as variables. But, like any other stream it has to exit with a bottom line purpose. Your boolean values will be your referential value outputs so they can nullify other charts by creating true/false conflicts. You don't want to pack too many things together to work off of each other. If that is in determining a cam lobe, the airflow at multiple data points is needed to create an air profile with a referential chart to a lobe acceleration speed and duration for the head flow. Physically its like blowing smoke rings, in a cam lobe selection formula you are trying to mathematically quantify and predict how to "hold your mouth just right" to blow the perfect smoke ring. If it is determining octane requirements it can build on the other charts, but is a separate objective. They will be related and share data in the LOOKUP charts but should be treated independently, as would horsepower or any other prediction would do.

You can also use a set of database tables of real world telemetries by making referential queries across the tables that can make uncanny predictions over time. But you need a lot of data points in each table for reliable compound results. And you need to have your logic stream worked out to avoid bad references. MS Access is a good place to begin, it is very intuitive and if you want to use it as an FTP server source for a web based Visual Basic form, it is easy to protect on the server.

Keep it up, you will get it the way you want it It is a whole lot of fun working with this isn't it?