Camshaft advance/retard decision making process

clochard68

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How do you guys go about camshaft timing, once it is decided which camshaft is used:

-) Do you put the cam in at 0°, then check with dyno (or with test runs) where the torque and power peak occur, and then advance or retard the cam based on the results?

-) Is there a formula that gives a reference point where to put the cam (advanced/retarded and how much)?

-) Do you guys use software for that (and maybe even for cam selection)? If so, could you give a recommendation for a good program (free or purchasable)?

Thanks!
 
Hi,

Most of the time cam manufacturers recommend setting the intake lobe center at 4 degrees advanced. It is not uncommon for cam timing to be slightly adjusted for an engines specific need. The thing to remember is cam timing in our case affects all valve events, opening and closing of both the intake and exhaust. The valve events are what’s important not necessarily the intake lobe center by itself.

Cam selection starts off with an educated guess whether it be collected data from similar builds or computer programs. One of the nice things about this forum is we can collect data on things like what works well and what doesn’t. I know pmuller9 keeps very good records on this mater.

I like to use programs as a learning tool but they can also be deceiving if you’re not careful. The one I use most is engine analyzer pro. It’s not cheap. The basic version is a little more affordable.

Hope this helps.
 
Thank you Wesman, I didn't know that program.
It seems the engine analyzer plus should fully meet my needs, I think I will try it out, thanks again!
 
Its splitting hairs, Ive done this in the past on SBF 3o2s with both stock and sig erson cams, the difference between 0 and an 8 degress of advance was barely perceptable, it mainly takes up the inbuilt slack in the timing chains. The Australian VCT versions of our SOHC sixes advanced the cam the cam about 15degrees under 3800rpm, that does make a difference you can feel. Under that, hardly worth talking about.
 
Its splitting hairs, Ive done this in the past on SBF 3o2s with both stock and sig erson cams, the difference between 0 and an 8 degress of advance was barely perceptable, it mainly takes up the inbuilt slack in the timing chains. The Australian VCT versions of our SOHC sixes advanced the cam the cam about 15degrees under 3800rpm, that does make a difference you can feel. Under that, hardly worth talking about.

My stock cam was 4.5 degrees retarded when I got the engine.
Do I interpret your post right, every adjustment that I do that stay let's say under 9° (advancing the cam from -4.5° to 0° installed, or advancing further to +4.5° advanced installed) would not really be noticable or have a lage effect on rpm where peak numbers (torque and hp) occur?

I am asking specifically because I was rereading the 'horsing around' article about AK Millers Mustang, where he put an 260 duration Isky Cam straight up into his 200 and I was wondering if that 0° was already the optimum for that combination (small log with 240cfm carb) ...

Abd thank you, every input on the subject is appreciated!
 
Yes pretty much that correct, the main thing is to cover for the inbuilt retard in the cam change. As to Ak Miller stuff, that was centuries ago and dealing with the 170s etc. If you had a dyno and were willing to experiement you might be able to make some improvement, for a street application, its not worth the cost. A 260 degree (at lash im presuming) is tiny and would hardly matter. As to the effect on where the peaks occur, again it would be almost imperceptable. From my experience with chassis dynos (not a great deal admittedly) you could not notice 5-10bhp on the road. The engine analyser programme mentioned above I had many years ago and did a lot of work with it, I got good results that I could confirm by the seat of the parts on road vehicles. The best way i found to get good results was to start with a know stock engine, then work from there. I was mainly working with clevelands with 2v closed chamber heads that we have down here, I also did work with 250-2vs and Windsors. As with ALL engines the torque is in the BMEP which is a direct result of cylinder filling, anything you can do to help here will reap benefits, spend your money there. Keep in mind torque is the measured value, power is only a calculated value based on torque and rpm.
 
My stock cam has an advertised durstion of only 240°, and I want to stay with my C4 transmission with stock converter (stall at around 1800 rpm, car was on a chassis dyno):

dyno2.png

That's why I'm trying to get a good understanding of the camshaft advance/retard: the plan is to put a cam between 260 and 267 and not more than 50 degree overlap into the engine to make it 1) more efficient and 2) stil be able to use the automatic transmission with stock converter.

For example user "mad_science" postet his 250ci dyno results with the clay smith 274/274 (108 lsa) camshaft and made peak torque at around 2700rpm, that would be way too high for my converter.
[ https://fordsix.com/threads/built-250-dyno-results.84052/ ]

250 dyno.jpg

And I guess if the rule that 4° advance should get the peak torque rpm around 200 rpm lower, than I would have to advance the cam at least 20° (bad idea I would guess, valve clearences? valve events too much off from where they should be?)
 
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And one more question I couldn't find an answer too: What factor has the most influence on the rpm the cam is used? Is it overlap? Is it the duration?

I made an overview of available 108-109 lsa camshafts for the Ford 200, but couldn't find rpm ranges for the 256 and 267 Clay Smith cams:

camshaft chart.jpg

What confuses me a little is that the 264 Clay Smith (duration 264, overlap 48) and the 321262 Isky cam (duration 262, overlap 44) and even the Howard cam (duration 263, overlap 47) seem so similar in their specs, but differ so much in their rpm range!? Why is that?
 
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Notice what the Cam Duration Spec's are at .050 these are a more accurate way to compare different Camshafts versus their Advertised Duration.
 
My stock cam has an advertised durstion of only 240°, and I want to stay with my C4 transmission with stock converter (stall at around 1800 rpm, car was on a chassis dyno):

That's why I'm trying to get a good understanding of the camshaft advance/retard: the plan is to put a cam between 260 and 267 and not more than 50 degree overlap into the engine to make it 1) more efficient and 2) stil be able to use the automatic transmission with stock converter.

For example user "mad_science" postet his 250ci dyno results with the clay smith 274/274 (108 lsa) camshaft and made peak torque at around 2700rpm, that would be way too high for my converter.
[ https://fordsix.com/threads/built-250-dyno-results.84052/ ]

And I guess if the rule that 4° advance should get the peak torque rpm around 200 rpm lower, than I would have to advance the cam at least 20° (bad idea I would guess, valve clearences? valve events too much off from where they should be?)
And one more question I couldn't find an answer too: What factor has the most influence on the rpm the cam is used? Is it overlap? Is it the duration?

I made an overview of available 108-109 lsa camshafts for the Ford 200, but couldn't find rpm ranges for the 256 and 267 Clay Smith cams:

What confuses me a little is that the 264 Clay Smith (duration 264, overlap 48) and the 321262 Isky cam (duration 262, overlap 44) and even the Howard cam (duration 263, overlap 47) seem so similar in their specs, but differ so much in their rpm range!? Why is that?
As bubba said, the biggest factor in the power band is the .050" duration, not the advertised duration.
Secondly, where the power band begins relies on the .050" intake valves closing point.
All of this is relative to the engines displacement. The more displacement the engine has the lower and wider the torque curve will be.

Right now it looks like the cam makes it's best torque around the stall speed of the torque converter.
If you install an aftermarket cam, the torque peak will move upward in the power band and the engine will make more horsepower thanks to the improvements you made on the intake and exhaust systems.
It doesn't mean there will be less torque at 1800 rpms.
If the cam change is moderate it can make more torque at 1800 rpm but will continue to increase to its peak further up in rpm.

To start with "Mad Science" has a 250 engine which is 50 cu in. more than your engine.
Because your engine has 50 cubes less displacement it will actually move the torque peak up at least another 500 rpms with the same cam.

If you look at the stock 240 cam there is 62 degrees between the advertise and .050" duration.
The aftermarket cams have a lot less difference.
I'm thinking that you looked at the specs for the stock 200/250 cams and saw 256 degrees and thought that a 256 degree aftermarket cam was comparable. It is not. They will have a lot more .050" duration than the stock cams with the same advertised duration.

If you want to keep a low rpm torque band for a 200 six, use the smallest cam on you list.
That would be the Isky 321M.

These cams are used in the 144 to 250 cid sixes and because there is such a large variation in displacement there is no way to post an accurate rpm range for the cams unless the supplier wants to specify which engine they are referring to and even then it still won't be correct because most people are modifying the engines to varying degrees.
In other words, you CANNOT use the rpm range being shown with the cam specs.

The next important factor is the intake valves .050" closing point, and this is what is affected by moving the cam timing.
The stock cam you listed with the intake lobe center at 111 closes the intake valve at 20 degrees ABDC.
That is very early and is why it makes a lot of torque at 1800 rpm and below.

The Isky 321M cam's intake valve will close at 26 degrees ABDC which isn't far from the stock cam but the extra duration and valve lift will create a much longer and higher torque curve and a lot more horsepower.

Question: The 240 cam is shown as being the stock cam for the 170 but you have a 200?
How did your 200 end up the 240 cam instead of the 256?
 
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Wow pmuller, thank you a ton!
In your post alone was so much information I was looking to get on the internet but couldn't find it this clear and coherent put into words. I have a lot to think about all that for sure...

When I installed my dual timing chain, I put the stock 240 cam in 4.5° advanced (I read everwhere that 4 degrees is a good number, didn't do my research first!) now the intake closing valve point is at 12abc... your honest opinion: that would be way too soon, right? Should I correct that mistake and put back 4.5° retarded?

Regarding your question: I was wondering that too. I know my engine was rebuild because I have .030 over pistons. I suppose the changed the cam when they had it apart. And I am certain that I have the 240 cam, I degreed it about three times and got the same .050 numbers that are mentioned in the falcon performance book for the 170 as you mentioned...
 
When I installed my dual timing chain, I put the stock 240 cam in 4.5° advanced (I read everwhere that 4 degrees is a good number, didn't do my research first!) now the intake closing valve point is at 12abc... your honest opinion: that would be way too soon, right? Should I correct that mistake and put back 4.5° retarded?
12 degrees ABDC is way too soon.
When the piston is that close to the bottom there is very little piston motion as the crankshaft rotates.
Between 12 and 20 degrees ABDC the piston only moves up .042" and the Dynamic Compression Ratio only increases 0.11
There is very little change in low end torque.

Put the cam back to the retarded postion.
Better yet install the Isky 321M and make a lot more torque and horsepower.
 
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Good to know, I didn't even think of piston motion in this regard.

Now that I have to take the radiator and fan out to get the timing cover back, I really consider getting the 321M as soon as possible. I was planning on doing a cam change next winter, but I think now would be the appropriate time...

Thank you again for answering me in such detail, it helps a lot understanding how camshafts and valve events influence our beloved inline sixes!
 
Following along, hope you will do another chassis dyno after installing the aftermarket cam so we can compare the results.
 
Following along, hope you will do another chassis dyno after installing the aftermarket cam so we can compare the results.

Yes I will definitely be doing another dyno test after the cam change and post it here and also in the small log head porting thread.

The dyno will show the combined results of all the changes I made to my Mustang, the porting, new carburetor, 1.65 rockers and new exhaust. I am also curious how it will turn out.
 
Since you have the head off, would you take the time to see how much valve travel there is on both the intake and exhaust valves by simply pushing down on the valve stem with till the valve stops against the guide.
It can be done using a drill press and dial indicator.

What valve springs does the head have on it now?
 
Since you have the head off, would you take the time to see how much valve travel there is on both the intake and exhaust valves by simply pushing down on the valve stem with till the valve stops against the guide.
It can be done using a drill press and dial indicator.

What valve springs does the head have on it now?

The head is disassembled at the moment. I plan on using, the beehive springs I posted in the 200 valve spring thread, I am still waiting for a response from Isky what seat pressure the cam needs.

I will also check for valve seal to retainer clearance, my head is prepared for positive valve stem seals. If necessary I will mill the guides a touch down.


EDIT:
I talked to someone at Isky today, seat pressure for the 321M would be around 100-110lbs...
 
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Has anyone experience on using oiling lifters with non oiling pushrods? (Isky only has oiling lifters for their cams)

Would that cause any problems, maybe regarding the oil pressure?
 
If you don't need to use the Oiling Hydraulic Lifters and Push Rods for your Rocker Arms than just ask for a set of 12 of the Ford FE Hydraulic Lifters.
 
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