Camshaft advance/retard decision making process

[clochard68]

The FE lifters have an OD of 0.904". Should be 0.874" right?

 

[drag-200stang]

No, they are .874. but aways double check. It is possible that the pushrod seat could at a small difference in height depending on what yours is, not sure just keep that in mind.

 

[drag-200stang]

Do not shorten the valve guides unless absolutely you have to, they are already too short.

 

[clochard68]

I know I shouldn't take the from the manufacturers suggested rpm ranges as a given, but I have to ask to fully understand this:

Compared the Howards to the Isky cam, the have almost identical specs, why are the rpm ranges (orange) so offset?
I would understand differences at around 200-400rpm, but 800rpm? That seems like a lot to me.



I am asking because I also have the Howards cam in mind for my 200 with the C4 automatic transmission: with power starting at 1200rpm I think that cam would be fine for an automatic, but with power starting at 2000rpm I wouldn't even consider this camshaft... so what is the more likely true lower rpm limit for the Howards?

 

[Frank]

I know I shouldn't take the from the manufacturers suggested rpm ranges as a given, but I have to ask to fully understand this:

Compared the Howards to the Isky cam, the have almost identical specs, why are the rpm ranges (orange) so offset?
I would understand differences at around 200-400rpm, but 800rpm? That seems like a lot to me.

View attachment 14643

I am asking because I also have the Howards cam in mind for my 200 with the C4 automatic transmission: with power starting at 1200rpm I think that cam would be fine for an automatic, but with power starting at 2000rpm I wouldn't even consider this camshaft... so what is the more likely true lower rpm limit for the Howards?

The Howards # on your graph does not match, but if it's the cam I'm thinking: the Howards has 108* Lobe Separation Angle. The Isky has 109*. The graph above shows the Howards advanced 4*, the Isky has 0* advance. So the Isky closes the intake valve@ 60* ABDC, the Howards closes it @ 55.5* ABDC. This is the RPM difference. BTW- 55* closing will 100% require premium fuel if using the EFI head, the dynamic CR is 7.4:1. But low-end torque is fantastic. . The reality is, both cams will start to pull strong by the low to mid teens.

 

[clochard68]

...the Howards has 108* Lobe Separation Angle. The Isky has 109*. The graph above shows the Howards advanced 4*, the Isky has 0* advance. So the Isky closes the intake valve@ 60* ABDC, the Howards closes it @ 55.5* ABDC. This is the RPM difference.

In the last row I put the numbers for the Howards when installed at 0° for comparision...

I just don't understand how 4° cam advance make a difference of 800rpm. Everything I found online says 4° should move the powerband only about 200rpm, so we are off by a factor of 4. Is there any other important parameter I don't see?

The Howards # on your graph does not match

This is the camshaft: https://www.howardscams.com/hydraul...ford-140-250-1200-4800-howards-cams-280028-08

 

[THE FRENCHTOWN FLYER]

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.

I tend to agree with aussie7mains on this and here's why -

Advancing or retarding the camshaft will rock the WOT torque curve about the peak torque point, i.e., if advanced, it will add torque to the area below the torque peak while subtracting torque above the peak torque point. And vice-versa with a retarded cam. So for most users who run their engines both above and below the torque peak it becomes a "zero sum gain" affair - you'll gain a little here and lose a little there.

Now in extreme applications it may help to donk with the amount of advance / retard.
Let's take a high RPM only application like my Super Pro drag roadster. The stall speed of the racing converter is 5500 RPM. My red line is 7000 RPM. During a run the engine sees RPMs between 5100 and 7000, so it would make sense to have sufficient retard built into the cam to optimize the power in that range. I don't care about torque below the torque peak, which is likely below that range.

I'm trying to envision an application where the engine always stays below the torque peak, to take advantage of an extremely advanced cam. Can't.
Not rock crawlers. Probably not any industrial applications, save those that have a governor. Maybe a guy who drags a trailer down a twisty rocky 2-track to his hunting cabin??? Maybe a guy who just likes to lug his engine down like a diesel just because. Anyhoo, there may be somebody who needs this but they are as rare as a six cylinder drag racer on the other end of the spectrum.

Most users use their engines by taking them throughout its operating range and therefore the advance becomes a moot point. If you're going for getting the last little bit of fuel economy at your particular driving schedule it might help a skoosh to monkey with the timing. I have not heard of anybody yet who has disassembled their engine several times to change the cam advance to squeeze the last bit of fuel economy out of it.

That is why I say set it to the manufacturer's spec - or close to it - and fuggadaboudit.

 

[pmuller9]

I know I shouldn't take the from the manufacturers suggested rpm ranges as a given, but I have to ask to fully understand this:

Compared the Howards to the Isky cam, the have almost identical specs, why are the rpm ranges (orange) so offset?
I would understand differences at around 200-400rpm, but 800rpm? That seems like a lot to me.

View attachment 14643

I am asking because I also have the Howards cam in mind for my 200 with the C4 automatic transmission: with power starting at 1200rpm I think that cam would be fine for an automatic, but with power starting at 2000rpm I wouldn't even consider this camshaft... so what is the more likely true lower rpm limit for the Howards?

These cams are for 144 to 250 cu in engines.
The 144 will have a very different power band than the 250 for the same cam.
There is no way to specify an RPM range for one of these cams unless a specific displacement and component combination is also specified.
We ignore catalog posted rpm ranges and rely on the data that has been accumulated by the many engine builds found in this forum.

 

[Lazy JW]

...I'm trying to envision an application where the engine always stays below the torque peak, to take advantage of an extremely advanced cam. Can't.
Not rock crawlers. Probably not any industrial applications, save those that have a governor. Maybe a guy who drags a trailer down a twisty rocky 2-track to his hunting cabin??? Maybe a guy who just likes to lug his engine down like a diesel just because. Anyhoo, there may be somebody who needs this but they are as rare as a six cylinder drag racer on the other end of the spectrum...

I probably come as close to meeting that definition as anyone with my White Ox Torque Motor, especially since I haven't even licensed it for about five years now as it never leaves the homestead nowadays and rarely even gets out of granny gear.

That said, I installed my extra-short duration Reed Cams Economaster cam straight up. I also used deep dish EFI pistons with the carby head to lower the static compression since I also had the block zero-decked.

This engine is so smooth and strong ~1500 rpm.