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Camshaft Selection for your New Engine
Cliff Ruggles:
Had a few extra minutes this morning and wanted to put up some information on currently available camshafts.
The purpose here is not to "bash" any particular company or line of camshafts, just to provide useable and accurate information on the subject based on what is currently happening with this sort of thing in our hobby.
In the past decade or so companies grinding and selling camshafts have came up with quite a few different types of camshafts and pushing this "new" technology pretty hard.
It's pretty much the same thing, you will hear words like "more area under the curve", improved idle quality, more power on top end, improved street manners, etc, etc.
Folks, when the smoke clears and dust settles with this sort of thing there isn't much improvement, if any waiting for you by going to "modern" lobe profiles over what's been available for decades.
Now I'm talking about flat camshafts here, not roller profiles because when we take the lifter diameter out of this equation there are going to be some really nice benefits waiting for you in the areas these companies are promoting.
A roller camshaft will truly allow for reduced seat timing for improved vacuum production, smoother idle, and improved street manners but still offer excellent cylinder filling abilities at higher rpms. This means that the end user can sort of have their cake and eat it too.
Trying to do the same thing with a flat cam is not nearly as easy. Think of this whole situation like you are sitting in front of a large window in your kitchen and the wind outside is blowing pretty strong. If you lift the window up and down very quickly but never stop the movement how much air will get into the room vs throwing the window open completely, hesitating for a moment, then very quickly slamming it shut while keeping the actual time the window was open for both scenarios EXACTLY the same.
Rest assured the very quick movements to fully open, leaving it there for a moment, then very quickly slamming it shut will allow more air to enter the room for each cycle. This is how a roller cam works in comparison to a flat camshaft.
What's happened in recent years is that companies making these cams have removed seat timing (actual time the valves are off the seats or "advertised" duration), then picked up the .050" numbers considerably. With this move they have came up with all sorts of names for the "modern" lobe profiles as well, claiming greatly improved power, better idle quality, blah, blah, blah, you get the idea at this point.
Continued below....
Cliff Ruggles:
What actually happens with a flat cam is that this super-quick seating velocity has pushed the envelope too far. Flat camshafts that used to be fine with 80lbs seat pressure and 200lbs over the nose now require a LOT more pressure to keep things in check to prevent problems with harmonics at high rpms and noise with the valve bouncing off the seats, etc, etc.
Super strong springs are NOT favorable to flat lobes and we are seeing a very high lobe failure rate in the past 10 years or so with this sort of thing. It doesn't help that many lifters are now "off-shore" production, but that is another topic I'll cover on another day.
What I'll say here is that currently we are getting and have been getting a LOT of complaints to the shop from folks who have just built a new "high performance" engine for their pride and joy and are having considerable running issues with it.
The common denominator I'm seeing are these "new" camshaft profiles with "modern" lobe designs. They also more times than not have much tighter LSA than stock type cams and older designs used to do the same thing. The tight LSA alone produces more overlap, so idle quality, power right off idle, and power in the normal driving range is negatively effected. This happens even if they have taken out some actual seat timing to improve vacuum and cylinder pressure.
The camshaft companies seem to be targeting the audience that wants that "aggressive" idle quality or "lope" in the exhaust note. That's all good but remember here that increasing overlap does a little more than make for a rough idle. It allows unburned fuel over into the exhaust, and reduces cylinder pressure which both hurt combustion efficiency at idle and low rpm's and also make for "stinky" exhaust.
A couple of other things happen as well. Tight LSA also narrows up the power curve and pulls peak power DOWN in the rpm range. Both of these facts increase octane requirements all else being equal. So for the guy who just chose a compression ratio for his new engine that typically is fine on currently available pump fuel, he quickly finds out that it isn't when the engine is placed in service.
This happens so often I felt needed to mention it here.
Second problem is that with these tight LSA camshafts with greater .050" and .200" numbers is idle quality is greatly reduced and vacuum production at idle low for the CID and compression ratio. This requires MORE timing from the distributor at idle and greatly increase idle fuel from the carburetor.
This is how I get involved in the first place as folks put these engines into service and very quickly find out that they idle very poorly with "normal" timing and idle fuel settings. I'd like to have a nickel right now for every phone call I've received in the past 4 or 5 years where the owner of one of these sort of engines calls up and says that the idle mixture screws have no control, engine refuses to idle much below 1000rpm's or so, and the that the exhaust is so stinky it runs him right out of the garage on start up and stinks up his cloths, his wife's hair (never a good thing), and it's stalling at stoplights/consuming more fuel that it should, etc, etc.
Continued below.....
Cliff Ruggles:
So basically I just wanted to put up a post this morning for folks who are contemplating their camshaft choice for a new engine build. Nothing has really changed with this sort of thing as far as a bunch of power waiting for you with a modern cam profile. That technology is all played out with flat cams and has been for many years. Since we still can't get past the laws of physics with these things choose the camshaft for your new engine based on CID, true static compression ratio, drivetrain specs and intended use of the vehicle.
Also look very closely at the camshafts that the factory used for similar engines. Yes, the engineers really did know what they were doing with these things and designed and used camshafts that worked very well back in the day and still do.
I would for sure avoid any cam on a really tight LSA for most builds, and look very closely at the advertised duration to .050" specs and spring requirements. Also avoid any lifters that are not USA production.
Hope this thread helps some.......Cliff
429bbf:
nice right up cliff thanks .has anyone on here ever used a cam doctor . i have not yet seen a cam that is ground perfect some are plum bad . if anyone gets the chance put your new (supposedly perfect cam on one) and you will see how bad some are and its not just one brand.fwiw
markedmondson:
Thanks Cliff; very insightful.
I posted a link to this on the NCRS forum; the guys there will find it useful.
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