As suggested by Captain Fred in his blog entry on his 1940 Plymouth build, he wanted something done on cams.
Well, that can be quite a topic, and while you can find all kinds of article on the "inter-web" on how cams work in an engine, my goal is to put a Flathead Mopar slant on the topic.
Of course as my Grandfather used to say, an engine is nothing more and a large vacuum pump. Your cam turns lifting up intake valves, as pistons are being turned by a crank and that creates a vacuum. The vacuum sucks in whatever is near by into the engine. The cam turns a little further, closing the intake valve, we "light a candle" to whatever is in then in the cylinder and after what we hope is a controlled explosion, the cam turns a little further lifting exhaust valves and those pistons coming up push out whatever is left out of the engine..
In the V8 world a great deal of people used to think that making power, aside from the "no replacement for displacement" concept was putting in a wild cam. As time went by in the racing world, while the cam was important, we know it is the heads that are a much bigger factor to the V8 world. Sure superchargers or turbo chargers, trying to jam more stuff into the cylinder and the type of fuel you use for your controlled explosion also became a big factor, but in the world of cam vs heads it is the heads that lead that world.
In the flathead Mopar world, fuel isn't entering via the heads, and so it is definitely a cam that leads this world over the heads.
Next lets talk about stock lift and duration and even there, Chrysler Corporation made a huge number of cam profiles so the second I toss this out here, its easy for someone to say - "my stock cam is different" and yes I know that.
But in high level terms, a cam has two major factors and a few lesser factors. Lift and most of the p15-d24s were a 375 lift and then duration. Lift is how high the cam lifts the valve from its closed position, and duration is the degrees of the 360 degree circle that it keeps those valves open. In other terms how high we lift the valves and for how long we keep them open, whether intake or exhaust valves.
Again high level - you are limited by how high you can lift the valves in a flathead by the head. Lift the valve too high and it hits the head. On the duration side, there becomes a point where you have kept the valves open too long and it starts to effect the actual vacuum level in your engine. Remember again, a big vacuum pump. as we open and keep open valves we loose the seal on the vacuum. Of course we do that because we want to get and fuel and air mixture into the engine.
The change in duration also does things to the torque curve on your engine, but that is a whole different level of the discussion and I am trying to keep this more on the basic side.
Again in general if we keep the intake valves open longer and lift the intake valves higher, we get the opportunity to get more fuel/air into the engine. More fuel and air, and yes, clearly effected by the compression ratio, the more "bang" when we ignite the mixture with the spark plug firing.
Now, in the cause and effect department, generally as we raise up the valves higher (aka the lift) and hold those valves open longer (increased duration) we tend to change the rpm idle and things become what most of us call "lumpy". In the good old mopar v8 days of the 1970s I am sure lots remember pulling up to the lights with a guy running a "cammed up" motor and it was idling rough, shaking, coughing an weezing and yes that was also how the timing was set, but it was the duration of the cam that was causing that. When the light turned green and they hammered it, assuming the timing was set correctly, the goal was for that high lift cam to allow for a lot more fuel to get into the engine dramatically raising the RPM and turning the lumpy idling engine into a smooth running race engine.
Yes I am isolating and slanting this entire discussion towards cams, when timing can also be a huge factor. No better example being when Big Daddy Don Garlitz was forced to use a 426 hemi after they actually ran out of 392 hemis. He couldn't get the 426 to run as well, and out of frustration he advanced the timing way way beyond what anyone would have thought would work. In fact Don often tells the story that he intended to blow the "blanking" thing up. But as the engine rev'd up that advanced timing suddenly brought out the inner Monster of the 426 Hemi and all of a sudden the 392 Hemi was obsolete in Don's mind!
Back to our cams and remembering that the generation of car cams we are talking about were 375 lift. There are two school of thoughts on creating high performance cams. 1st is to raise the lift gradually and some pretty famous high performance cams raise the lift to 380 an and then increase the duration to 242 degrees. The 2nd is to raise the lift up as extreme as we can and also increase the duration. in the 1950s a pretty famous performance cam used a 400 lift. and 250 degrees of duration.
The other factor without diving into the details to much, is what I call the split. A great deal of cams have the intakes open and the exhaust close at exact same time, but some use a split. So for example an Esky 3/4 miles cam the intake opens intake valves at 20 degrees and closes them at 50 degrees and the exhaust opens at 57 degrees and closes at 13 degrees.
The Schroller full race cam - again a stock car racing - Higher lift and increased duration the Intake - has the intake valves open at 18 degrees and closes at 54 degree. The exhaust opens at 54 degrees and closes at 18 degrees.
If you are using a turbo or a blower, you often want a period of time (number of degrees) in which the intake is close and the exhaust hasn't yet opened, or visaversa.
The age old question is of course - so how much lift can I have before the engine sounds like it is misfiring. Almost always visions of those 1970 v8 engines coughing and wheezing are the reason for thing that. In reality the flathead just doesn't really act like a great deal of those badly timed, over cammed engines.. lol The reality is in the flathead world it is more a case of the rpm rises at idle than it is about it sounding like the 1970;s v8.
Of course most want a cam that sounds like it is rock stock, idles like the engine isn't running, but then they want a Top Fuel Monster to come alive when they hit the throttle. That becomes a delicate balance and is always a compromise.
So lets talk extreme. Maybe there is a wilder cam out there, but if there is we have never seen it. Ill keep the origins of this cam a little bit of a mystery, but the cam we use in the Velociraptor is the most extreme cam we know of. I chuckle these days as this phrase that seems to be in vogue again, but decades ago my Grandfather used to refer to a car that had this cam as "The Hot Mess Express".
Today we call if the AoK Velociraptor Grind . It is tough to get it to idle below 22-2300 rpm and we have with a ton of work have actually gotten our dragster to idle around 2000 rpm. It will wind up to North of 7200 rpm. You can run an engine on alcohol and will need 3 carbs and need to shift to 6 exhaust pipes for at least 42", to get it to run properly. Its lift is are you ready, 446 and its duration is 280 degrees. At this point we definitely have issues with vacuum and it would be extremely rough at idle, thus increasing the RPM just to get it to idle. For those that figure that isn't possible, by reply is gather up and bring all the cash you can find, because I am happy to say - "How much would you like to bet!".
Now from the extreme, to lets say a mid-50s truck cam which topped out around 3600 rpm, becomes the topic where many recipe's for performance have been made. Some by Chrysler Corporation for everything from cars, to boats, to combines and even Massey Harris 101 Super tractors powered by Chrysler Flatheads. The later were built for high torque and low rpm, which is great for plowing a field, but achieving a high way speed, not so much!
Today I think we have a catalogue of around 25 cam profiles. Of those we have cam patterns that we use , made for about 6 or 7 cams and of those, the number drops down to 3 or 4 for most engine builds. I think right now among the Kingsbury motorized items we have 14 different cams in use. In the Asche fleet of motorized items I am going to say they have 7 different cam profiles. The major difference, lol, yes I have more junk... I have a marine version, several truck versions, a combine, a water pump, a welder, a compressor which actually uses 4 cylinders to run the engine and 2 cylinders to make air, and an engine that used to be in a certain motorcycle.. lol.. Oh and I have an actual cam from a tank engine, but it isn't in an engine. I could make a pattern if someone ever needed one !
For Fred's engine, we used what many call an Esky 3/4 race cam. The 3/4 stands for stock car racing on a 3/4 mile long track.
This is what I today call, a fairly mild cam and we likely sell the most of these. I suspect part of that reason is as I talked about earlier, that people think back to those lumpy, poorly idling v8 engines with wild cams.. The .380 lift cam is going to give Fred 4500 rpm quickly. Its been around a long time and has a quicker rev over stock and was used historically for stock car racing. As you can likely figure out by reading this thread so far, we likely sell the most of these because most guys think they want power..... but..... they want to start it and not hear the engine running or running like a sewing machine. Tons of guys call this cam a race cam.. For me, its far from that. The tech side = 242 degrees of duration and .380 lift
Finally I will end the cam conversation for now, with the cam I am using in my 1949 Plymouth. It is what I call a little lumpy but still very much streetable and no, it is nothing like a 1970s over cammed v8 with bad or good timing..
lol but it is definitely aggressive, with a .435 lift and 258 degrees of duration. This cam was developed from tweeking a full race cam through the 1950s and 1960s and was what Harry Hein #90 (NASCAR hall of fame) used at the end of his career. Harry who is still alive would be the uncle of one George Asche Jr. The intake valves open at 20 degrees and close at 58 degrees, while the exhaust opens at 58 degrees and close at 20 degrees.
I hope that helps a little Fred, without confusing things too much!
Now what is in that Engine of yours, I can not confirm or deny what was originally put in the engine is what is in it now.. Who knows what happens in the middle of the night in George's shop... Only the shadow, or in this case the 1929 Desoto knows for sure.. lol