Camming to suit gearing

Brian

Brian

Well-known member
I think all this dialogue about the best cams to use needs to be looked at from a different perspective. My thinking about it is; just as an example we'll use my street driven vehicle, that will be driven at the speed of say 60 MPH most of the time. The vehicle has 28" tall tires, 1;1 top gear ratio and a 3.78 ratio diff. At 60 MPH the engine is turning 2,723 RPM. Surely, I would be better off having a cam that is producing maximum torque at that speed; this should return best fuel consumption and engine efficiency. What use is it putting in a full race rumpety rump cam, because it sounds 'cool', if it produces power at the top end of the [admittedly] increased rev range when the vehicle will never get driven that fast? I feel a lot of our engines are actually overcammed for the application.
Let the debate begin.... Brian
 
Well said, I agree 100%, without the right gears the engine will NOT perform. It would be nice if we could all dyno our motor and know our particular torgue curve, but that being said. Being a little on the conservative side in cam choice would make a lot of people happier.
 
it does no good to have a cam that doesnt work till you get to the top of your rpm range,unless you want to run in first and second gear most of the time, you want a cam that starts developing power from idel to around 2500 rpm, which is the best rpm for the flathead
 
Brian
You are very correct about over caming. I have been grinding cams for flat heads since 1989 and build a lot of Ford Model A and B engines. I dyno test most of my cams and the best cams for street use is a mild touring cam developing Max torque at 2100 to 2400 like 175 Ft Lbs and 100 HP at 3500 RPMs.
I have ground a lot of lopy cams for Motor city flat head years ago and I have a hard time thinking these were any good for the average street car.
We are tooling up to start making new billet flat head V-8 cam very soon and feel most of the need will be for a good torquey street cam.

Bill Stipe
Specialty Motor Cams
 
I am not sure how this applies to flatheads but as a rule higher compression ratios are used with cams that have a lot of overlap. The scavenging effect is more efficient at higher rpm's but not so much at slower speeds. Exhaust tuning to match the intake is also important. I know straight pipes on a Harley kills the mid range. May sound good but run like crap.
 
This is a perfect place for the L-100. It starts building torque at around 2400, at 27 it's in the sweet spot. Maybe that's why it gets good gas mileage. Ask someone that runs one.
 
Great choice Ron. My engine built by OL' RON has the L100 and I couldn't be happier. Very driveable around town and gets good gas millage on the interstate. Oh and what a sweet idle! Have taken many 600 mi trips and love it.With the 3.78 gears you will find the sweet spot alot.
Don
 
What is often seen, when cams are discussed, is the void which is present because there is nothing available for quick comparison. It is one thing for a report to be issued about how happy a particular engine is with cam "X" but quite another to compare cam "X" with other cams at the same speeds and loads. Just for example, and certainly not to denigrate or defame those who love the L-100, SU1A, or any others, it is an absolute fact a stock cam will make more power in the above described 2400-2700 RPM range than nearly any "performance" cam. The fact that a cam does not cause fluttering, stumbling, mis-firing, blubbering, or engine stalling does not mean it is suited for the application. The fact that a car will accelerate or cruise from relatively low to relatively high engine speeds, with no noticable problems, does not mean it is "pulling good". If there is nothing to compare with, almost, any cam will "pull good" from 2400 and up. Nothing in the engine requires more design compromise than a camshaft. To work well at high speeds it must suffer at low speeds. Conversely, to work well at moderate speeds it must suffer at high speed. Modern engines are equipped with variable valve timing mechanisms. These have been developed because cam timing compromises are recognised as a fact of life and the variable systems help expand the efficient RPM operating range.
 
JWL said:
What is often seen, when cams are discussed, is the void which is present because there is nothing available for quick comparison. It is one thing for a report to be issued about how happy a particular engine is with cam "X" but quite another to compare cam "X" with other cams at the same speeds and loads. Just for example, and certainly not to denigrate or defame those who love the L-100, SU1A, or any others, it is an absolute fact a stock cam will make more power in the above described 2400-2700 RPM range than nearly any "performance" cam. The fact that a cam does not cause fluttering, stumbling, mis-firing, blubbering, or engine stalling does not mean it is suited for the application. The fact that a car will accelerate or cruise from relatively low to relatively high engine speeds, with no noticable problems, does not mean it is "pulling good". If there is nothing to compare with, almost, any cam will "pull good" from 2400 and up. Nothing in the engine requires more design compromise than a camshaft. To work well at high speeds it must suffer at low speeds. Conversely, to work well at moderate speeds it must suffer at high speed. Modern engines are equipped with variable valve timing mechanisms. These have been developed because cam timing compromises are recognised as a fact of life and the variable systems help expand the efficient RPM operating range.
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Roger on all that...
One big reason the formula one engines went to computer controlled, no cam valve train. They can have optimum valve timing at all engine speeds, all the way up to 19K rpm.
 
Those of us that are stuck with this 30's technology that we so love, don't have the luxery of VVT. I think I've been building and 'improving' flatheads for so long now, that I've forgotten how a stock engine runs. Every engine I build is 'better' than the predecessor, now I've got an engine that loves 6000-7000 RPM, I love it, it really performs, but I'm certainly not getting maximum performance out it as a daily driver. Winding it out in 2nd gear is exciting, but really, tooling around at 60 MPH in top gear, it still hasn't got to that 'sweet spot' that Ol Ron refers to. But, at that same speed a stock motor has 'peaked', hasn't got much more in it. When it comes to cams, it sure is a compromise. Brian
 
I agree with jWL and Ol' Pete, The stock cam will give more torque at low RPM and give good mileage. The hot cam is an aesthetic thing for the ear, just like all that chrome and Billet "Stuff". However if abig IF your building a hotrod, ya gota have a cam and the L-100 does a good job of driveability and economy.
At present I'm building a 276ci stock engine for my grandson for his 47 Int. PU. I'm going to try and get the best performance and mileage from this engine I can. Then without changing anything except the cam (EAB) I will install an L-100 and compair them. Then we;ll talk. "6000-7000" out of a Flathead? WOW1
 
Yes Ol' Ron, 6-7000 RPM out of a flattie. It is only a little 221, small, light reciprocating mass loves revving out. How it holds together I don't know! Brian
 
I agree with you all LOL Thanks for the lesson and for my 24 stud motor I will stay with the close to stock bore add some Offy or Edelbrock heads and a couple of carbs and glasspacks and call it a day. I learned alot from reading this thread thanks guys.
 
OK GHOST: So your not going to "over cam your engine" but you may OVER carb the engine, put two on, but block one off, make it look like its running, but not, and add tube headers to the glasspacks .... stand-by... we are going to open the " OVER CARBING YOUR ENGINE "... question soon .... Hey: Ken,CT...are you reading?.... OLD...BILL
 
Heh heh.... so the stock cam is best for all round on a stock displacement engine.... and a single carb is best so it does'nt get over-carbed... and as per another thread, headers produce negligible increase... and as per many other posts I've read, stock heads can perform as well as aftermarket heads.... and porting and relieving is a marginal benefit...
hmmmm..... so what we've got here is a stock engine as Henry built it... :D:D
 
Ghost of elmirage said:
I agree with you all LOL Thanks for the lesson and for my 24 stud motor I will stay with the close to stock bore add some Offy or Edelbrock heads and a couple of carbs and glasspacks and call it a day. I learned alot from reading this thread thanks guys.
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Go with two Stromberg 81's and you will be fine.
 
If you're a real Hot Rodder you put as many carbs and the Longest cam you can find on and in your engine. Np self respecting Rodder would be caught with a stock cam
 
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