Of course, the answer will be a generalization, as every specific combo will want the valve events to be "right", BUT....

Let's look at a car with a PG or a 700R4, where you would have a big RPM drop on the 1-2. Would a wide or narrow LCA cam work best in this application. Let's assume a mild (tight) converter that does not allow the shift recovery RPM to stay in a narrow range.

Just curious what the experts think.

wide lsa = wide powerband, tight lsa = narrow powerband. large rpm drop would like a wide lsa-I would think.

wide lsa = wide powerband, tight lsa = narrow powerband. large rpm drop would like a wide lsa-I would think.

I have conflicting thoughts... that is why I am posting this question.

While I agree with Badbob (flat torque curve is good for wide spread), part of me disagrees.

I also know that tight LSA cams are known for big torque peaks. If you drop down to near peak torque on a shift, I can't help but think that the tight LSA cam might pull harder in 2nd, as you will have more HP available at shift recovery rpm.

Which thought is right?

Generally a wider separation will have a slightly broader torque curve with less mid range torque all else being equal according to the book & this is what you would want.
The problem is it seems these engines do not always read the same crap we do :D

If the narrower lsa cam happens to make the best torque where you end up on a shift or close to it, then it would probably be faster. ;)

The cam needs to compliment the rest of the engine combination in both duration & separation which is why it is a good idea to discuss the cam with your favorite cam designer

On a manual trans car the rules apply but in a car with an auto trans the convertor can hide all sort of things. I know people that run 7000rpm convertors in SB glide cars and build the motor for a pretty narrow power band.

Most trans will keep the RPM drop in the 3000 - 3500 RPM range between gears. So LSA in regards to powerband width isn't really the issue. Driveability and how docile a motor seems is more of a function of LSA. A tight lobe center will have more overlap and naturally more topend and less bottum end power, but you can keep the motor in the powerband by shifting it accordingly.

My 402 motor has a 112LSA cam. Lope at idle but not radical. I have to shift 1-2 at 6000 to keep the 3000 converter fully engaged on the 1-2, but can shift 2-3 at 5500. Any less and it is a mute point because the motor only sees 3000+RPM under load.

Typed this on the fly, had to edit this.

Also, LSA will become important as the cam duration grows. I am sure to get some response on this statement, but I am convinced that on a stock/near stock (home ported/cleaned up) iron head - say a CC oval port; a BBC will respond better to an increase in duration as opposed to shear lift. Even though guys run .600 lift cams with stock heads, doesn't mean that a .520 lift cam with appropriate duration and LSA to manage overlap wouldn't have ran as good or better. Now if you go to aftermarket heads with raised runners and improved port flow, that is a whole new set of circumstances. But factory BBC heads have a certain range of lift and overlap that they work best. In my own experience, I have ran BBC's with 280 - 290 duration cams with 112 to 114 LSA and have good predictable results. The newer fast ramp cams that are down in the 270 range most likely need 110LSA to achieve any effective overlap.

As a comparison, I was advised years ago to keep .050 overlap to 10* or less for "civil" street manners [ie. 402 motor, auto w/ AC car.]. If you ever listen to engines that have a lopey idle quality, that 10* reference seems to be the point where the motor changes from lopey to radical.

Interesting. A quandry I've often pondered...

In fact, wish I could easily pop a 112 LSA version and a 108 version of the same cam in the 427 to see. Problem is, where do you put the ICL? Same, or to keep DCR the same? Point is, it wouldn't be a true apples to apples unless you kept the relative advance the same. Namely you'd be putting the cams on the same phasing diferential I suppose, and then leaving cylinder pressures unequal ( hence the 108 lsa version would show more peak torque ) and not hold everything equal as regards the powerband issue.

Untestable?

Anyway, have noticed that in a few race cam profiles, the "manual trans" version is often a bit wider. Hence my curiousity. Hypothesis is that in a clutch car without a squishy converter to "hide" or "mask" things,, a slightly wider powerband might be in order sicne you're likley using more rpm band than a typical strip converter would. Still think 110 lsa is a great compromise in a bbc. The mid range pull vs a 114 ( at least in a torque-challenged 427 hp motor) is quite different! :eek:

Although admittedly, the gearing was optimized for 1/4 mile just about the same time, and for the short time the 114 lsa cam ran through the 5 speed box, it felt like we had a 100 shot onbroard vs the old Muncie - honestly. so again. All else not equal.

I'd love to try it with 112 at the strip as well as 108 and see.

I would be in the Wolfplace camp - there are a lot of other parts of the combination that will affect the torque curve, like intake runner size and length, intake manifold configuration, exhaust system design, etc. I would consult a cam designer with your setup and performance requirements.

When we built the 331" motor for road racing, the cam designer recommended a 110° LSA, based on the driving conditions and engine design. This engine had a very broad power curve, peak torque at 4500, peak power at 6500.