I cant agree more, get the email tune and AKM cable so you can administer them yourself as many times as you need.

-Dustin-

 

Yeah, the idea that a narrower LSA makes more bottom end is not accurate. But the problem in talking aboiut any of this stuff is that to isolate the effect of changing any one cam design spec would require changing nothing else, which would be an interesting experiment but without much real world applicability. Changing LSA will increase overlap, but if the ICL (intake center line) is left the same it will also have the effect of advancing EVO and EVC (exhaust valve open and close). So, things can get difficult to analyze pretty quickly.

Without a long dissertation on cams, maybe the best way to sum it up is as follows. For any cam duration, there is an "optimal" LSA for producing maximum power. If you look at the specs of small block race cams, you will see that the LSA's are as low as 106 degrees, though most often a bit higher. Some race cams have an LSA as large as 114 degrees though. So, what gives? It has to do with the duration as much as anything else. As duration increases, LSA must increase to avoid huge increases in overlap. Also, the optimal LSA for peak power will give a very narrow power band. Take a look at the drag race section for SR SBC cams in the CC on-line catalog at http://www.compcams.com/Technical/Cu...ML/128-169.asp.

For example, look at CC 312AR-7 and 313R-6. The duration for these are 312/322 and 313/322 and the LSA's are 107 and 106 degrees respectively. That would be about an "optimal" LSA for a race cam with this sort of duration. Now look at 318CER-14. The duration is 318/339 and the LSA is 114 degrees. So how is it that I say wider LSA makes a more streetable cam? Well, the approx. overlap for all three is ~100 degrees. The LSA is widened to compensate for the longer duration. Look at the catalog and the rpm ranges and cam specs and you can learn a lot. The outiers from the general trends you will see are special purpose cams.

Now, these race cams have HUGE overlap compared to a street car. That, plus the duration is what makes them "hi-rev" cams. A difference of 2 degrees, as talked about here, won't have a huge effect but it will be pretty much as I outlined: more low end with a wider LSA and lower peak hp and a lower (and broader) rev range. But the "optimal" overlap for a cam in range being discussed here would proably be less than 106 degrees due to the short duration. When you started to get down toward that area is where you see a dramatic effect of changing the LSA.

Rich

 

To add on to all of this.....

In terms of LSA it's really only a byproduct of the proper Intake Centerline (ICL) Exhaust Centerline (ECL) and overlap area. I don't really think that the LSA has a horrible amount to do with the flattness of the TQ curve although in some circumstances it does play into that. As far as low end a top end power I've seen lower LSA cams (with the same duration specs) make less low end power than a higher LSA cam.

Mindagames article from Vizzard is good. The one thing that should really be looked at is the ICL rather than the LSA. A lower ICL number means that the cam is closing the intake valve earlier (for the same duration) which will increase dynamic compression and usually improve TQ numbers. The placement of the ECL doesn't have to be dependant on the ICL, this becomes very useful on non natrually aspirated motors.

The rule that a tigher LSA vs. a narrower one to be on the safe side has always been a good idea. Some situations are very tricky when it comes to the proper overlap area, especially on street cars where max power and very good streetability are needed.

Shooting for a certain overlap area based on cylinder head design and RPM range of the motor will always help get you the right LSA for a cam. Overlap area is much more important than the LSA. I've had strong LT1 cams with both 114LSA's and 108LSA's it just depends on the application. The LSA itself really doesn't mean squat.

The whole biggest cam I can get in a car is never something I like to see because the additional 5hp a "bigger" cam can give you could be trading off 20 ft lbs at stall and just kill the performance of the car.

Bret