This video explains much of the reasoning and importance behind selection of the LSA for your cam. It's a little repetitive and can seem rambling but really good info. It presents a formula from DV for selecting the proper LSA for greatest torque and HP.
It is my guess that Straub also uses this formula.
You can jump to 28.44 if you just want to see effects on a chevy 350.

 

Interesting......I have a lot of stuff ground on a 108....years ago it worked great in any small block we ever dyno'd.....my own 406 has an ancient 292H Magnum ground on a 108......from 110.....sounds better too......

Jebby

 

My cam is ground on 110 Jim dowel at racer Brown thought in my application that was the best compromise for performance and still being able to run the power brakes and vacuum headlights was about what we were safe with. I'd have to say he nailed it.
Always remember the application maters, peak torque and horsepower may be great on a Dyno but real life has compromises.
That's why I went with Jim, he has been specking cams for about 50 yrs and then grinds it himself. And he dresses the grind stones after each cam.
I guess what I'm getting at is there is a lot more to cams than we normally think.

 

Very true.....I went 108 on mine because it is a 400 inch engine.....I have 244@.050 and still pull 11 inches of vacuum....

Jebby

 

I run a 108 LSA on my 350. 10" is the least vacuum I see. Everything works fine on 10" of vacuum. I've had the 108 for 10 years. It works great and is somewhat explosive in the way it delivers power, which I like. Plenty of fun.
It's important to manage the overlap period. So a reduction in duration may be neccesary. With how good heads are now it's not even a penalty to do so.
As the video pointed out, the intake valve events with the proper LSA creates more cylinder pressure. That's torque.
The proper LSA also allows for carrying the RPM. That combined with the additional torque creates additional HP.

 

I've listened to that clown before. He gives up 20* of duration to keep a certain overlap? Overlap is a by product of the correct lobes.

You can manipulate LSA in several ways with duration, ICL and ECL, lobe shape (symmetrical/asymmetrical).

I would never select a cam based on LSA first.....his tests just move LSA around with a given set of lobes. Just changing one of the lobes completely negates the whole concept.

Vizard has some good testing and this hack is stealing his stuff and making some of it his own. Even the screen shots are David's. David has done a lot of head and cam and dyno testing and has a very strict concept of how he likes to do things. Of course with most things...there's more than one way to get things done and I don't necessarrily subscribe to much of his stuff...but it IS interesting and I can learn from it. This guy...not so much.



And nope...Straub doesn't do it this way.

JIM

 

Yes most of his screen shots are from Vizard. He seems to be a strong supporter of vizard. I didn't get the feeling he was stealing his work, but supporting it.

I didn't get the impression that LSA was the first criterion so much as it's an important one. As is overlap in a street driven car. When I chose a cam I went with overlap then LSA and then duration. This is for a street driven car needing some level of vacuum for brakes and accessories. I am willing to give up duration to manage the overlap due to good head flow.
It was similar to what Vizard teaches from a different perspective is how I took it. Vizard can sometimes be very dry and hard to extract the pertinent info from, at least in his video's. In his books Not as difficult and more to the point.
What method do you use, if I may ask?

 

Agree, it's the total package but some things are too often overlooked. I'm not at all convinced that modern lobe designs are the be all end all things they are made out to be. No one single thing dictates if a cam is good or not.

 

I look at a LOT of things. But having an idea of what duration it's going to take to get the RPM range I'm looking for with the selected heads is where I start. The better the heads for a given HP/RPM range I can drop duration somewhat. BUT..I can always push the RPM some and make more HP if that's what I want. Of course worse heads....will take more duration typically to get the same RPM range. This is where you have to really determine what RPM range the heads can support on the selected cubes. Might be better off with a smaller engine and a little more RPM..or less RPM on more cubes. Gotta narrow all of that down first.

Then you look at lift required for the selected heads to get the airflow you need. If the desire is 500 HP....then there's X airflow required. You have to get lift to allow the needed airflow and ideally you're timing it to the piston movement so you get max airflow at the point of highest piston speed away from TDC. Stroke and rod length gets in there now as it will place that point at different points of crank rotation which relates to where you want the ICL...but again...different lobes might have similar durations...but different shaped lobes. Finding info on lobe shape is tough without a Cam Doctor printout but you do the best you can.

Then you look at exhaust the same way....but it's a little easier. You don't need as much lift on exhaust side....it's all about opening it at the right time. The exhaust really wants out when you crack the valve...and then you have a piston pushing it. But opening too early hurts TQ....too late introduces pumping losses.

Selecting those cam positions pretty much selects the LSA for you and thus overlap.

Now you CAN rock things around a little with LSA....but HOW you do it can vary. Did you change ICL or EX? Or both?

Vizard makes a good discussion about valve curtain area. Larger intake valves are more susceptible to reversion issues and overlap. Just something you have to be aware of.

WHERE restrictions are also matter. I was fortunate enough to spend a lot of time with Billy Godbold when he was at Comp while designing a cam for a magazine project. Very interesting data to demonstrate how to manipulate things based on where the restriction occurs. For example...a large carb on a restrictive intake has no choice but to add intake duration if you want to increase RPM/power and crutch the poor intake. Small carb on a good intake/heads (think old NASCAR Busch 390 CFM engines). In those cases they can use relatively small cams to "pull" hard on the small carb and make it flow a lot more than you think. With the carb as the restriction you're limited....so you pull on it hard.

Same concept on exhaust. Is the restriction at manifolds right at the port...or further downstream? Vizard actually does good work there too with his discussions of the type of muffler and where the muffler is placed etc and how the engine responds to the pulses in the pipes...which change how overlap effects the engine.

And don't even get me started on DCR stuff. Yes it's real...but the calculations are very general in most cases and have no way of accounting for actual engine efficiency..they just insert a number. I can easily build a 13 to 1 street motor that will run on pump gas with a huge cam.....but eventually...IF the engine is capable of revving high enough.....the cylinders are going to get very full and then detonation will set in. Good heads/intake tract will make it happen earlier. Poor heads will happen later or maybe not at all. Crower actually designed some cams to lower DCR to make musclecar engines run on pump gas.....but they were dogs. Think again of those 9.0 compression Busch motors...you better have GOOD fuel in them because those heads DO flow well!

I've also tested some back to back cams on the dyno. The tight LSA stuff made good TQ and then ran out of steam after peak HP. Similar to what the video showed. If you're running something hard and want it to carry RPM past peak HP and not fall off a cliff....you have to get cam in place to do it. If it's a 5500 RPM deal that will never get to 6000...the tight stuff can feel good. But again...it's not just LSA. It's the selected lobes, heads etc. I've got some engines running around with 107-109 LSA's and relatively small duration lobes that are very streetable and will also pull hard up top and not fall off due to good heads. I did a 528" pump gas Hemi with a 108 LSA and smaller lobes to make it pull like the owner wanted...but it's also a Hemi...so the heads will carry it to higher RPM. For a Hemi..it's a TQ monster..whereas they usually aren't. It peaks around 6100 RPM but doesn't lose much of anything at 6700.

Another thing to think of...if you want power to hang on after peak HP and not drop off....you need good exhaust ports, headers and proper cam.

Heck...my 8-71 blown 408" Clevor Ford engine is using a 106 LSA cam...which everyone just knows is no good for a blower!! LOL.

Cam stuff is fun! We could keep going for hours!

JIM

 

"Modern lobes" is the cool thing these days....but what I've seen is a lot of designs being pushed to the limit as far as longevity/noise/valve control. There's a reason they call them "Xtreme" etc.

Way too many folks complaining about noise with their new cool hyd roller cams. The ONE thing a hyd street cam should do is be quiet. If it's going to make noise I might as well put a solid cam in it. This is especially true with flat tappets. Pushing a flat tappet to the edge is asking for trouble.

I would take great heads over a more aggressive cam any day. The "old school" cams had softer ramps and were a lot easier on parts. Some of the best cams I've used are made with very old lobe designs. The best one in my 555 while N/A was an ancient Engle design. I also have an old design Crane we call the "magic cam" as it's proven to beat much more radical cams with up to .100" more lift and not destroy parts like the other did. I've got some favorite Crane flat tappets that just work great. Also use some Crower circle track cams in small blocks with stock type heads.

So can a "new style" cam make more power? Absolutely...but at what cost? The LS stuff has advantages of having a huge cam lobe size, short pushrods etc that all helps stability.

JIM

 

OMG!!!! Thank you! All the words I have wanted to put together and could never do........this is exactly the school of thought I was taught by the master builders.......the DCR deal I was just explaining to a member via PM two days ago.....
The reason the LSA video is nothing more than interesting is it places a set pair of cam lobes at different LSA's....which is something nobody would ever use as a tuning tool.....it doesn't track as the lobes determine LSA and not the other way around......
I put my own cam on a 108 from a 110 book spec as I felt it would work better and it does.......but would I do this on a 350 with **** heads? No.
There is a fuzzy logic to engine design, you need to be able to "see" the combonation.......and although I am fairly well versed now in creating combos.......there are many who are much better than me......but they are better though experience.....

Jebby