Vizard on 106* LSA vs 112* LSA in a BBC

[GARY C]

... NO exact LSA will always be best even on same size and brand motor due to different needs or usage.

Actually, size, brand, needs have very little to do with LSA.
LSA really doesn't do much. Its terms used for manufacturing or checking a camshaft. The valve events, themselves, are what defines the real relationship; the openings and closings and ramp rates.

To me, LSA is not a design criteria, its a calculation from the timing events, and a manufacturing criteria. But I dont want to start that discussion, for fear of missing out on all the conversations, if I cant check the site.

So, I will just simply talk in terms of the relationship of the intake and exhaust lobe (LSA). LSA is the relationship of the intake lobe to the exhaust lobe, and that is not a design criteria, brand criteria, or usage criteria. It is based on the inlet and outlet parameters and their relationship to the displaced cyl volume within the intended rpm criteria.

In general, a restrictive motor (defined as a limited flow capability in comparison to the displaced cylinder volume and very high port velocities) do not require early exhaust valve activity. Therefor LSA will trend narrower. The real answer will be driven by E/I system relationships.

An unrestricted motor (defined as a LESS restrictive flow capability in compariosn to the cylinder volume and decreased port velocities) will trend towards earlier exhaust valve activity. Therefore the LSA will trend wider. Once again, the actual answer is a function of the inlet and exh systems and the cylinder geometry.

A motor that unrestricted in lower rpms, can become restricted at higher rpms.

ITs all relative, narrow for one combination, may be wide for another.

I like post like this, it's starts out telling you there is no purpose or design and then finishes by telling you what purpose it was designed in for.

[kimosabi]

So do cam grinders decide to go for a given lobe center or is the lobe center just a result of valve events, ramp design, lift and duration? I mean you don't have alot of space to work with.

[hoffman900]

So do cam grinders decide to go for a given lobe center or is the lobe center just a result of valve events, ramp design, lift and duration? I mean you don't have alot of space to work with.

You had both Mike Jones and Harold Brookshire say it’s just a result. Go the beginning. Harold probably is/was the most decorated person to post here in terms of race wins and accomplishments. Mike certainly is not far behind.

[swampbuggy]

The way i see it in my limited mind on this L obe S eperation A ngle discussion is, the camshaft designer designs the intake lobe for the best overall performance for the intended usage. Then he designs or chooses an exhaust lobe for the application the same way. He then decides on the LCSA (Lobe Centerline Separation Angle ) between the Intake lobe and the Exhaust lobe on a given cylinder (all cylinders the same) to increase (or) decrease the amount of overlap (degrees of crankshaft rotation between when the Intake valve leaves its seat and the Exhaust valve touches its seat. Is this somewhere close to correct thinking ? Learning and wanting to learn a LOT more! Mark H.

[rfoll]

If you really want to throw a monkey wrench into the discussion, start talking about fuel economy and part throttle performance. The OEMs live in this realm with a close eye to emissions as well.

[kimosabi]

So do cam grinders decide to go for a given lobe center or is the lobe center just a result of valve events, ramp design, lift and duration? I mean you don't have alot of space to work with.

You had both Mike Jones and Harold Brookshire say it’s just a result. Go the beginning. Harold probably is/was the most decorated person to post here in terms of race wins and accomplishments. Mike certainly is not far behind.

My fault for not reading from the start. I know Mike Jones' work. I have one of his cams spinning in my car. Purrs like a kitten around town when cruising but brown pants at WOT.

[hoffman900]

If you really want to throw a monkey wrench into the discussion, start talking about fuel economy and part throttle performance. The OEMs live in this realm with a close eye to emissions as well.

Harold mentioned this was part of the success of Buddy Baker’s Daytona 500 win that he did the cam for. Watching the race, it’s clear that car has a buttload of power too. Harold also did Benny Parson’s Daytona 500 winning cam, and some endurance racing leaders / winners as well (12hrs of Sebring, 24hrs of Daytona). He was also doing the cams for the Dodge NASCAR Truck engines in the middle/late 2000s.

https://m.youtube.com/watch?t=8293s&v=QX5zEETRjN0

I’m sure Mike could talk about his experience with the Indy Car, NASCAR, and 24hrs of Daytona cams as well in regards to fuel mileage.

Fuel mileage is just as important in those worlds as outright speed and the wrong cam centers can cost you dearly.

[GARY C]

So do cam grinders decide to go for a given lobe center or is the lobe center just a result of valve events, ramp design, lift and duration? I mean you don't have alot of space to work with.

If you end up with the correct cam does it matter where you started from?

I have seen 3 different methods presented on ST and they all end up with basically the same cam, the one constant is that regardless of the method it takes experience with that method to apply it.

[MadBill]

A few years back there was a planned cam shoot-out reported here on S/T between David Vizard and Mike Jones. I never saw detailed result, but I understood it was pretty much a draw...

[hoffman900]

The test was never done because it was said the specs were pretty close and wasn’t worth testing. Mike was going to grind both cams anyway.

I think David’s rules of thumb work very well for the applications they are intended for. It doesn’t teach you about cam design however and will not work for other platforms (multi valve, smaller (or extremely large) displacement racing engines, rules restricted applications, limited p-v clearanc, etc). Designers like Mike and Harold have to / had to know how to pick a cam out for all types
Of uses and platforms. If you have a typical street/strip type build, then all the power to you. That’s what most are building anyway.

Another thing with David’s techniques is it assumes a symmetrical cam. Guys like Mike and Harold (RIP) can put the valve just about anywhere (with limitations) and right where they need it because they are actually designing the lift curves.

Do I think David is capable of it? Absolutely, he’s worked with a lot of platforms. I also hope he writes more technical articles about a wide range of applications and to stop coming up with silly rules of thumb for one boring subset of the automotive world.

[gregsdart]

One thing i notice from some of the responses in this thread are some guys aren't taking into account things like the differance between single and dual pattern cams in relation to lsa. To keep the overlap, intake events and exhaust closing the same, take the difference in duration between intake and exhaust, divide that number by four, and that is how much wider the lsa on a dual pattern cam with more exhaust duration needs to be. I ordered a cam from a well known cam designer a while back, and it came with a 114 lsa. I run a bb mopar with 15/1 compression. My first thought was it is too wide! Well, when you ask a guy to cut a cam for you, trust him even if YOU think the numbers look off a bit. You would think that a 114 lsa cam with very similar duration numbers would lose a significant amount of overlap, right?
Not so when i started to measure the duration and lift per degree of VALVE LIFT between cams. Things i didn't think about were the differance in running lash, (19vs 28!) Lobe design, change of rocker ratio. My cam guy needed that 114 lsa to keep the true overlap duration and flow potential where he felt it needed to be. Even with a wider lsa and the cam card duration being close to that of the old cam, there was significantly more area under the curve at overlap.
Guess what? My car picked up more than enough power and reduced et to make me very happy.

[GARY C]

One thing i notice from some of the responses in this thread are some guys aren't taking into account things like the differance between single and dual pattern cams in relation to lsa. To keep the overlap, intake events and exhaust closing the same, take the difference in duration between intake and exhaust, divide that number by four, and that is how much wider the lsa on a dual pattern cam with more exhaust duration needs to be. I ordered a cam from a well known cam designer a while back, and it came with a 114 lsa. I run a bb mopar with 15/1 compression. My first thought was it is too wide! Well, when you ask a guy to cut a cam for you, trust him even if YOU think the numbers look off a bit. You would think that a 114 lsa cam with very similar duration numbers would lose a significant amount of overlap, right?
Not so when i started to measure the duration and lift per degree of VALVE LIFT between cams. Things i didn't think about were the differance in running lash, (19vs 28!) Lobe design, change of rocker ratio. My cam guy needed that 114 lsa to keep the true overlap duration and flow potential where he felt it needed to be. Even with a wider lsa and the cam card duration being close to that of the old cam, there was significantly more area under the curve at overlap.
Guess what? My car picked up more than enough power and reduced et to make me very happy.

All that is addressed in Vizards 128 threads and his writings.

[hoffman900]

Billy Godbold talkes about centerlines at the 30:00 mark: https://www.youtube.com/watch?v=whmOxK4XDYQ

[pcnsd]

Billy Godbold talkes about centerlines at the 30:00 mark: https://www.youtube.com/watch?v=whmOxK4XDYQ

Thanks Bob. It was an interesting almost 2 hours. Bob Godbold starts at about 18:48 for those that would like to skip the preparation, some of which is interesting. Trying to understand camshafts has been a struggle for me. This helped, but still leaves me wishing for greater clarity. I subscribed to channel and went looking for other Bob Godbold videos. I found several, but will need to consume them on a weekend.