Lobe separation angles and the 300

[Walken100]

LSA discussions are new to me so I've been doing some research. At this time this is an academic exercise that will let me better understand some of tradeoff decisions when building my engine. Though there are lots of discussions with LSA included I was hoping to have more of an broad theory discussion relative to the 300 but not specific to engine build goals (high rpm, low rpm, turbo etc.) Then again if someone has a link they really like I'd love to read it. And if I missed a post during my search please let me know.

My baseline for this discussion is one of my early builds that used the cam below (just for fun). This was in a 350 Chevy and resulted in an engine with a nice lope at idle and nearly instant torque off idle as measured by my calibrated butt dyno. I was a fun street engine.



Looking at the cam card above I believe that the LSA was 112 degrees (on the "wide" side by internet standards). Are my calculations correct? Would this cam profile in a 300 have a similar effect?

Also I'm a little confused (the internet does that) so can we discuss LSA and specifically how it impacts a 300 engine build? Some of the items that I read go a little counter to what I understood. Other issues are just not understood. So in no particular order:

• A tight LSA helps the low/midrange torque but can create a rough idle condition. Accurate or oversimplified?
  • I always equated a rough idle to a cam that targeted power in higher RPMs. Something is going on here beyond just LSA I'm sure. Clarification?
• A tight LSA creates a "narrow power band". This doesn't feel accurate, thoughts?
  • The graph below is the result of testing a cam with different LSA's. The tightest LSA created torque and horsepower curves with the greatest area under the curves which, to me, implies a wide power band. Ok I understand that across an rpm range is probably a more common view of power band but….. Thoughts?
  • The chart and comment are from this article, https://www.hotrod.com/how-to/camshaft-shootout-lobe-separation-angle-tested-explained/

• It feels like overlap amount and overlap timing should be discussed more when talking about LSA. Am I missing something here? For instance in the model above cylinder pressure was highest with the tightest LSA but isn't the reality more of a function of valve timing. In other words by changing the timing of the events couldn't the cylinder pressure have been maintained even though the LSA's changed?
• Other LSA "impacts" that should be understood?
• Finally, for a 300, what is considered a tight/wide LSA?

Any input and discussion would be appreciated.

Sorry for the long post but this is now becoming interesting to me.

Bart

 

[aussie7mains]

IMO the LSA is academic only, the timing events are more important. However the LSA does describe the events. Do read up on this. A Graham Bells texts on this subject are very good, tuning 4 stroke engines is IMO one of the best. Another comment here is that long duration cams are trying to cover up poor breathing. For an engine designed to WORK, rather than speed, small overlap cams are what you want, somewhere around 30-40 degrees.

 

[Walken100]

Graham Bells

Dam, he is proud of that book. Prices started at $40 and went to $180. I have found one that only partially chewed by a Rottweiler for $15.... I'll keep looking. One of my buddies may have one.

long duration cams are trying to cover up poor breathing

Doesn't this describe the 300?

 

[pmuller9]

The cam card does not show the .050" duration which is what is needed to discuss overlap and power band.
Edit: The SSH-23 cam has 224 degrees of .050" duration and has a 112 LSA which yields zero degrees of overlap
What can be said is that the 300 six has much larger cylinders and will have less lope at an idle than a 350 Chevy given the same camshaft profile.
The 300 six is equivalent to the 400 V8 in cylinder size.
The engine displacement has a very large effect on camshaft profiles.
In general, the larger the engine, the more lobe duration and LSA is needed to get the same response as far as idle quality and power band.

As aussie7mains said, it is more about the opening and closing valve timing events and how they are affected by both LSA and lobe duration.

Referring to the 300 six only:
You will start to hear a lope at idle as the overlap period approaches zero from a negative value.
As the overlap increases positively past zero, so does the lope at idle
Again, the overlap period is a function of both the lobe duration and the LSA.
As the overlap increases the initial timing must also be increased.
The lope at idle is affected by the idle speed and some lope can be smoothed out by increasing the idle rpm.

For a given lobe duration, as you decrease (tighten) the LSA, the intake valve closes sooner and the exhaust valve opens later, both events lend themselves to increased low rpm torque.
The early closing intake valve increases cylinder pressure while the late opening exhaust valve allows the cylinder pressure to act longer on the descending piston.
If you have a tuned exhaust system that creates good scavenging it will help start the intake cycle early during the extended overlap period.
This is the condition where the tight LSA does not shorten the power band.

The discussion on lobe duration and LSA depends on the type of power band you need to get the job done.
As an example.
On the truck pulling engine, we decided it needed a lot of midrange torque and be able to pull to 6000 rpm.
We went with a solid lifter roller camshaft with a .050" duration of 237/247 degrees with a 106 LSA and .600" valve lift
It idles fairly smoothly at 1000 rpm and the ignition timing is locked at 32 degrees.
It makes a ton of torque from 1200 rpm to 5000 rpm and will pull to 6000 without the load of the sled.
It competed well against stockish big block V8s
The Promaxx cylinder head is the limiting factor at this point.
The engine broke the frame in the F150 and bent the frame in the F250 that it is presently in.

The stock car 300 six has a roller cam with 250/250 duration with a 108 LSA and .600 valve lift.
Very rough idle with power coming in abruptly at 3000 rpm and pulling to 6000 rpm.

For street stuff with small duration cam lobes, the 108 LSA cams do provide a very good midrange but require a lower static compression for pump gas.
The 110 LSA is good all around and the 112 LSA provides a good idle as lobe durations go beyond 220 degrees.
But again, it depends on the type of power band you need.

 

[pmuller9]

What do you need for a power band?

 

[Walken100]

As aussie7mains said, it is more about the opening and closing valve timing events and how they are affected by both LSA and lobe duration.

Let me test my understanding. So for a given LSA if I change the intake closing event to occur later but maintain the LSA I change the dynamic compression (decrease it)? I assume this decrease peak torque?

The engine broke the frame in the F150 and bent the frame in the F250 that it is presently in.

I would be upset but smiling at the same time. Did I mention I love torque.....

 

[Walken100]

What do you need for a power band?

Still determining that. While I'm doing the engine swap and a couple other items I'm trying to learn before I leap. Truthfully, the term I keep saying to myself is that I need to lean hard into the 300 torque potential. But I'm trying to keep an open mind until I learn a bit more.

 

[pmuller9]

Let me test my understanding. So for a given LSA if I change the intake closing event to occur later but maintain the LSA I change the dynamic compression (decrease it)? I assume this decrease peak torque?

No. The peak torque is determined by the Volumetric Efficiency at specific rpms.
That is a function of the camshaft, cylinder head, induction system and exhaust system combination.
For a given camshaft, the LSA is set so the only way to change the valve opening and closing points is to advance or retard the camshaft.
Advancing or retarding the cam simply teeters the torque curve around the center.

 

[Walken100]

No. The peak torque is determined by the Volumetric Efficiency at specific rpms.
That is a function of the camshaft, cylinder head, induction system and exhaust system combination.
For a given camshaft, the LSA is set so the only way to change the valve opening and closing points is to advance or retard the camshaft.
Advancing or retarding the cam simply teeters the torque curve around the center.

I said that wrong. If i replace the cam with a new cam with the same LSA but later intake closing what is the effect on dynamic compression and torque.

 

[pmuller9]

Still determining that. While I'm doing the engine swap and a couple other items I trying to learn before I leap. Truthfully, the term I keep saying to myself is that I need to lean hard into the 300 torque potential. But I'm trying to keep an open mind until I learn a bit more.

You will be looking at one of the hydraulic roller cams from Straub Technologies

 

[pmuller9]

I said that wrong. If i replace the cam with a new cam with the same LSA but later intake closing what is the effect on dynamic compression and torque.

By later intake valve closing you have to be referring to a longer duration camshaft profile.
That will move the torque curve and peak torque higher in rpm and in most cases will increase the peak torque but at a higher rpm.
The Promaxx CNC ported head makes great peak torque up to 4000 rpm so the torque will increase as you push it up to that point.
It is stubborn about pushing the peak torque any higher without a loss in torque.
It can be done using a custom intake manifold tuned to ram the intake charge at a higher rpm but what we really need is a better breathing head.

For your purpose, you probably are not worried about peak torque as high as 4000 rpm.

 

[Walken100]

By later intake valve closing you have to be referring to a longer duration camshaft profile.

I don't think so. I'm thinking about moving both the intake/ exhaust open and close events to the right in the diagram below equally. I may be suggesting something that is not likely but this is an "academic" discussion.

 

[pmuller9]

I don't think so. I'm thinking about moving both the intake/ exhaust open and close events to the right in the diagram below equally. I may be suggesting something that is not likely but this is an "academic" discussion.

View attachment 25336

That's what I was referring to in post #8

For a given camshaft, the LSA is set so the only way to change the valve opening and closing points is to advance or retard the camshaft.
Advancing or retarding the cam simply teeters the torque curve around the center.

It makes a little difference in the power band but nothing significant.
It does help the Dynamic Compression Ratio in respect to being able use a lower octane pump gas or the same octane with a higher Static Compression Ratio.

 

[Walken100]

That's what I was referring to in post #8

Ok, I'm a little slow on the uptake.... Got it. Thank you.

 

[pmuller9]

What type of job will this engine have to do?

 

[Walken100]

What type of job will this engine have to do?

Street/strip. Basically get my blood flowing and make my heart race a little. By "strip" I'm just looking to hit my local drag strip (about 2 miles away) and do some of their "Saturday Night" run what you brung stuff. Hit the hot rods and coffee once a week etc. Not worried about mileage, not a daily driver. The reality is that I want to reactive an previous hobby and have fun. Also I still like learning new stuff......

 

[pmuller9]

Automatic or manual transmission?
Two wheel drive truck?

 

[Walken100]

Automatic or manual transmission?
Two wheel drive truck?

C6 (for now) and a 63 Econoline van. As you can see I have a few months before it's on the road. Its getting the drivetrain out of a 95 Econoline. 4.9 and the C6.

 

[pmuller9]

Performance intake manifolds stick out a long ways from the head.
There isn’t much room in the engine box.
What are your plans for that?
I see you are also at 4700 feet in elevation?

 

[Walken100]

What are your plans for that?

Build a new box. I need to get the engine in place to pick my poison. The area behind the drivers seat is essentially unused and ripe to allow me to fit lots of stuff like a new plenum and electronics etc. Yes I'm at 4700 ft. In the future I'd like to do a turbo but I'm leaving that off the table for now. I'm trying to do this is "stages" so that it doesn't become a 10 year garage queen pile of parts. I refer to this as the "Craigslist" build. Trying to get mostly used stuff or fabricate stuff. Obviously some items like engine components will need to be new.