Camshaft lsa and low end torque

[user-23911]

To me, using the term LSA is a bit like using the word horsepower.


It's an average of 4 different and independent events, IO, IC, EO and EC.any average is meaningless in its self.
I only play with DOHC engines these days so IO and IC are related, EO and EC are related but LSA is variable. Cams are not symmetrical either.
When you're able to play with LSA you can change the overlap but you also change IC and EO.
Any change in LSA makes a large % change in overlap compared to the % change in the other events.


So.......when you change LSA, is it the change in overlap that makes the difference or is it the change in IC and EO that makes the difference or is it both?


Going a step further, with DOHC solid lifter cams you can also change the duration to an extent by changing the tappet clearance.
Not that you want to because it makes too much noise but you still CAN.

[kimosabi]

All I know is the next build, a 355, is going to be less stinky exhaust. Mike Jones, hope you still ship to Norway.

[MikeB]

The first thing I look at is how the engine is going to be used and what type of fuel.. Tight lobe centers are great. But if its a driver and you don't want your garage to stink like raw fuel when you get home. And your running 9.75 to 1 compression with 89 to 91 grade fuel. I have repaired a few knocking and stinking engines by removing short seat duration with tight lobe centers. keeping .050 duration at the same. And loosing a small amout of low and midrange. But pulls much harder on the top end.. No more knocking or stinking garage. I'm talking about street cams in the range of 212 up to 240 at .050 that was in the range of 106 to 110 lobe center. Adding more seat timing and moving the center to 112 to 114. Cranking compression would change from 220 to 180.

Again, lower cranking pressure is a function of ICA, whether or not LSA is also changed. I mean, you could simply retard the cam 2-4 degrees to reduce cranking pressure, and LSA would not change.

[user-23911]

Cranking pressure is a function of Intake closing point, nothing else.

[statsystems]

Cranking pressure is a function of Intake closing point, nothing else.

And starter speed. Cranking compression means nothing.

[77cruiser]

What if you just let the cam float, so it can be what it wants to be?

[hoffman900]

Cranking compression is meaningless in regards to cam design. It’s only use is a diagnostic tool from a known baseline. There was a great thread here with a lot of gems from Harold Brookshire, Mike Jones, and Clint Gray.

https://www.speed-talk.com/forum/viewtopic.ph ... 6923846d6c

[ajbeng]

Resurrecting an old thread, regarding LSA torque V peak power how does it work for instance if you had a
Longer duration can say 280 @.050 but a tight LSA of 102 deg with the cam timed in at 100-101 deg rather than a more conventional 106 LSA & 106 deg timing? Would it be possible to compensate at all & give torque and power increases or produce a cam that doesn’t really work? I know it’s a lot of ifs or butts!

[Tom68]

Resurrecting an old thread, regarding LSA torque V peak power how does it work for instance if you had a
Longer duration can say 280 @.050 but a tight LSA of 102 deg with the cam timed in at 100-101 deg rather than a more conventional 106 LSA & 106 deg timing? Would it be possible to compensate at all & give torque and power increases or produce a cam that doesn’t really work? I know it’s a lot of ifs or butts!

Would have thought that would put you outside of practical limits.

If that was on a 350 your idle would need to be 2000 RPM, what do you call low end torque ?

[ajbeng]

More of a fast road, mild race engine

[Chris_Hamilton]

I'll add another noob type question. Why is it that in general smaller displacement stuff (2 valve) have tighter LSA's than bigger displacement stuff? I've noticed a lot of performance type cams for small displacement engines will be in the 99-103 LSA range, while rarely will you see anything tighter than 106 for most American V8's. Is this simply a result of the amount of overlap required by a smaller engine to make good power? Again forgive my ignorance.

[Tom68]

I'll add another noob type question. Why is it that in general smaller displacement stuff (2 valve) have tighter LSA's than bigger displacement stuff? I've noticed a lot of performance type cams for small displacement engines will be in the 99-103 LSA range, while rarely will you see anything tighter than 106 for most American V8's. Is this simply a result of the amount of overlap required by a smaller engine to make good power? Again forgive my ignorance.

Smaller displacement with smaller cams ?

Ignore the LSA and look at what they are trying to achieve, once you understand that and see the valve events required then you can look at the LSA.

The only time you'd use LSA in the selection process is if you picked a cam based on the intake and exhaust duration, say you're hell bent on 210 intake 230 exhaust, if it's with a stock converter on a mid size motor you're going to want something like 120 LSA to make it useable. If it's going in your manual track car and you don't want to rev it you might pick 106.

[BLSTIC]

Also notable, overlap might get you good scavenging and torque, but at less than full throttle you've also got a good path for reversion and reduced efficiency at part throttle.

[Chris_Hamilton]

I'll add another noob type question. Why is it that in general smaller displacement stuff (2 valve) have tighter LSA's than bigger displacement stuff? I've noticed a lot of performance type cams for small displacement engines will be in the 99-103 LSA range, while rarely will you see anything tighter than 106 for most American V8's. Is this simply a result of the amount of overlap required by a smaller engine to make good power? Again forgive my ignorance.

Smaller displacement with smaller cams ?

Ignore the LSA and look at what they are trying to achieve, once you understand that and see the valve events required then you can look at the LSA.

The only time you'd use LSA in the selection process is if you picked a cam based on the intake and exhaust duration, say you're hell bent on 210 intake 230 exhaust, if it's with a stock converter on a mid size motor you're going to want something like 120 LSA to make it useable. If it's going in your manual track car and you don't want to rev it you might pick 106.

Plenty of old Datsun/Nissan L motors used cams with 99-103 LSA and are revved to 8000 or beyond. Stock LSA for an L-Series (4 or 6) was 109.

Here are some cam specs from a popular current Japanese manufacturer. All with what is considered very tight LSA's on this forum. Text is in Japanese but scroll down you can see the valve events (@1mm) and LSA.

280 advertised Duration
http://www.kameariengineworks.co.jp/tor ... 230618.pdf

292 advertised Duration
http://www.kameariengineworks.co.jp/L-7 ... 230528.pdf

300 advertised duration
http://www.kameariengineworks.co.jp/tor ... 230618.pdf

308 advertised duration (this cam is used with several JDM Z's making 360+ hp from 3.2 litres, and revved to 8000 or more.)
http://www.kameariengineworks.co.jp/L-7 ... 230528.pdf

Why I'm asking if LSA is just an incidental number resulting from overlap needed.

[Tom68]

Had a couple of L series, 4s and 6s.

Revved to 8000, made power to ?

Still got the books.

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