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MOTORHEAD 02-06-2019 07:56 AM
Lsa
 
All other specs being equal, what would be the power difference between cam lsa's of 112 deg and 108 deg ?

cycleguy55 02-06-2019 11:17 AM
Quote:
Originally Posted by MOTORHEAD (Post 1457823)
All other specs being equal, what would be the power difference between cam lsa's of 112 deg and 108 deg ?

LSA at a Glance

Narrower LSA:
  • Moves torque to lower rpm
  • Increases maximum torque
  • Narrow powerband
  • Increase chance of engine knock
  • Increase cranking compression
  • Idle vacuum and quality is reduced
  • Valve overlap increases
  • Decreases piston-to-valve clearance
Wider LSA:
  • Raise torque to higher rpm
  • Reduces maximum torque
  • Broadens powerband
  • Decrease chance of engine knock
  • Decrease cranking compression
  • Idle vacuum and quality is improved
  • Valve overlap decreases
  • Increases piston-to-valve clearance

Source: https://www.hotrod.com/articles/cams...ted-explained/



More: https://www.enginelabs.com/engine-te...-relationship/

MOTORHEAD 02-06-2019 06:01 PM
Thanks Brian, for some reason The "Search" button in my head was "inop"
today !!

Ted

Gaz64 02-06-2019 09:08 PM
Quote:
Originally Posted by cycleguy55 (Post 1457834)
LSA at a Glance

Narrower LSA:
  • Moves torque to lower rpm
  • Increases maximum torque
  • Narrow powerband
  • Increase chance of engine knock
  • Increase cranking compression
  • Idle vacuum and quality is reduced
  • Valve overlap increases
  • Decreases piston-to-valve clearance
Wider LSA:
  • Raise torque to higher rpm
  • Reduces maximum torque
  • Broadens powerband
  • Decrease chance of engine knock
  • Decrease cranking compression
  • Idle vacuum and quality is improved
  • Valve overlap decreases
  • Increases piston-to-valve clearance

Source: https://www.hotrod.com/articles/cams...ted-explained/



More: https://www.enginelabs.com/engine-te...-relationship/
I think these two are mixed up back to front. I agree with the rest.

Gary

blykins 02-07-2019 05:21 AM
I think it all depends on the application and engine. For the most part I've seen a tighter LSA make more torque, but a tighter LSA also can increase overlap, which decreases vacuum, etc.

You can't really make a generalization though that changing from a 112 LSA to a 108 LSA will get you this, that, this, and that. It doesn't work that way. It all depends on the displacement, cylinder heads, intake, rest of the cam specs, etc. You can generally say that changing nothing else, going from a 112 LSA to a 108 LSA will increase overlap, which will decrease engine vacuum, and could make the engine inefficient.

A couple of random notes....

I run a 119-120 LSA on my pulling truck engines that need to pull hard up to 8500-9000 rpm.

On a small displacement engine with a big fat intake port (think 351C or 427 Tunnel Port), a tighter LSA is necessary to make big power at all. It's not because we're trying to juggle horsepower or torque curves, but we need overlap to scavenge the intake charge.

MOTORHEAD 02-07-2019 08:03 AM
Thanks to all for your input. The Hot Rod tests show the basic differences I was wondering about.
Now for the rest of the story:
When I built this engine I was camming it for Webers, and asked Barry Robotnik for his opinion and he got me a Comp hyd roller with 112 LSA, which worked well with the webers, but I had what turned out to be a sealing problem at the port head/intake junction. As a last resort,I took off the webers and manifold and installed the original holley and manifold, and it runs just fine, been using that set up for quite a while with no problems, just wondering if I was losing power by keeping the "weber" cam with the 4 bbl set-up.

blykins 02-07-2019 08:14 AM
Hot Rod tests on a SBC don't reflect everything....

blykins 02-07-2019 10:39 AM
Quote:
Originally Posted by MOTORHEAD (Post 1457876)
Thanks to all for your input. The Hot Rod tests show the basic differences I was wondering about.
Now for the rest of the story:
When I built this engine I was camming it for Webers, and asked Barry Robotnik for his opinion and he got me a Comp hyd roller with 112 LSA, which worked well with the webers, but I had what turned out to be a sealing problem at the port head/intake junction. As a last resort,I took off the webers and manifold and installed the original holley and manifold, and it runs just fine, been using that set up for quite a while with no problems, just wondering if I was losing power by keeping the "weber" cam with the 4 bbl set-up.
Too many variables to say. You'd have to pick apart each cam timing event separately.

I will say this: camshafts revolve around overlap. If you have too much overlap for a given displacement/cylinder head/rpm combination, then the engine will be terribly inefficient and power will be lost. Hydraulic rollers for large displacement engines typically have large advertised durations, which increases overlap. Going to a shorter LSA may hurt things. Just depends on the entire combination and the camshaft specs.

There are no general rules.

cycleguy55 02-07-2019 11:00 AM
Quote:
Originally Posted by Gaz64 (Post 1457862)
I think these two are mixed up back to front. I agree with the rest.

Gary
Check the charts at the linked article. https://www.hotrod.com/articles/cams...ted-explained/

LSA Torque
101 493.9 at 4,400 rpm
107 487.1 at 4,600 rpm
113 472.4 at 4,700 rpm

blykins 02-07-2019 11:12 AM
Articles like that turn me against the internet LOL...…

Making a general statement that a 112 LSA will have plenty of vacuum and make everything work well with EFI is just a gross overgeneralization.

My 7500 rpm hydraulic roller dyno mule FE had a 114 LSA and wouldn't have enough vacuum to do squat. It all depends on the combo.

cycleguy55 02-07-2019 11:34 AM
Quote:
Originally Posted by blykins (Post 1457886)
Articles like that turn me against the internet LOL...…

Making a general statement that a 112 LSA will have plenty of vacuum and make everything work well with EFI is just a gross overgeneralization.

My 7500 rpm hydraulic roller dyno mule FE had a 114 LSA and wouldn't have enough vacuum to do squat. It all depends on the combo.
Agreed. Complex subjects can rarely be explained by simplistic tables, much as complex problems are rarely fixed with simple solutions.


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