Someone mentioned plug wire length being a timing factor on the older engines.

 

The lsx are not knock senitive!

I think one must take step back and think of what timing in reality is for.

The ignition advance is used to compensate for the "slow" combustion process in any engine.
The max presure from the combustion process should end at aprox 15 degrees ATDC.
Since it take time to burn the gas/air mixture, we must start the fire well in advance of the point where the max pressure should happen.

The igition advance in crank degrees is a way of measuring this "start the fire and let it burn" time.

What we (in theory) would like to se, is NO ignition advance before top dead center to get the pressure top at the right crank degres ATDC.

When more advance is needed to get the max pressure at 15 degres ATDC, that mean that there are more losses.
The losses that happen is heat loss due to that the flame is exposed to the "cold" metal for a longer time. More advance = longer time.

The other loss is that the piston will have to make it´s way up the bore, using energy from the crank to fight the increasing pressure from the combustion taking place for several degres of movement.

This show that what we rally want, is as little ignition advance as possible, to get max pressure at a certain point ATDC. (15 degrees)
This advance, max pressure at the right place ATDC, is called MBT timing.
(Mean Best Tourque)
Advancing the timing further give no gain, what will happen is that the losses start to mount up, and there will be knock soner or later, all to no use what so ever.

So to answer the question, the reason the LSx engines dont take so much igition timing before knock, is because the combustion goes so fast that large numbers in advance generate the pressure top at the wrong place, as measured in crank degres.

The Lsx engines don´t WANT a lot of timing advance.
The MBT timing numbers are low for this engine family (28 degrees@Wot typically) compared with Chevy SB and BB, this is because the combustion is quick and efficient.

Br//

 

Thanks Tahoe,(everybody else too) Thats the explanation I was Looking for. Now I have a better understanding of it..

 

The more efficient the cylinder head/combustion chamber design, the less timing it takes to make max power. I know that everyones setup is different, but there is a point where more timing does not equal more power even if you are not getting any knock, only generating more unnecessary heat. I tuned on a friends truck at the track, went from 29* to 32* and picked up nothing at all. I didn't get any knock retard but it didn't run any better.

 

Stock Z06s respond the same way. We bumped timing up to 30* and no power was gained. The LS6 heads only wanted 22-23* of timing for most power.

 

Yeah a lot of my "old schooler" buddies ask: "Why don't you run more timing than that, heck I run 36* on my 406!" And I say: "Well, you're not running a 15 deg cylinder head with an excellent chamber design either and these motors make power with less timing needed....period".

 

tahoe, as technical as that was I actually understood.. excellent explanation!