We all know (or at least think we do) that FI engines require us to run less timing to avoid detonation (assuming the fuel octane is not changed and nothing other than gasoline and air is in the cylinders). So how does GM run more timing in nearly all of the hi octane timing table for the LSA vs the LS3? See below.




LS3 Hi Octane Timing




LSA Hi Octane Timing




Differences


I'll concede that down in the high load low flow area the LS3 is running more stock timing but everywhere else the LSA is higher. In some spots >+20 degrees. The cylinder volumes are the same so the charge density should be close (one may run richer/leaner than the other). I know the LSA heads have the swirl wing in the intake but if it was this effective in preventing detonation then why don't they use them on other NA engines?

I know that more efficient heads typically require less timing to reach maximum output but I wouldn't think GM would design the LSAs to be less efficient as it was their highest hp engine at one time. I don't know, I am just having a hard time wrapping my head around this one. Any theories?

 

Look at the other adder tables and there you will find your answer...

Just because it says 23 doesn't mean that it necessarily is giving it that much. The IAT and ECT Adders are all over. Been a while since I have done a LS3 but do my buddies 11 V pretty regularly and do see first hand they can handle more timing then you would expect.

Doing my buddies stock car on pulls it was hitting in the mid 20's for timing with the stock tune, I didn't want to screw with that and played with the fuel a bit and picked up ~30whp.

Everything is always a little bit different.

 

The big difference is LS3 10.7:1 and LSA 9.0:1 or whatever it is. Those timing differences are huge! I wonder if the ZL1 has about the same map as the LSA?

 

Piston squirters!

 

I am pretty sure the difference in the cam will play a part also.

 

RAWR256,

Thanks for the input and these adders are more pronounced than I am used to. The IAT Spark Adder actually has positive numbers down in the area where the LS3 base timing was higher than the LSA so it further reinforces my question. See below:





LS3 IAT Spark Adder





LSA IAT Spark Adder





IAT Spark Adder Differences

IMO the Engine Coolant Temperature Adders are a wash. See below:





I was very surprised to see the positive IAT spark adders for the LSA. I am not sure why you would not just put this in the base spark table but I suppose it is likely related to how the ECM uses the Maximum Torque Timing Table.


LS3 ECT Spark Adder





LSA ECT Spark Adder





ECT Spark Adder Differences

 

Hank,

You are probably right (at least I know that it does play a role). I am just surprised to see this large a difference.

MR2,

Hell yeah! I am going to pull my engine now and add some squirters to get the free hp.

913,

Yeah I know cams play a role in timing but I would think not anywhere near these differences. I may be completely wrong about that but, well, that is why I posted this to find out what I am missing. Any more details about how the two different cam profiles would affect timing this drastically?

 

Your trying to compare two different motors, main reason the timing is so different.

 

Yes, I am very aware of that fact and thought most who responded would be as well. The reason I am comparing these two different motors is they have the same displacement and were released by GM in very similar time periods and utilize very similar engine management schemas (LS3 E38 ECM vice LSA E67 PCM). While there are numerous differences I was attempting to gain insight into one of the differences I observed in the tune. The ignition timing.

I am not trying to be an *** but if I am digging through the stock tunes from the different motors and state as much in my posts I likely know they are different motors. My question again is what DIFFERENCE in these two motors contributes to the vast difference in timing. I suspect that Hank hit the nail on the head when he referenced the differences in compression ratios. I just did not expect the static compression difference to cause that large a change in the timing.

Also, there has been a lot made of the swirl wing in these heads (e.g. http://www.corvetteactioncenter.com/..._pursuit6.html. I wonder if they contribute to the greatly advanced timing. I know this article states that you would lose power if these were used on an NA application but I wonder if that is only an anecdotal comment with no actual research conducted (e.g. actually putting these heads on an NA car and adjusting the timing then putting it on the dyno).

The reason I am so interested is that I am running these heads on my blown LS2 and it is taking gobs of timing. In many instances more the the V2. This is obviously with more static compression so while Hank is likely right it is not what I hoped to hear. Maybe there is just a ton of timing left on the table with the LS3 but that really would surprise me. Either way I am stumped as to why my car is taking all of this timing wo knock and gaining hp in the process.

 

I guess I should have been more detailed in my reply. Literally about the only thing the same is the displacement, so comparing them doesn't really do anything IMO. You can compare the tunes for GM for different vehicles with LS3's and they all have different timing, then look at one of their crate motors (Erod setups) and it will use a different ecm and run different timing again.

How much timing are you running at what boost level? What fuel? Are you tuning it on a load bearing dyno? Some setups can be very misleading on how much timing they will take or like, especially on an inertia dyno. The last 4 or 5 re-tunes I done that were boosted I made more power with less timing or the same power with less timing than they came in with but I am on a loaded dyno.