[PRAY]

I am personally seeing higher flow numbers with my LT heads than my LS3 heads. The exhaust on the LT can be out done by a hair by the LS3 head. The only difference is up to about .300 lift where the LS3 can flow a hair more on the intake due to the 2.165" valve in the LS3 vs the 2.130" intake valve in the LT. But I have them very close down low. My LS3 head flow matches my LT head but at .100" higher lift. So I am seeing 370cfm at .600" in my LT head and 370cfm at .700" in my LS3 head. This is also comparing my STG 1 head. I just finished up STG 2 heads but haven't had a chance to get them on a car yet.

The problem lies with the LT's 2.130" valve. You can only cram so much air past a certain size valve no matter what you do. That doesn't necessarily mean you are power limited with the smaller valve but that gets into a whole other discussion of static flow on a flow bench vs the dynamic flow of a running engine and how cam specs effect the ability of an engine to process air. Considering the camshaft's VVT ability in the LT and not in the LS3 (L99 has VVT) we can do more to create bottom in power numbers to make the car faster. The L99 can even that up if done correctly.

Another consideration when comparing the two heads is dry flow vs wet flow. The LS3 head has to deal with flowing and mixing fuel above the valve where the LT head that isn't a consideration.

I will say that the LT head with a ported MSD attached out flows the ported LS3 head with the stock ported IM attached. There were no discernable gains for the LS3 with a ported FAST 102 over the ported stock LS3 IM.

As noted, the LT valves are swapped/flipped which creates unique difficulties for the LT head to get them right. All you have to focus on is getting the air to the outside of the hook wall and maximizing the usable diameter of the smaller valve. The LT casting is very thin in some very critical areas that limits their potential. I would love to see what a 2.165" valve would do in a LT head. I really wish GM would have gone with taller valve covers and longer valves to raise the valve pocket another .200". That would have been awesome.

I have made over 580rw with three different A8 combos SAE with the LT motors so far. I have two M6 cars over 580rw as well. That is with the benefit of E85 though. Put the LT and LS3 on pump gas and things start to line up real quick. Stock for stock the LS3 takes a beating. The LS3 is a good motor, apples to apples it can be close depending on how we want to determine what apples to apples is.