I've got them and I love them

 

Anybody have any dyno numbers on these?

 

What gains did you get?

 

Here's a link to an article... header comparison
I think the Thorleys would work well for mild-to-moderate 4.8L's and 5.3L's or mild 6.0L's. I have considered them, but my concern is whether they flow enough for a modded 6.0L. Thorleys only have 1 1/2" tubes compared to 1 5/8" or 1 3/4" seen on other brands of LT headers. Also, the tri-y design seems to work best in the mid-RPMs, and with a heavy truck you want as much torque as you can get at the low end.
Most of the people who have commented about the Thorleys seem to like them.

 

How would they compare to AS&M long tubes?

 

"1 1/2" Where did you get that number from? I looked on the Doug Thorley Header website and they have a 1 5/8 primary. Summit even shows them having 1 5/8 primaries.

 

that's what it says in the article, the problem with that is their using it on a regular old school small block. SO I am sure their is some difference.

 

The article is using a carburated small block, there is a major difference in HP and TQ compared to fuel injected (FI) engines. In the old small block, a FI engine always made better power and torque with smaller primaries and longer tubes than the carb version. On my stock 64 FI corvette your loss of low end torque with 1 5/8 headers noticible up to 4500 rpm compared to about 3200 rpm with 1 1/2 headers. On a LS1 engine (specifically made for FI) a Tri-Y header will make more low and mid range torque then a 4 to 1 header and less top end HP. If you plan on running over 6200 rpm or setting up for drag racing, the 4 to 1 header is the way to go. For towing, hauling equipment, street and higway usage, the Tri-Y design would be better. IMHO