I understand the '01 manifolds and cats flow much better than the '98's. I have a low mile set of '01's in the garage, and was wondering what kind of gain could be expected from this swap?

 

if you're lucky.....5hp

cats are the same...manifolds are slightly better.

not worth the effort

 

No EGR hook up on the '01s ...

 

You live in TX, put some headers on it!

 

You should a LS-2 intake on it. They flow almost as much as a fast but for alot less. But answering your question. Yes they will both bolt up.

 

That's assumiing he is also using the '01 y-pipe ... a '98 y-pipe will not bolt-up to '01 cats and manifolds.

 

Sure if you want to lose intake charge velocity. On a stock cubed LS1: LS6 intake > LS2 intake.

Plus you won't have the hassle of the TB....

 

If you have way more time that funds, why not. But if money is a real problem then be aware that the 01 manifolds have no provisions for EGR so you'd have to eliminate that, which will set a code that you'll either have to live with a perpetual SES or pay to have it turned off. And the A.I.R. flanges are turned 90° from one to the other so you'll have to try to twist you pipes or buy the 01 pipes.
I have the manifolds off a 99 here and the manifolds off my 00 and there's a huge difference in the size of the ports and internal passages. Our stock 98 M6 car has run a best mph of 107. And my 00 A4 car ran 108.

 

ls2 intakes are made like garbage. as said above, get an ls6 intake with some nice headers and itll really wake up