I am swapping my 305 TPI out for a LS6 408 and I'm having a hard time finding headers that will fit right in with no mods to the firewall, wheel wells or k member I'm fine with denting a header pipe or two since I'm thinking of wrapping them. Will normal LS1 headers work.
-Thanks-

 

If this LS6 is a LS motor (97-up small block) then it's not a "big block", and yes.

If this LS6 is a early 70s big block then it's not a 408, and no.

Your post has these 2 motor types conflated. It's impossible to answer your question until you straighten it out.

DON'T wrap headers. Gotta be about the worst thing you can do to them. Get stainless ones, and have them coated.

 

If it's actually a BBC, use these.
https://www.thirdgen.org/forums/engi...y-bbc-3rd.html

If it's a lsx engine, than there are a million options for you from a pile of companies these days.

 

The 408 is actually a 396 bored 60 over into a 408 it is from a 1967 Chevelle ss.

 

OK, so not a LS6; just some random big block. A relatively ordinary one among big blocks as far as that goes.

Use big block swap headers. They won't care about the bore. None of the rest of that ... other ... matters in the least.

 

an ls6 is a 454 which is a big block and a very specific and coveted engine found only in a 70 chevelle ss(and possibly certain corvettes of the same era).
were did you get the idea it is an ls6?im very curious,is this information found at the same place that states every 350 sbc is 350 horsepower?(in fact very few 5.7's are 350 horsepower)


a run of the mill 396 is going to weigh a lot more than a regular small block and not put out much more power,it will make your car ill handling,nose heavy and irritating if that is important to you.
the difference in weight between a sbc and a bbc is around 110 pounds give or take and if you compared that to a new style ls motor that difference would be closer to 200 pounds.

 

actually a decently built lb9 305 would probably kick the crap out of a regular old 396 depending on what is done to it,there are a few guys getting into 13 seconds and one or two into the 12 second range with 305's and they dont weight 800 pounds.


if you want serious power build an ls as it has much better weight

can deliver insanely good gas mileage and a "potentially" bulletproof
6 bolt main bottom end.this is something you need to research.

 

Ummmm... no.

You've obviously never owned or even driven a big block.

Granted, the 396 is near the bottom of the list of BBCs; but given that it's pretty easy to build a carbed 305 that will kick the crap out of a LB9 and still get over 20 mpg (guess how I know this), 25% more CID with no effort devoted to it at all will kick the crap out of a TPI motor.

The comments about LS motors are on the money though.

In 2018, I would not put a 50 yr old motor into one of these cars. Even if it WAS a LS6, and not just a 396. (in whatever overbore, which basically doesn't make it anything other than a 396)

 

hey sofa,i value your opinion and what i was referring to was perhaps a 396 impala vs a 1991/1992 lb9 t5 third gen,not a lowly 1983-84 lg4 automaticvs a 396/375 horsepower vette.



i currently have an lg4 305 in my car(a 1986 trans am)Ive done a few things as time and money allowed and i currently have a holley ultra 650 double pumper,an edlebrock rmp intake,and freshened up the hei(vacuum advance model).the car already had the original quadrajet removed as well as the computer controlled carb and the rest of the emissions equipment.i dealt with the hand i was given the best i could with what i have.


now i also have a gmpp 3896962 cam and lifters as well as hew flowtek shorty headers and y-pipe,should i install these or focus on installing another 305 that came with the car.it is a clean low mileage LB9 305 but does not have the tpi from a 1991 5 speed car.what are your thoughts and how would you proceed?

 

Probably your next best improvement would be gears. After that, a T-56.

I'd suggest 3.73 and a good posi. Not a stock one, not a Gov-Bomb; an Eaton or Torsen or Tru-trac maybe.

Nothing wrong with the Impala motor; it was the same as a Chevelle, part for part.