will 2.5 s/b ex manifolds increase performance

[Michael F.]

adding these to a 70LT-1 will they help performance over the stock 2.0 manifolds and will they bolt up to stock pipes???

[Joe L.]

Re: will 2.5 s/b ex manifolds increase performance

michael-----

Adding the 2-1/2" exhaust manifolds to a 1970 LT-1 won't improve performance to any appreciable degree. Any difference would be minimal.

Notwithstanding the above, the 62-65 2-1/2" outlet manifolds will bolt up perfectly to the 70-72 LT-1 forward exhaust pipes.

One other thing: ALL 1970-72 LT-1s were equipped with the air injection reactor (AIR) system. NONE of the 62-65 2-1/2" outlet manifolds have provisions for AIR. So, if these manifolds are used on a 1970-72 LT-1 (or, any other small block originally equipped with AIR), the AIR must be removed.

[Duke W.]

Re: will 2.5 s/b ex manifolds increase performance

I think it would be measureable on a chassis dyno - something on the order of one to three percent, but probaby not SOTP disernable.

Like Joe said, you would also have to acquire compatible front pipes and you would not be able to install the AIR tubes.

Duke

[Joe L.]

Re: will 2.5 s/b ex manifolds increase performance

Duke and Michael-----

I mis-spoke regarding the fact that the 2-1/2" manifolds will bolt up to the 70-72 LT-1 manifolds. I don't know what I was thinking of when I said that. The LT-1 forward pipes are swaged down to 2" for connection to the 2" outlet manifolds. Obviously, they will NOT bolt up to the 2-1/2" outlet manifolds.

For that conversion, the 63-65 forward pipes used with 2-1/2" outlet small blocks MAY be usable but, if so, will require some rework. Most 63-67 forward pipes are slightly different than their 68+ counterparts. So, I don't think that there are any "off-the-shelf" pipes that will fit perfectly. You might want to consult with Mike Allen of Allen's Corvette Exhaust if you decide to do this. He may have been "down this road" before.

[Chas Henderson #28127]

Re: will 2.5 s/b ex manifolds increase performance

Joe,
wouldn't BB front pipes work from a 70-72?

Chasman

[William C.]

Re: will 2.5 s/b ex manifolds increase performance

BB exhaust outlets are at a different location and angle than the smallblock versions