exhaust manifold replacing from headers

[Wayne P.]

I will be replacing my headers and going back to a cast
iron manifold.

I am running the 2 1/2 inch off road exhaust. I have a set
of 2" exhaust manifolds.
Would the original 2 1/2 exhaust come with a reducer to 2
inch or would it be better to look for a 2 1/2 inch exhaust manifold.Alternator
on left side. I am hoping this will help it run a little cooler under the hood.
Also looking at replacing the torker 2 with a duel plane intake.
327 small block solid lifters

Thanks for any advice.

[Joe L.]

Re: exhaust manifold replacing from headers

I will be replacing my headers and going back to a cast
iron manifold.

I am running the 2 1/2 inch off road exhaust. I have a set
of 2" exhaust manifolds.
Would the original 2 1/2 exhaust come with a reducer to 2
inch or would it be better to look for a 2 1/2 inch exhaust manifold.Alternator
on left side. I am hoping this will help it run a little cooler under the hood.
Also looking at replacing the torker 2 with a duel plane intake.
327 small block solid lifters

Thanks for any advice.

Wayne-----


The off-road exhaust is a 2-1/2" system. However, it can be used with front pipes that are designed for fitment to either 2" or 2-1/2" manifolds. Whichever pipes you have determines which manifolds you need. Or, you can simply replace the forward pipes, if necessary, to mate up with the manifolds you have.

For 1964-65 the off road systems supplied with 300 HP manual trans as well as all 350, 365, and 375 hp engines used 2-1/2" manifolds with, of course, forward pipes designed for attachment to 2-1/2" manifolds. For 1966-67 all small block manifolds were 2" outlet. So, the forward pipes for all 2-1/2" systems were necked-down for attachment to 2" manifolds.

For an intake, I agree with your decision to replace the single plane with a dual plane. I do not like single plane manifolds for strreet use, especially for a small block. You can use any of the GM dual plane manifolds (ALL PRODUCTION manifolds were dual plane) or you can use an Edelbrock Performer 2101.

[William C.]

Re: exhaust manifold replacing from headers

If it will help, the '66-67 part numbers for the front pipes to connect the 2 inch exhaust manifolds to the 2 1/2 system are 3877209/210 ('66-67) same as '68-and '70-71.

[Wayne P.]

Re: exhaust manifold replacing from headers

Thanks I was looking at the Edelbrock 2703 intake manifold with front oil tube. Need to check.if it will fit. Will I notice a decrease in hoarse power going to the 2 inch manifolds ? My headers are3 inch to 2 1/2 . If I can get a good used set of 2 1/2 might be the way to go. Thanks

[William C.]

Re: exhaust manifold replacing from headers

The '62-65 300-340-365 hp manifolds are generally accepted as the best of the cast iron 2 1/2 inch setups.

[Clem Z.]

Re: exhaust manifold replacing from headers

if you are not worried about the correct dates here are dorman cast iron corvette manifolds. http://compare.ebay.com/like/2204757...Types&var=sbar your local auto parts can also get them for you

[Joe L.]

Re: exhaust manifold replacing from headers

Thanks I was looking at the Edelbrock 2703 intake manifold with front oil tube. Need to check.if it will fit. Will I notice a decrease in hoarse power going to the 2 inch manifolds ? My headers are3 inch to 2 1/2 . If I can get a good used set of 2 1/2 might be the way to go. Thanks

Wayne-----


You won't notice any difference in power with the 2" manifolds.

[Wayne P.]

Re: exhaust manifold replacing from headers

Thanks Joe . I wonder if their is no noticible difference why were the manifolds chainged to 2 1/2 inch .
I will end up using my 2 inch and order pipes from corvette central number 322417 . would their only be a difference with a dyno test ? Would it make any sound difference ? Ya I know to many questions. THX

[Joe L.]

Re: exhaust manifold replacing from headers

Thanks Joe . I wonder if their is no noticible difference why were the manifolds chainged to 2 1/2 inch .
I will end up using my 2 inch and order pipes from corvette central number 322417 . would their only be a difference with a dyno test ? Would it make any sound difference ? Ya I know to many questions. THX

Wayne------

Let's put it this way and for example: the 1965 L-79 was rated at 350 hp and it had 2-1/2" manifolds. The 1966-67 L-79 was rated at 350 HP and had 2" manifolds. If there was a real difference in horsepower I suspect it was de minimis. As far as a different sound, I think not.


Why did they ever use the 2-1/2" manifolds? That I do not know. Maybe they thought it was advantageous but later determined it was not really much of an advantage.


All things being equal, I'd probably use the 2-1/2" manifolds. But, as long as you have the 2", I would just use them.

[Paul J.]

Re: exhaust manifold replacing from headers

Wayne, I iimagine that Joe is correct that you won't see an "appreciable" difference in horsepower between 2" and 2 1/2" manifolds. But you will probably see a difference of around 5-8 horsepower less than with the headers. I'm sure you remember the old hot rod mantra about getting an engine to breathe better to create more horsepower. The heads, intake, and exhaust is key.

Paul