Headers and exhaust size

[nsmall]

I have 1973 exhaust manifolds and I am considering putting on some TTI headers.

A concern I have is that my exhaust system is all new (seems vain to replace it) but unfortunately it's pretty small.  It looks like it's 2.25 inches all the way down except under the trunk it's only about 2 inches.

So my main question is....is this a waste of time/money to put headers on to my existing exhaust which is hard for me to want to replace as it's new?  I'm looking for the 340 to breathe better as it does seem a little congested.  Basically I want some more performance as the engine is out....seems like a good time to make the change.

Lastly does anyone know if I'll have to get a mini starter or is there a way to get a good set of headers in there with a stock starter as my starter is new.

Thanks

[usraptor]

While I'm not an expert, I would think a header system and X or H  pipe would greatly improve your performance even with the 2.5 inch exhaust.   With a 340 unless it is very highly modified a 2.5 or even 2 inch exhaust system should be more than adequate. 
Maybe Chryco or others with more experience at engine building will chime in on this. 

[nsmall]

@Chryco Psycho

Please chime in sir.

I have a H pipe in.  I want more flow.  The engine is modified, nothing radical, but definitely not stock.

This has been something I've been debating for two years.

Another question....Do headers really add that much heat in the cabin? 

Thanks

[Chryco Psycho]

The term is velocity ,I bet right now you get a fair amount of fast moving exhaust  exiting the tips ?
This is a good thing as it will create a vacuum behind it which helps pull more exhaust out quickly .
The book I read tested this & proved that as the exhaust cools it also contracts & to maintain velocity reducing the pipe size at the furthest point from the engine ,get this, Increases power !! So the factory did it right knowing this !
So on a 340 not stroked & not running at 6500 most of the time my bet is you would gain very little if anything at all .
The H pipe is a balance tube so if here is too much flow / pressure on one side it can cross over  rather than effect the engine so an H pipe is very benficial .
So my take is $ spent elsewhere will give more gain /$ spent

Will headers give off more heat yes & no , the exhaust can be 1200* when the engine is working hard contiuously which is very rarely the case , so the exhaust manifold tends to act as a heat sink absorbing the heat & directing most down the exhaust  & cooling again as the engine works less hard . so because the  header is thinner more heat is passed through into the engine bay when the engine is working hard in short bursts / typical driving , so given a different case such as puling a trailer the thicker manifold will reach the same temps & cool much more slowly .
The big thing with headers is using a top quality header  like TTI or Dougs one you can buy them coated so the heat is retained better & two they have proper clearance for spark plug access , starters , steering , & the ground below the car SO do not be tempted to go cheap

[nsmall]

@Chryco Psycho

Thanks for your thoughtful response.  Correct my 340 is not stroked.  I changed the rear end and there have been other mods so I'm thinking it's time to save and wait for my current set up to break.  I can do headers when I do something radical with the engine down the road.

Im still debating changing my carb, but it has been reliable.  I have a Carter AFB, I think it's around 600.  It's been rebuilt so I have hard time changing it.

Thanks for your input.