exhaust diameter

[Nacho-RT74]

whats the exhaust diameter on stock BB HP exhaust ?, I'm thinking on replace the flanges, but dunno if they are 2.25" or 2.5". I guess 2.5" but preffer to ask first.

[oldcarnut]

Looks like 2 1/4 for 383 and 2.5 for 440.  However the H pipe I bought for a 70 RR from the parts place was 2 1/4 so it might pay to check anyway. .  Here's a link with some info. http://www.accurateltd.com/Complete%20Systems-B-Body.htm

[Nacho-RT74]

Looks like 2 1/4 for 383 and 2.5 for 440.

really ? I have allways though BB and RB were the same

[Nacho-RT74]

ok, I don't understand... on BB and RB sections of that link ( 71-74 ) no matter if turn down or tail pipes ) are stated same exhaust casting number.

so my question is... initial pipes are diff even with same exhaust manifolds ?

[firefighter3931]

From the factory ; B engines got 2.25in headpipes and RB engines got 2.5in headpipes. Both the B & RB engines got 2.25in tailpipes to keep the noise down. Technicly the pipes are different even though the same ex manifolds were used on both due to the different deck heights.


Ron

[Nacho-RT74]

Oh Ok... so I can get 2.5" flanges and will match perfectly with my manifolds, just will need to fit bigger pipes ( what won't be a bad idea either increase performance! ) IF they are 2.25"

[Nacho-RT74]

ok.... another question.

what do I win with 2.5" first section pipe IF THE FINAL PIPE IS STILL 2.25" ?

[Ghoste]

I'm no engineer but it wouldn't surprise me if the exhaust had cooled enough by the time it got to the tailpipe that the smaller diameter was not as restrictive as you would think.

[Nacho-RT74]

mmm sounds logical. somebody else ?

[firefighter3931]

Ghoste is correct....exhaust gases cool as they move away from the engine. The larger (tail) pipes would make the car louder but will not improve performance. 


Ron

[Ghoste]

Pursuing the same armchair engineering would it also be logical to assume that having the bigger tailpipes could even be detrimental to performance?  Reason being that as the exhaust cools it's also slowing and thus losing some of it's scavenging velocity?

[firefighter3931]

Pursuing the same armchair engineering would it also be logical to assume that having the bigger tailpipes could even be detrimental to performance?  Reason being that as the exhaust cools it's also slowing and thus losing some of it's scavengin velocity?

Not really, scavenging is pretty much done before the mufflers. I had a long conversation with a retired Chrysler employee who spent most of his career in the cylinder head/exhaust lab. Learned a lot of good stuff from him and he is also a racer with a low 9 second car. Definately a smart cookie. 



Ron