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down tubes

  
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down tubes

 
marbil marbil
New User | Posts: 45 | Joined: 04/13
Posted: 03/15/14
07:18 PM

I want 3" mandrel bent exhaust but cant find any kits with 3" down tubes, they are all "header back"
I am building a 69 Firebird with a 455, factory long branch manifolds from ram air resto.
I was thinking of a pypes system and finding a local shop that could make the down pipes.  Anything out there that Im just not coming across?
Thanks Bill  

barneyformula barneyformula
Addict | Posts: 3306 | Joined: 01/07
Posted: 03/15/14
07:26 PM

Pypes sells the downtubes seperately for the RA manifolds, but you may not get them in 3" only 2.5". Check their website.  
A little help... 'cause we don't all have to learn the hard way!

ROWSLEY ROWSLEY
Guru | Posts: 1016 | Joined: 07/11
Posted: 03/15/14
07:53 PM

what size are collectors on the long branch manifolds?  
76 455/4spd TRANS AM
69 GRAND PRIX 455/5SPD

wayne712222 wayne712222
Moderator | Posts: 235 | Joined: 10/13
Posted: 03/16/14
04:15 AM

http://pypesexhaust.com/c-702438-downpipes-pontiac.html


running the stock 2 1/2" down pipes allows you to hook directly to the manifolds..

i don't think it will be easy to seal a 3" pipe as its bigger than the end of the manifold..

you will also get a boost from the 2 1/2" pipes inside the 3" pipes  so the exhaust can expand slightly into the 3" section.

you won't have this much difference.. but you might want to leave several inches inside the 3 inch tube to create this anti reversion effect..

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back in the 80s.. a friend swapped a small block into his brothers AH3000..   he got the flexible exhaust pipe and installed it as a sample piece.  you have seen this pipe.. its wound.   he bent it into place..  so it fit just perfect.. then he  welded each loop in 2 or 3 places.. so it could NOT unbend..

he was then able to hand it to a friend at the tube bender that was out in glendale and had them mandrel bend and flair some tube to match his sample perfectly.  

marbil marbil
New User | Posts: 45 | Joined: 04/13
Posted: 03/18/14
05:28 PM

2 1/2" pypes stainless mandrel bent system is on its way to me, they say the 2 1/2 system will handle up to 550hp so that should be fine for my build.  

marbil marbil
New User | Posts: 45 | Joined: 04/13
Posted: 03/18/14
05:29 PM

2 1/2" pypes stainless mandrel bent system is on its way to me, they say the 2 1/2 system will handle up to 550hp so that should be fine for my build.  

ROWSLEY ROWSLEY
Guru | Posts: 1016 | Joined: 07/11
Posted: 03/18/14
11:13 PM

2 1/2 works for my 500hp 455. did you get the xpipe? it realy sounds good and added hp to boot!!  
76 455/4spd TRANS AM
69 GRAND PRIX 455/5SPD

marbil marbil
New User | Posts: 45 | Joined: 04/13
Posted: 03/23/14
07:03 PM

Yes got the X-pipe, I am hoping the exhaust isn't too loud for road trips, I thought I would be firing up the motor this coming week end but the radiator leaks like a sieve.  I was planing on an aluminum rad when the motor goes into the car anyway, so new radiator is on its way  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 496 | Joined: 11/13
Posted: 03/23/14
08:28 PM

i hope your rad is a us made one like us radiator, cool craft, northern, griffen or flowdyne.

most of the chinese ones use narrower tubes than the us ones and therefore hold less water and cool less.

what mufflers are you getting?  

marbil marbil
New User | Posts: 45 | Joined: 04/13
Posted: 03/26/14
07:12 PM

It is a cool craft AKA US radiator  

ROWSLEY ROWSLEY
Guru | Posts: 1016 | Joined: 07/11
Posted: 03/27/14
09:06 PM

if the interior exhaust noise is to loud throw a heavy blanket on the trunk floor you won't beleave the differents it will make.  
76 455/4spd TRANS AM
69 GRAND PRIX 455/5SPD