Best Header and Xpipe Size
Thread Starter
Racer
Joined: Sep 2007
Posts: 417
Likes: 0
From: St. Albert
Best Header and Xpipe Size
So what is the best size header and Xpipe to get, I have the BB Bullet exhaust 
and this one gent I was talking to said to go with the 1/34 inch to me that does not make sense being the Bullets are 2.5 inches wouldn't be good to go with the same size for better air flow? any recommendations would be great. Did you also notice the difference in power once the mods were done and how much 
and this one gent I was talking to said to go with the 1/34 inch to me that does not make sense being the Bullets are 2.5 inches wouldn't be good to go with the same size for better air flow? any recommendations would be great. Did you also notice the difference in power once the mods were done and how much
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
1 3/4 is the primary tube size. You have 8 of those primary tubes.
Those 8 tubes run into the two collectors, which merge the primaries into either a pair of 2.5" or 3" tubes from there on back.
1 3/4" primary size is the most popular and effective size for stock 346 engine size, with or without modifications. Some very radical high rpm/high hp setups might benefit from a 1 7/8" system, as do larger CI and supercharged engines. Very large (440+ CI) engines might even see the need for 2" primaries.
There is a lot of science behind header design, and for them to work effectively, you need to size the primary dia and length appropriately for the engine output and desired rpm usage range. Bigger is not always better when it comes to primary dia, in fact bigger can be worse. There is also much debate about primary tube length...generally speaking, longer primaries make more torque at lower rpm ranges...short primaries are better suited to high rpm performance.
Also, headers aren't really about "flow"...They are about scavenging...the fine art of tuning the arrival time of each exhaust "pulse" at the collector in such a way to literally have each exhaust pulse help draw the next pulse out of the engine.
A header that scavenges effectively is essentially sucking the exhaust out of the engine, instead of the engine pushing it into the tubes. This is why the best designed headers can make for such a dramatic increase in power.
And as for X-pipe size, 3" dia is the better way to go. Even if it still gets reduced to 2.5" at the catback...it's still been shown to make a little more power than using 2.5" tube from the collectors back.
Those 8 tubes run into the two collectors, which merge the primaries into either a pair of 2.5" or 3" tubes from there on back.
1 3/4" primary size is the most popular and effective size for stock 346 engine size, with or without modifications. Some very radical high rpm/high hp setups might benefit from a 1 7/8" system, as do larger CI and supercharged engines. Very large (440+ CI) engines might even see the need for 2" primaries.
There is a lot of science behind header design, and for them to work effectively, you need to size the primary dia and length appropriately for the engine output and desired rpm usage range. Bigger is not always better when it comes to primary dia, in fact bigger can be worse. There is also much debate about primary tube length...generally speaking, longer primaries make more torque at lower rpm ranges...short primaries are better suited to high rpm performance.
Also, headers aren't really about "flow"...They are about scavenging...the fine art of tuning the arrival time of each exhaust "pulse" at the collector in such a way to literally have each exhaust pulse help draw the next pulse out of the engine.
A header that scavenges effectively is essentially sucking the exhaust out of the engine, instead of the engine pushing it into the tubes. This is why the best designed headers can make for such a dramatic increase in power.
And as for X-pipe size, 3" dia is the better way to go. Even if it still gets reduced to 2.5" at the catback...it's still been shown to make a little more power than using 2.5" tube from the collectors back.
hell of an explanation
