Re: Why headers don't increase power on v6 engines
Well that is not entirely true. On a boosted engine headers are much less important than on NA engines since you are forcing (forced induction) the charge in and with care in the valve overlap that can also be used to force the residual gases out. As long as unclogged and the flow is essentially lamiar, you could just stick a tin can on the exhaust (why supercharged aircraft enginess often just had stub stacks).
So a header will not do much on a SRT.
With a naturally aspirated engine the rules are different. The more exhaust gas you can suck out, the more charge you can suck in. Intake is a whole different subject that we will skip for now.
OK now six cylinder engines are special as long as even fire (why the XF has offset journals like a 1987 Buick) in that the exhaust pulses overlap. You can tune a street 6 very well with a single tailpipe. OTOH a race engine with a lot of cam may need duals to avoid collisions (and a proper set of duals like a Jag with bananas or a Corvair with trombones has the sweetest sound in the world).
Probably should mention that I really like a good six. Know what to do with a proper V8 particularly with FI but just like sixes better.
That said a street six that doesn't wind past 6,000 just needs a single exhaust and a tuned equal length exhaust manifold can really be sweet, exhaust pulses every 120 degrees can be used to scavange (the exhaust pulse has charge inertia that can create a vaccuum behind it to help suck the next pulse along. Doing this requires maintaining lamiar flow and a near constant charge speed which is more art form than science.
So a proper exhaust will help suck the exhause charge out of the cylinder and make room for the next intake. Some people have trouble getting their minds areound the fact that both the intake and exhaust charge have both mass and inertia.
Bottom like: with a boosted engine particularly with a belt driven supercharger, the exhaust flow dow not really matter, it will get pushed out of the cyl. A nine exhaust will make a small difference but nothing turning up the boost wouldn't do.
OTOH a NA engine needs all of the help it can get, both intake and exhaust. That said if you understand that the XF 3.2 really is a product of the last century with all of the limitations that implies, it can still do a lot and make the best use of the technology then available.
So the title should really be "Why headers don't increase power on supercharged v6 engines"
ps to really understand an IC engine I'd suggest beginning with a copy of Sir Harry's "The High Speed Internal Combusion Engine". Mine is a 1958 edition.
Last edited by Padgett; 08-20-2014 at 10:35 AM.