Dan the man

My buddy who is into tuning cars too (albeit crappy Ford cars) tells me that upgrading headers is a good idea. I haven't even heard of this w/r/t Audis. What ARE headers, and why would I upgrade them? Or, why not, as the case may be.<p>Secondly, I'm noticing that there are tiny tiny little flecks on my windshield. Water and usual washing doesn't seem to clean them up. Are they IN the glass? I have an older A4 (96). What do you guys suggest for cleaning windshields of these little nasties?<p>Thanks,<br>Dan.<br>96 A4 2.8, w/ clear side markers, strut brace, Brullen exhaust, K&N air filter, aluminum race pedals...(known as "the green monster")

CW Hunter

Okay first of all, my second car is a FORD Mustang, and my third car is a FORD Modelt T. Please don't bash FORD's.<p>Headers are exhaust manifolds. They bolt to the heads (where the valves and spark plugs are) and when the exhaust valve opens, all the spent gases from the cylinder are pushed out into the header by the final stroke of the piston. In Ford cars they use very cheaply made mandrel bent headers(okay some parts of Ford are crappy) that have kinks and hard bends in them not allowing the gases to "flow" as freely as they should, so a typical first mod to a Ford is to replace the headers which will garner an additional 5-15 HP depending on what you do to the stock intake. Generally if you haven't modified the intake in the Audi, you shouldn't need to modify the headers. If you put a bigger header on the Audi without increasing the intake you will actually hurt your performance because it will reduce torque (the exhaust always needs a little back pressure).<p>On your windshield, it just might be the debris that has hit it over the years. First try some vinegar with a cotton cloth. If that doesn't work, check out www.eastwoodco.com - they have some heavy duty window cleaning systems that take out minor scratches.

DRF

I have a question, in the lat week or so I remember reading on this board that a turbo engine doesn't need the backpressure that a naturally aspirated engine needs. Is this true? Why?

Mark

I love how products claim to &quot;Take Out Scratches&quot; - a scratch to me is missing paint(etc)

CW Hunter

Honestly everything I have learned about engines is from NA engines. My understanding of exhausts are that they create a siphon with the pressure. The siphon helps suck the spent gasses out of the cylinder. If the exhaust is too big, then the velocity of the gasses cannot create the siphon therefore it is totally up to the cylinder to push the gasses out of the cylinder. Creating a loss in torque. Maybe since a turbo pushes more air and fuel into a cylinder, it needs less help pushing it out and creates it's own siphon???? I don't know ....<p>I'd like a better answer to this one myself.

Paul H. (in MD)

My understanding is that the turbo itself provides the backpressure to the engine. Since the engine is getting what it needs, any additional backpressure as seen by the turbo would just slow it down (or prevent it from getting up to speed as quickly).<p>At least, that's how I understand it. Someone please correct me if I am wrong!<p>Paul H. (in MD)

RangeR BoB

The points you guys have brought out are true, in the right circumstances.<p>Headers are welded up of steel tubing. The goal is to have equal length primary tubes, 1 per cylinder, leading into tuned length collectors, which then reduce into the exhaust tubing.<p>Examples from my racing 7.6 liter big-blocks were 1 5/8" primaries, 32" long, leading into a 3 1/2" collector, 12" long (cut at the end of the smoke ring, and then a collector added) leading to a 2 1/2" dual system with Flowmasters, with a crossover behind the collectors.<p>Factory manifolds typically are cast from ductile iron, and the primaries are not of the same cross section, nor are they the same length. This leads to each cylinder having a different resonance, which makes it hard to tune for good cylinder filling.<p>Backpressure is the resistance of flow thru the combined exhaust system, from the valve on. In a racing engine, with a header leading to a straight pipe, there is low backpressure. Under certain conditions, this can hurt low end torque, because the incoming intake charge flows right out the exhaust valve, which is partially open. <p>Having both intakes and exhausts open at the same time is called overlap. Overlap is present in most all engines to a certain degree. Racing engines, where valves are held open longer (duration), and pushed open higher (lift) suffer more from this.<p>Having too much back pressure can result in reversion, where some of the exhaust is rebreathed into the combustion chamber on the intake stroke. This replaces fresh charge, so it hurts power.<p>In general, a street engine such as an Audi v6 does not have enough overlap to really worry about either loss of torque or excessive reversion. The exhausts are restrictive enough to have a bit of reversion at all times, because the cylinders never get completely purged of exhaust gas. In general this is not a big deal.<p>I have not seen the exhaust manifolds on the v6, so I do not know how restrictive they are. Replacing them with tubular headers may help exhaust flow, and has the potential to add 5-10% power, depending on how badly the original exhaust was. The tradeoff is increased noise and underhood heat, because the thin sheetsteel of a header is not as good at keeping in the heat/noise. Ceramic header coatings (Jet hot etc) and thermal wraps (Thermotec) help to some degree here.<p>Chances ae that you won't overscavenge your cylinders, leading to a loss of low end torque on your V-6. You might gain some power. I don't know who makes the headers and what they cost. If you live in California, they have to be CARB certified, or you will fail your emissions test.<p>On turbo engines, headers are a bad idea. You want to keep as much heat in the exhaust as possible before the turbo, because heat = energy to drive the turbo. The poor tuning of exhaust resoonances is masked by the turbo's ability to cram in a bunch of air, so you don't have to be as precise at making the exhaust. <p>This will catch up to you in the case of the 1.8T, because at 150hp, the exhaust manifold has sufficient flow capacity to make power. If you try to get higher boost levels, the restriction of the manifold starts to hurt you.<p>The biggest backpressure item in a turbo is the hot section turbine wheel itself, which makes worrying about the system after the turbo irrelevant as far as tuning for scavenging goes. However, a restrictive exhaust will still hurt overall flow, and limit the total power you can make.<p>Sorry about the novel-length dissertation, just trying to share what I know...