headers and exhaust

Old Heater Boxes work... look kind of funky nasty but work... at least you get the right formings and flanges.

I've been told the differnence betweeen cheapy and expensive exhaust/header systems is that low end ones aren't tuned and balanced.

Timmy

I have no interest in providing heat to the cabin.

How are exhaust systems tuned? I thought what you really have to keep in mind is keeping the length of the headers equal. If I kept the diameter equal to that of stock, will have have a good 'balance'?

klashniv

if all tubes are equal-length and equal-diameter(essentially equal volume) you should have nice scavenging going on...steel should be fine but it would rust unless coated

-james

exhaust/header

now that is interesting...hmm *gears turning* lol

sounds like a good idea but wouldnt the smaller diameter pipes be more restrictive than the larger pipes? the velocity would be good for scavenging but what about high rpms?

-james

In a way, VW did that on some TIV engines. Check it out. One side has smaller diameter header pipes than the other.

i believe, when tuning an exhaust, what one is mainly interested in is the timing of the exhaust pulse. If the 'small' primary tubes were adequately sized (near the exhaust valve diameter, for example), but were longer than the shorter-but-larger pipes, one should get the same results. so if you or i were going to try this experiment, we'd want the smaller-but-longer pipes on the 1 and 3 cylinders, and larger-but-shorter pipes on 2 and 4. I'm sure there are formulae to calculate the propagation of the exhaust pulse, as varied by diameter and length. this would let one build the short pipes of the appropriate length and diameter, so their slower-moving pulses would be in time with the longer pipe pulses.

I've thought of build> now that is interesting...hmm *gears turning* lol

Horse Poopy. Total nonsense.

On Thu, 18 Sep 2003 14:20:26 -0500, John Stafford left Mt Vesuvius in a state of jealous awe as he began spewing from the mouth thusly:

Oddly enough, you misspelled "losing." :-O *runs for cover* Sorry, cabin fever....

-- Travis '63 VW Camo Baja...

:wq!

I always do. Maybe I should spell it Luzing.

Now you have a tiny, tiny, itty-bitty idea of what some of us far northern Yanks go through for months. Harh! What doesn't kill me, makes me wonder. ;)

You bring up an interesting point I hadn't thought about before. The problem is one of your assumptions is out of whack. The thing is that when gas cools, for the same pressure it takes up less space. In other words, in the same space it has lower pressure. Its the old pv = nrt. I can't remember what all the variables are (pressure, volumne, N=amount of gas, r=???, temp).

So, while cooler gas IS more dense, its also "smaller". I'm not saying anything about how big a pipe you need.

This 'grow' stuff isn't true. The gas just shrank when it cooled.

Can't we dig up real data from Hooker or Headman or the like?

Chris

Yes, this is getting interesting. I poked a hornet's nest, and I'll stand here to take the bites.

But to get to your point - the hot gas may shrink in volume, per se, but it's not a discreet packet: new gas moves to occupy the same space - you get more in there and it 'stuffs' because... well, there is more in there! It's not like the gasses are constricting and a cold superconductor fills in like a pipe liner to make up the unoccupied space to let it shoot out unimpeded. :)

Yeah, no kidding.

This is probably a standard test question on a fluid dynamics final exam. Way above me, though.

Chris

Would this also lend to a vacuum on the end of the exhaust pipe. Meaning that as the gas cools and shrinks that as you said "new gas" would try to occupy the area that is now being formed? This new gas would be... outside air maybe? Being pulled in from the outside backward through the tail pipe, since by this time the exhaust valve has shut and no flow can be gained from that direction. Or at least attempting to form a vacuum from the tail pipe, which would increase the resistance in the pipe. This condition would be remedied as the next exhaust pulse was released, and this would repeat the process again. While I would doubt that any air would make it all the way into the pipe while the engine is running, there would still be a negative pressure or pulse at the end of the tailpipe just before the next exhaust pulse.

But what would I know, I am just guessing and trying to learn something.

Hi Guys,

I found some interesting stuff on Hooker's web site:

Header primary tube sizes vary on many factors: engine combination, transmission type, gear ratio and intended use of the vehicle. For example a truck header will be designed using longer length and smaller diameter primary tubes to enhance low to mid-range performance, where a header for a Pro Stock race car will have larger primary tubes and large collectors for the highest flow available.

Bigger generally is not better when it comes to street driven cars. when you put too large of a header or exhaust on a street driven vehicle, you usually notice a severe drop in low to mid-range performance due to a lack of backpressure. To combat this issue, Hooker sometimes builds 3 or 4 different headers for a particular application with varying tube and collector sizes.

Should I use exhaust wrap on my Hooker Headers? If your vehicle is being run on the street or for extended periods of time, you should never wrap headers. Exhaust wraps insulate the exhaust too much and the exhaust temperature is raised to a level that fatigues the header material causing cracks.

If under hood temperatures are an issue, we recommend using Hooker's Metallic Ceramic Thermal Barrier Coating. Our coating is applied inside and out. It is corrosion and heat resistant up to 1600°F. It also reduces underhood temperatures and has a polished high luster finish. Holding exhaust temperatures inside the header increases the exhaust gas velocity producing more horsepower.

It sounds like you are talking about reversion, but frankly, I don't know enough about the whole field to comment further. It gets very complicated, and it is not intuitive. For example there are issues regarding resonance, heat, cam timing... the list goes on. I am inclinded to think that over the many years, and especially since the seventies the very few very smart builders have, by means of hands-on experiments and trials, come up with good merged headers for the ACVW.

And besides the exhaust, there's issues regarding the intake. :( Stand-off, manifold design... my aching head.

I disagree. Maybe Hooker is just trying to cover their butts. Look at that another way. I have wraps on one of my engines because #1 and #3 pipes pass right by the cylinders and heads. After wrapping up all four headers all the way to the collector, temps dropped dramatically. Wraps do a good thing that way (keeping radiant heat away from the engine) - and they keep the pipes and exhaust gas HOT and that's what you want. Hot air moves faster. (Rejet!) Oh, if you do a real good job, don't stand close to the open header when the engine is reving. You will torch yourself.

Sure, it shortens the life of the header, but we are talking go-fast applications, not 100,000 mile machines. Chances are you will replace a nonwrapped header sooner than later anyway.

Sounds good, if it really works, but I have reservations. I _know_ wraps work.