typical header HP gain?

[68_Gladiator]

whats a general number to expect in HP gains from a header im thinking between 4 and 10?

[Dmntxn77]

I would say closer to 15 or so, plus (depending on headers style) possibly up to double that in trq...

[Jeepguy77]

I would say closer to 15 or so, plus (depending on headers style) possibly up to double that in trq...

then how come people on here say no to headers, 15 hp or so and double that in torque is a great improvement. then theres always that 3 in single vs duals debate

[Dmntxn77]

then how come people on here say no to headers, 15 hp or so and double that in torque is a great improvement. then theres always that 3 in single vs duals debate

Who knows... Broke people will always argue against items that cost money.

The biggest issue is that there are dozens of different headers out there, and some of the cheaper ones are total crap. They often are not tuned, have small primaries, thin flanges, poor materials, ect...

In order to get a good result from headers you need to spend the money and buy good headers...

[Knuck]

Just ordered a set of Thorleys this week.

[tgreese]

Other than being hot, noisy, leaky, expensive and fragile, headers are great.

They do provide some HP and torque gain, by lowering the exhaust tract pressure and increasing the amount of exhaust gas leaving the cylinder. This can result in an increase in O2 in the fuel-air charge (less diluting exhaust gases left behind), so you need to check your air-fuel mixture after installing headers.

With headers, you also have the opportunity to tune the exhaust by shortening or lengthening the tube length. At the right RPM, you'll get an 'extraction' effect, where the next pressure wave of exhaust gas arrives at the low-pressure trough following the previous pressure wave. The longer the tubes, the lower the tuned RPM. Works pretty well on inline engines, where you can group the cylinder tubes so the firings are separated by equal intervals. Not so easy on a V8, unless you cross cylinders over to the other side. The cross-over tube on dual exhausts performs the same function, accounting for the uneven ignition grouping on each bank.

[tgreese]

Another comment - headers won't help much if you follow them with a restrictive exhaust system. To get your money's worth from headers, I'd suggest you add a large diameter dual exhaust system with free-flowing mufflers. If you search the net, you'll find some interesting articles on the relative performance benefits from various aftermarket mufflers.

Also, the pre-80 AMC V8 manifolds are said to be pretty good, as iron manifolds go. The driver's side manifold changes in 1980, presumably to accommodate the driver's side drop, and has a more restrictive shape. The earlier manifold will fit the engine, but the routing of the pipe may interfere with the driveshaft and whatever (according to other posters).

[DAHoyle]

Who knows... Broke people will always argue against items that cost money.

Then again, some folks are very well informed, and can afford them, and don't think they are worth the various downsides. There is more gain in some "free" improvements, than there is in a set of headers. A properly tuned carb, and ignition can add more power and drivability than a typical generic pair of headers. If someone ever comes out with headers with the quality of a good pair of iron manifolds, then a lot of the naysayers will climb on board, but some of us don't want to bother with noise, cracks, thin tubes, and constant leaks, that while aren't universal with headers, they are prevalent enough to be a real concern.

I'm working on a header for my 4BT, that will have a 1/2" flange, and schedule40 weld "L"s for tubing. It is more work than bent tubing, but it needs to be able to support the weight of a turbo, survive 1300+ EGT's, and not self destruct with the typical vibration of a diesel. Repairability is also a concern in the unlikely event there is a failure. Given that it is a low RPM engine (<3000 RPM), there is no way to tune to the necessary length, but the boost will take care of that. There is no reason that you can't build a tuned length header for a 360 the same way.

I would gladly pay real money for an option like that, but in the end, the various manufacturers are all about "performance" at the expense of durability and quality. One could argue that thin light tubing is also much cheaper to purchase, and to fabricate, so I'm thinking their profit margin has as much to do with it as performance. They could do better, but don't bother.

I would gladly buy a quality header, made to last, but for my money, it just doesn't exist to the level I expect. It isn't that the capability to bend heavier tubing doesn't exist, it's just too much bother for them to offer it as an option.

Guess what I'm saying is that your assumption is hardly valid, as there are many people who have the money to spare, and choose to go a different way. Your little one liner is a bit presumptous, as you seem to think you can speak for others motives based on your own.

[Dmntxn77]

Take it however you prefer.

Good headers are out there and they dont require much searching. The reason that companies dont make headers out of schedule 40 is 1) pipe is for poop, not performance, 2) that thick of material is not necessary, 3) that would be WAY too much weight to hang off of your head, especially on an off road rig that gets bounced around all the time...

I challenge you to find one accomplished racer who has not installed headers on his/her vehicle. My money says that you will not. The reason is that headers are a time tested and proven performance add-on.

Like I said before though, you cant buy cheap headers though. If you buy crap, then expect crap. Its simple and applies to most things.

[Elliott]

Headers cost you in low end torque. If you spend all your wheeling at higher RPM then headers would have a lil torque advantage but I think that is less the case. If you like high underhood temps they are great for that.
Run some dyno sims, you'll get the picture.

[DAHoyle]

Take it however you prefer.

Good headers are out there and they dont require much searching. The reason that companies dont make headers out of schedule 40 is 1) pipe is for poop, not performance, 2) that thick of material is not necessary, 3) that would be WAY too much weight to hang off of your head, especially on for an off road rig that gets bounced around all the time...

I challenge you to find one accomplished racer who has not installed headers on his/her vehicle. My money says that you will not. The reason is that headers are a time tested and proven performance add-on.

Like I said before though, you cant buy cheap headers though. If you buy crap, then expect crap. Its simple and applies to most things.

The very best header available still takes a distant second place to a pair of quality manifolds where durability and quiet is concerned.

The argument about racers is in no way a valid comparison, because there are many, many sacrifices made in all areas in the name of performance. I wouldn't run slicks on the street, or any number of other "improvements" that racers make to their vehicles.

Add to that, the fact that for any given driver or even circumstance, the selection of headers is a compromise. While they do reduce backpressure, their real gain is in exhaust scavenging, and unless you are building for a specific, narrow RPM range, such as a racer uses, then your performance gains will likely be compromised. The idea that you can maybe get a 15 hp peak gain isn't in dispute, but it will not be across the power band, and will typically average much less than that. A pair of shortys will likely not show more than 4 or 5 hp.

There is certainly a happy medium to be found, especially for vehicles with intended street duty. The trend towards stainless has gone a long way towards improving durability, but even they have a tendency to crack. A heavier gauge tubing would be welcomed by many.

The fact remains that your attitude seems to be that there is no possible opinion except your own. I made my own decisions for my own reasons, and quite honestly, cost never played into it. I'm reasonably certain there are others who see it as I do. Some so called improvements are not worth the problems associated with them, or are just not very high on the list.

[Elliott]

The headers on my TR were great and I never had a problem other than heating my carbs/gas up with them... combined with everything else I did on that motor down to the dual 3.5" velocity stacks it ran a real sweet 8-9,500 rpm.

I'll add, other than for sound effect I don't think they really have an effective place on a motor that can't turn a regular 6,000. If I ever build a Javelin I'll be using headers but it won't be built for low rpm. Now forgive me a lil, I am kinda prejudiced because I grew up with motors that you could dump the clutch off the line ('72 240Z) at 6,500 rpm time after time... and never, ever, had a V8 even stay close at the line for that reason... they'd catch me at the 1/4 and then I'd pass them again at 120 and keep running on the long stroke. I guess that's why I always thought this "no replacement for displacement" was such a funny concept because it only was realistic in a very narrow confine between the 1/8 and the 1/4 and then the short stroke always gave way to the long... I guess maybe it was just their nerves but I really don't think they had the gears to stay up with the longer stroke.

[Dmntxn77]

DAHoyle.... I agree with most of what you have said. Opinions vary, yours is clear, as is mine. Its no big deal, thats how it goes. Just think of how boring it would be if we all had the same opinion...

Regarding the topic. It was a simple question, and I gave him a simple answer. He didnt imply that he wanted us to list the pros and cons of running headers, so I didnt feel the need to open that bag of worms.

I am a fan of headers, and I do understand how they work. However, because I am a cheapskate at heart, I have had many more bad experiences with them than I have had good. Hence my advise to spend money on quality headers the first time around. Not to mention good gaskets and fasteners...

[Dmntxn77]

BTW, FWIW, the ceramic coated Doug Thorleys that I put on my 5.9 ZJ reduced my engine temps. I never took under hood temp samples, but my engine runs cooler with them installed.

[Elliott]

That would be especially nice if you didn't have to wrap them. The Thorleys are about the only header I'd consider for an AMC. I've got the non-smog '72 manifolds though... not that you've ever heard them run. Ok, so... I'm thinking of paring the projects back....