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Old 07-23-2003, 08:50 PM
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Exclamation Long or Short Tube Headers?

I am not really knowledgeable when it comes to exhaust that is why i am asking all the questions about exhaust systems and parts. I am asking what is the difference and what applications are typically used for long tube headers and short tube headers. Any information or input on this is greatly appreciated.

Short Tube?

Long Tube?

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Old 07-23-2003, 09:44 PM
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I think it has to do with what will work in your set up. Sometimes long tube headers will interfere with other mods you have made to your rod and you will have to goto short tubes.
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Old 05-10-2011, 09:35 PM
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kinda depends on what your doing.and the app.for street cars or race cars the header needs to be sized for the app.both length & tube size.and for camshaft,CI,heads,rpm,weight,trans, auto,4 speed,5 speed,lenco.it can all make a difrence.but not somuch on a smog street car, it needs a small well desigined header for the app. sorry not much help. but custom headers arnt cheep. off the shelf headers work ok in most cases.but genuraly a long tube will make more power.and get squished easyer.
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Old 05-10-2011, 10:20 PM
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Quote:
Originally Posted by Ray102386
I am not really knowledgeable when it comes to exhaust that is why i am asking all the questions about exhaust systems and parts. I am asking what is the difference and what applications are typically used for long tube headers and short tube headers. Any information or input on this is greatly appreciated.

Short Tube?

Long Tube?
My take on this is to always use long tube headers when you can. Shorty headers are better than many factory exhaust manifolds- at least when talking about pre Gen 3 SBC engines (the LS-type engines actually have decent factory exhaust manifolds in some applications), but not as good as LT headers for making power.

As has been said, there are times where there just isn't space enough to run LT headers, or by using LT's there would be a need to switch to a floor mounted shifter for example, and some builds don't call for an aftermarket shifter. Some 4WD trucks have a hard time mounting LT headers because the transfer case/crossmembers get in the way.

A low restriction exhaust system (having as few bends as possible) using good flowing mufflers and a true dual exhaust system of a sufficient diameter is also very important. It's been shown that a connector pipe between the two sides mounted after the collector and before the mufflers will often boost the mid range power, and most guys like the change this brings to the sound.

I won't get into which muffler flows better than another, but I can say that terminating the tailpipe under the vehicle is a recipe for getting an interior "drone" that will drive you nuts. I've found that running the pipes at least to the rear axle, and preferably out the back or side of the vehicle will be a lot easier to take from inside the vehicle.

The diameter of the primary pipes (the ones right off the head) and the collectors (the length of large diameter pipe that the primary tubes connect to) is also important. Too large hurts the bottom end, as does too short. Too small hurts the top end, as does too long. The lengths mentioned here would be mainly pertaining to an open header w/a collector more than a header w/collector into an exhaust system that contains a muffler.
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Old 05-11-2011, 08:31 AM
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on a long tube system a big tube header will be shorter than a small tube header,in most all cases,due to the big tub not having as much velocity as the small tube. and what some consider small tube and big tube headers can be a lot different. like our race car has 2 1/2" primary tubes,witch is a big tube. genuraly 1 1/2-1 5/8-1 3/4 is for small block and 1 3/4 & up for big block. but there may only be 2 or 3 for your app.if that.so sometimes your stuck unless you go custom header.
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Old 05-11-2011, 09:03 AM
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I'm going to try to explain this, but I can't guarantee I'll explain this well because it's been 12 years since I did header design so the engineering is not fresh in my mind.

In general, longer headers will tend to improve performance at higher RPM's while shorter headers wil tend to improve performace at lower RPM's. For circle track racing, engine design is a substantially simplified problem because most of the time the vehicle operates at high RPM, so you do just about everything with performance at high RPM in mind.

Other forms of racing present the problem of requiring performance across a broader operating range, so in those cases you might tune your header length based on trying to fill a dip in a torque curve.

Here's where the simpliied approach of trying to do anything to boost peak horsepower can go wrong. Peak horsepower tends to be measured at high RPM. How much does it matter in a 1/8 mile run how fast you go from 70 to 80 if it takes too long to get from 0 to 70...

A smooth torque curve is usually the best approach to tuning, so if you have a particular RPM range that is weak you might tune header length to improve that range.

Now, the equations we used when I was engineering header design were set up by a master's student in fluid dynamics who was going on to work on is PhD when I graduated... If you wanted to go that far I'd just start mocking up with flex exhaust and experimenting on a dyno.

The basic principles are that at certain RPM's the momentum of exhaust flowing out means it's moving in waves, it will bounce back and forth between the muffler restriction and the restriction at the closed exhaust valve. The idea is to tune so that the wave is moving away from the exhaust valve when the valve opens, as this will create a vacuum and help pull exhaust gas out of the cylinder.

What will happen is shorter pipes will have these harmonics at a lower RPM, and there will be more peaks which are closer together in terms of how many RPM's there are between speeds at which you'll find harmonics. Longer pipes will be advantageous at higher RPM because they will be less restrictive while the shorter pipes may start to choke flow at high RPMs.

Logically, another thing to bear in mind is that between these peaks in performance improvement you're also going to have points where you'll have the exhaust wave moving towards the exhaust valve when it opens and those will be RPMs where you will have less performance - and you'll also have more of these with shorter headers.

Now one more point - if you have forced induction (turbocharging or supercharging) then the scavenging effect is an order of magnitude less significant than boost, so you will typically tend to go for less restrictive. I haven't done any exhaust design for forced induction, so all I can offer on that topic is broad overview of theory.

Last edited by Slipangle; 05-11-2011 at 09:28 AM.
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Old 05-11-2011, 10:15 AM
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good post.kinda like tuning intake& cam, helps in some hurts in some.witch is not real good ona street car but a 5 speed or lenco racecar you leep themotor in the rpm range you want it and everything is optimized for that narrow rpm range.
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Old 05-11-2011, 01:40 PM
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Quote:
Originally Posted by Slipangle
In general, longer headers will tend to improve performance at higher RPM's while shorter headers wil tend to improve performace at lower RPM's.
While I stopped reading at this point (time restraints), a shorter primary and/or collector tube favors the top end and vice versa- unless I've been wrong for a long time. Collector length is probably more critical than primary length- FWIW, Vizzard seems to thing there's a lot of leeway in primary length and to not be overly concerned w/it. Rule for diameters (primary and collector): larger = top end, smaller = bottom end.

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Old 05-11-2011, 07:02 PM
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it all makes a difference.the bigger the motor the less collector has to do with it . and just shortining a header dosent make it a high rpm header.there are too mant factors.and yes collector shape makes a big difference in the way it works.
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Old 05-11-2011, 08:20 PM
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Quote:
Originally Posted by cobalt327
While I stopped reading at this point (time restraints), a shorter primary and/or collector tube favors the top end and vice versa- unless I've been wrong for a long time. Collector length is probably more critical than primary length- FWIW, Vizzard seems to thing there's a lot of leeway in primary length and to not be overly concerned w/it. Rule for diameters (primary and collector): larger = top end, smaller = bottom end.
What I was speaking to in general applies to the volume of the exhaust system between the exhaust valve and the muffler restriction. So larger tube diameter figures into the equations similar to the way primary length etc. figures into it. The equations I used did not really get into the more complicated maters of the placement of the transition from primary to secondary etc. That's getting to a level of modelling the system in 3D and using computational flow dynamics software. You probably can't afford to go to that level unless you're a Formula 1 team.

In general as far as primary length and collectors, what you want is smooth transitions and equal length of primaries. I don't know if there was any science behind it, but we generally shot for equal length for primaries and secondary. And we pretty much were set on 4-to-1 collector, and it was for a 4-cylinder motorcycle engine as far as our application was concerned.
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Old 05-11-2011, 08:55 PM
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3-D modeling aside, using a simple calculator, enter whatever arbitrary values that come to mind (I used a SBC 350 w/a cam having 60 EVO, 295 advertised duration and a 110 Exh C/L. This happens to be a solid lifter cam I have in a 355 engine going together now) and use, say, 6000 RPM Peak Power RPM and note the results for the primary length, primary diameter and collector diameter.

Now, enter the exact same values as before, except use a higher RPM for Peak Power RPM, say 7000 RPM. Note the difference- you will see the higher Peak Power RPM requires a shorter, larger ID primary and a larger ID collector.
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Old 05-11-2011, 10:13 PM
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yes cobalt has it pretty close. slip angle the equel length tubes are for race situations .well some of the time. an unequal length tube set of headers will broden the power band and torque curve ,witch can make it faster and more streetable,and probably better in some race cars.I would think a road race car would benefit also. yamaha has on some engines(2 stroke) different port timing(like different cam timing for each cylinder)& different cr. to broaden the torque curve. there probably not the only ones to do it. Im sure there is some formulas for building headers ,and I would imagine there is a lot of data to go into them for custom race headers.and a little for street headers.probably very little for street headers.
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Old 05-12-2011, 05:45 AM
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A couple thoughts, feel free to disagree...

The header manufacturers have "decided" for us what we will use in many circumstances, by what they offer. Obviously, custom headers can be fabricated by a dedicated individual, and professional race applications will go to any and all effort to maximize every segment of the entire vehicle, not just the headers/exhaust system. But most street/strip-type engines running a full exhaust system w/mufflers, etc. will use an off the shelf header, correctly sized as closely as the length and diameters offered will allow. This generally means headers will be selected that have a minimum of 1/8" difference in diameter- so the choice for most SBC engines is going to be either 1-5/8" or 1-3/4". Length is also predetermined by the manufacturers due to 'packaging' requirements- they have to fit the vehicle, after all. But as long as the length isn't excessively short or long, they're going to work OK- at least when compared to most factory manifolds.

It seems most NA SBC Gen 1 and 2 street bound performance engines work fine with 1-5/8" diameter primaries and 2-1/2 or 3" collectors. Seldom is a primary needed that's over 1-7/8" or a collector diameter greater than 3" on a SBC unless it's a max-effort build. The Gen 3 and up engines seem to do better w/1-3/4" primaries.

I agree w/the assessment that equal length primaries are not needed or even necessarily wanted in a "normal" performance build. According to some engine gurus, there's about a 6"-8" "leeway" in primary length before there's a detrimental effect in exhaust tuning (I'm simplifying here to a large degree- I'm sure not a fluid dynamicist), and the difference in lengths of the primary pipes in the average V8 header is going to be less than that, anyway. And as said, the differing lengths tends to broaden the curve and this is generally going to be better than a narrow range where the engine is "on the pipe".
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Old 05-12-2011, 09:16 AM
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good post, thus the reason for searching different manufactures for the header that might be right for you and your budget.oops dont for get your car, it needs to also be right for your car. I had an olds cutlass with a 260 v8. what a turd.the cross over pipe was less than an inch.the valves were about the size of a nickel&quarter.tiny small ports.aluminun intake with open plenum, funkey ex manifolds.well I tor into the top end, ported polished,opend it up ,did a lot of intake work,a pile of pocket work, recurved the dist, milled about .060 off the heads. built a turbo 200r with lock up converter on a switch.(it had a std 200 with no lock up converter)then it came time for headers.well the only header for thst car with olds motor was hooker.and me worken at a big speed shop/machine shop/vette shop,racecar shop etc. the price wasent too bad(this was in 86)well I think the tube size was I think 1 7/8 for a big 455 motor. it ran great , what a difference but dyno said it almost doubled the hp.and the lock up converter was just like an extra geer. and that realy helped the mpg.it also had the 1/2 quadrajet carb that I did a lot of work to,think I even bored the ventuiri's out a bit. I cant help but wonder just how much better it would of run with a correctly sized primary thbe header.probably around 1 1/2" dia. but it wasent available. and dont for get the hookers were the best header on the market, and they were for race cars so they were made for power in the upper rpm and a motor 2x the size of this. size isant everything but it is very important. the car now probably had as much power as a stock 350,possiably more. with the correct sized header???400??? and I left the stock tiny valves in the heads.but lots of port work on the tiny square ports.
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