View Full Version : straight pipes


desoto-S15
12-07-2009, 10:56 AM
Will running straight pipes cause engine damage

Kail
12-07-2009, 10:59 AM
I am not aware of it causing damage to a motor, but having no back pressure can cause you to lose low end power unless the motor is built for it.

Peter Mc Mahon
12-07-2009, 11:03 AM
How would you build a motor to keep low end power with no back pressure? Peter

Jalopy Kid
12-07-2009, 11:15 AM
I run 1 3/4" straight pipes on most of my cars, no problems so far.

Ruiner
12-07-2009, 11:16 AM
Are we talking full pipes the length of your car, or zoomie headers? There's a big difference when your asking about engine damage...

kickstarts
12-07-2009, 11:21 AM
It might not hurt your engine but it definately won't help it.

If you do any long rides with it, you'll be exhausted by the time you get to your destination from listening to all that racket and it doesn't help with your gas mileage either.

Straight/open pipes just scream "I Need Everyone To Notice Me!". A nicely tuned full exhaust just sounds so much better and it will help your engine run much more smoothly.

MarkzRodz
12-07-2009, 11:23 AM
We've always heard stories that it'll bend your exhaust valves because when you shut off the hot engine cold air will crawl up there and shock the valves thermally.Never happened to me,,I never ran one that long as I can't stand the noise. There are ratrodders who drive their cars that way and I havent heard any damage stories.

I do know one thing though, that happened to me, is that if the engine sits outside over an extended period of time or in a wet/humid environment,,,moisture will get into those cylinder(s) and cause rusting. That's the cylinders with the exhaust valves open (to the elements and no manifold or a short pipe for an exhaust).
Like I said it happened to me and I lost an aluminum V8 that way (iron liners).

theHIGHLANDER
12-07-2009, 11:50 AM
With zoomies cold air will certainly warp valves but everything has to be just right (or wrong) for it to happen. Back pressure...I love when that comes up. I'd like to challenge this post to someone explaining in professional terms how constricting an exhaust system builds power, high RPM or low RPM, and some of the associated dynamics. Now I'm pretty familiar with small engine requirements on that score since some mixture is pulled back in to help run the motor. I'm stopping there because we're not talkin about mini-bikes or lawn mowers here. Any takers?

tommy
12-07-2009, 12:22 PM
I'd venture a guess that most of the responses here that say it's harmful are repeateing stories that we have heard over the years. I certainly heard it when we were trying to test start an engine with NO manifolds way back when. It never happened. If you can list a specific instance with all the details that caused the valves to warp on a perfectly good engine because you had short pipes, I'd love to hear about your actual experience. Until there are an overwhelming number of detailed cases proving this old wives tale, I will treat it as an old wives tale.

29nash
12-07-2009, 12:23 PM
Will running straight pipes cause engine damage
No, but drivin' habits associated having them on there can tax a motor to it's limits. If it's a hotrod, it needs straight pipes!:D.
And ignore all of the negative (guessing) that reducing back pressure will result in a loss of power or 'warp' the valves on a 4-stroke automobile motor.

I've never seen a warped exhaust valve. Seems like somebody that ran short headers and ruined their valves would have a picture of one?.

Actually, allowing a motor to breathe by clearing obstructions in the exhaust pipe, almost without exception, will result in better performance.

Kail
12-07-2009, 12:36 PM
Some interesting reading material:
The header's job is to remove exhaust gases from the combustion chamber in a controlled fashion. I think we all agree here. The part needing clarification is the backpressure issue, and the elements of the header design and how they affect the engine's ability to make power.

So, how does the engine make power? A fuel/air mixture is ignited creating a high pressure region directly above a piston which creates a force on the piston dome. If we've done everything right, the piston moves down swiftly and transfers the force to the crank. While the piston is moving downward a couple of things are happening:

1. The volume of the trapped, expanding gas is increasing

2. The heat generated by the mixture burn is being turned into kinetic energy and being absorbed by the engine's components in direct contact with the gas.

These are the two most important thermodynamic effects. So how does the header design affect this process? When the exhaust cam opens the exhaust valve, there is still pressure in the cylinder from the expanding combustion process. This is called blowdown because there is a very strong gas pulse created in the exhaust by the (usually large) pressure differential between the exhaust system and the cylinder. The ability of the exhaust system to create this pressure differential is what discriminates between good and bad.

The ideal exhaust system will provide a very low pressure somewhere in a vacuum range to extract as much of the combustion effluents as possible. If we really get it right, we'll actually be able to use this process to pull fresh intake into the cylinder at overlap (the time when the exhaust valve and intake valves are open at the same time) because we have developed a very large pressure differential between the intake manifold and the exhaust. If we get it wrong (well, maybe not wrong, but that's a different discussion), we get natural EGR (exhaust gas recirculation) because the inert exhaust gases left in the cylinder will dampen the combustion process in the next cycle.

Now to the hard question, why do people believe backpressure is necessary? Because they've read in some magazine that an oversized exhaust can negatively affect performance from a loss of backpressure. Nothing could be more inaccurately stated. As Tchi mentioned, an overly large exhaust affects exhaust velocity. One of the fundamental exhaust concepts is the exhaust is a series of pulses, not a continuous stream. Those pulses can be engineered to control exhaust pressure through the exhaust system, and pressure control for blowdown is critical to performance.

BTW, I define performance as thermal efficiency, not maximum measured power. Generally improved thermal efficiency leads to more measured power, but not always.

So our header gives us the opportunity to manage when and where high and low pressure areas exist at any given point in time. It also gives us the opportunity to optimize when blowdown occurs. If the exhaust is "restrictive" because it is designed to optimize low rpm torque, blowdown is slower to permit the pressure on the piston to remain longer. If it is "freeflowing" it is optimized to get the exhaust gases out of the cylinder as quickly as possible consistent with creating a low pressure region in the cylinder at overlap. Neither is right or wrong, they are just different for different applications. The header features most important to this part of the process are diameter and length of primary tube. Larger diameters tend to favor high rpm torque, longer primary tubes tend to favor low rpm torque. The header designer has to strike a balance between low and high rpm operation with the primary tube diameter and length.

The other thing a header does is allows the designer to use the exhaust pulses of other cylinders to affect the cylinder actually having an exhaust event. By combining primary tubes with complementary pulses, it is possible to further control the location and size of high and low pressure regions. This is sometimes called extraction. The idea is to use the exhaust pulse from another cylinder to "pull" the exhaust from the next. This is part of the theory behind 4 - 2 - 1 headers for 4 cylinder engines. By merging the complementary (360 degree apart firing events) cylinders in pairs before merging them into the final collector, the header provides better "scavenging." Scavenging is a term used to simply describe creating a very low pressure region in the combustion chamber at the right time and thereby ensuring the most complete extraction of inert exhaust gas.

The other thing going on with extraction is again, controlling when and where the pressure zones exist. In our ideal model, we have our lowest pressure zone at the exhaust valve seat when the intake starts to open. This encourages the fresh fuel/air mixture to move into the cylinder and jump starts the intake process. When you are really on top of your engine's tuning and you know where in the rpm range it is most important to make power, you can use this to get better than 100% volumetric efficiency, meaning you get more air than if you filled the cylinder at ambient pressure. It's a sort of supercharging effect all tuners like to find because it makes a smaller engine breathe like a larger one.



Another one:
Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.

hotroddon
12-07-2009, 12:39 PM
The old wives tail about warped exhaust valves is just that, an old tail.
It most likely came about from guys a long time ago doing short little straight headers and leaning out the motor to the point of burning the inferior material valves that existed back then and not realizing what really casued the problem.
It was NEVER the cause of straight pipes per se.

As for back pressure, that is also complete and utter Bull Shit. Highlander has it right here. The only time back pressure can help is in a system that is way too big of a diameter for the engine and back pressure can be a band aid, but a properly designed exhaust system will ultimately have as little pressure in the system and is possible. The idea behind a proper exhasut system is to extract the exhasut frm the cyclinders and dispose of it while not allowing burnt gases to reenter the combustion chamber during overlap. There is a lot of science involved with figuring out optimum diameters, lengths, timing of the two pulses (gas particles and Pressure waves) refracory waves etc. But "Back pressure" is Never part of the equasion when it's done right. PERIOD, End of Story.

BJR
12-07-2009, 01:40 PM
Will running straight pipes cause engine damage

No but it may cause brain damage from the noise.

Winged Avenger II
12-07-2009, 02:10 PM
no(i hate answers that go on forever)

silversink
12-07-2009, 02:50 PM
I'v had them on my flathead 6 for the last 20 years, don't notice any damage.:rolleyes:

Bosco1956
12-07-2009, 03:57 PM
I'v had them on my flathead 6 for the last 20 years, don't notice any damage.:rolleyes:


I have them on my flathead... Noise isn't bad at all. My Flowmasters I have on some of my other cars are louder than the flatty straight pipes:eek:

Ol Deuce
12-07-2009, 04:05 PM
Straight pipes.........Saves Lives;).....No damage at all to any engine . only to your EARS. I would like to hear more on the street if the cops would use ear plugs:D:D:D..............Ol Deuce.......:eek:

hotrod-Linkin
12-07-2009, 04:09 PM
Straight pipes.........Saves Lives;).....No damage at all to any engine . only to your EARS. I would like to hear more on the street if the cops would use ear plugs:D:D:D..............Ol Deuce.......:eek:
whut did you say?????

CRASHNBURNS
12-07-2009, 04:28 PM
I have run straights on everything I've owned and never had a problem one. I have never heard a car with properly installed straight pipes that sounded like shit or that was "too loud". It's definately not a rat rod thing. The baddest ass hot rods I've ever seen had straight exhaust on them, and Flowmasters and the like, are for gay muscle cars and jacked up ree-haw shit.

Unibodyguy
12-07-2009, 04:46 PM
Hmmmmmmm??? well if straight pipes supposedly do damage, I guess we better get in touch with Harley-Davidson then, theres a lot of them with straight pipes in my neck of the woods. The Cop's never seem to bother them for noise.

Michael

COS
12-07-2009, 05:00 PM
I have been running them for 5 hard years now with now problems!!! It only gets loud when you really get on it but idle and cruzing down the road not bad at all no louder than a flowmaster......

pontiac
12-07-2009, 05:25 PM
I've never had any problems. I have a straight pipe on my 52 Pontiac with a Flathead 8 and it's not even loud.

My 64 also has dual straight pipes and I haven't had any trouble with it either. It's not loud at idle, just if i rev it up... cruising isn't bad either. With the windows up the sound in the car is just like having a mild muffler.

big creep
12-07-2009, 05:57 PM
i have straight pipes on my 69 caprice! 350 small block. no mufflers! and an h pipe! not loud when it idles or when im driving! just when i get on it! been like that for 7 years! and no problems! i dont care what people think or say! its what i like!!!!!

32skidoo
12-07-2009, 06:08 PM
Been running open, lakester headers on my roadster for 3 years. Knock on wood, no engine damage yet and I've driven her down the interstate at well below freezing and in 100+ degree weather (Are you tough enough?). Pretty loud at idle, really loud when you get into it, but as has been said, when cruising the hwy, it's really nice. I would suggest earplugs or turn off the hearing aids. In a roadster, on a long road trip the wind noise and buffeting are more annoying than the headers. After 3+ hours you are ready for a stretch and a cool one or a hot one or both. If it ain't loud, it ain't a hot rod and besides loud pipes save lives.

Hyway Hauler
12-07-2009, 06:16 PM
Will running straight pipes cause engine damage

NO NO NO! Before asking a question, ask it out loud (to yourself) first and then think about it before posting such a question...:rolleyes:

Jalopy Kid
12-07-2009, 06:18 PM
If the straight pipes are run out to the back bumper it is not loud inside at all. Even my edsel which runs open lake pipes that dump at the back wheels is not loud inside unless you are right next to a concrete divider or in a tunnel.
When it's idling it is no louder than cherry bombs or smitthys and really only gets stupid loud around 3500rpm and up

mratt
12-07-2009, 06:40 PM
I've run straight headers. The engine runs better with a collector.

64sled
12-07-2009, 07:01 PM
:):):)

plym49
12-07-2009, 07:15 PM
How would you build a motor to keep low end power with no back pressure? Peter

Looks like this has been beat to death by now but I will chime in anyway.

If the pipe diameter is too large and/or the pipes are too short, a given engine will see poorer performance, particularly at lower rpms.

Have you ever tried to run an engine with no headers at all? They run like crap.

You need a certain amount of flow to help scavenge. Similarly, the frequency of the reversion pulses changes as pipes get shorter or larger. Almost like a boat running through a canal. Some of the wake of the boat hits the walls of the canal and comes bouncing back. For a given boat speed, these wave reflections can interact with your original wave (wake) to cancel each other out, or to end up twice as much, and everything in between. This is what 'tuning' an exhaust is all about.

Harley guys are the worst when it comes to going to open (no baffles) and larger diameter and shorter pipes. They look great and sound great but in most cases take away some performance.

If this was the route to maximum power every race car would have super short, super large diameter exhausts - and these are modified motors looking for max power at elevated rpms. They don't, and that tells us something.

That said, I swapped out the headers on the car in my avatar for a set of lake pipes. These are basically open although there is a rudimentary baffle at the outlet. I did lose low rpm torque but they look better and sound better plus you can see them pop at night when you back off the gas. Plus they leave nice soot marks down the side of the car, like a WWII bomber.

So, in the end do what you want - just be aware of whatever baggage is associated with whatever you decide upon.

carnuts
12-07-2009, 09:37 PM
I've heard the same thing from people about the warped valves. I just wouldn't have them any other way. That's one of the things I really enjoy about hot rods, the rebel attitude!:cool:

panic
12-07-2009, 11:47 PM
So, why aren't the people who "ran straight pipes for 20 years" bothered by the noise?

They're DEAF.
They just don't realize it.
No, I'm not kidding.

333 Half Evil
12-08-2009, 12:50 PM
If valve damage is caused when running straight pipes, then wouldn't you think that all the old modifieds that just ran stub pipes would have had tons of bent valves? This model a dirt modified runs a buick nailhead with 8" long stub tubes....never had a valve problem!!!!

tommy
12-08-2009, 12:57 PM
The silence is deafening!:rolleyes::D

twinturbo496
12-08-2009, 12:59 PM
Yes,
I believe you can reduce power by increasing backpressure.

I never tried it, but I think if you put enough pressure in the exhaust ports of a multi cylinder engine, it might be possible to make it run backwards, although I don't think the fuel tank will fill back up.




With zoomies cold air will certainly warp valves but everything has to be just right (or wrong) for it to happen. Back pressure...I love when that comes up. I'd like to challenge this post to someone explaining in professional terms how constricting an exhaust system builds power, high RPM or low RPM, and some of the associated dynamics. Now I'm pretty familiar with small engine requirements on that score since some mixture is pulled back in to help run the motor. I'm stopping there because we're not talkin about mini-bikes or lawn mowers here. Any takers?

plym49
12-08-2009, 06:48 PM
Yes,
I believe you can reduce power by increasing backpressure.

I never tried it, but I think if you put enough pressure in the exhaust ports of a multi cylinder engine, it might be possible to make it run backwards, although I don't think the fuel tank will fill back up.

LOL

Think about the two extremes of operation. The first is with no headers or manifold - the exhaust ports open to the atmosphere. The motor will run like crap. Now the opposite extreme - run the exhaust through a teeny tiny pipe. Of course, it will not run that way, either.

Just like a guitar string can be too tight or too loose, it is a thing of beauty when it is tuned just right. For any given engine, assuming that a bigger/shorter header/exhaust pipe will always increase power is just as wrong as saying that every guitar will sound better by loosening the strings.

39 All Ford
12-08-2009, 07:29 PM
To me it is simple. common sense prevails.

Im my way of thinking, more important than 'straight pipes' or not, is a "reasonably sized and 'tuned' exhaust. With the tuned part being more the size of the tubing than most any other variable.

A well sized exhaust will add to the scavenging effect as a properly sized MOVING column of gas tends to keep moving. I don't see where the absence of mufflers can possibly damage an engine or hurt performance beyond any very narrowly defined circumstance.

Can many other folks just see this in their mind or is it a curse I bear almost alone? :D

HotRodFreak
12-08-2009, 09:15 PM
I LIKE LOUD PIPES!
12" resonator mufflers are OK too.