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Air flow thru your engine

Discussion in 'Performance & Tuning' started by chris4x4, Apr 5, 2017.

  1. Apr 5, 2017 at 8:20 PM
    #1
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    Have you ever noticed that if you make a quick "puff" at a candle from a short distance, that the air, even though you are not blowing anymore, still makes it to the candle and blows it out? That's because air has "mass", and when in motion, it must be acted upon to stop it. Have you ever noticed that as a kid when blowing bubbles, if you try to blow a bubble to keep it aloft, it seemed that sometimes the bubble would be passed by the air, only to wiggle around, and then "follow" the air you just blew? These little things also apply in an engine.

    As the air is going through the intake, and through the throttle body, there is a bit of turbulence created by the throttle plate. As it continues on to the intake runners, the air is straightened out into a nice laminar flow, as the intake valves open, and the piston is rapidly moveing downward, the air rushes in to fill the combustion chamber, flowing down the sides of the cylinder wall, hitting the top of the piston and moving up the other side and thru the middle, and swirling. as the intake valves close very fast, its like a door slamming shut. The air that was following in to the combustion chamber is now suddenly stopped. This sends a "shock wave" backwards through the intake runners, and if timed properly, this "shockwave" or "Pulse" is now helping to "push" more air into another cylinder.

    Meanwhile, as the air in the first cylinder is being ignited, and producing power on the downward stroke, the piston now begins its upward stroke. The exhaust stroke.This is where scavenging comes into play. Scavenging is when the exhaust valves open and the exhaust exits the cylinder leaving a vacuum behind it. At that point the piston moves the exhaust out rapidly in a "puff". This puff, once again has mass. There is a high pressure area leading the way in front of the exhaust pulse, and when the exhaust valve closes, it happens abruptly, creating a low pressure area behind the exhaust pulse. This pulse travels down the exhaust, and past another cylinder. The low pressure of the pulse "pulls" the exhaust gasses from the next cylinder, when doing this, it creates a vacuum in the combustion chamber helping to "pull" more air into the cylinder as the intake valve is starting to open while the exhaust valve is still open, this is called overlap.

    All these pulses need to keep up their velocity to remain efficient. They do this by staying hot, and by the size of the exhaust pipes. Newer vehicles with variable valve timing (VVT) keep these pulses timed throughout the rpm range. There is a "Goldie Locks" effect taking place. Too large of a pipe, and the pulses slow, exhaust cools too fast, and the engine looses efficiency. Too small of a pipe, and the exhaust is sped up beyond how the timming of the valves was designed, the exhaust temps rise, and the engine looses efficiency. Any change in the system, be it a larger exhaust, or whatever, has an effect on it. Sometimes positive, as the auto makers have to abide by emissions standards, but many times negative, as some aftermarket manufactures just want it to "sound cool".

    When installing a Turbo, or Supercharger, the scavenging effect is not as important, as the higher pressure "pushes" everything through the system, in which case, a larger free flowing exhaust would be the most beneficial.

    I have oversimplified this just a bit, as I don't have time to go into EVERY thing, or break down the physics involved, but thought it would be a good read for those thinking about changeing their exhaust system and wondering how the new exhaust may affect performance. :)
     
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  2. Apr 5, 2017 at 8:21 PM
    #2
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    And what I found in another forum:

    I. IntroductionOne of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

    II. Some basic exhaust theory
    Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

    III. Backpressure and velocity
    Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

    The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

    Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

    IV. So how did this myth come to be?
    I often wonder how the myth "Engines need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

    V. So why is exhaust velocity so important?
    The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).
     
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  3. Apr 5, 2017 at 8:37 PM
    #3
    OFFGRID

    OFFGRID Well-Known Member

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    Way cool Chris! I've been reading up a lot lately on the science of engines. I could not have said it better in so brief of an article. I bet you would really like Billavista.com
     
  4. Apr 5, 2017 at 8:42 PM
    #4
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    I worked with a race team years ago, and my team was solely responsible for the exhaust systems. We did some pretty cool stuff with exhaust. Learned a lots of stuff about flow dynamics, scavenging, temperatures and such. nothing makes me cringe inside more than hearing someone say "Man.....you gotz ta redoose dat back pressure...."
     
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  5. Apr 5, 2017 at 8:47 PM
    #5
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    Intake discussions are just as bad. The biggest restriction in the intake, is the throttle body........and the valves. I mean........the air cleaner tubing is about 4" in diameter. The TB is about 74 mm (?).......the intake valves are about 39 mm.......
     
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  6. Apr 5, 2017 at 8:56 PM
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    OFFGRID

    OFFGRID Well-Known Member

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    I like playing with header exhaust combinations. I like to take a mild built engine, nothing radical. My CJ for example. 258 with a mild Comp cam Skinny head pipes @ 1 5/8 in, 3in collector, 2.5 in exhaust. The skinny head pipe keep up the back pressure of the engine building low end torquewhile the larger exhaust lets it run free. This combination would choke a race motor, but is great for a mild street car or 4x4.
     
  7. Apr 5, 2017 at 8:58 PM
    #7
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    :annoyed:
     
  8. Apr 5, 2017 at 9:02 PM
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    OFFGRID

    OFFGRID Well-Known Member

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    I know you said you don't like the phrase keep up back pressure but there is a point where the exhaust is too free and you rob torque. So maybe my experience has the right idea, but my terminology is incorrect. In my mind the opposite of too free is back pressure. Maybe balanced is better.
     
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  9. Apr 6, 2017 at 6:55 AM
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    OFFGRID

    OFFGRID Well-Known Member

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    Here is an article on exhaust pipe diameter sizing and effects on torque.

    Exhaust Diameter and Back Pressure
    How does the size of your exhaust pipe affect horsepower?
    Bigger isn`t aways better. Dispite what you may have heard having a 3" cat back pipe on a 4 cyl Honda isn`t a good idea, unless it`s making over 300hp. If the pipe diameter is too large you then run the risk of losing horsepower. No back pressure causes a loss of low end torque. Some back pressure is required. Your goal is to increase the flow, without robbing the engine of the power gain.

    An exhaust system that creates too much back pressure is called a restrictive exhaust. Most OEM exhaust are build as a restrictive type with cost and gas ecomony in mind. A restrictive exhaust hampers performance in two ways. One is that the engine has to work harder to push out the exhaust gases from the cylinders. Second is the engine has left over gases in the camber which then get diluted with new incoming air and fuel mixtures. This can help gas mileage, but performance suffers.

    Yet, backpressure is needed to remove gases from the engine. Back pressure creates something of a suction to help remove spent gases when it isn`t too restrictive. Too much backpressure and it can`t all escape, too little and the engine will pull it back in through the exhaust valves when open. It`s a balance your trying to achieve as you increase the power of the engine.

    It is usually associated with a popping or burble noise coming from the exhaust, not a backfire. You should expect properly tuned engine to burble or pop when the throttle is close from a high RPM. Think of a top fuel dragster and how the engine at idle makes the popping noise. That engine is creating a lot of backpressure. That is also the reason for the short open headers and with the remaining small amount of back pressure the gases are removed easily. If your car is making loud pops under hard accleration/decleration then that is backfiring.

    Backfiring is not a good thing. We`ve all heard of a car being called a fart can. It`s due to the unburnt fuel getting into the exhaust system and then it is being ignited. Commonly it`s a small air leak in the exhaust system connections. It can also be due to a lean air fuel mixture or it could even be related to the ignition system. The ignition sequence could be off, or the plug wires worn, and the coils themselves could be bad.

    If you plan to upgrade your exhaust then you should look for a system that is .25 to .5 inches larger than the existing stock exhaust piping. This will give you the best increase. Also to consider is what RPM will your car or truck operate at, most of the time. A exhaust pipe with a smaller diameter will produce more low to mid range RPM torque, where as a larger pipe diameter will increase mid to high range RPM torque.

    Article published by SFX Performance on 3/8/2011
     
    Last edited: Apr 6, 2017
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  10. Apr 6, 2017 at 7:18 AM
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    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    That's probably an older article? Just guessing. Given a few of my friends are engineers for manufactures, I like to think the info they give me is more accurate than some of these folks....That being said, I think everyone has experience one way or another that can show both sides.
     
  11. Apr 6, 2017 at 7:44 AM
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    OFFGRID

    OFFGRID Well-Known Member

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    True, You'll notice that the article said that Balance was key. I want to post one more that explains the effects of headers and their lengths and diameters of the primaries on torque. It does not go into the effects of collectors though. This is where I find most people have trouble deciphering how to purchase a specific header and are at the mercy of the recommendation of the guy behind the counter or the shop owner.

    Header Theory (Part 1): Looking at the Science Behind Exhaust Header Tuning
    Posted by Wayne Scraba on October 30, 2015 at 11:57 am

    Good quality drag race headers, such as these Hooker Super Competition race headers, make use of primary tubes that are close to equal in terms of length.

    Tube diameter has an effect upon inertial scavenging. With all other factors being equal, you will obtain a superior scavenging effect with an increase in exhaust speed.

    To a point, a header builder can control the speed of the exhaust gas by changing the diameter of the primary tube. The smaller the diameter of the tube, the faster the exhaust will flow.

    This is an example of a “zoomie” we discussed in the text. This type of header simply does not work well in naturally aspirated applications.

    On a race header such as these Hooker examples, the primary is “adjustable.”

    Basically, the collector can be unbolted and you can add primary extensions such as this in order to tune the header.

    Common header questions are centered around tube diameter, tube length, collector diameter, collector length, and so on. Some folks will tell you none of this matters. Others will tell you it all matters. We tend to agree with the latter, but when it comes to the racing world, one thing is pretty clear:

    Experience and knowledge are absolutely paramount.

    To answer to your questions, we went straight to two well-respected expert organizations in the biz—Hooker Headers and Reher-Morrison Racing Engines—for the lowdown on headers.

    Exhaust Scavenging 101
    Inside a header (with the engine running), “waves” of exhaust passing through the tubing are more or less manipulated to extract the burned gases from the combustion chamber. Simultaneously, those waves of exhaust help the intake side by pulling in a fresh air-fuel charge. If properly designed, the header set will provide a beneficial pressure balance between the intake and the exhaust.

    An engine benefits from two different types of scavenging: Inertial scavenging and wave scavenging. Header design can have an effect upon both.

    Inertial scavenging of gases begins as soon as the exhaust valve opens. Here, exhaust gases move past the valve and exit through the exhaust port into the header primary tube (and eventually working their way into the atmosphere). Hooker says the best power is produced with an exhaust gas speed of approximately 300 feet per second (as an example, if an engine has a 36-inch primary tube, it would take 1/100 of a second for the exhaust “pulse” to pass through the tube). Hooker notes that once the exhaust valve is closed, these gases still continue to move down the exhaust tube at a rate of 300 feet per second. But as it travels down the pipe, the exhaust cools and actually slows in speed. Behind this “pulse” is an area of low pressure that is expanding as the exhaust flows away. Once the last of this exhaust gas reaches the end of the primary tube, the area of low pressure has increased in size to include the full length of the tube for that particular cylinder.”

    Wave scavenging does not involve the physical movement of exhaust gases up and down the header tubes. Instead, it deals with the sound waves created inside the engine. Hooker says that when an exhaust valve first opens, a pressure wave begins to travel—moving in excess of 18,500 inches per second (more than the speed of sound), which at sea level works out to 13,397 in./sec., depending on several factors). This sonic wave is moving quickly—much quicker than the ever-expanding exhaust wave we discussed above. When the sonic wave arrives at the end of the primary tube, a negative shock wave is generated, and this wave travels backward toward the exhaust port (because it is reflected).

    What the header builder has to do is time the arrival of this negative pressure wave to occur just before the exhaust valve closes and while the intake valve is opening. If the negative wave arrives too soon or too late, the power potential of the next combustion chamber cycle is diluted.

    If the engine has no collector (for example, a one-cylinder powerplant or an engine equipped with zoomies) the exhaust enters the atmosphere once it has left the primary tube. But in most headers, the exhaust enters a collector. If the low-pressure area we talked about above spills into another primary tube for a cylinder where the exhaust valve is just starting to open, that low-pressure area will help to pull exhaust gases from that cylinder. Here, the engine will gain an advantage, because there is less residual exhaust gas remaining in the combustion chamber (which can foul the incoming charge of fresh fuel and air).

    By manipulating the diameter and length of a specific tube, a header builder can influence the size of that low-pressure front.

    Header Diameter and Length
    Reher-Morrison Racing Engines tells us there is a direct relationship between the diameter of the primary header tube and the exhaust velocity:

    “The key when selecting a tube diameter is to find a happy medium between the free-flowing characteristics of large tubes and the superior scavenging of small, high-velocity tubes. Header tube diameters normally range from 1-3/4-inches to 1-7/8-inches for smaller, low performance engines up to big 2-3/8-inches tubes for large displacement, high-horsepower applications.”

    Remember when we talked about how inertial scavenging helps to pull the exhaust from the combustion chamber? This also helps to draw in the air-fuel charge, with the end result being higher volumetric efficiency.

    Hooker notes that by varying the length of the primary tube, you physically change the time it takes for the vacuum pulse (low-pressure area) to reach the header collector. Essentially that’s what “tuning” header tubes is all about. This tuning can help to complement the components you’ve selected for the entire car (camshaft, torque converter, transmission gear ratios, rear axle ratio, tire diameter, and so on). Header tuning can also have an effect on how the car works at a specific track.

    As a rule of thumb, the need for a long primary tube is reduced as the speed of the engine increases, because there’s less time between cylinder firing, and the low-pressure area we talked about has less time to travel to the collector.

    Getting the tube diameter and length right is extremely important. With all other factors being equal, the proper header tube size will allow you to obtain a superior scavenging effect with an increase in exhaust speed. Some folks will even tell you that the exhaust valve diameter determines the header tube diameter (not exactly correct). To a point, a header manufacturer can control the speed of the exhaust gas by changing the diameter of the primary tube. The smaller the diameter of the tube, the faster the exhaust will flow (keeping in mind the exhaust flow slows as it cools). A clever header builder will recognize that by varying both the length and the diameter of a given primary tube in a header, those tubes can be tuned to provide the largest amount of inertial scavenging.

    As you can see, it can get complicated.

    So where on earth do you start? Reher-Morrison offers excellent advice:

    “At lower engine rpm, long tubes help maintain good exhaust scavenging and increase torque output. As engine speed increases, exhaust gas velocities increase and a shorter tube length tends to work better. The best you can do is find a header tube length that offers the best compromise between low and high end power. This is also why header length can be an effective aid in tuning the rpm range of a racing engine. Most racing engines will work best with (primary) tubes between 28 and 30 inches long. It is also very important that all header tubes are as close as possible to the same length. The tubes from the rear cylinders are closer to the collectors and need a few extra twists and bends to be as long as those (tubes) at the front of the engine.”

    When it comes to cheap, universal “fits-all” headers with seriously mismatched tube lengths, Reher-Morrison points out these unequal tube lengths actual create a different tune for each cylinder. Hooker Headers adds there can be as much as a 50 horsepower difference between 5,500 and 6,500 rpm when compared to a set of pipes with more or less equal lengths. That’s why primary tube length is significant.

    What about zoomies (the kind of headers you see on a supercharged funny car or dragster)? The truth is they will actually run pretty well in a couple of different power bands (for example, from 3,500 to 4,500 and then again from 7,000 to 7,500 rpm). But Hooker Headers tells us they can give up something like 25-35 horsepower or more between those two ranges.

    Next month, we’ll examine collectors and tuning.
     
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  12. Apr 6, 2017 at 8:26 AM
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    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    Variable valve timing greatly helps with the scavenging tuning in modern domestic vehicles too. For example, the 3.6 pentestar engine has a crazy flat torque curve. Compared to what manufacturers had just 15 years ago, they are getting performance equal to much larger engines. Hell......those little Honda 4 cylinder engines are fetter torque outputs that are better than the domestic V8 engines in the late 80's and early 90's
     
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  13. Apr 6, 2017 at 8:53 AM
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    OFFGRID

    OFFGRID Well-Known Member

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    I agree with you there. The age of computers has really taken off, especially with the help of VVT. I have been looking into an LS 5.3/6.0 swap for my 08 JKU. Most of the companies out their that provide harnesses and reprogramming of your donor computer don't want to mess with the newer VVT motors I think 2010 to current. I have found a couple that actually prefer this (the VVT) route and are cheaper. I think that it is wild that because of the electronic and computer gains of this generation a bone stock v6 Camaro today greatly out performs the 85 IROK with TPI (the heyday car of its time for computer controlled injection). To think I used to just be a gearhead. Man jeeps are fun.
     
    Last edited: Apr 6, 2017
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  14. Apr 6, 2017 at 11:23 AM
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    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    LOL!! I was actually thinking about the 85 IROC. Man.....when I was a kid, I LOVED that car!!
     
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  15. Apr 6, 2017 at 12:31 PM
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    OFFGRID

    OFFGRID Well-Known Member

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    Me too. I bought one a few years later, and my buddy bought the Pontiac GTA. Even though it cost a little more, I would tease him that its just not the same.
     
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  16. Apr 7, 2017 at 7:57 PM
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    JKBob 25

    JKBob 25 Well-Known Member

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    2" Superlift kit. 315/ 70/17.
    Very interesting read guys. Thank you very much. I knew some of what was posted. Back pressure, exhaust diameters, headers. But no where near what I learned from reading this post.

    So I have several questions. The most turbulent air into the engine is through the TB. Do TB spacers work, and are they worth the money? Another. I had an open end so called "cold air induction system" on my XJ. And i didnt really see any improvement to fuel economy. Just throttle response. Without changing my stock exhaust in my JK. Is there a benefit to installing one or both for fuel economy? I'm not looking to run 13's in the quarter. Just increase my fuel economy alittle.

    Again....awesome read guys. Thank you
     
  17. Apr 7, 2017 at 9:31 PM
    #17
    OFFGRID

    OFFGRID Well-Known Member

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    Peter
    Houston
    Vehicle:
    1979 Jeep CJ7, 258, TH350, NP208
    Howell fuel injection, header, HEI distributor, TH350, NP208, SOA lift with YJ springs in the front & GW springs in the Rear. AMC20 with G2 1 piece chromos trussed, Dana 30 with G2 chromos and 760x ujoints and MM Stainless Hubs, Geared 4.56. Tom Woods shafts, Metal cloaks, Caged, 37" Toyo MTs.
    My opinion is that your going to get the best fuel mileage you can get from the factory these days. My last three trucks Ford, Ford diesel, and chevy gas, no matter what I tried it always hurt the fuel mileage and took it back to stock. The car manufacturers are just too much under the gun these days. Although, Banks claims as much as a 4mpg increase with their system. The trick will be to stay easy on the gas.
     
    Last edited: Apr 8, 2017
    JKBob 25 and chris4x4 [OP] like this.
  18. Apr 8, 2017 at 8:34 AM
    #18
    chris4x4

    chris4x4 [OP] With sufficient thrust, pigs fly just fine Moderator

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    The way to get the best miles per gallon, is thru regular maintenance, tire pressure, and your right foot.
     
    JKBob 25 likes this.
  19. Apr 8, 2017 at 10:25 AM
    #19
    OFFGRID

    OFFGRID Well-Known Member

    Joined:
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    First Name:
    Peter
    Houston
    Vehicle:
    1979 Jeep CJ7, 258, TH350, NP208
    Howell fuel injection, header, HEI distributor, TH350, NP208, SOA lift with YJ springs in the front & GW springs in the Rear. AMC20 with G2 1 piece chromos trussed, Dana 30 with G2 chromos and 760x ujoints and MM Stainless Hubs, Geared 4.56. Tom Woods shafts, Metal cloaks, Caged, 37" Toyo MTs.
    JKBob, When I used to race, we played around with the TB spacers. Companies would give us their products making lots of claims. My take is that it felt like it was quicker response on the throttle, but who's to say it wasn't my imagination. In the end we decided not to run it. We had our air fuel mixture dialed in so tight that any upset in that could mean a blown engine if we ran even a smidgen lean which the spacer was likely to do. A leaner fuel mixture will run like a scalded ape, but causes so much heat that especially in a race application you will overheat and seize a motor. So I probably was feeling a little more HP.
     
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  20. Apr 8, 2017 at 2:58 PM
    #20
    JKBob 25

    JKBob 25 Well-Known Member

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    2" Superlift kit. 315/ 70/17.
    Awesome. Thank you very much guys. I'll save my money for other modifications.
    And thanks to Chris4x4. I have my tire pressure dialed in now. :)
     
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