Turbo Manifold Designs By Engine Basics 6w653p

Turbo Manifold Designs A look at log, tubular, and twin-scroll manifolds.

Contributed by: Enginebasics.com

When it comes to turbo manifold design there is actually a lot more to it then just connecting all of the exhaust ports together to feed the turbo. The reality is there is a lot more physics at play. The exhaust flow, pressure, and runner length are all very important in deciding the many characteristics that make up a turbocharged car. Hopefully this article will be able to give you the basics to understanding what is involved with the designs of different turbo manifolds. Basics of Turbo Manifolds

The idea behind a turbo manifold is to collect all of the exhaust gases from the motor to a common turbo flange where the turbo may be bolted. The following are the basics that can be changed to control the characteristics of a given manifold. 1. Runner volume based on runner pipe/tube

size. 2. Collector angle towards turbo flange

3. Runner length 4. Wastegate placement 1. Runner Volume Runner volume needs to be considered when building a turbo manifold. While a larger runner diameter does facilitate lower exhaust backpressure for better flow on the top-end, it does cause a lower exhaust velocity. A lower exhaust velocity will cause longer spool times, and less transient response out of the turbo. 2. Collector Angle

The collector angle is important in dialing in how the exhaust gasses will come together and merge before the turbo. The less the angle the better the flow, but often times the space you have to work with will dictate the collector design. While a proper collector is important, it is not as important as the individual runners design, so better to give up some angle on the collector if it gives you an advantage on the runner design. 3. Runner Length

This is arguably one of the most important factors. First would be to make sure that the runners are as equal length as possible. The idea being that the exhaust pulses will be spaced out evenly and arriving at the turbine wheel

on the turbo at there own time in the firing order. If they arrive sooner or later, they may interfere with the exhaust pulses from the next firing cylinder. Next, a longer runner manifold will have better flow up top, while a shorter manifold can yield a faster spool, with also less transient lag. This is only a small description. The importance of runner length has been fully discused in the article called: Short vs Long runner length exhaust manifolds. 4. Wastegate Placement

The wastegate should be placed in a location where it can be fed by all of the exhaust runners. It also needs to be able to receive good flow from the runners. The idea behind this is that the better the wastegate can flow, the better it can control boost and keep you from getting spikes or over boosting. Common Types of Turbo Manifolds

There are two main types of turbo manifolds with many renditions of each of them. 1. Log Manifold

The log type manifold is the most economical manifold on the market. They are almost bullet proof when it comes to

reliability and they are the most compact manifolds available. Most manifolds you find on factory turbocharged cars are log type manifolds. This is understandable when you figure a manufacturer is all about reliability. When it comes to performance, a log manifold will leave you wanting. All of the exhaust gases flow into a common plenum where they often collide with each other causing a lot of turbulence before the turbo. This hurts the turbo’s performance and hurts the motors performance as well being that a log manifolds common plenum is so close to the other cylinders, it causes a lot of back flow of exhaust. 2. Tubular Manifold

A tubular manifold is one that is custom made for that particular s goal for the car. Most road racing cars will build an avg. runner, equal length manifold that will great flow characteristics throughout the entire rev range. A car being set-up for drag racing will use a long runner tubular manifold, which will favor flow in the upper rev range. Tubular manifolds are VERY efficient when compared to a log manifold. They offer superior flow characteristics, and offer less back flow of exhaust gases back into the motor. Now for the negative……tubular manifolds are often prone to cracking causing them to lose points in the reliability column. For those focused on getting the most performance they can, a tubular manifold is a must. a. Single scroll Manifold

single scroll on right, twin scroll on left. A single scroll manifold is one where all the exhaust runners come to a common collector where they enter the turbocharger. Also all the runners share a common wastegate to expel exhaust gases. This is the most common type of tubular manifold. b. Twin Scroll or divided Manifold

A twin scroll manifold is designed for the most ideal exhaust flow a motor can offer. These manifolds are built so that runners that come together are paired to be 180 degrees apart from each other on their firing order. This is done so that there is little chance of exhaust flow interference from another cylinders exhaust gases. This not only helps the motor to better expel its exhaust, but also helps to keep the exhaust velocity as high as possible, aiding in the turbochargers spool and the motors torque output. A twin scroll manifold must be used with a turbo that is equipped with a twin scroll housing that keeps the exhausts divided all the way to the turbo’s exhaust wheel. To truly do this, separate wastegates should be used as well as keeping each side fully divided. While this might be one of the best flowing set-ups when it comes to turbo manifolds, it is also the most expensive.

While the gains are noticeable, a well-built single scroll tubular manifold can perform almost as well. One should weigh the costs before deciding whether to go with a single or twin scroll manifold. As you can see there is a lot more to a turbo manifold than meets the eye. This is only just the basics of turbo manifolds. There is a lot of physics that goes into deg the perfect manifold, but hopefully this article has given you the basics you need to understand the pro’s and con’s of each manifold and which manifold would be best for you. If you have any comments or questions be sure to us. For information and a how to on building your own turbo manifold, follow the link below:

Long tube vs Short tube header manifold Design

A look at how the design of a tubular or log based manifold effects performance of an engine, turbocharged or N/A. Contributed by: Enginebasics.com In a previous article we discussed building a turbo manifold. We talked about the pro’s and con’s of different types of manifolds from log manifolds, to tubular. In this article we are going to take a closer look at the importance of runner length.

Recently Mazda has released a new turbocharged motor with technology called “Sky Technology”. While this motor has many innovations that improve efficiency, one of them is the motors high compression ratio. At 14:1 running on pump gas it is quite amazing. Recently the motor was released in the U.S. but sadly the compression ratio was dropped to 13:1. When asked about why the compression was dropped for the American version Mazda said: “We were unable to fit the long tube turbo header on the American versions causing us to have to lower the compression”. REALLY…..so manifold design plays a pretty big roll in not only exhaust flow but many other things as well.

How tuning of manifold runner lengths changes things:

1. How responsive the turbocharger is. 2. How much exhaust reversion the engine experiences. 3. Exhaust flow. 4. Detonation Suppression. Lets take some time to talk about each of these topics: 1. How responsive the turbocharger is

The longer the manifold runner length, the more area that needs to be filled by exhaust gasses to build the pressure and heat required to spin the turbine of the turbocharger. Short tube header manifolds, with their small runner areas are excellent at transferring the energy of the combustion of fuels in the engine to the turbine. This allows the turbo to spool several RPM sooner than a long tube manifold. 2. How much exhaust reversion the engine experiences.

One of the problems with short runner length manifolds is that they suffer in the power department when it comes to all out peak HP. This is mainly due to something called exhaust reversion. Exhaust reversion is when exhaust heading out of the combustion chamber in the exhaust manifold reverses direction, and heads back towards the combustion chamber. This causes exhaust gases to not completely evacuate the cylinder. The cylinder will

therefore have not only less room for clean air and gas to enter the chamber when the intake valve opens, but also that air will be hotter and more prone to pre-ignition and detonation. Longer tube manifolds help to keep the exhaust gases flowing in the right direction and don’t allow reversion from cylinders to other cylinders. One of the huge benefits of a twin scroll divided set-up is that it pairs exhaust runners who are 180 degrees apart from each other in their firing order together. This cuts WAY down on exhaust reversion. For example, on a four-cylinder motor you would pair cylinder 1 with 4 and 2 with 3. 3. Exhaust flow

Longer tube headers before the turbo allow for more area before the restriction of the turbine wheel of the turbo. This added area allows for more expansion and flow of the hot exhaust gases. This increase in area provides you flow just like going from a 2” to 3” exhaust ads exhaust area and gains exhaust flow. 4. Detonation Suppression

Longer tube headers allow for more exhaust flow and hinder exhaust reversion. This helps in controlling combustion cylinder temperatures by allowing more area for fresh cool air to enter the combustion chamber. Since cylinder temperatures directly correlate to detonation, it is important to keep them as cool as possible. Long tube vs short tube turbo header design

So it looks like you have choices to make when it comes to deg or picking out a turbo manifold. The length and design of the manifold will greatly control the responsiveness of the turbo, and the compression or ignition timing you will be able to run without causing detonation or pre-ignition. Short tube headers will provide a fast responsive turbo, while a long tube header, like the

one on the Mazda sky motor, will allow you to run higher compression, more advanced timing, and have higher exhaust flow. There is no best option here as it really depends on what you’re going for with your set-up. Whatever you choose, now you can make an educated decision for your goals.

How to build a Turbo Manifold Contributed by: Enginebasics.com

The following is a short article on the steps to take to build your own turbo manifold. The following was build for a 4 cyl motor that was going to be using a divided ( twin scroll ) type set-up. It took roughly 20 hours to build. The first thing to do is to get the header flange and the turbo flange that you will be using. Their are many times where a header flange is not offered for your particular engine, in which case you will have to build one. The easiest way is to take an exhaust manifold gasket and trace it out onto ¼” mild steel. Then cut out the design with a plasma torch leaving yourself space to grind down and match the design perfectly after you have cut it entirely out. As for the turbo flange, most fabrication companies sell the turbo flanges of the major turbo flange designs. These would be the T3, T4, T6, and Mitsubishi inlets. These flanges should also be purchased in mild steel in ¼” size. Be sure at this point to decide if you need a single entry or twin entry design. The next step is to construct the collector. Some argue this to be one of the most complicated steps. You must decide not only your collector’s length, but the entry angles of the pipe into the collector. If this is your first manifold that you are building, you may want to purchase a pre-cut collector.

Once the collector is welded to the turbo inlet you can begin to design the manifold. I would suggest using Stainless Steal SS 304L Sch10 Weld El Pipe for a turbo manifold. I have found to have the least amount of cracking going with the thick pipe instead of tube. If your worried about the weight, then using SS tubing can be used, but be sure to use a slip-t at the collector to help avoid cracking. STEP 1. Take some ¼” rod and position the turbo collector where you want the turbo to sit in not only location but angle as well. With the rod, weld the collector in place to the header flange so that between the flange and the collector, nothing will be able to move. Also, be sure to bolt the header flange down to a large piece of metal or a spare head so that as you weld on the flange it doesn’t warp and make it impossible to seal on the engine. Step 2. Measure and look for all obstacles that you will have to avoid while building the manifold. Some fabricators will actually tack in small wire to show obstructions to avoid. I usually just construct a design on graph paper showing how much room I have to work with in building the manifold. Step 3.

Begin to lay out the first runner. that your goal is to make all the runners as equal in length as possible, so the length of this first runner will decide the length of all the runners. Try your best to make the runner have as few bends as possible and to keep the gaps on manifold tight. Do not fully weld the t but instead tack them in 2-3 places that are easy to get to if you need to break them and make some tweaks or changes.

Step 4. Lay out all other runners keeping a close eye on the length and bends doing your best to have each runner have the same amount of bends and length.

Step 5. Now with the fully tacked manifold, place it on the motor and check that everything fits and there are no obstructions. Also make sure there is room to add the wastegate or gate’s on the manifold. Step 6. Once completed with all the runners begin planning which runners you will remove to begin welding. On a 4 cylinder I find removing cylinders 1 and 3, or 2 and 4, to give me the most room to weld. Weld the two removed cylinders on a table and weld the other two cylinders runners on the manifold itself. Then weld in the two removed runners to the manifold. Be sure to back-purge the set-up as you are welding so you don’t get sugaring inside the runners and weaken the welds. Step 7. Lay out wastegate if building a manifold to an external wastegate. The wastegate should be placed in the collector where all cylinders have access to the gate. to bias flow to the wastegate or spiking may occur in your boost control. Once laid out fully and tacked, weld the wastegate plumbing onto the collector.

Step 8. Bolt the turbo and wastegate onto the manifold and make sure everything fits on the engine. Now step back and ire your work of art. http://www.enginebasics.com/Advanced%20Engine%20Tuning/Turbo%20manifold%20How%20to.h tml