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46 Posts
Discussion Starter #1 (Edited)
Latest Update: #3 Wastegates
There are many designs and options when it comes to buying a turbo kit for any vehicle. Here at Alpha Powersport we strive to provide the highest quality parts possible, and ALWAYS made right here in the USA. Here are some things to consider when choosing a turbo kit for your Slingshot.

Manifold Design
Log Manifolds
This Type of manifold is most often used in the industry to cut cost and provide a kit that works but does not perform as well as it possibly could. This design does not direct the exhaust gases straight to the turbo as smoothly and fast as possible, like a design with runners and a collector would. There is no collector and most times the runner lengths are not equal providing uneven flow to the turbo which tends to produce more back pressure, lots of heat and uneven cylinder burn (Some cylinders could be richer or leaner than others).

Cast Manifolds

Cast manifolds can be a great cost effective way to provide a great flowing, strong manifold when they are designed correctly. Equal runner lengths, smooth flow and a good material make all the difference.

Tubular Manifolds
There are many parts to a great tubular manifold setups. A good CNC'd Stainless Steel flange, Correct runner diameter and length, and a great collector all work together to provide a great flowing manifold. If an external wastegate is used then one must be sure that is it able to vent the exhaust gases as smoothly as possible to prevent boost creep. Runner wall thickness and material type play a huge roll in how long a manifold will last before it starts to crack under the extreme pressures and heat of a turbo system. 304 Stainless Steel is a great material for manifold construction, though there are also better materials for a much higher cost. TIG welding is a MUST in the production of a quality manifold as well as back purging to prevent contamination when welding.


A quality turbo is a very important choice when looking at a kit as well. Chinese built turbos are an absolute NO NO! They are cheap and they perform like it. A quality american made turbo will be the best choice for your turbo kit.
Things to consider:
Ball Bearing or Journal Bearing
Water Cooled or just Oil Cooled.
Bolted Connections, or V-band
Billet or Cast Compressor Wheels.
First question.... How much power do you want to make. You must ask yourself that when looking at turbos for your Slingshot. There is no use putting a huge turbo on that will make WAY more power than you need, all you will end up with is a lot of LAG and no fun. Ball bearing turbos will provide a slightly better spool but also cost more. Usually ball bearing turbos are also water cooled to control the internal temperatures. Bolted connections are good but V-bands are the way to go, they seal better and don't work loose over time. New billet compressor wheels are more efficient and stronger than the old cast wheels and will produce more power on less boost which equals more bang for your buck.. Given the Slingshot only has one rear tire we are going to be doing a turbo that will provide a smooth power band so we can keep the turbo from hitting super hard and giving us as much traction as possible.

11/20/14 UPDATE

What is a wastgate? How does it work? Is bigger better? What type should I use? These are all great questions, and I am going to go over all the differences and options in this update!

What is a wastegate? To understand this better we are going to use water as a good metaphor. Think of the exhaust coming out of your engine as water flowing down a river. In the skinny parts of the river the water is moving very fast and in the wide parts it is moving much slower. Now as we funnel hot exhaust gases through the manifold toward the turbo it is combined with other cylinders exhaust gases (Tubular manifold) at the collector. It is in the collector that we really start to funnel the gases down in to small space, at this time the gases are traveling very fast and are very hot. Now if we push ALL these gases through the turbine wheel it will spool the turbo up as fast as it can make it go. That is not what we want. We want to control how fast the turbo spins which will control our boost PSI. This is where the wastgate come in. The wastegate used to route some of the gases around the turbo to control the speed of the turbo and the boost. The more we open the wastegate the lower the boost we can run.

Is bigger better? Well not all the time. Here at Alpha we want to design a kit that will have ZERO boost creep. What is boost creep: as RPM's go up boost does as well in an uncontrolled manner. The larger the gate the lower you can make the boost without dealing with that dreaded boost creep. Boost creep is very difficult to tune for and can change with altitude, temp or humidity.

What type of gate should i use? This is one of the hardest questions to answer because it really depends on the goals and design of the specific kit. In general an external gate is better at controlling boost than an internal gate, especially when you get up into the higher power levels. This is mostly because external gates are larger than their internal counterparts. We are planning our design around a quality external gate that has been proven over the years to work great!

Check back again for our next update!

Update #4 Tuning

Tuning is considered one of the most important parts of a turbo kit. When choosing a turbo kit be SURE to choose a kit that includes some forum of ECU tuning. Some will use "Fuel
Management Units".. Don't be fooled this is not a tuning solution, rather it is a fuel pressure regulator. These units work buy raising fuel pressure a specified amount per pound of boost. Because the fuel pressure goes up, your engine gets more fuel. This is not a reliable or accurate way to tune an engine.

ECU Flashing.

ECU Flashing is one way to tune and engine. With the Slingshot we are finding that the ECU is not just a regular GM ECU like we has hoped. Rather it has been programmed by Polaris and uses their communications system. This means it will take some time till a company can finally "crack" or unlock the factory ECU.

Piggy Back
There are many options for piggy back units on the market. Some are not so great but some are very good. These units are placed between the ECU and the engine to change the signals coming from the ECU to the engine per the tuner. In most cases this will work great for adjustments needed when adding a turbo.

40 Posts
Andy sounds awesome. Cannot wait to hear / see more. A question, is there something between stock and full on turbo that can be done to add a little "zip" to the SS? Are you turbo only or will you be coming out with something a little less aggressive such as a chip of some kind? I read somewhere that someone is working on a OBDII adapter that will plug into the current Polaris proprietary plug: Which will open the door for such a thing. I understand these motors have all kind of things that can be done. Does Alpha Powersport have an alternative to turbo coming by any chance?
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