You typical cast iron turbo manifold or also known as a log manifold (as shown on the left) is usually found on most engines out there as they are an oem part that come standard on most production turbocharged cars, tubular turbo manifolds are after-market manifolds typically for adding a turbocharger to your engine or upgrading / replacing you old manifold.

Both manifold types do have pros and cons, for example cast manifolds are extremely strong and durable and tubular manifolds (especially the cheap eBay ones) crack very easily due to the thickness of steel, quality of the steel, fluctuation of heat and vibrations.

It has always been a general rule with any exhaust manifolds / turbo manifolds that tuned length pipes will give you the most amount of power available from your manifold, a lot of tubular turbo manifolds will do this easily where as this really can’t be achieved on cast due to the thick and bulky design.

Custom Designed Manifolds can be made with tubular steel, so when your pressed for room in the engine bay you can always get tubular manifold fabricated to suit your application, this can’t exactly be done with cast iron material unless you know someone who has cast production factors and thousands of dollars of tooling at there dispense.

Customising an existing manifold can prove to be a challenge with cast material, trying to add a external wastegate port or or change your factory ct26 flange to T3 is quite expensive with cast, but is quite easy with tubular steel.

Now with boost the biggest killer is heat soak, so keeping those temperatures down in you engine bay is very important, a hot engine bay = hot piping = warmer air = less power = more detonation, cast manifold are relatively good at keeping in the heat and work even better with nice thick heat shield covering them also, this can be a pain in the muffler when you try to remove that manifold and all the studs / nuts have seized but that is why got created WD40. Tubular manifold look great in the engine bay and even better when covered in heat wrap but they tend to throw our a lot more heat than cast manifolds.

In reality it depends on your application and what you prefer, for me I tend to stick to cast for durability and less heat soak but if I needed a custom manifold I would use tubular if not flange adapters would suit, not to mention cast also looks stock so it doesn’t stand out in the engine bay to the 5 – 0 to pick on.

External wastegate sizing is a critical decision and from what I have read on forums people seem to think bigger is better and the more power you plan on running the bigger wastegate you need, wrong.

You see the idea of an external wastegate is not only for better control of your boost levels or a really cool sounding screamer pipe you cousin Ahmed welded up in his garden shed that will get you defected faster than you can hit boost! No, a really import function is to bypass the excess exhaust gas before it enters the turbine housing, and in order for the wastegate to do this efficiently you need to choose the right size wastegate.

The more boost you are running then the smaller the wastegate, because you want to run more boost less needs to bypass the turbine, and if you plan on running low boost then a bigger wastegate is required, use this simple guide below:

Small Turbo/High Boost = Smaller Wastegate
Small Turbo/Low Boost = Bigger Wastegate
Big Turbo/Low Boost = Bigger Wastegate
Big Turbo/High Boost = Smaller Wastegate

Now that you know how to choose a wastegate you can understand that just buying any wastegate is not a very smart move, work out you engine specs, turbo and boost level and depending on you goals choose wisely.

This guide is to provide information on turbochargers, what’s inside a turbocharger and how it works, what is included in a turbocharger kit, and then right into the technical side of things so you can understand what type or size of turbo will suit what engine/set up, what terminology like 60 trim turbine mean and why everyone you know seems to pretend to have a friend with some T66 bullshit car that runs a over-rated amount of boost that usually turns out to just be a misfiring ford laser, So lets start with turbocharger terminology so that you will understand what I am talking about later on down the track.

Enjoy!

Class 201 – Terminology

• CHRA, Centre or Cartridge – This is the centre of the turbocharger that hold the bearings, the seals and shaft, oil flows in for lubrication, common and factory turbochargers also have coolant passages surrounding it to keep it cool known as a water and oil cooled turbo, some Turbo Diesels and aftermarket turbocharger kits are oil cooled only, essentially the CHRA is a turbocharger without the compressor and turbine housing.                                            *CHRA = Centre Housing & Rotating Assembly

• Wastegate – This device is designed to limit boost a turbocharger is allowed to create. This is done for two reasons, one to protect the engine from over-boosting, two to prevent you blowing your turbocharger as they are only designed to spin up to a certain rpm. It works by a Pneumatic Actuator (air valve) that connects to a valve which can be mounted into the turbine housing itself (Internal Wastegate), Or can even be mounted in the exhaust manifold before the turbo (External Wastegate), A Line from the compressor housing to the pneumatic actuator allows it to sense to boost pressure and open the Wastegate, the turbo is able to limit its maximum boost output. This result is increased durability, quicker time to boost, and controlling of the boost levels depending on the setup.

• Free-Float – A free-floating turbocharger does not have a wastegate, this turbocharger is not able to control the amount of boost. These are seen on large applications mostly dieses, but for performance an external wastegate is a must.

• Trim – Basically it is a area ratio used to summarise the turbine and compressor wheels in one neat little formula, the trim is calculated by using the diameters of the inducer and exducer  to give you one unit like 62 Trim, the greater the trim is the more air flow the wheel is capable of, Example how to find the trim below:
  Compressor wheel Inducer diameter = 61.4mm
  Compressor wheel Exducer diameter = 82mm
  Trim = Compressor Inducer²/ Compressor Exducer²
  Trim = 61.4²/82² = 56 Trim

So around 75% all the compressor wheels on turbo’s are Billet, it has been proven with no major issue’s ever arising apart from of course the poor sole who got talked into buy a cheap Turbocharger that’s about as reliable as a Hyundai Excel thats clocked over 800,000kms, which we have talked about cheap turbo’s before.
Turbonetics seem to heavily market there forged wheel technology, and with their proven track record of providing some of the best Turbochargers seen to mankind, of course there is a new line on forged compressor wheels from Garrett® dubbed there new range The “GTX-R Turbochargers”, Pretty cool name and it would be hard to toss up between the two companies and decide which brand to buy. The one thing about Turbonetics is they degrade the standard compressor wheels, saying that casting leaves air pockets, This is true to a certain extent.

Most modern Alloy engines have Pistons manufactured from cast alloy pistons, even some Hi-Torque engines such as Holden/Isuzu’s 6VE1 or 6VD1 or a Turbocharged Renault Megan Sport, none of these have ever had issues with broken pistons due to air pockets in the casting. It all comes to to the company’s quality control. That is why you should stick to the Trusted brands and not the El-Cheapo’s that I have talked about Before.

So to sum it all up Yes a billet wheel is considerably stronger that a Billet but for a street car or weekend cruiser I wouldn’t bother spending the extra 200+, I would just stick to what has a good review and what is suited to your build.

Until next time Keep Spoolin!