Been getting a lot of *** about this lately so I figured I would make a condensed thread with all the info I can put together for IDI turbo options. Keep in mind this is just about turbo costs, sizing and upgrades, making these turbos fit is whole other ball game. The only available options for improving the location of the turbo is the R&D kit, and the Moose Boost kits. Both are worthwhile investments and I recommend doing due research on both options. Im hoping to have my factory turbo bolt-on upgrade kit and my complete turbo kit available soon, both being in the final stages of endurance testing.
The first thing you need to decide on are your goals. There needs to be some power numbers in mind, as well as a general idea of budget, unless the later does not apply to you. Secondly, if you dont have plans for studs you do not need to upgrade the turbo, this applies to all of the banks, ats, and hypermax turbos. If you feel your turbo is holding you back, talk to typ4 aka Russ and he'll work his magic on your stock style turbos to make more than enough boost to blow your heads off, literally.
Okay, so you have a studded engine, and you want to use the new found potential of your idi. Lets start with the turbo basics, a breakdown of components and reading wheel and housing specs. Here is an image of the rotating assembly of a generic turbo where the housings, bearing cartridge, and backing plates are not visible.
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Noting the image above, lets say this is a factory turbo T04B H3, the smallest diameter of the compressor wheel is called the inducer since it is pulling air into the turbo, which on this turbo is 58mm. The largest diameter is called the exducer, since it is forcing air out of the turbo, and on the factory turbo measures 70mm. You will note on the hotside the labels a reverse of the coldside. This is because the fins are reversed of the cold side. On the factory turbo the specs are 64/56 mm, significantly smaller than the cold side, this is key and will come up later.
Now lets take a quick look at housings. I could talk a long time about this but I will keep it short for the sake of everyones time. Here we see a cutaway view of a turbonetics journal bearing turbo showing the flow of air, and an inside view of the bearing housing.
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The most important things to note for housings are A/Rs, which stands for area/radius. This in its most simplistic form refers to how much volume your housing holds as a direct ratio of the wheel radius. This is an extremely important part of turbo tuning, and allows you to cheaply adjust your responsiveness and power potential of your turbo, without changing the rotating assembly.
Now that we have some of the basics out of the way, and we are all certified internet turbo experts, lets get back to the main topic: choosing what turbo is best for you.
Heres the factory turbo specs again:
Cold side 58/70 .70 A/R
Hot side 64/ 56 .82 A/R
Now lets look at one of the most commonly used diesel aftermarket turbos, the borg warner s366. Heres the specs I will be using for this comparison.
Cold side 66/91
Hot side 73/80
You can see this is much much lager than the factory turbo setup, and although it is a more efficient design, and very responsive on modern diesels, I can tell you right now you will hit the gas today and it will spool next week.
So how can we figure out what turbo will work well without just buying twenty grand in turbos and testing different setups? Luckily, the top turbo manufacturers invest in getting their turbos tested at various flow levels to produce flow maps that tell us exactly that.
Here is a compressor map for the factory turbo. Theres a lot going on here, but its really quite simple. the circles or islands as they are referred to, show at what flow the turbo is running most efficiently, you will see that the smallest island has a 74% marked on it, this means that anything inside that island is running an average of 74% efficiency, ideally you want your power band to be within the smallest islands but it is almost never the case.
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Theres a ton of math involved in these maps and choosing turbos correctly, but I will show you a quick way of finding if a turbo will work for you with as little math as possible.
Okay, so you have you power number goal ready right? Go ahead and divide that by 2.75 For this example, I will be using 300 crank hp, which I get 109.1, this is approximately how many ccs of fuel you will need to make that power. This is the most common power level of idis I build, using my max-effort db2 build which makes around 110 ccs at 3000 rpms, general hp peak. From my experience, you need about 7.5 cfm to burn 1cc of fuel in an idi, so for 300 hp goal we need about 825 cfm minimum, however very few maps show cfm, so we will need to convert that to the most commonly used lbs/min. We can do this by dividing our target cfm by 14.47, which we get about 57 lbs/min. Looking at the map above of the factory turbo, you can see the turbo wasnt even tested past 53 lbs/min so you know instantly that this is not the turbo for you, so lets look at some options.
Justin at R&D offers a drop in turbo that is a machined s257 to work in the factory turbo location, and rates it at 300-350 wheel hp.
Heres the specs and map for the s257 sxe
Cold side 57/76
Hot side 70/61
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You can see this is well within our 57 lbs/min goal, and sits around 70% efficiency at that flow level making it an excellent choice for this power level. Well, say you want to go with a mild setup first, but you want to go to that next step once you get some cash recouped and some honey-dos done. Lets say 450 crank hp. Using the equations above youre gonna need about 164ccs of fuel at hp peak, and about 85 lbs/min. Remember that big honkin s366 we talked about earlier? Too small.
An s369 sxe is a great choice for this power level, but will be quite laggy. This starts to get into the realm of compounds being a huge improvement in driveability. Heres the specs and map for the S369 sxe.
Cold side 69/91
Hot Side 80/74
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You can see 85 lbs/min sits at 72-70% efficiency and has room to grow.
Hope this helps some people who are looking at upgrading to a new turbo for their idi, and dont know where to start. These calculations are as basic as it gets, and are very rough estimations that have worked for me. The probability of my own error in this thread is at least 72% so please point anything funny out so I can correct it! If theres interest I would be happy to make a part 2 where I go through the intermediate calculations like when you want boost to start building, mid range boost and the like.
Wes.
. I'm not sure when I will get around to doing these things. I started planning the build for my topside creeper so it will be after I finish that anyway. We bought a IH TD-6 a couple months back and I am still working on getting everything setup around here so I can bring that home. I will be rebuilding the engine in that but then will hopefully get a little side hustle going with it.
