Toolmaker

Hey everyone, I wanted to start a thread here to document this Turbo Manifold I'm putting together. I have been doing some research on making my own and thought it may be of use to someone that wants to do one too.

I've found a few manifolds here and there, like on eBay, etc. But the selection is pretty slim nowadays. So I decided to just build my own. I thought I would do a thread on it so I can get suggestions along the way and hopefully end up with a better manifold than what's currently available.

So the heart of my manifold is going to start a 4-1 merge collector like this:

Header Fabrication Parts




This is a stainless steel, 1.5", 4-way collector with a T3/T4 flange on the bottom. This is going to be what I use to design the manifold around. My manifold will end up being similar to the Descendant manifold. Though I'm going to make some changes but the construction itself will be similar.

I'll try to document this as it comes along. Next step is to get the dimensions I'm working with in the tC engine bay. Then come up with a design that keeps all 4 runners as close to same length as possible. If this turns out OK I'll be doing my own intake also. Hopefully it will be an interesting thread anyway.

ETA: I'll be making my down pipe too, once I get the mani fabricated and everything mounts up and checks out, then I can figure out the down pipe layout. I'll include it on this thread too.
Along with the Intercooler piping and CAI which will all be made by me. It'll take me a little while, lol, my goal is to have this stuff built within a years time. I'll update with pics as I come along.

Any suggestions are welcome...

___

Toolmaker

So first step, I've got to figure out which turbo I'm going to run. I started looking into matching a turbo to the 2AZ-FE that will do what I'm looking for. I quickly became overwhelmed with the amount of info. So I decided to take a shortcut and look at the turbos that were offered with full kits when they were still available. I then tried to find comparable turbos. I think I've narrowed it down somewhat, here are my candidates for now:

- TD05H-18G
- T04E Hybrid T3/T4
- GT2871R

I should be fine with the collector I'm planning on running for either the T04E or GT2871R. But if I go with the TD05H-18G, then I will have to go with a different collector setup as this turbo has a different flange layout. But I've heard it's a good turbo so I haven't crossed it off the list. So I'll keep digging and see what I can figure out so I can make up my mind on what turbo I'll be running.

I also found a place that sells a 3/8" Stainless Steel exhaust manifold flange plate:


https://www.verociousmotorsports.com...4-SS-3-8-Thick




I'll be using 304 Stainless Steel ell tubing for the runners. I imagine it will be a lot of trial and error to get it tacked up and fit. Once you have it all fit together and tack welded, you can remove either runners 1 & 3 or 2 & 4 and weld one set on the bench, then the other on the manifold so you have as much room as possible to get into each one and weld it.

I luckily have access to a passivation machine at work. So once I get it all welded up and happy with it I will passivate all the welds on the outside anyway. Not much I can do to the inside. But the passivation process does a great job of cleaning up the heat marks and gives the affected Stainless back it's "skin" or oxide layer. It makes the weld less prone to corrosion which in turn will help it hold up longer.

I'm going to make a heat sink for welding the flange also. I have a big chunk of 2" plate that's a perfect candidate. I'll just lay the flange down on the plate, mark the bolt/stud holes, drill and tap them so I can pin the flange down when welding the runners. This will hopefully minimize flange warpage. It's amazing how much steel moves/warps when welding on it.

So if any of you have any recommendations on a turbo choice please feel free. I would like to be around 250-275hp at the wheels. I guess if I were to try to summarize the use my car will see I would lean towards an autox type build.

ETA: One other thing, depending on which turbo I go with would also determine whether I will go with an internal or external wastegate. The TD05H-18G has an internal wastegate which would simplify plumbing. The other two options I would likely be running an external wastegate. Which will require I cut into the collector to add another carefully placed outlet for the external wastegate.

Also, I have to sort out how to lay out my runners. My next post I'll get into what order I plan to run them to from the flange to the collector.

DannoXYZ

Those are +500bhp turbos, are you sure you want that kind of lag? I've seen all those get 500bhp! That's 425whp.

For 250-275whp, you're looking at pressure-ratios of 1.5:1 or so. Which will be underflowing those turbos and redlining engine before even hitting efficiency island sweet-spot.

With that low of boost, built-in wastegate is OK. No issues with boost-creep and if you get divorced dump-pipe, it'll be easy to control flat-boost with EBC.

Toolmaker

Copy that DannoXYZ, I appreciate your help. I just don't see my needs ever exceeding that 250-275hp range. I've driven FWD cars that had over 350hp and while they were fast, they were a chore to drive. Not to mention scary because they want to pull the steering wheel out of your hand, I would have to wrap my wheel with sandpaper or something, lol... I guess what I'm saying is I don't want to have to constantly fight it because it is constantly breaking traction under boost.

If I could convert this car to RWD I would be looking to push the power to those levels. But that's major surgery with hard to get parts that I don't think I want to get into.

I am still learning how to size turbos. It's a new realm for me so I'm trying to get over the learning curve, it appears to be pretty simple once you have your mind wrapped around it. I can always upgrade to a larger turbo later if I feel that's viable to make more power. I enjoy building engines as much as I enjoy driving fast cars so I can get carried away with building and I'm trying to maintain with this one.

I'll do some research on this and see what I can come up with. I definitely don't want to be oversized.

DannoXYZ

You can use various calculators on web to arrive at flow-rates and power-generated. I came up with following table:

2k 1.34 5psi 7.1 lb/min 86bhp
3k 1.5 7psi 13 lb/min 151bhp
4k 1.7 10psi 21 lb/min 225bhp
5k 1.7 10psi 26 lb/min 269bhp
6k 1.7 10psi 30 lb/min 293bhp
7k 1.7 10psi 33 lb/min 305bhp

Then plot them on various compressor-maps.

GT2871R is simply too big.


GT2560R is just about right. Flows right through its max-efficiency island and just maxes out on edge of map at redline. You even have option of running 14psi for another +40bhp if you wanted (~290whp).

Toolmaker

Man I can't thank you enough for helping me out with this. You've been a big help, now that I've done some more research I see exactly what you mean.

The GT2560R fits my needs just about perfectly plus it's a ball bearing turbo which is on the list of specs I want. Should make all the power I will want and they are also on the more affordable side to boot.

So on the topic of the downpipe. When you say "divorced" you are meaning to separate the wastegate and exhaust at the exit of the turbo and join them further downstream into a larger pipe? I will be making my own which would give me the ability to do this vs. relying on aftermarket parts. For my exit flange I'm looking at something like this:

https://www.exoticspeed.com/products...s-2-25-and-1-5


​​​​​This is a stainless exit flange for GT25/GT28 with 2.25" and 1.5" wastegate opening. So I could run a 2.25" main exhaust and the 1"-1.5" divorced wastegate pipe down and into a larger 2.5"-3" exhaust from there. I'll have to look at everything to decide on final pipe diameters. I thought of maybe trying to make a single pipe with a baffle between wastegate and main exhaust but I think it would be very easy to just run the divorced WG pipe separately.

So since I'm going to be going with a smaller frame turbo, T25, then I'll have to look at a different collector with that flange. I've heard that welds cracking can be an issue with tube runner manifolds. So I'm thinking about going with a cast collector vs. welded. Something like this:

https://www.treadstoneperformance.co...mc-t25/p103513



​​​​​This one is on the pricier side but I do like the quality of it. It's 304 investment cast, takes a lot of weld out of the picture. There are similar ones out there too but this is what I'm leaning towards for a collector.

I definitely plan on running EBC. I haven't done much digging into one unit vs. another but it's on my to do list...

DannoXYZ

Yes, divorced downpipe separates wastegate dump to avoid interfering with main flow. Rejoin 8-12" downstream, with wastegate tube on inside curve of bend if you can.

There's two topics involved with headers cracking: material and design.


1. material - due to high heat involved, you'll want to avoid commonly used 304/304L stainless. Carbide formation in HAZ will do it in. Use 321 alloy which is designed to be more heat-resistant. Even better with butted tubing if you can find it.

Also do post-weld annealing of entire header after welding to stress relieve. Then skim flange surfaces as there'll probably be some warpage.


2. design - good thing you're building your own because I have yet to see a single aftermarket header that's worth using. They all hang weight of turbo off exhaust studs. This also means entire weight of exhaust also hangs off headers as well. So no wonder they crack!!!

You'll want to design a turbo-mount bracket that's separate from headers to remove ALL weight. Mount should attach firmly to engine so there's no relative movement.

Here's turbo mount from Porsche, it's integrated into engine-mount. Has internal passage for oil-drain and short hose connects to top of oil-pan underneath. Downpipe off turbo also bolts to block to prevent weight & vibration of exhaust from cracking turbine housing.


To keep velocity high, don't dump into large exhaust pipe too soon. Use 2.5" for middle section. Then expand with long cone to 3.0" for cat-back section.