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I'm making a big push this week on the exhaust. I cut out all the manifold pieces, tacked them up, and then had it all TIG welded up by my fab guru. Turned out really nice, if I do say so myself.

In the end, we decided to go with the "weld-el" approach at the collector. I will still need to do some grinding just inside the turbo flange, but nothing too serious.

The wastegate is a 44mm TiAL unit. The runners are 1.25-inch ID, 1/8-wall pieces. Note that they're situated on the outside bends of the main runners, where they will get good flow and, therefore, allow for decent control of boost. Way too often it seems that people just stick the wastegate runners anywhere on the main runners, with little regard to flow. Getting a smooth transition into the wastegate is important to controlling flow (and therefore, boost) through it.

Next up is some frame rail mods near the turbo, so that we can start fabbing the downpipe and plumbing the wastegate outlet into the exhaust. Then it's back to the rear of the car and installation of a muffler.

-Bug

Fantastic job, gorgeous welds!

Moti

Very nice sir!

WOW! What a nicely laid out system.

You guys know that he wrote a book on turbocharging, right?

http://www.amazon.com/Street-TurbochargingHP1488-Installation-High-Performance-Turbocharger/dp/1557884889/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1231872522&sr=8-1

Kurt, thanks for the shameless plug for my book, Street Turbocharging!

I should return the favor for Kimini's excellent book (http://www.kimini.com/book_info/) but of course everyone here probably already owns it. I know I do.

-Bug (a.k.a. Mark Warner)

Nice work/welds. Thats it, Ive had enough, Im buying a TIG as soon as im done my project. You've convinced me.

Andrew

That's a work of art in its layout, fit-up, and welding.

Andrew, owning a TIG machine won't guarrantee welds that look like that. My TIG welds currently are less uniform than Moti's MIG welds. It's like learning to play the piano. It takes two hands, a foot, good eyes, rhythm, (and sometimes a contortionist's body) and lots and lots of practice.

That is understood, but definitely a skill that I want to develop. Ill never get there without hrs of practice, experience and the tools to get there. This work is the standard I aim to attain.

Andrew

This is a really cool build that I really enjoy following. Well done. And do keep us updated.

Of course the fabrication is amazing. I'm new to TIG and getting welds like that is a challenge. Like Jon said: There is so much to do and it takes so much practice. The good news is the welder is under the arc a lot more than MIG, so practice kinda comes naturally.

FWIW, Kimini is an increadible fabricator as well. Have you guys seen his new work?

Anyway, bugeyebug, thanks for the update.

--Chris

Just out of curiosity, how much of the twin scroll benefit do you lose by only having one wastegate? It seems like exhaust manifold pressure would equalize between the two sections of manifold through the large opening at the wastegate... that is unless you have installed some kind of divider to prevent this from happening?

This is a good question. A few years back, some engineers I know at a major turbocharger supplier did some testing on a 2JZ-GTE Supra that was fitted with a big single turbo with divided entry. They ran it back to back on the dyno with single and dual wastegates. Both configurations made identical top end horsepower. The dual wastegate setup made power a little sooner throughout the lower rpm ranges, but it was a relatively small difference. My friends concluded that for all-out performance, a dual wastegate setup was probably ideal, but for the average street car it was overkill. (Unless of course you're going for the bling factor.)

There are a number of effects to consider when thinking about divided turbines like mine, including the aforementioned pressure equalization. Just as important, however, is pulse timing. Keeping the pulses separated AND arriving at the correct time at the turbine wheel makes a difference. This means equal effective length runners. (Note the use of the word "effective" as two runners can physically be the same length, but one that has more bends and twists and turns is effectively longer than the other. The more bends a tube has, too, the more pressure loss that is realized.)

In my case, I know all this theoretical stuff, but I'm also a big fan of the whole KISS approach to design. In addition, the reality of making everything fit within the tight confines of a Bugeye Sprite's engine bay AND within the tight confines of my wallet led me to the solution I have here. It's not perfect, but it's pretty damn good. Or, as we like to say in engineering "perfect is the enemy of good enough." Just as importantly, too, I've got a dozen other issues to worry about, such as how to package a big intercooler, radiator and oil cooler in the engine bay and ensure that they're helping and not hurting performance. Their effects on performance will be significantly more pronounced than the difference between one and two wastegates. It's like raising kids: it's all about picking your battles.

-Bug

I don't see why you can't run a dividing plate right up to the face of the wastegate and have the best of both worlds.

+1 to what I was thinking, it doesn't have to be a perfect fit or even fully welded around its entire edge, just something to keep the two sides relatively separated.

I'm no turbo expert, I definitely haven't written a book or anything , but I know what you mean about the KISS strategy. People here seem to get into some theoretical arguments (recently about tubing triangulation considerations) where I took the KISS/good enough argument.

I'm thinking about making a manifold similar to yours (schedule 40 pipe, 90 bends, twin scroll if possible) for my SR20 and a holset HX35 turbo, the way yours came out is quite inspiring!

That's actually a pretty damn good suggestion, Kurt. It would be pretty simple to slip a 3/16-inch divider down into the wastegate main runner and weld it in place. Cool!
-Bug