DIY Tubular turbo exhaust manifold

[staticbrainwash]

Can't be worse than aluminum. . . my lord.

 

[absolute_DSM]

Can't be worse than aluminum. . . my lord.

Holy crap I just came here to say the same thing.

Its not as fun as aluminum.

 

[Mr Peepers]

An article that I'd like to share on turbo exhaust systems:

The following excerpts are from Jay Kavanaugh, a turbosystems engineer at Garret, responding to a thread on http://www.impreza.net regarding exhaust design and exhaust theory:

"Howdy,

This thread was brought to my attention by a friend of mine in hopes of shedding some light on the issue of exhaust size selection for turbocharged vehicles. Most of the facts have been covered already. FWIW I'm an turbocharger development engineer for Garrett Engine Boosting Systems.

N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.

For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side."

"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.

A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.

If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.

Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.

Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.

Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.

Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc."

"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.

There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.

As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length."

"Here's a worked example (simplified) of how larger exhausts help turbo cars:

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure

So here, the turbine contributed 19.6 psig of backpressure to the total.

Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would."

 

[Boosted98gsx]

well that's all fine and dandy, but not really relevant to the subject at hand. That is about post-turbo exhausts.

 

[tkelly27]

Thin stuff is worse than aluminum. Thicker is more like mild steel, but it's so easy to burn through. Practice on a lot of mild steel, then find scrap SS.

If you do go SS, tack EVERYTHING in more than 2 places. Bolt it to something flat as well. SS loves to warp, especially thin stuff. The class I had gave us what was basically SS foil to weld (thin gauge stuff) and if you didn't tack it at least 4 times you'd wind up with one half the piece welded and the other half having a half inch gap.

The primary sizes depend on your goals. It is true that big primaries can slow down the exhaust flow, but too small primaries are restrictive. From everything I've read 1.75" is a good size for making big power. Maybe you can do an experiment and go from 1.75" at the head down to 1.5" then when you do SS go full on 1.75". My opinion is that the better flowing piece will beat the faster moving gases in spool up time. Although looking at Shep and Rau's pieces, you'll probably be fine with the 1.75 : D

I do know that when people on turbomustangs.com ask "is 2" too small for 2500hp?" the general answer is that it's borderline too big.

Another design I think looks cool and is much easier to make is the swept log. I dunno where you'd put the turbo in a DSM, but they were making over 1100hp (highest recorded was 1400hp on accident I think) out of 2.5's in the late '70s
http://www.penskeracing.com/boat_gr...DealerLibraries/7522/69-Donohue-Indy-Lola.jpg
Some interesting things on that one, the sewer pipe post turbine, the ~2.5" main primary, and open wastegate. I lost all the pictures of the more advanced ones, but they have longer curled runners that spit the exhuast all going toward the turbine vs. a standard log that has T's to the turbine and adjacent cylinders.

The best post-turbo exhaust is a non existant one.

 

[Mr Peepers]

Oh come on, just fab up an aluminum exhaust manifold and it'll weld itself at full boost

I did find a link on a DIY turbo manifold:
http://www.sdsefi.com/techheader.htm
I'm not too into the collector, but interesting nevertheless.

Could be worse
http://www.max-boost.co.uk/max-boost/images/LET/new_turbo/exh_manifold_handmade1_lg.jpg

well that's all fine and dandy, but not really relevant to the subject at hand. That is about post-turbo exhausts.

Site froze during the middle of my second post... If you look at the first part in bold, it goes into runner size on a turbo manifold. The second bold part touched a *little* on the collector, but more so on the o2 housing, which many people interested in making a manifold would also be curious about, myself included. The whole article has some all around turbo exhaust system info, thats why I posted it.
And, to hit on my main question of leaving it 1-3/4 ID for flow or stepping it down for velocity.

Edit: Thanks for the info Tom!

 

[tkelly27]

Hehe, it's all just bench racing until you make it!

No matter what you make, it will be much better than any cast manifold and cost much less than any decent header. I'm excited to see progress!

 

[gixrman]

Burns stainless has some of the best collector and turbo flange setups in the business. Its not cheap but quality is top notch. They state also that SS321 is best for high heat turbo applications.

 

[hostile]

Buying from burns to build your first manifold is a waste of time and money. He would probably be out 500+ in materials alone.

Buy some schedule 10 1.5 inch pipe fittings and a 1/2 inch head flange and turbo flange.

You should only be out about 125 dollars.

 

[gixrman]

Thats true and I stated that it was'nt cheap, and yes for his first manifold its probly not the most cost effective route, but you get what you pay for. Also you can run thinner 321 tubing because of it strenght properties over 304 which cuts down on weight.

oh and talk about turbo location

 

[awdrst]

No matter what you make, it will be much better than any cast manifold and cost much less than any decent header. !

Not true you can build a manifold all wrong with a poorly designed collector and really bad fittment and you run a big risk of the manifold flowing alot less than say a evo3 one. All of the exhaust manifolds I've built were made using sch10 ss pipe. You just order up the elbows , bends and straight pipe you need. It will come beveled which is nice and the pipe isn't to expensive. You can get it from mcmastercarr or ace stainless and places like that. A good site to check out is honda-tech.com odd I know but go to the welding/fab part and check out some of their manifolds. They will give you good ideas and places to buy materials.


Also if you never tig welded I'd suggest a whole lot of practice before you attempt to weld up a manifold. If it's not done properly you will run a huge risk of the welds cracking. Just practice on flat stock as well till you get the feel of how to control the heat and torch. One of the biggest mistakes people just learning is using tubing to practice welding on and it makes it just that much more complicated.

 

[bpestilence]

FYI 1.5" schedule 10 (well, any schedule of 1.5" pipe) has a 1.65" ID, which makes it perfect for the OEM port size.

 

[Mr Peepers]

Mr. Peppers did you ever finish this?

Haha you and Oldman calling me peppers....

No, it kind of fizzled out. My current job has left me with more money than time instead of the other way around(back when I made this thread).

I do work at a foundry though, and if they let me use some of their equipment...

 

[Zex4g63]

Honda-Tech.com: Main Forum List 's fabrication forum has some of the best info on building a manifold, what collector design is best, where to buy materials cheap, and how to weld it.

 

[turboglenn]

I swear i posted a link in this topic last night. It was toa great tutorial on building a tubular turbo manifold from steel plate and things called "weld els" for the tubing.

I'll post it again now and see if it dissapears this time

There's so much more great informative info on this page you'll sh!t your pants if you look through the right stuff

here's the main link
Building a Turbo Manifold

 

[Mr Peepers]

I swear i posted a link in this topic last night. It was toa great tutorial on building a tubular turbo manifold from steel plate and things called "weld els" for the tubing.

I'll post it again now and see if it dissapears this time

There's so much more great informative info on this page you'll sh!t your pants if you look through the right stuff

here's the main link
Building a Turbo Manifold

You did. It's a little sneaky, but I seemed to snag it in post #31

 

[turboglenn]

You did. It's a little sneaky, but I seemed to snag it in post #31

So what happened to it, and why?????

And my link happened to pop up in post #31.. iv'e enver had it pop up in a google search, i found their site when i called them about some info on their unit ( i had heard about if rom another guy)


weird shit!!!!

 

[Mr Peepers]

Yours was deleted because I posted the same link a couple months ago...

Are you drunk??

p.s. I bought the car in my avatar from a guy in Omaha. Random, I know

 

[turboglenn]

OH i see how it is Anyway I'm not drunk ( wouldn't mind being though ) and that is fairly odd and or random that you bought your car from omaha.

 

[gixrman]

Thanks for the reply, I'm holding off for now and running this 16g until summer. Theres a speed shop not to far from me that sells bends for cheap. I have my head, and t3 flange just need those bends.

 

[turboglenn]

Thanks for the reply, I'm holding off for now and running this 16g until summer. Theres a speed shop not to far from me that sells bends for cheap. I have my head, and t3 flange just need those bends.

Cool, at least you got what you needed from the thread!

On the other hand, do you ride a gixxer? Just assuming so from your name unless the "gixr" stands for something else.

I have an '03 Gix 750 (4th bike street bike , 96 SRAD before this one) NO mods to it really just -1 in the front and the TRE. I kind of want a slip on for it, But i don't want to do anything that might require a power commander. It's the one thing i own that i want to leave the fuel and spark settings to the suzuki engineers so i can just hop on and ride without any issues from changing the airflow. I wanted to keep it quiet, but this is the loudest stock bike i've ever ridden *shrugs* so i'll be happy with a yosh slip on and a few apearance mods. I've cut the fender and put shoty turn sigs on the back, custom made bar ends from my lathe and custom rear bobbins for a rear stand.

 

[gixrman]

Yes an K7 1000 its my third Gixxr. 93 600, 96 750 which I sold to get the 1000. The 750 was modded with lots of goodies. My K7 has a yosh slip on and a power commanded not that it needs it.

 

[SpeedAddict62]

Back from the dead....

I revived this thread because its probably the most informative one regarding DIY exhaust manifolds on this forum. I have a Holset HX35 with the stock 12 cm^2 divided housing, and I want to build a divided manifold to run the stock housing (no, I don't want to run the bolt on housing). Speaking of which, if anyone knows where to buy a non wastegated housing used, let me know. You can buy them new for $195 but I'm trying to do this as cheap as possible.

I'm currently designing the manifold in Solidworks so I can get a rough idea of how much material I'll need and how it will all fit together.

My question is: what material to use?

I've decided to go with mild steel, because A. its cheaper than SS and B. I've never welded SS before. I was originally planning on using some 1.5" sch 40 pipe. You can get straight pipe and weld elbows pretty easily and for a decent price. OD is 1.900", ID is 1.610" and wall thickness is .145". After talking with a fabricator, he thought sch 40 would be too thick and suggested using some tube with .095 wall. However, I don't know if it would be thick enough, nor if I could even find it. Does anyone know what kind of dimensions are run on vendor's manifolds? (OD, ID). Of course, they are made of SS, but it will at least give me something to shoot for. Flanges will be 1/2" mild steel.

Any comments, suggestions, are appreciated.

 

[gixrman]

Back from the dead....

I revived this thread because its probably the most informative one regarding DIY exhaust manifolds on this forum. I have a Holset HX35 with the stock 12 cm^2 divided housing, and I want to build a divided manifold to run the stock housing (no, I don't want to run the bolt on housing). Speaking of which, if anyone knows where to buy a non wastegated housing used, let me know. You can buy them new for $195 but I'm trying to do this as cheap as possible.

I'm currently designing the manifold in Solidworks so I can get a rough idea of how much material I'll need and how it will all fit together.

My question is: what material to use?

I've decided to go with mild steel, because A. its cheaper than SS and B. I've never welded SS before. I was originally planning on using some 1.5" sch 40 pipe. You can get straight pipe and weld elbows pretty easily and for a decent price. OD is 1.900", ID is 1.610" and wall thickness is .145". After talking with a fabricator, he thought sch 40 would be too thick and suggested using some tube with .095 wall. However, I don't know if it would be thick enough, nor if I could even find it. Does anyone know what kind of dimensions are run on vendor's manifolds? (OD, ID). Of course, they are made of SS, but it will at least give me something to shoot for. Flanges will be 1/2" mild steel.

Any comments, suggestions, are appreciated.

Mine was built with mild steel header tubing. Are you planning on TIG or MIG welding it? If your TIG'n it it will weld mild just as easy as SS, in fact SS MIG is the same. My next one will be SS using weld el's. My pics of mine are under the HOLSET thread. Make sure you bolt down your flanges! I had mine milled after because of this.

 

[SpeedAddict62]

What is header tubing (dimensions)? I'm looking readily available diameters/thicknesses that aren't too small or too big.

Not sure what it will be welded up with yet actually. I might not be able to weld it (I can weld, but I don't own one). Right now I'm just focusing on designing it and buying all the materials. SS is nice, but this manifold will be made of mild regardless, to keep cost down.

I saw your pics in the Holset thread, good job. What did you use to weld it?