Turbo Elbow

[Keira]

Do you think the side exit exhaust will have a detrimental effect power wise on a fairly standard set up aswell?

no, it cant possibly harm anything by being shorter.

anyone into the old porsche gt cars will know what those exhausts look like, the turbos hang out the back and have a stupid foot long if your lucky bit of pipe on the end of them 8)

the only thing a side exit will have a detrimental effect on is your wallet :lol: unless you do it yourself, it would be £600 or whatever ridiculous figure people are being charged wasted. as theres about £100 of parts in one tops and not alot of welding

 

[Keira]

what people (bob :lol are forgetting is the standard elbow is designed to allow for fitment of aircon, with the pump there you struggle to do anything bigger than what nissan put on there, you can make it better inside but as far as curve/size goes you're tight for room.

f*kc the aircon off and you suddenly have plenty of room to make a far better designed more effecient flowing turbo elbow...

this one really isn't rocket science chaps

the biggest restriction you have in the whole system is the turbine wheel, anything else you can take care of, better flowing, straighter, shorter pipe run will be of benefit

 

[pulsarboby]

by just removing the standard turbo and replacing it with something better flowing and then running a 2.5" system (goose) would be good enough for most cars on here, and you would see gains from that alone, the standard elbow is hideous


this is what im on about kieron!
the fact that a lot of people want to spend a lot of money on a non restrictive elbow, that are running a standard tubby at maybe 1 bar or less in a lot of cases, what benefits will they honestly see for there money?
if your running a bigger turbo at higher boosts then fair enough, the elbow is a erestrictive item and should be changed!
i understand fully what you mean regarding the hose and water theory, but i do not believe for one minute that the standard system MINUS the cat will make a car run any worse than if you went out and bought a 3''elbow with straight through system running the same boost level, infact i think it would run worse unless you upped the boost!

yes kieron, in theory you are right again i have to admitt, but i still cannot see the point in people on here wasting hundreds of pounds on elbows and whatever, for the sake of minimal and very minimal differences in bhp, when all they simply have to do is up the boost a little, which will give a better result in everyday use!

 

[Keira]

by just removing the standard turbo elbowand replacing it with something better flowing and then running a 2.5" system (goose) would be good enough for most cars on here, and you would see gains from that alone, the standard elbow is hideous

this is what im on about kieron!

bob, i've just edited and added the word i'd missed, that word being elbow,

it makes no odds what turbo you have, if you increase effeciency (reduce back pressure) of the exhaust you will see some gains regardless of what boost/turbo you run.

 

[Keira]

even at 1 bar you'd see'd an increase in bhp and torque, whacking up the boost is all well and good but that thinking explains why so many people blow them up

the more efficient you make everything work the better, more reliable your engine will be,

power and reliabillity costs money, as im sure you are more than aware, theres no getting away from that fact, unfortuanetly the prices people get charged for things in the uk are a different matter, and is the main reason costs add up as they do over here

 

[Keira]

full read up for those interested :

The following excerpts are from Jay Kavanaugh, a turbosystems engineer at Garrett.

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.

elbows/dumppipes

The advantage to the bellmouth setup from the wg's perspective is that it allows a less torturous path for the bypassed gases to escape. This makes it more effective in bypassing gases for a given pressure differential and wg valve position. Think of it as improving the VE of the wastegate. If you have a very compromised wg discharge routing, under some conditions the wg may not be able bypass enough flow to control boost, even when wide open. So the gases go through the turbine instead of the wg, and boost creeps up.

The downside to a bellmouth is that the wg flow still dumps right into the turbine discharge. A divider wall would be beneficial here. And, as mentioned earlier, if you go too big on the bellmouth and the turbine discharge flow sees a rapid area change (regardless of whether the wg flow is being introduced there or not), you will incur a backpressure penalty right at the site of the step. This is why you want gradual area changes in your exhaust.

i'll get my coat

 

[pulsarboby]

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.”

you have just answered my theory regarding a standard or slightly modded car!

 

[Keira]

i did that a page ago :lol:

by just removing the standard turbo elbow and replacing it with something better flowing and then running a 2.5" system (goose) would be good enough for most cars on here, and you would see gains from that alone, the standard elbow is hideous

 

[pulsarboby]

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.”


but this is saying different! you will just end up with a noisy exhaust, its contradicting what you said earlier!

i gotta do some work now anyways, cant sit on here arguing over a bit of pipe, its making my head expand to an un-natural size:lol: me eyeballs are on stalks now!

 

[Keira]

jesus christ can you not ****ing read :lol: (day off for me, i can try and educate you all day) in simple english so you can understand.

my quoted point from earlier : get a 'BETTER' (better does not mean bigger bob ) flowing elbow and mate it up to a 2.5" exhaust, (mongoose) will be fine for the majority and you will get a gain just be losing the restrictive standard shitty elbow.

understand ?

chap from garrets quote :

250-300 2.5" is fine, by going bigger you're exhaust ( the whole system, not just the elbow) will be noisey without any other real gains,

300 and 2.5" will begin to be ineffecient, 3" would be fine,

400-450 3" should be considered barely adequate.

understand ?

you old folk are bloody hardwork :lol:

 

[Swampy]

Wise words as ever Kieron! the fountain of knowledge!
I would be doing it myself, well with the assistance of the welder at work.
Which would you say is the best value stainless elbow supplier, and the most efficient to use bearing in mind my car is not going to be a Bhp monster like you boys are building?
Cheers.

 

[Keira]

get all the bits off fleabay i guess, or atp (excluding the backbox), they have all of it

probably be the five bolt flange 2 90's in an s shape, straight into the back box.

matching the shape of the 5 bolt t2 flange wiill be the hardest part

although these 2 little fellas would give you a good start.

clicky

clicky again

 

[gunmetalgtir]

get all the bits off fleabay i guess, or atp (excluding the backbox), they have all of it

probably be the five bolt flange 2 90's in an s shape, straight into the back box.

matching the shape of the 5 bolt t2 flange wiill be the hardest part

although these 2 little fellas would give you a good start.

clicky

clicky again

Magic!! cheers mate! Gonna buy one of those and a bit of pipe bent to shape, welded and job done!

 

[Keira]

no problem, glad to have helped.

tbh you dont even need to be able to weld to get it sorted, aslong as you get everything worked out, cut and lined up on the car so you're happy it will fit, with those bits from atp you could flick through yellow pages, dig out the number of a welder/metal fab place and get them to weld it up for you

on another note, thats 2 people i've helped and one old man thats hopefully learnt something today..

time to go back to being an @rse i think :lol:

 

[rayman75]

this is interesting reading. like as already been said i would of thought a better elbow with a goose on std tubb is better than a std elbow.

good find on the flanges, im gonna have ago at doing a elbow my self.

 

[pulsarboby]

i give in then, admitt defeat! but i still would not waste my money on a standard setup and spend £££ on a bit of pipe that will not see significant gains, unless i was uprating everything else with it, so we'll have to agree to differ on this one!

and oy! less of the old bit, i aint that bloody old! you, you, you professor of all things gtir:lol: have you thought about jacking in dry lining and becoming a guru or something!

 

[fubar andy]

Andy, Are you coming this Sunday? I'll be there in my shi**er and Stu(mo) might be in his too. As you know I've just had my full pipewerx system fitted, Stu should be getting his done today. We were chatiing about exhausts briefly on Sunday.

You could always do your front section first and your back section later? Pipewerx are pretty local

Can talk ideas on Sunday if you want.

At the moment I’m still not 100% sure if I can make it Jim, as i’m trying to sort out this elusive misfire on my other car. If I can make it, I’ll look forward to a nice in-depth discussion!!! ;-)

Everyone seems to have good points regarding this 3” exhaust issue.
For me the point of going from a (goose) 2.5” elbow and downpipe to a 3” elbow and system was to help with the extraction of gases and help with efficiency. As for a minimal tuning on a GTiR it doesn’t seem worth it and as Bob says it’s just throwing your money away.

However, as my cars performance continues to increase at some point you have to look towards future planning and up rating other parts before you can install the “big guns”. I’m personally just trying to get a “feel”, read peoples experiences, personel views when its worth to make the move to a 3” elbow and downpipe, is it worth it and how far should you go from just an elbow to a full system?

even at 1 bar you'd see'd an increase in bhp and torque, whacking up the boost is all well and good but that thinking explains why so many people blow them up

the more efficient you make everything work the better, more reliable your engine will be

Personally I don’t want to be over stressing my engine just for the sake of a couple of hp’s more (say upping the boost). Perhaps it’s the cheaper way of going, but if I can reduce the amount of stress inflicted or help the engine in other areas then I don’t mind, but it has to be a viable move.

the more efficient you make everything work the better, more reliable your engine will be

Even if my cars not got the right hp at the moment, I’d like to be prepared as in a few months it going to have a hike in power and I’d rather be ready knowing that everything else is adequate for what I’m wanting to achieve!

 

[Keira]

For me the point of going from a (goose) 2.5” elbow

the mongoose doesn't have an elbow, it bolts up to the standard one.

the standard exhaust is iirc 2 1/4inch, the standard elbow at its worst point gets as small as 2, maybe 1 3/4 inch, it also has some ugly, nasty, lumpy shape to the inside of it, its not a smooth bend at all on the inside, its cr@p, simple as

 

[fubar andy]

the mongoose doesn't have an elbow, it bolts up to the standard one.

Missed that one before I posted :doh:

 

[Dan_GTiR]

What's peoples view's on divorced elbows, where the wastegate side would be dumped to atmosphere, and not plumbed back into the system?

I'm in the middle of designing one at the moment, and would like some opinions.


Dan.