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Factory boost pressure?

62K views 31 replies 15 participants last post by  dkmusic 
#1 ·
How much boost is the stock turbo on the Juke putting out? Does anyone know what size turbo the Juke is equiped with?
 
#2 ·
I've been curious about this aswell. We traded in my wifes '01 Jetta 1.8t to get her the Juke. I noticed that the turbo on the Juke is smaller than the KKK K03 on the 1.8t. Given that the Juke has 38hp more than the stock, K03 equipped, 1.8t with smaller displacement AND smaller turbo, I'd really like to know how much psi it's pushin'.
 
#5 ·
I've been curious about this aswell. We traded in my wifes '01 Jetta 1.8t to get her the Juke. I noticed that the turbo on the Juke is smaller than the KKK K03 on the 1.8t. Given that the Juke has 38hp more than the stock, K03 equipped, 1.8t with smaller displacement AND smaller turbo, I'd really like to know how much psi it's pushin'.
The physical size of the turbo isnt what determines its flow potential, its the size of the intake/exhaust wheel area thats important. A lot of times a turbo may be a little smaller in actual physical size, but that dosnt mean it flows any less.
 
#11 ·
The Juke is actually build at 26psi of boost, factor in atmospheric pressure already of 14 lbs, subtract and you get the factory reading of 12 psi. A lot of older cars you can play around and increase it, 2011 technology, the ECM has other ways to find out if boost is going past that to shut it down, already researched into it
 
#16 ·
The thing about turbo vehicles and larger exhausts is this: The larger your exhaust, the lower your backpressure. Lower backpressure allows for quicker turbo spooling. You increase your horsepower, but lower your torque in the mean time.
Torque is what gives you your off the line acceleration, but horsepower is what gives you better at speed acceleration (60-100 for example)

With the Juke being either AWD or FWD, you don't need to worry about torque numbers as much as if you were in a RWD vehicle. Too much torque with FWD and you simply spin the tires (this goes for any set-up, with enough torque.)

...Least, this how its been explained to me by other, far more experienced, AWD guys; one being a Subaru technician.)
 
#14 ·
You realize this thread was from 2 years ago? I haven't seen that guy at all in the 5 or so months I've been on here.

And to answer your question, a CAI and 2.5 catback will get you a nice bit of performance upgrade.

As well and slightly increase gas mileage. I would suggest reading some posts around here since there are all over the place.
 
#23 ·
Yes and no. An "open header" ie no downpipe after the turbo isn't going to be the best. Certainly not for a street car. Is it best for turbo spool and boost pressures.. you betcha. You don't run open manifold on a n/a car. So why would you do the equivalent to a turbo'd STREET car. You still have to deal with that 800 to 2500 rpm band on a daily basis. This is where you spend almost all your time in a street car. It's the last place you want to gut your torque out of.

With a log style exhaust manfold like we have, you have none of the manifold parameters that are designed to help n/a cars. No tuned length runners, no tuned diameters, these things are dreadful for n/a motors. THey are made to get the expanding gases to the turbo quickly to spool it fast. That's it. So the manifold is against you, put too large a pipe on and you'll have that against you as well. It's going to hurt low end performance. You'll be fast as hell around a track, but you'll be miserable when you have to get the groceries.

Now. As I said up earlier, you need to find balance. We don't know what that balance is yet. For all we know it's 3 inch. We won't know until your dyno results come back. Where your powerband is is also more a matter of preference than necessity. It's should be tailored to your drive style.
 
#24 · (Edited)
We don't know what that balance is yet. For all we know it's 3 inch. We won't know until your dyno results come back.
Now this part I can agree with! :)

So far everything done to date has improved both torque and HP across the "entire" power band... yes it will be interesting to see where the limitations to lower the torque band occurr ....but I highly doubt 3" piping off the turbo will reduce low end torque...
 
#26 · (Edited)
Great technical article from Cobb with respect to "turbo'd" exhaust systems considerations: (particularly read "post turbo exhaust" section)

"One thing I do want to explain before I get too far into this is backpressure. I hear "You need backpressure to make torque." all the time. And it even comes from "tuners" as well as customers. This is flat out not true...The reality is that backpressure is the enemy. You want to keep it as low as possible...The perfect exhaust system would keep the gasses moving as fast as they did coming out of the cylinder and have zero backpressure".

"The exhaust system before the turbo and the turbo itself have a greater effect on backpressure than the exhaust behind it. You want the least restriction after the turbo as possible for both top end power and quick spool-up."

http://www.cobbtuning.com/Technical-Articles-s/70676.htm

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And as you can see (below) these are actual improvements that have been made so far with low end torque response coming on much earlier in the powerband....And this was accomplished without a tune or downpipe by simply opening up the rest of the exhaust system with 2.5" pipe, improving the breathing (CAI / hardpipes / DV), and elevating boost levels.....

Now the general consensus from everyone I've been working with (for whats that worth :)) is that with a good tune and full Turboback exhaust system installed torque response will be further improved both at the lower end as well as raised uniformly across the entire power band which in turn will also increase max hp....The increased downpipe diameter will greatly improve the turbo's exhaust efficiency and therefore allow for it to also pull or intake more efficiently increasing overall performance across both power and torque bands...Currently the 2" stock pipe off the turbo exhaust port and restrictive primary Cat are limiting overall response greatly...

To be determined/continued......

 
#27 · (Edited)
Great technical article from Cobb with respect to "turbo'd" exhaust systems considerations: (particularly read "post turbo exhaust" section)

"One thing I do want to explain before I get too far into this is backpressure. I hear "You need backpressure to make torque." all the time. And it even comes from "tuners" as well as customers. This is flat out not true...The reality is that backpressure is the enemy. You want to keep it as low as possible...The perfect exhaust system would keep the gasses moving as fast as they did coming out of the cylinder and have zero backpressure".

"The exhaust system before the turbo and the turbo itself have a greater effect on backpressure than the exhaust behind it. You want the least restriction after the turbo as possible for both top end power and quick spool-up."
Thanks for making my point for me. As you just re-iterated, reducing back pressure behind the turbo clearly increases top end power and spool up, which is what I said earlier. I'm well aware of "back pressure". It's a bit of a misnomer. You don't want backpressure, you want exhaust velocity. People like to get the two confused and seem to think they are interchangeable. Increasing pipe diameter reduces back pressure in the system, so does shortening the lenght of the pipe and removing bends. What it also does is decrease exhaust velocity. This is where fluid dynamics come into play. (air is considered a fluid and follow the laws of fluid dynamics).

So increasing volume will decrease velocity, while also decreasing pressure. Again, balance. Velocity is what keeps the exhaust moving out of the pipe before it cools. As the exhaust cools in the pipe, it becomes denser, travels even more slowly and takes increased work for the engine to pump it out. You want to exhaust to leave hot, fast and thin to decrease pumping losses. That is essentially what you are managing by tuning an exhaust. You are freeing up horsepower lost to pumping losses, i.e. the amount of power required for the engine to rid itself of spent fuel/air. Larger pipes suit high end power because there is more exhaust volume per unit time and rotation speed has the exhaust moving at a higher velocity out of the engine. Conversly, smaller pipes suit low end power due to smaller exhaust volume per unit time and decreased velocity as compared with high rpm.

One could take the premise a step further and say that removing the pipe completely will free more horsepower because the engine won't have to spend any energy to get rid of the exhaust. You'd be wrong though. This is where scavenging and resonance waves come into play. As the exhaust moves down the pipe (it does so in pulses due to the nature of a 4 stroke engine) it creates a low pressure wake behind it. This low pressure wake helps to "pull" the next exhaust pulse out of the next cylinder in firing order. Typically, header length is tuned to time these low pressure events so that they coincide moments before the exhaust valve opens. This is the whole premise behind true headers vs those crappy stock manifolds. The theory also applies to the intake manifold as well, and those intake runners are specifically tuned lengths.

This applies to turbo'd vehicles as much as naturally aspirated ones. It all comes down to maintaining velocity and temperature.
 
#28 · (Edited)
Hey your welcome...all good stuff JD...Albeit I think some aspects you referenced are mainly applicable to n/a vehicles...

To summarize....(taken from Cobbs technical writeup with respect to after the turbo exhaust systems)

http://www.cobbtuning.com/Technical-Articles-s/70676.htm

"You want the least restriction after the turbo as possible for both top end power and quick spool-up."

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And for those interested here is another writeup posted below which should hopefully serve to clear up some common misconceptions regarding the loss of low end torque by increasing of exhaust system pipe size in a turbo'd system (downstream of turbine)....

Now the following "excerpts" below are from Jay Kavanaugh, a turbosystems engineer at Garret regarding Turbo Exhaust Design and Theory:

Turbo Exhaust Theory (complete writeup)

"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.”

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.

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.
 
G
#29 ·
Way before the juke, I had a 2001 grand prix that I turboed. The car was running stock 9.5 to 1 CR and boosting 15 psi through stock restrictive 2.5 inch exhaust system. The first cat was 2 foot away from the turbo. I installed an electric exhaust cut-out between the turbo and the first cat who completly opened the exhaust. From stock to straight pipe in 2 seconds with 1.5 foot of 2.5 inch pipe from the turbo. I was spinning the tires at 50 km/h with the electric exhaust cut out closed and spinning the tires at 80km/h with the cut out opened. So I guess the lower the backpressure, the better the power in a TURBO application.

As for the debate regarding HP vs TORQUE. My point of view is that the torque is mesurable. 100 pound on a one feet lever.

The HP is not mesurable but is "calculated" using the torque and mathematical formula. Look at that formula and you will understand why the HP and TORQUE always cross each others at 5252 rpm on a dyno sheet while using the same scaleand an HP/LB-FT measure. Im not saying that to curious or JD cause i guess that you already knew that.


Sent from my Autoguide iPad app
 
#31 ·
Stock yes but get an mbc and you can go to 16-17 spiking and a tune can go way higher with most running 19-20 or a little over.
 
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