What turbo to just extend the powerband

[Wurf]

What's the boost at 6500 RPM? If there's any significant boost, say 5lbs or more, my guess is there's power to be made by porting either the exhaust side of the head or the waste gate, or removing whatever is the primary restriction in preventing gases from getting through the motor.

I would also say if you find it, and remove it, you'll not only pickup power at higher RPM but you should drop peak boost, pickup power at peak boost, and basically increase efficiency.

Just talking theoretically if you increase the efficiency of the motor naturally aspirated, then the turbo doesn't have to work as hard and that's a good thing. Less heat, less chances of detonation, etc.

I would rather go that route instead of trying to cram more air through it with a bigger turbo and more boost.

 

[jboucheb]

dont waste your time with a GT28. get a GT3076

you will get board of the GT28

But doesn't the 3076 put more stress on the motor? Was the 28 at least fun in the beginning...and then you started to get bored? How often do you go WOT? I can only go WOT on highways since this car is so quick.

 

[mazdaspeed32007]

What's the boost at 6500 RPM? If there's any significant boost, say 5lbs or more, my guess is there's power to be made by porting either the exhaust side of the head or the waste gate, or removing whatever is the primary restriction in preventing gases from getting through the motor.

I would also say if you find it, and remove it, you'll not only pickup power at higher RPM but you should drop peak boost, pickup power at peak boost, and basically increase efficiency.

Just talking theoretically if you increase the efficiency of the motor naturally aspirated, then the turbo doesn't have to work as hard and that's a good thing. Less heat, less chances of detonation, etc.

I would rather go that route instead of trying to cram more air through it with a bigger turbo and more boost.

i agree. build the motor not the turbo. if your planning on spending the money to upgrade the turbo, parts, tune etc... i would say your better off building the stock 2.3 up to handle the airflow and not overwork the turbo which otherwise would be like trying to blow a tunnel of airflow through a straw. build up the motor to handle the flow and increase power and efficency of the turbo the whole rpm range because the turbo has to work half as hard. and with that your increasing the life of the turbo due to the lesser work load.

 

[8.5MS3]

What's the boost at 6500 RPM?

on stock tune theyres still 6-10 psi at redline, with a tune you can get that up to 16-17 with BAT's in the 120s

 

[TheDoc]

For TheDoc's thoughts:

Here is a volumetric effeciency analysis done by a member on another board, in the attached pdf file. He seems to be using a different compressor map for the K04 and reaches a conclusion that the choke line is even lower than you suggest and that even stock boost levels cannot be maintained at 6,500 rpm regardless of tune.

I'm confused. Are you both saying the same thing in different ways, or if you have differences in your calculations, where are the differences, and what does this mean. I sense that either calculation means that there's not a lot left in the stock K04 for operation above about 5,800 rpm or so.

Well, I never went into the math involved with the K04 as your attachment certainly does.

The graph I got was just from typing "Mazdaspeed3 K04 Compressor Map"... I guess it's possible that I didn't get the correct one, but that's always been the one I've seen passed around. I would almost be willing to bet that one of the maps belongs to the Speed3/6's and the other to the CX-7's turbo... but that's just an idle thought.

Any differences in math could be attributed to using different VE values and different BATs for the calculations.

Regardless, as I've read it, we're both saying that the K04 isn't going to make power to redline.

You'll need a higher flowing turbo, a flash that will prevent the throttle plate from shutting as it approaches redline, and a reworked intake/exhaust tract, starting at the air filter and ending at the head. At any rate, it will take more than just a turbo to make power like I think the OP is imagining.

 

[Wurf]

I would summarize to the OP, forget about 6500rpm power.
SHIFT at 5500 and if you need more, make sure your tires can use it before you invest.

 

[MSMS3]

Good summary, Wurf.

It also appears that even if you can tune to hold power to some degree above about 5,800 rpm, the heat generated will cause the turbine shaft to soften and ultimately result in turbo failure, according to aftermarket suppliers of K04's:

http://www.mazdas247.com/forum/attachment.php?attachmentid=153750&d=1248708049

 

[8.5MS3]

Good summary, Wurf.

It also appears that even if you can tune to hold power to some degree above about 5,800 rpm, the heat generated will cause the turbine shaft to soften and ultimately result in turbo failure, according to aftermarket suppliers of K04's:

http://www.mazdas247.com/forum/attachment.php?attachmentid=153750&d=1248708049

ive seen this at least 1/2 a dozen times. what engine did they use for the test? neuspeed does not indicate it on the pdf nor on the website. Mazda isnt even a carried manufacturer. That makes a big difference.

 

[Wurf]

Probably Audi or Volkswagen.
How would that matter though?
Is the K04 built different for Mazda than the German makes or is it a matter of maybe more boost AND those rpms ?

 

[8.5MS3]

Our turbo is different than the VW version. How much so, I'm not sure so I won't attempt a half assed answer. The engine makes a huge difference. Displacement is first. A bigger engine will push more exhaust out with each stroke of the engine. Then the design of the manifold comes next, followed by the level of exhaust restriction. I'm sure other things like cam design and overlap as well as head design play a huge role too. Bottom line is you are comparing apples to oranges. Take the ko4 and put it on a V8 and it will be inefficient at 3psi at 2000rpm.

 

[MSMS3]

There are several different K04's with different sized compressor blades and turbine blades. To my knowledge they all have the same inconel 5mm center shaft. I don't know if the VW-Audi K04 upgrade kit is using different sized compressor vanes or turbine vanes. What I do know is that the turbocharger is absolutely dumb to the type of engine it is connected to when it is pushed into its ineffeciency. It does not know or care.

Any individual K04 model has a limited ability to push exhaust through its turbine side in terms of maximum cfm, depending on its design, not on the system it is attached to, assuming that the engine has enough power to flow exhaust that exceeds that cfm limitation in the turbo itself. When its design limits are exceeded in terms of cfm flow, it turns that extra exhaust into increasingly climbing exhaust temps which then soften the center shaft with resultant failure over time.

It is appropriate to know what particular models of K04's we are comparing. It is not appropriate, IMHO, to think that the turbo cares what engine it is connected to.

If our K04 is the same model or very similar in specs to those being sold by Neuspeed for Audi and VW customers, then it will soften the center shaft the same way under the same conditions.

Guys with aggressive tunes on MS3's may find themselves in the same boat as Neuspeed software modified ECU users. Neuspeed's aggressive tune had to be dialed back to save the turbo's center shaft, and customers told not to exceed 5800 rpm.

Do I know if this is essentially the same K04 as we use? No. Am I cautious about the wisdom of exceeding stock boost levels on our K04 at rpm levels above 5,800, even if the an aftermarket tune says it's making power? Yes.

Only way to really be sure is to install an exhaust temp sensor close to the wastegate and see just how high the temps go during redline runs at high boost levels. Maybe we won't have the same problems.

Just one point of view. You pays yer moneys and you takes yer chances. It's pay to play with performance mods.

 

[8.5MS3]

Any individual K04 model has a limited ability to push exhaust through its turbine side in terms of maximum cfm, depending on its design, not on the system it is attached to, assuming that the engine has enough power to flow exhaust that exceeds that cfm limitation in the turbo itself. When its design limits are exceeded in terms of cfm flow, it turns that extra exhaust into increasingly climbing exhaust temps which then soften the center shaft with resultant failure over time.

It is not appropriate, IMHO, to think that the turbo cares what engine it is connected to.

Gonna have to disagree with you here. The engine it is mated to makes a huge difference. Your telling me that a 1.8T, 2.0T 2.3T 3.0T etc. with different cams, heads, manifolds and tuning all push the same cfm across the turbine at 5800rpm? It is illogical to think that it reaches a limit at a certain RPM on one engine, it must be the same for another. The same goes for bolting on a big turbo setup. SU mark hit a wall with the GT40. Its spec'd for over 500 hp, yet he cannot achieve 400 since the engine cannot flow enough cfm on the intake side to get big power. Thats where PnP and cams come into play. The turbo is dumb to the engine its connected to yes, but the engine it is connected to has a unique CFM of exhaust and level of restriction at any given RPM when compared to another.

Also, softening of the shaft is dependent on how much further you push a turbo beyond its efficiency and for how long a period. At the limits it is running hot, but go 1 cfm further and you are at the point of metal fatigue? The article you posted even says to allow cool downs after hard running to prevent drooping. Metal does not turn to Jello instantly, and running over 16psi for the 12-14 seconds in a quarter mile, or 30 seconds during an autoX will not result in molten CHRA.

Do i think the turbo is undersized for this car absolutely. can it run slightly higher (.14bar or 2psi) more than stock for short periods, yes. Can it go 400rpm beyond its stock configuration and continue to make boost yes. does it degrade the turbo, sure. But the rate at which the turbo degrades is ultimately dependent on your right foot.

 

[Bravnik]

you can still pull power to redline if your turbo is big enough i call bs that cams are the restriction, i can show you a bunch of big turbo dynos where they pull to redline

You can call BS all you wish. Please provide Dyno's of said MS3's holding max power to Redline? I have yet to see such a Dyno from any BT. However, I have not been keeping up lately so maybe there are. Should be simple to prove. Post up the Dyno's.

 

[8.5MS3]

You can call BS all you wish. Please provide Dyno's of said MS3's holding max power to Redline? I have yet to see such a Dyno from any BT. However, I have not been keeping up lately so maybe there are. Should be simple to prove. Post up the Dyno's.

nope no one has, Race Roots has a T67 on an MS3 and it still drops at the upper RPM band on MSF.

bf your on msf how can you say that lol

 

[Bravnik]

The only dyno I have every seen that held power to Redline was the one on MSF that dyo'd with a 150 Shot. It held power but I can assure you it was the Shot that made it do so. So I guess BF is right. You can do it if you have the balls to run a 150 Wet Shot on top of a BT upgrade

 

[8.5MS3]

The only dyno I have every seen that held power to Redline was the one on MSF that dyo'd with a 150 Shot. It held power but I can assure you it was the Shot that made it do so. So I guess BF is right. You can do it if you have the balls to run a 150 Wet Shot on top of a BT upgrade

I wont do it, guess i dont have big balls lol

 

[Wurf]

I think MSMS3's point might be the turbo itself can only spin so fast and continue to make boost pressure "x" at the same time regardless of what is spooling it, be it a 2.0 or 2.7 engine. That is of course in theory where we are talking about same impeller and turbine construction throughout, which is reportedly not the case with the VW, Audi, and the Ms3 applications. There's just too many variables here to call it an absolute and say the K04 regardless of how it's built or what's bolted on cannot make power above engine RPM X. Suffice to say any OEM K04 is a small turbo and it can't make big power up top because it's not designed to do that. Push it a little and you can extend the power band at the risk of melting the little sucker.

Frankly I like the fact that the turbo is small and boost comes on early and gives the car lots of low speed torque to squirt around town. I would not want to sacrifice this aspect for a higher RPM, more peaky powerband from a bigger turbo. It's what makes this car fun on the street. Sure you can get waxed by a built MS3 or a SRT4 or whatever but so what. Like they say, there's always somebody faster.

I will live with 5500 and mod it to make more where it's designed to run by making breathing mods.

 

[8.5MS3]

I think MSMS3's point might be the turbo itself can only spin so fast and continue to make boost pressure "x" at the same time regardless of what is spooling it, be it a 2.0 or 2.7 engine. That is of course in theory where we are talking about same impeller and turbine construction throughout, which is reportedly not the case with the VW, Audi, and the Ms3 applications. There's just too many variables here to call it an absolute and say the K04 regardless of how it's built or what's bolted on cannot make power above engine RPM X. Suffice to say any OEM K04 is a small turbo and it can't make big power up top because it's not designed to do that. Push it a little and you can extend the power band at the risk of melting the little sucker.

Frankly I like the fact that the turbo is small and boost comes on early and gives the car lots of low speed torque to squirt around town. I would not want to sacrifice this aspect for a higher RPM, more peaky powerband from a bigger turbo. It's what makes this car fun on the street. Sure you can get waxed by a built MS3 or a SRT4 or whatever but so what. Like they say, there's always somebody faster.

I will live with 5500 and mod it to make more where it's designed to run by making breathing mods.

key thing is if the turbo is pushing say 350cfm, the amount of boost is different on different engines. on a 2.0 it may be 20psi, 2.3 15psi, 3.0 12psi etc. since the engine size is directly related to how much air it can take in per rev. This is my arguement. If its out of efficiency at X rpm at Y psi on engine A, Its not going to be the same on engine B.

 

[MSMS3]

My point is exactly as Wurf states. 350 cfm at 15 psi is 350 cfm at 15 psi no matter what engine exhaust manifold delivers it to the turbo.

As stated earlier, I do not know if the impeller or compressor wheels and their vanes materially differ between our K04 and those being sold as upgrades for VW-Audi. All I do know is that once you push the turbo into the inefficient stages of its mapping, heat skyrockets. All OEM K04's to my knowledge do have the 5 mm (very small) size inconel center shaft, and that is the weak link for heat related failure.

That's why Neuspeed recommended that those wishing to explore the outer limits of their K04's with high boost and rpm above 5,800 rpm needed to think twice about it and if they went on ahead, be very religious about extended cool down and needed to install and carefully monitor exhaust temps as close to the turbo as possible.

Given our six speed tranny and its gearing with a drop of only 1,000 rpm or less between shifts, together with the very fat torque curve we have, it makes little sense to me to hold the lower gear past 5,500-5,800 rpm anyway, unless you are autocrossing or need to hold a gear at the very end of the dragstrip. That would mean being able to trap at least 110 mph and thinking about reaching for 6th gear, which I don't think any of us can do.

Guys, this is just my personal take on the limits of the turbo. One man's view. I'm a skeptic about K04 power above 6k under load. I'd like to see those dynos too and would like to see what turbo outlet temps into the downpipe actually are when running WOT at 6k and above. This is why I thought that going with a slightly larger Garrett turbo might make sense for someone wishing to get above these limitations without losing a lot of bottom end power in the process.

 

[mazdaspeed32007]

does anyone know what the factory k04 egt's can reach before you run into something undesirable for the turbo? i am currently running pretty heavly modded, and minus an egt gauge which i plan on picking up to save the turbo, i dont want to burn the k04's center shaft. its one thing to monitor how the engine behaves with your bolt on's and how your pushing the hp and tq curve higher towards redline but at the risk of what? creating a pos turbo that will fail you in the end. i shift at 5500 rpm which puts me directly into the fat part of my dyno curve because of this close gear ratio...but not knowing what your egt's are doing would be the biggest concern here when trying to move higher towards redline correct?