Found this on Rennteam - what do you guys think?

http://www.rennteam.com/showflat.php...gonew=1#UNREAD

 

It's interesting, but I think the main point (speaking about tuning) is the cars were built to do everything anywhere. If you start modding it, you get heat and concerns about being able to use that power anywhere. I would assume most of us never drive our cars in extreme conditions and there will be no issue.

 

I'm hardly an expert, but I would think there are aftermarket solution to this problem, if in fact it's a problem. It was my understanding that new intercoolers from imagine or EVO really helps. I could be wrong.

 

Chris

i was a little disappointed with vtg myself, mainly because there's turbo lag at low rpm and there's a flat spot mid-throttle. however after installing a fabspeed exhaust system (thanks, Marc997gt3!), my 997tt feels fairly responsive and most of the lag is gone.

i compared the dyno charts from porsche and those from giac and imagine auto. the graphs were very telling as the shape of the factory curve doesn't look anything like the measured curves ... power/torque comes on a lot later and the shape of the curve is very different. see for yourself below.

i may regret making this post as it will bring out all the 997tt bashers.

factory chart




imagine auto hp curve
- blue line is stock hp; red is with giac chip



imagine auto torque chart
- bottom line is stock tq; top is with giac chip

 

here are the plots from giac. they are closer to the charts from Stephen (porschephd) at imagine auto than the factory charts.

 

intereting information

 

Not sure what is so interesting about them.

Golfguy thanks for the effort but really, comparing these dyno charts to a Porsche factory chart is totally irrelevant. Stephen uses GIAC so they are obviously similar charts.

I had posted the KKK VTG limitations to 550 HP here before from a VERY reliable source, but as long as you have tuner chassis dynos showing 600HP+ on them, people keep dreaming. RC on Rennteam is 100% right.

 

Jean

i guess i wasn't specific in my post but i was referring to the following differences between the charts comparing the measured dyno measures (lower lines in overboost mode without giac chip) and the factory plot. you can see the following differences:

- measured power and torque come on significantly later than the factory shows
- shape of the curves are different; giac and ia curves are more similar
- factory curves are more linear than the curves measured by tuners

i'm wondering why the differences are so dramatic and how one correlates dyno results? dyno testing definitely useful in comparing before and after results.

ps. my comments about lag are based on my not so accurate butt dyno comparing my 993tt to the 997tt. boost is available at lower rpms on the 993tt and the delivery seems to be more linear; that's why i feel some lag on the 997tt. clearly the 997tt is much faster that the 993tt. as i noted, the fabspeed exhaust eliminated most of the feeling of lag.

 

Jean I don't understand your arguments. To people who understand how to read a dyno the story is VERY telling. Porsche published a dyno plot showin g the torque peak of 460 ft/lbs being achieve at 2000 rpms. The actual dynos done by Imagine/AWE show that the relative peak does not arrive until 3200 rpm. That is a HUGE discrepancy. Even more curious are the plots of the boost pressures - they are nowhere near a square waveform as one would expect given the Porsche torque plot, and peak boost is not achieved anywhere near 2000rpms. Peak torque is not achieved in any turbo car at less than peak boost - this is without exception.

Regarding 550hp being the limit of the VTG turbo - there are multiple dynos done here in the US showing that the VTG has been taken to well over 550 hp at the flywheel - some are to the point of almost 600 hp to the wheels using race fuel. This is empiric data. This along with accelerameter data (driftbox) that show the same modified cars dropping their 400m acceleration times down to under 11 seconds, and their traps speeds increasing >10 mph. Are you contending that this is false data?

You might ask how the VTG has been so successfully pushed? It has to do with compressor and efficiency maps. Each and every turbo is a pump that is flow limited by 2 things on the compressor side - the crossectional area of the compressor inlet, and the design of the compressor blades. The inlet size determines the choke line on the map, the blade design determines the surge line. No more flow occurs outside these lines. Looking at the diagram, flow is on the X-axis, pressure is on the y-axis. The more you go to the right, the more flow occurs. Each blue circle shows you a turbo's efficiency map at a given pressure. Notice that the larger blue circles show the same turbo flowing more at the same pressures ratios (circles extend more to the right). This is what happens when you remove backpressure from the turbine - you can make a turbo more efficient. How does one achieve that - less restrictive exhaust. Pressure and temperative are also directly proportional. Less backpressure also results in less exhaust temperature.

As much as I enjoy Rennteam, it is NOT a technical board whatsoever and the discussions are lacking in engineering acumen. I am a Porsche enthusiast and really appreciate the fact that Christian has developed and maintained an excellent resource for news and discussion of upcoming vehicles. It is hard however to ignore some of the junk science that is thrown around.

 

eclou,

I agree about the technical aspects of these boards. Being an engineer like you I appreciate real science.

Reducing the turbo backpressure increases the input-output differential which increases throughput. This why we see the hp gains with only the exhaust mods. I my case the "feeling" between the before and after (exhaust/header) was less delay and "kick" due in part to a quicker spoolup and earlier (less rpm) torque (see dynos graphs above) response directly attributed to less backpressure. I know the "feeling" isn't a good engineereing term (don't have access to a dyno), but this is backed up by the real science aspect of reducing backpressure and verified by the RELATIVE dyno measurements above.

Mike

 

The intercoolers have nothing to do with the turbochargers themselves overheating, they only cool the charge air going into the motor.

 

Not quite true.

1)Any impedance to the flow of the compressor (cold) side creates more resistance and will make the turbine work harder (less efficient) to spin as well on the hot side. Remember the turbine and compressor wheels are directly coupled on the driveshaft of the turbo.

2)intercoolers that are less efficient will be less able to cool the intake charge, thus lead to higher combustion chamber temperatures, and hotter exhaust gases.

To be fair, the effect of the above are usually far less dramatic than exhaust path restrictions.

 

^You are right. However, the point I was trying to make was that this particular problem cannot be cured solely by more-efficient intercooler design.

 

LOL, I don't know what the "real" number is and honestly do not care. I sure as hell am not playing that game. What I can tell you is that the turbos are killed by the heat. Porsche had 25 faliures in Italy right before production hence the "sport" mode.
<O
When we actually started tuning we found all sorts of issues. Even Porsches original code was flawed. After we started changing and moving the programs around and testing it was clear that there was lots of room for improvement. The biggest plus INHO was the 120 C degree drop in EGT. Back pressure brought the powerband down and the knock level is gone up top where it was causing a dip.

Clearly the car was not ready for production. There have been 3-4 new releases in software since production. <O
Lastly, I don't know what chart Porsche is using for their figures, but I have yet to see a chart like that. I call marketing BS on this one. I have dynoed a lot and not one shares a chart not similar to the factory and very close to mine.
<O
Lastly, use the dynos for a baseline and the gain. Not a pissing match. I get so tired of this. I give the gains and that is it. A dyno is a tuning tool. <O

 

ZAMIRZ- you are absolutely correct. No intercooler mods will ever cure an EGT problem and keep your valves/turbo from burning up

Stephen- I have to say I think there is a bit of disbelief that you, AWE, EVOMS, Alex, and Giac were able to achieve so much without any factory assistance - especially far beyond the palty gains of the euro tuners to date. Hats off to you - the guys across the pond are stupified!