I have Champion 68s, Cobb tune, catless AWE exhaust and other supporting mods. I go to Mosport once a year and datalogged with the Cobb Accessport. I run a tune with 22.5psi boost from about 4k to redline. There have been a few threads saying that vtgs cause high iats if high boost is used on long pulls.


For 99.9% of my needs the tune works without issue. The graph below will show that the iats do climb on the longer pulls and then timing gets pulled, the lambdas get rich, and boost is reduced. Obviously performance is then reduced. At the start of the day I was able to pull my friend's 2015 C7 Z06 with upgraded tune and CAI. After the iats rose we were pretty even. Clearly this will not do!


hmmmm....I'm having trouble uploading the picture, let me try again...

 

 

you might check out the new easy photo uploader tips in the sticky at the top of the site news and feedback section

 

Around 140mph the iat exceeds 120F and things start happening - lambdas get really rich, boost drops, etc... Ambient temp was in the high 50s or so.

The options are: lower boost, accept this performance drop for the 1 day a year track day, get better intercoolers. I'm sure someone will say "get alphas" but I'm not interested in changing these vtgs.

Is there any proof that another intercooler would be able to keep the iats down below 43C or so on my car? I'd be interested in a modestly priced I/c if it worked but no interest in spending 4gs for AMS I/cs or similar.

 

Thanks Chuck. Usually it's no problem but this time even when it "finds" the photo on my computer, shows it in the "preview" window, then as soon as I press "insert" nothing happens. I was able to load the picture by using the "old way". So much for "easy photo uploader", lol.

 

i think i meant to say the new easy photo uploader sucks...try the old way

 

Was going to say get ams intercoolers but that rules that out. How about meth?

 

There aren't modestly prices ICs that outperform the .2s. Either AMS or the Proto ones, both around the same price.

Or run e85 for the once a year race event. That would solve the temp issue as well.

 

Contact Markski. He may just be able to help you out with this.

 

Are you sure that's it's the IAT that causes that performance drop around 140 mph? You're just at 48C (120F) while the safeline IIRC is 55C (131F). Have you logger EGTs, the cause may be there...if you're above 980C (1767F)? Which is quite possible with those turbos, big compressors with relatively small turbines.
I did a small experiment with my own car, adjusting control vane settings at upper rpm/boost range while the boost was dropping slightly from desired (1.3 --> below 1.2) over there, this based on 3rd/4th gear loggings at track. Yes, I got "better" boost curve, but the EGT also rose, quite much. Especially in 5th/6th gears. I did one airport mile run in September and the log wasn't anything beautiful to see...:
-delta T 44C with max IAT 74C! (rise stablized again at 250 kmh)
-max EGT 974C (exceeded 950C at 265kmh)
Disclaimers:
-started with heat-soaked engine from crawling in the queue, OAT was around 15C while IAT at start 30C.
-used 996 turbo's ICs because RS's end tank was blown off earlier in August...
-despite 996 GT3 Cup's rear wing and all that **** above the end speed at mile was still 283 kmh... And 1/4: 11.769s (organizer's timing) /196 kmh (DL-1), it was my first 1/4 ever and I did not try launch at all.

Quote from factory tech manual:

Exhaust Temperature Sensors, Banks 1 and 2
The signal from the exhaust temperature sensors of banks
1 and 2 installed at the turbine inlet is used in the DME
control unit for component protection. The exhaust
temperature is evaluated for each bank in the DME control
unit, and is restricted to a maximum temperature of
1,767° F. (980° C) by enrichment or boost pressure
adjustment. The two sensors are combined into one
component unit together with their control unit. The
measured signals are evaluated in this control unit.

 

A few options from least to highest cost:


1) as you said, reduce boost -you will take a 60-130 and 1/4 mile performance hit


2) meth kit with a big tank -use it for cooling and not extra fueling


3) E85


4) non-VTG turbos (hybrid K24s work well!) -root cause, you're seeing the effects of sustaining 700-800 hp worth of airflow through K04 exhaust housings.


5) Marston ICs (roughly 10K)

 

There simply isn't any way to make a tune that performs to its utmost for every possible situation. For instance, for most situations such as a good street tune, 60-130 runs, 1/4 mile you want to run the motor in a way that maximizes its area under the curve, otherwise, you're not using all of its potential.

On the other hand, without appropriate cooling systems in the car such a tune can't be truly ideal for 1 mile runs, 30min road course sessions where most of the time is spent at WOT, etc. I know given its coming from me it may come off as a marketing pitch but I truly believe and know from experience that customizing your tune to what you need for a given set of driving conditions is the ideal way of approaching it. We work with race teams all over the World and our tunes are always custom to their needs. A lot of times from the tuning side of things they're boost limited, airflow limited, etc. We have cars coming out 1st in class in 12hr races in Australia in horrible conditions but a tune made for a car that'll go through that sort of racing is nowhere close to something you'd want on a car seeing mostly street duty as it'd be weak/boring and leaving a ton of fun on the table. You have to balance everything when customizing the tuning and advise the customer accordingly. It is simply wishful thinking that one tune can do it all, bottom line.

Octane and intercooling always help. I keep mentioning methanol injection not because of just octane but because the tune made for the street where area under the curve is maximized has a much higher chance of staying consistent without incurring heat soak if you take it to a road course or 1/2-1 mile events. Many race teams run meth for these exact reasons.

This same concept applies not only to tuning but suspension setups, gearing, daily drivability of the car. You can't have a race level suspension on a car that sees street duty and expect comfort. You can't have tall gearing set for a specific road course setup and expect the car to perform the same as a different set gearbox/final drive setup with the same tune. You can't strip your interior to lighten the car..and still have your interior looking nice as it came from the factory

Let me know if any other questions at all.

Dzenno@PTF

 

I don't want to hijack Bogg's thread, but as this is close to the original subject, here's some comments.

First thing to do, 1/4 mile's not my primary goal, but track driving. Like Dzenno said, tune and boost curve must be optimized to the primary use.

Additional weight for track, especially if doing TT. For the street it's OK.

In domestic use yes, but for trips to the 'Ring not possible. Not available near Nürburg. Standalone could use flexfuel solutions, but I'm running Motronic.

Yes again, but I just happen to like VTG's low boost threshold. And I'm still -AFAIK- the only one that uses electroncally controlled VTGs in a 996...

For my power level (and std VGTs) GT2 RS's ICs will do just fine. I just have to increase airflow to ICs. If I had pockets deep enough those would be quite nice though!
BTW Earl, will you some day post your experiences with Marstons?

 

lol.


I thought about meth because there are many good reasons to do it - more power, cooling effect, not ridiculous cost. However, I have no experience with meth and even though there are failsafes I believe there is a certain amount of risk involved in its use. I'm not sure I'm comfortable with that...yet. I know Dzenno runs it on his car so I'm sure he could tune my car with it. Something to consider.


The other option of just using e85 for track day is interesting. Might not be practical for me but something to consider. There is racegas at the track but I don't think that changes iats, right?

 

Thanks Earl, Pete, and Dzenno for your input.


If it wasn't for those other guys bringing ever more powerful cars each year I would just turn the boost down for the day and be done with it, lol.


I'm not that good at the track that I'd notice the difference in weight a meth kit would add.


I'll check egts and see what they are doing at the speeds up to 140ish. Maybe you are right, Pete. I have catless AWE but it still may not be enough to liberate the hot gases.