Curious on the max pressure capabilities of the stock VTG prior to self destruction? 22PSi, 25PSI?


Would a tuner be able to over push its capabilities?


Some members have reported a self destruction state with their near stock setup, broken turbine blades, etc. Can any of these members comment on their issues at failure?


I welcome all opinions.


Thank you,

 

Altitude will be another important element at play here that people should report. To develop the same 25PSI at 5000' (for example) as at sea level, the turbo at altitude will have to spin quite a bit faster to compress the thinner air to the same PSI as at sea level. In Denver (for example) at moderate summer temps, you will have a density altitude of about +8000'. I've seem track temps measured at 120F which puts density altitude in excess of 10000'! Compared to sea level atmospheric pressure, at 8000' you will have 25% less air pressure as at sea level. Consequently, your turbos will have to spin 25% or so faster to develop the same PSI. If your turbos operate at their threshold of efficiency at sea level, spinning them faster "may" push them over their limit....

 

Not sure about limits the way you guys in the US talk about bhp etc but some excellent info on tuning VTGs here

http://911uk.com/viewtopic.php?t=103813

Hope this is helpful

 

As I am sure you know our stance Elite1, we tend to only push the turbos as far as when we start to see back pressure become an issue.

Altitude is a huge factor for this (as you know!) and that is why it is a per case basis on when we start to try and "push" the VTG's to a higher limit. They are more fragile than other turbos so we try and keep that in mind when tuning them. Measurements such as EMAP can be very helpful in helping to determine a safe limit, which is why we have started to use it a lot more in the Porsche's when gathering data to determine what we feel is safe.

On the other hand there is always a chance that a part can fail when pushed past a stock limit regardless of how careful you try and be. That is part of modifying cars and just the way it is sometimes.

-Mitch M
Mitch.Mckee@cobbtuning.com

 

Guess, bigger turbos would help at this elevation. If they only made a track 5,280FT below sea level. I would have a 1200hp beast


I agree with the turbine speed. Blades break and bearings fail.

 

Great info! Thanks for sharing it. Didn't you move away from VTG's?

 

Thanks for your input Mitch!


Just to be clear, I wasn't pointing this thread to Cobb by any means. great tune and great results.


With Emap, would the Motec system be something that I should look into regarding this?


It's fun to modify our cars but, I wouldn't want a piston to eat a turbine blade. If, this is an issue with the 997.1 VTG's, I would upgrade to maintain or (increase) the tunes output with slight peace of mind (even with a modded car.)

 

No I stuck with VTGs as my engine is stock and bought a GT2 (RS) solution from 9e.

I'd love to go built 3.8l stroker with GTX 3071 but cost is main issue

 

You fall into a unique category of users. I don't know anyone that runs their 997TT as hard as you do for 20-30 minutes a time at such a high altitude. That puts a unique level of stress on the turbos that other users won't see doing 60-130 blasts or the occasional run down the drag strip, at lower elevations to boot. Heck, I'm in the same boat but luckily I don't have VTGs. There is only one other person we both know that tracks a 997.1TT in a similar fashion and he blew up his motor a few years back. Turbocharger let go (overspeed perhaps?) and the motor inhaled the carnage. Game, set, match...

I would say keep an eye on the IATs will give you an idea of how hard your turbos are working. Seeing excessively high IATs might indicate that the turbos are starting to operate out of their efficiency range pumping hot air. I keep a much closer eye on my IATs now than I used to. It would be interesting to find out from some of the tuners what they feel is the max IAT temps you should be seeing under hard continuous use, or what IAT temps would indicate you are getting outside of the turbocharger efficiency range.

One of the reasons I'm going to the Motec is to be able to monitor the engine better under race conditions and have another layer of protection. It's cheap insurance....

 

I mean if you are worried about the VTG's failing then I would say to run a bigger turbo as it will help to do things like keep back pressure down.

On your car for example we don't try and hold the boost pressure to redline as this is what can cause the excessive temps, wear and tear especially on cars at higher elevation.

I have tuned for Pikes Peak for many years, and continue to do so and I know what causes cars to break, especially turbos. We make it so that if the turbo speed gets to be too high or emap does, we reduce target boost pressures to make sure the turbos make it to the top. Most would be surprised how much power cars lose and how hard turbos will try to make boost pressures. The Garrett engineers eyes about popped out when we told them that our shaft speed is above 185K on low boost on a 35r style turbo haha. But we setup comps on the mountain based on this and other variables that we measure to ensure engine and turbo safety. We use a lot of this same data and methods when we make calibrations and test on the dyno.


-Mitch

 

So my short 3" cat/muffler delete setup below on my Gen 2 Turbo PDK should help matters somewhat with minimal back pressure / lower egt's?

I have Accessport in the post with Cobb tune from PTF to come shortly.

 

"There is only one other person we both know that tracks a 997.1TT in a similar fashion and he blew up his motor a few years back. Turbocharger let go (overspeed perhaps?) and the motor inhaled the carnage. Game, set, match..."

I do believe I resemble that remark......

Elite, if you match your induction, exhaust and engine components to your tune and keep an eye on operating parameters while on track, that's probably the best most of us can realistically do. Keep a spare $50K in the cookie jar though.....just in case!

 

997.2 different story than the .1's. Bigger motor and bigger VTGs. I'm running upwards of 30psi on stock VTGs midrange with no issues. I am currently tapering down to 18psi redline since I'm out of fuel even running 100% meth dual 630 nozzles. But I bet once the fueling is solved (GIAC upgrading my car soon) the stock VTG's will hold boost to redline hopefully in the low to mid 20's.

 

Great points! I would like to know the optimal temps for VTG's running on the street and at the track. Cruising around town, I see 15F higher temps when compared to the ambient air at 70F. Will take better notes at the track next time.


Motec really sounds like a nice setup. They take logging and monitoring to a different level if your willing to pay for it.

 

What back pressure?