997 tt/rs

Guys, what is most common setup for upgraded turbocharger?
I'm looking for better spooling with more air volume and maximum 0.8 ar boost.
The most important thing is that the range of rpm usage will be wider.

which of this compressors will work best you think guys? the smallest one is oem size but performance design.

thanks
K

Metal Guru

This has been discussed ad nauseam and very recently too so I recommend doing a search.
Bottom line is that you will trade low end boost for screaming boost at the red line. No free lunches.

997 tt/rs

i was searching here but unfortunately didn't find.
Paul, yes you are right but this is related to much bigger compressors I believe.
Companies like TTH and TTE here in Europe are offering modification with 63mm inducer or even 65mm compressor which is crazy big.

fritz k.

I think the best way to get a wider usable rev range are headers that are guided direct into the turbo, e.g. the like ones from the 993.
And reconnect the auxillary air pump, it will give an afterburner effect to your turbo.

997 tt/rs

i found that years back they were using bigger compressors from k28 so from the diesel track

Metal Guru

Search in the Rennlist 930 forum or the Pelicanparts 930 forum to improve your knowledge on the subject.
To achieve your goals, I would recommend the following:
* Bifurcated Garrett turbo
* Custom header to take advantage of the bifurcated turbo
* LEASK adjustable WUR
* SC or 964 cams
* Lightweight flywheel
Except for the Garrett (I'm running a K27/K29 hybrid turbo rebuild by Durabilt before they went out of business), this is the part I've taken and at .8 bar boost, my car is now "fast enough" IMO.
This is not work for squeamish non-technical people.
This will require having the ability to record real-time data on AFR (a handheld Innovate LM-2 is highly recommended) to establish a proper fuel curve.
Try to work with a shop like Turbokraft on component procurement so you don't make any mistakes buying the wrong parts.

Metal Guru

The 993 Turbo is a different animal altogether. Twin turbos make for shorter exhaust runs. I doubt that the OP is looking for a big engineering project.
Even the factory had to work around the single turbo behind the 935 engine so it is what it is.
I've heard about the auxiliary air pump hack but I never heard of anyone actually doing that. The factory air header is made of steel and rots out. Everyone throws them away. Last I checked, a replacement is $600 so I won't be trying it any time soon.

fritz k.

I expressed myself misleadingly, I didn't mean the completely different headers of the 993 turbo, but those of the N/A 993, which are routed to the rear. I've seen customized turbo exhaust systems that were built using 993 N/A headers. Of course, fabspeed or something similar is easier.

The auxiliary air pump clue comes from a well-known engine builder, who rebuilds all turbo engines with it if the parts are available. The effect is well understandable on the dyno.
My AAI parts are in the basement and that's where they will stay.

Fritz

Megatron-UK

I am finding the use of the air injection system as a performance enhancing component difficult to understand. The injectors themselves in the exhaust ports are tiny and the pipework is laughably small diameter to get any meaningful flow .... What am I missing?

Metal Guru

You mean like this:


993 N/A Bishoffs into a custom merge:

Metal Guru

All engines have to be enriched upon cold start. Typical enrichment from the wur goes from 13/1 afr to 12.5/1 afr, depending upon ambient temperature (additionally, a fast idle is used to overcome the friction of a cold engine at the same time, as well as a cold start injector on the throttle body that squirts fuel for a very short time). For comparison, a stoichiometric mixture is 14.7/1, which leads to a more complete burn that a catalyst can clean up. This is the value that you run at steady state cruising. When you accelerate, the wur drops the afr to 12.5/1, which is considered to be the maximum clean torque afr (actually the wur doesn't operate lineally, so at low engine speed you might be getting 11/1 or 11.5/1 to achieve 12.5/1 at high engine speed).
So how to burn the rich idle mixture? Add more air into the exhaust system, just outside of the exhaust ports. That's what the cold start air injection system does. Thing is, the system switches the air flow from the exhaust to the catalyst when it senses that the engine is warmed up. Cats needs a fresh air supply to regenerate. This switchover valve has to be altered to keep pumping air into the exhaust. I can't think that doing this long-term is good for an air cooled engine, especially thinking back to the thermal reactor equipped 2.7 L 911 engines from 1975 - 1977. To make matters worse, these engines used a 5 bladed fan. This caused long term engine damage in the form of head studs pulling out of their magnesium cases, among other issues.
Fritz, I've seen that dyno data you mentioned over on the PP board a long time ago. The guys over there will try virtually anything to get more power, yet I can't recall anyone trying this. Might be too much trouble to do; I don't know.

Megatron-UK

I understand the use of the air injection system in standard form... What I don't understand is how the device in any way increases performance - that exhaust gas, whether leaned out with the air injection or not, is not going to impact the the intake charge; it can only ever alter the mixture of the exhaust gases after combustion - so I fail to see how it being there or not can change anything other than emissions figures.

I can't work out how it would be possible to use the injectors to lean out the mixture in the cylinders in any meaningful way (which might well be beneficial at some parts in the rev range due to the CIS fuelling limitations), as it would have to have the exhaust valve open to get into the cylinder.

What's the theory about using it to improve performance?

fritz k.

Hi, yes, I meant exactly this solution with the 993 headers. Looks good to me, addresses the turbo directly and provides original heating.

The point of improving performance with SAI is that afterburning of the unburned hydrocarbons in the exhaust takes place. Due to the full load enrichment and the lowering of the AFR, unburned fuel components inevitably get into the exhaust gas.

Due to the additional oxygen that the SAI blows in, the fuel components in the header get “afterburned“ and accelerate the flow of exhaust gas to the turbo. In turn, it responds better and revs up faster, but of course it is also subject to higher loads due to hotter and faster exhaust gases.

You can proof that effekt on the dyno when the same engine runs once with and once without the SAI toothed belt.

Fritz

Metal Guru

+1
I was assuming Megatron would read my mind on how air injection could be leveraged for more low engine speed exhaust pressure, apparently. Thanks Fritz, for saying directly what I was implying.
Another alternative is a two stage electronic boost controller. At boost onset, boost starts at a higher value (1.1 - 1.2 bar) to take advantage of the rich 11/1 mixture. Then the boost drops to the baseline of .8 - .9 bar until redline.
I think to do this safely would require an engine built especially to do this. Adding flame rings to the heads and high quality head studs would be needed to enable the engine to withstand the higher internal pressures.
Thing is, using two stage boost control pushes you one step closer to EFI. Had the values of these cars not skyrocketed (although high interest rates seem to be cooling the market off), I would have taken my car to EFI years ago.

Megatron-UK

Okay, got it - similar in principle to anti-lag, but since these cars dump a load of fuel anyway, instead of fuel (which is already there) adding extra O2 to encourage secondary combustion. I think I understand now.

Certainly seems that it would put a great deal of additional stress on the exhaust, turbine, etc.