Totally agree...

Have you tried brake boosting off the line? Does that improve your Vbox #s?

 

Audi boards are correct that you won't build boost without any load on the engine. Thats not a tuning issue that's just the way engines work, same way in every turbo car Ive had.






To get the launch youre looking for, maybe try brake boosting like you are launching with the stock TC so you can build the load, just will be at a higher rpm where there is more power.

 

Maybe you should ask Emre at esmotor he is a tiptronic expert

 

Hello All,


To build boost requires a load on the turbos. Revving the engine wouldn't tend to build boost as the load is about nothing until perhaps it bounces of the rev limiter. While you accelerate from a stop there is load yet the turbos have to spool up. Brake boosting allows for loading and turbo spooling however the loading is against the tip .


Best Regards,
Scott

 

Not sure how difficult it might be on the cayenne but I found the sweet spot on my old ls turbo mustang with a programmable 2-step rev limiter that I could set right at or before converter flashing point and it allowed me to load the motor enough to build boost just before the flash and netted my best 60 ft times. Might be worth a looking into if you are serious about drag times. But the flip side is that if you find a way to build good boost off the line, that pretty new tranny isn't going to like you for too long. The converter flashing with decent boost at the same time on these heavy awd girls has to be harsh on them for sure

 

Thanks fellas!

You are spot on here. I will have to adjust my technique which means brake boosting to right before the flash stall speed, then launching at 3000 RPMS.

I just have to be careful not to still be on the brakes when the TC reaches its flash stall speed since I could overload the tranny again and have another failure. I suppose I might be playing with fire, so have to have at least a couple hundred RPMS of buffer.. just in case.

 

Guys, after looking into this a good amount, you are all correct - kudos. I think I was unintentionally mislead by ProTorque that I should be able to "build boost off the line". I wasn't searching for this initially, but got admittedly excited about the possibility launching pretty hard with AWD.

The bottom-line is that no turbo cars create boost in neutral or park without load; actual or artificial (not sure about diesel). The interesting part is that using a few techniques, you can simulate or apply load and build boost while sitting on the line.

Here are the only techniques I have came across:

1) Brake boosting -
2) Transbrake -
3) 2-Step Rev Limiter -

 

I'm with you on the small shot to get you out of the hole. There is a way that you can wire in a shrader valve (believe that's what it's called) which senses boost pressure and allows you back off the nitrous at a certain manifold pressure so you aren't spraying under boost. Some guys just sprayed the whole pass but the risk/reward never made sense in that to me... I had a tuner tell me that he could tune my hptuners on that old ls turbo swap so it had a 2step built in without having to buy anything additional. I had already begun installing the 2step that I purchased when he told me that and still wanted to retain the pride of building and tuning the car completely myself (silly, I know). Seems to me that with ecu/dme as advanced as it is on these, surely some tuner out there can and has done this before to the factory control unit. Not sure if it's worth checking into like you said or if you don't just put a small kit on her to get out of the hole. Should be lots of fun either way!

 

What about an intercooler nos sprayer ?

 

The 2-step is a much more viable option for a manual transmission. Since you still want to be in gear to launch, your tranny will still be holding a load, albeit somewhat less of a load than standard brake boosting.
I think a small shot of nitrous off the line is your best bet.

 

The Audi and VW guys that do there own flashing (nefmoto) have figured out how to do antilag with the motronic ecu.

 

Thanks for the input. Yes, I know what you are referring to by "schrader valve" on the fuel rail. The only issue is that our V8 is DFI and does not have a traditional fuel rail to meter flow off of.. so even if there was a schrader valve on it (which I didn't see in my recent pics), the nitrous system isn't designed to interface with it. Believe it or not, I have some Porsche documentation that says that the DFI fuel rail can pressure up to 2000 psi.. which is mind boggling.

I think the issue here is how do you implement two concurrent rev limiters on one single tune? You would either need a separate physical switch wired in somehow or hook into the ABS computer module to monitor wheel speed as well as the transmission computer module to determine if the vehicle is in first gear. All considered, the complexity of the CAN BUS might work against me in trying to get this to work on the stock DME.

This is essentially what we are discussing now..placement isn't the question, but rather if nitrous is the right answer.

I can see your trail of thought here, but you may have underestimated one key observation when launching with the high stall TC without braking brake boosting. Before the TC reaches its flash speed, it ONLY moves about 10 feet and never exceeds 1.5 mph (VBox verified), before launching. If I was to brake boost for this short period (while getting up to flash speed), it would be holding back only a negligible amount of torque to the drivetrain.

Remember that the TC is a fluid coupler and while it is spinning up to flash speed, it is essentially "decoupled" from the engine crank during this period. So while some inkling of power is seeping into the drivetrain (or it would stay stationary), it wouldn't take much power to hold it back.

So given its top speed of 1.5 mph, I would estimate that I am not see more than about 25 hp to the ground (wild guess) during this phase. If so, this means that a 2-Step would be helpful, while brake boosting, during this TC flashing phase.

Do you see any flaws in my logic here?

Remember, I already have methanol and adding nitrous would be another consumable I would get to go out of my way to secure, plus would take up space in cargo area, bottle warmers, remote bottle openers, purging valves... giving me a headache just thinking about it

Interesting... I didn't know that, will have to look into it; thanks! By the way, I did ask about the anti-ballooning plate for the TC and was told I didn't need it. Apparently, it is for the guys using transbrakes since their ATF fluid heats up about 50 deg F per sec! So if you stay on it for a handful of seconds, the fluid can get very hot (expansion), plus the rotational inertia from the engine flex plate.

 

Bro , you have an upgrated torque converter , so I think its time to change the turbos to 20T(only 800$ ) . it with spool better and have a lot more power in all rpm . I am thinking of doing it myself

 

No, I believe you're right. I'm just not sure it's enough of a benefit over brake boosting. Depends on how fragile the transmission ends up being, I suppose If you're concerned about overheating the converter, the 2-step is definitely an advantage.
I have a built GMC Typhoon that I brake boost to launch. I can build plenty of boost prior to launching (launching above 10 PSI on drag radials tends to break traction). I have a 2-step, but just never found the need to install it since powerbraking was so effective. I do rev to the flash speed, but just have to be careful not to be on it for very long.

 

Hey Kent,

I hope everything is going well with your 750 HP 957 TT Monster.

I'm down the same route (a little different though) and I'm sure at some point I will hit the same problem with the limits of the Tiptronic Tranmission like you.

First of all, I think the 6 speed Tiptronic Transmission we have is very lazy in shifting and hurts the overall performance of the car a lot. 958 TT 8 Speed Tiptronic is a much better option, and ultimately PDK is the best option.

Having said that the most cost feasible option to do would be modifying the TCU. You need to be careful how much firmer you make the shifts. After a point, it feels a truck hit you every time the car shifts. Still, a balance point could be reached where the shifts are firmer and the launch is stronger.

Have you thought about using the 958 TT 8 Speed Tiptronic and its TCU with your car? It will probably require serious programming to have the new transmission communicate with ECU, but if it could be done it would help a lot. Now, if you are going to use a stand alone to accommodate 2 step and anti-lag, it may make sense to use the better transmission option.

At this time, without any other performance adder such as the 2 step, brake boost or nitro option, do you think the ProTorque High Stall Torque Converter help your overall performance or hurt your daily driving at the end?

I don't think the small shot of nitro will make a lot of difference in the launch of your car and it may cause problems due to direct injection setup, methanol injection and the increased boost curve. If you go with the ProEFI route you will be able to use Anti-lag and Flex Fuel in addition to 2 step and will get some extra power.

I've heard Cobb has some tuning options for anti-lag and change maps on the fly with the stock Porsche ECU. It may be worth trying.

I'm very interested to see which option you would ultimately choose as the transmission is the weakest link in these cars. I've been brake boosting for launches and also for roll races and I feel like it's playing with fire with the stock transmission.