How to fix the sluggish tiptronic - Sprint Booster

[MagnusO]

Hi guys,

 

I bought my 1999 Porsche 911 C4 Tiptronic back in January and I've been doing little projects on it ever since. I used to have a 2016 Dodge Challenger R/T Scat Pack with a 6.4 liter V8 that I traded in last summer, but I was missing the sports car feeling too much so decided to buy the Porsche. One of the things that stood out to me on the test drive was just how sluggish and unresponsive the Tiptronic gearbox felt compared to the one I had in the Dodge. Since the rest of the car was in very good condition (invoices for every oil change & repair going back to 2003, IMS bearing changed, etc.) I decided to buy it anyway, assuming I would get used to having to mash my foot into the carpet everytime I wanted the thing to move.

 

Looking through this forum and others, I heard about the Sprint Booster and how it might help with this problem. For those of you that don't know what this is, it is a small plug that sits between the gas pedal and the cable harness running to the ECU and that changes the signal sent to the car from the position of the gas pedal. The factory set up makes it so that when you push the gas pedal, the revs rise very slowly for the first 50% of pedal travel. I think I read somewhere that halfway down, the pedal will only give you about 25% of the power. This means that in order to get the Tiptronic box to do a downward shift, you really REALLY have to mash the pedal and do it in a quick manner. In general it makes the whole car feel unresponsive and not at all like the free-revving, happy sports car I thought I was getting.

 

The Sprint Booster module (which only works on cars with electronic throttle control or "e-gas" pedal) will take the gas pedal input and modulate it to reflect a more aggressive pedal action. The only thing that changes really is the voltage that is sent to the car's ECU, and how this is calculated in relationship to the position of the gas pedal. The unit comes with a little control gadget where you can set it to one of three basic settings - Factory (simple pass-through, nothing changes from stock), Sport (about a 30% more aggressive response), and Race (about 50% more aggressive). Within both Sport and Race you can then fine tune with an additional setting from 1-9 for each of the two categories. By default the device will put you in "5" or the middle ground.

 

The device costs you about $300 and there is no discount to be had from any of your typical market places. I simply bought mine directly at the manufacturer's website. Since it was my birthday last week, I decided to treat myself and see if it might work. You have a 30-day money back guarantee and the install process is completely reversible, so I figured I'd give it a go. If it actually helps make my tiptronic feel peppy it will have been worth every penny. If not, I'll just return it.

 

For the installation my first problem was figuring out if my particular car had an e-gas or electronic throttle system or not. Looking at the gas pedal I can see a cable running up the bulkhead so I wasn't feeling too optimistic. With the help of others on this forum, I learned that all 996's have e-gas except the 98-99 C2. I also popped the hood and looked at the throttle body itself. To be extra sure, I also asked the vendor to confirm that my particular model would work with the product. The manufacturer's website only shows MY 2000 and beyond as approved for installation, but they came back and confirmed that in fact the -99 C4 does have e-gas and so I could proceed with the purchase.

 

3-4 days later I get the box in the mail. It is a tiny little thing and doesn't appear to be much for the $300 I paid for it, but whatever. The installation manual shows pictures of the device being plugged into a port located somewhere on the gas pedal assembly itself. It is clearly the most common spot for most manufacturers to link the throttle to the ECU, but that's not the case in a Porsche 996. The gas pedal pulls on a cable and if you follow the cable up from the pedal, you'll see it attaching to a metal box conveniently located under the actual dashboard, and at an impossible angle for any human being to get to.

 

In these cases I like to resort to child labor, so I bribed my 13-year old son to help me. By laying upside down in the driver's seat and sticking his head + one arm under the dashboard, he was able to get the device plugged in correctly in as little as 2 hours. I was basically reduced to cheer leader, and voice of reason to guide his efforts. We made use of my cell phone camera to try and figure out from the pictures how to disconnect the old plug and get the new Sprint Booster in place. The pictures attached to this post will show you how we figured it out:

 

 

 

The entire installation process is done by touch and feel as you cannot see any of the components directly. I would recommend our approach of using a camera, talking about what we need to do next, and then use your fingers & imagination to figure out what it is that you are doing. We found it helpful to start with where the cable attaches to the box, then run your fingers over until you hit the little metal flange that sticks out with the white plastic butt underneath it. When you have your hand there you know that the plug itself is just above it.

 

 

After the initial installation we immediately took the vehicle out for a ride. The gas pedal felt weird, and we had intermittent revving and a noticeable delay when pressing the pedal. I figured it was simply down to the device having to calibrate itself so we went for a ride. 20 minutes in we get a check engine light come on so we headed back to the garage. Ever the optimist, I simply disconnected the battery to reset the CEL and then went out for another drive. This second time it worked beautifully! The car felt like a different animal all together, and the gas response was crisp and immediate. Problem solved, or so I thought, and we called it a day. The second day I went for a drive and got not only a CEL but also the PSM and ABS warning lights. At this time I was ready to call it a day and send the device back since I don't want to have to deal with buggy electronics or stuff that I can't trust. 

 

Called up the son again to have him pull everything out and that's when he noticed that the OEM male connector at the end came lose by simply touching it. Turns out we hadn't been able to plug it in all the way until it latched onto the Sprint Booster module. I guess it is not manufactured to the same tight spec as the OEM stuff, and by a fraction of a millimeter the plug can't go in far enough to secure it with the latches. Using force and patience, we eventually managed to push it all the way in until we heard the very satisfying "click" of the plug latching onto the module. If I have to take it off again because it comes loose, I will certainly use a file to remove a bit of material on each latch and ensure that they lock into place without having to push too hard.

 

Since this point I have driven the car 4-5 times and about 50 miles, driving it as I usually do and without holding back in any way. No CEL or other warning lights and the thing runs really well. Having tried the different settings, I have decided to leave it in Sport-5 which I think is a happy medium for a sporty feel without compromising the ability to drive smoothly when you want to. Race mode makes it more binary, and it is like mashing the pedal at every stop light. It might be fun on a track, but for everyday driving it is just too aggressive. In Sport-5 it'll pull away softly in 2nd gear like it did with the factory settings, but if you simply give the pedal a little shove it'll immediately downshift to 1st gear and take off with gusto.

 

All in all I have to say that this was very much worth it. The car feels different - more sporty and responsive, just like you'd want a Porsche to feel like. I know this doesn't add any power to the engine but just by having the Tiptronic gearbox work more like a modern sports car it really changes everything. I'm now planning on driving it for the full 30-day money back period, and if I run into any issue I will post an update to this forum.

 

Cheers,

 

Magnus

 

Update - April 22nd, 2020:

 

I've now driven with the Sprint Booster for 6 weeks and I can honestly say that this was the best bang for the buck modification that I've done to my Porsche. I would rate my Alpine head unit & speaker system upgrade as the mod that I most appreciate, but that was $2,400 and this was only $300. Just be careful with the installation and count on it being a PITA...

 

 

Edited April 22, 2020 by MagnusO
Update - 6 weeks after modification