After my recent mods, I needed two more injectors to add enough fuel (even with the 5 bar fuel regulator)under load. You will see that there is one in each tube going from the turbo to the intercooler. The 996TT generally gets them installed between the intercooler and the throttle body as there is a lot of tubing coming from the fenders where their intercoolers are located. No luck doing that on our 993TTs. I took a couple of pictures listed below as you can not really tell by the photos, but they are a work of art.

<img src="http://boards.rennlist.com/upload/fuelinjectors001.jpg" alt=" - " />

<img src="http://boards.rennlist.com/upload/fuelinjectors003.jpg" alt=" - " />

 

viperbob
Thanks for sharing the photos.
I have some questions:
Firstly the need for extra injectors - I am pretty sure that the German tuners do not use extra injectors, even up to 600hp outputs. I think they use a different type of fuel pump only.
Secondly is it accepted practice to shoot mixture laden air through the intercooler, are there any advantages/disadvantages of doing this ?
What sort of fuel consumption does your 507hp car do ?
What boost are you seeing at peak power ?
TIA

 

same here, i would think managing the fuel as a complete system will be more comprehensive then piggy backing a couple of injectors. in fact, the fuel mix will almost never reach all the cylinders equally. usually the further most cylinders gets starved a little.
i could be wrong, but also it would be an easier job overall... ya?

 

Good qestions, and ones that I also had initially. First, as you TB993TT mentioned previously and that was the need for a smooth power curve. Under boost (1.0 Bar Max for now), my A / F ratio was very lean, hence giving away power and potentially it could cause a problem. My thought was just to add larger injectors, or larger fuel pump. But under normal driving conditions, I don't need the extra fuel. So larger injectors would make the car run too rich and hurt mileage (my mileage is still around 15 MPG city and 21 highway) and this over rich condition could also cause issues with emissions here in California. I was hesitant about running the fuel through the intercooler, but the there is not a good spot on our TTs. We have plastic intakes, and ideally you want the additional fuel to atomize prior to the throttlebody (air swirling and saturating the with fuel prior to entering the intake). So it was either tap a hole in the intercooler itself or add just prior to it. All that it can do is to cool the mixture heading into the intercooler which can't be a bad thing.

Superyellowfly, additional injectors are very common with systems that can control them (Motec, Unichip, etc). The reason you don't see it more is that the factory ECUs are not able to handle and control these extra units independently. They are tuned to ONLY fire when the additional fuel is needed. They are mapped into the Unichip after many runs on the dyno to level the A /F mixture, and maximize power. They are added upstream in the intake system to help atomize the mixture well in advance of the the air hitting the cylinders and preventing any starvation of a particular cylinder.

Also now, any other mods (Intercooler, Cams, whatever) will be able to be tuned by the Unichip and i won't have any fuel problems. I think it is actually easier this way.

 

do the cams... they're well worth it
... i can't say for certain what my mpg looks like, not that i've checked... but if i'm not mistaken, during normal driving... most ecu's will decreases the freqs of pulses accordingly. the last time i had the engine apart, the internals were spotless clean... leading me to believe the mix was probably right. I think either way if done right would work just the same. in anycase... relative to the stock tt my mileage definitely hasnt improved since i got my car back...(reads: heavy right foot syndrome)

 

Can anyone else comment on the fuel through the intercooler question. From the photos viperbob's turbo to intercooler pipes look like the older pre orange top ones -what happens if one of these pipes lets go of the intercooler flange at high boost (this has happened to me) and a fuel/air mix sprays all round the engine bay - sounds dangerous to me.

 

The turbo pipes are 97 TT (yes the improved ones). I have never had a turbo pipe come loose (three different turbo cars used for DE and racing all highly modified), but then again I do my own work and regularly check engine and suspension components for wear and looseness on most vital components. In the future, I do plan to plumb the injectors directly into the intercooler, but I do not have my final intercooler. I plan to get and Andial or a Carghaphic relatively soon, but until then I did not want to fuss with my current intercooler.

Superyellowfly,

I'll get around to the cams sometime in the future. I wanted to get my car ready for DE season, and just want to drive it. I've had the car now a couple of months, but between the weather and the upgrades I have not been able to drive the car NEARLY enough. What kind of cams did you install? Just for future reference.....

 

Hope you don't mind if I poke my head in here...

Couple of things to think about.

When your air path was flowed from the factory it was done with air. When you introduce fuel into the air path you are trying to flow the intake in the same manner that it did, now with dense fuel. The intake of any of the Porsches is fair at best. This is with air, with fuel you create hot spots and pockets. The intake was never intended to flow fuel. In time, no offense it will put a hole most likely in one of the two rear cylinders, if the fronts don't wash down first. We create BIG HP a lot and an additional injector as such is not something we use. I have two AICs in the storage room. We have the ability to map the computers and therefore the standalone injectors are not needed. If you must use such a device the proper and more reliable way is to use an injector block with two ports for two injectors. Piggy back a second rail with very small injectors and run an additional driver on a AIC and drive the 6 injectors. You now have fuel shooting to the back of the valve where it should be and not trying to move fuel and air in the same manner as air. We have had to deal with this on the older 930s. It likes to create holes without a doubt. It is not a question of if, but when.
<img border="0" title="" alt="[Eek!]" src="eek.gif" />

 

Thanks Stephen. Some very good points to think about.

 

Ruf part # R 93 105 246 05
works like a charm

 

thanks superyellowfly. I saw these on their website, but of course the specs are a closely guarded secret with some of these guys. Do you happen to know the specs? I would like to compare them to the Euro RS cams.

 

<img border="0" alt="[blabla]" title="" src="graemlins/a_smil17.gif" /> actually... i have a single cam sitting in my garage.
The fourth lobe was badly scored due to oil starvation <img border="0" alt="[crying]" title="" src="graemlins/crying.gif" />
so i had to change one bank.
I bet those measurements for lift and duration will be mighty important to some people <img border="0" alt="[icon107]" title="" src="graemlins/icon107.gif" />

 

My 81 Callaway 928 has a twin injector piggy back...Miller-Woods Microfueler. It works, but not very well. Good here, rich there, rich there and still rich there! I am removing it in favor of a proper MAF conversion with increased fuel pressure and correctly tuned injection system....8 injectors only. Mine will be a stock L-Jetronic with a split second signal conditioner and a MAF hot wire sensor. Then I get program capability over the 2-D curve. Slick and inexpensive.

My additional injectors were after the charge cooler and about 18" from the throttle body. The car ran well for 20 years, but it was time to change. The holes for the additional injectors will become the vent off ports going to my blow off valves which I will be adding to avoid compressor surging. It should all work quite well. I think I'll have to run 70 psig on my rail to support 14 psig at the manifold with the 914 injectors I'll be using.

 

viperbob;

You've turned your manifold into a wet plenum, this will definately disturb the airflow. Also, Fuel is combustionable, your intake charge can run through BOV and back through your turbochargers on bypass.

 

Kevin,

All good points, plus there are some additional downsides. In fact, I have removed the fuel injectors and I'm having the Unichip taken out. When I purchased the Unichip, I was under the impression that these additional injectors were REQUIRED because of larger turbos, cat bypass etc. I thought it was running lean because the car had exceeded the fuel flow capability of the factory injectors. But that was FALSE as I learned later.

The Unichip is a piggyback ECU that intercepts and then alters signals back to the factory ECU. One of the signal it fully controls is the turbo boost. The Unichip takes this signal so it can extend the boost, but then the factory ECU is never aware of any boost. Accordingly, it is then unable to alter the duty cycle of the injectors to deliver more fuel as it does not know that more fuel is required. The additional injectors were an attempt to add back in this additional fuel.

All in all, I have decided to go with a more traditional modified ECU to deliver the HP I'm looking for..... Thanks for all your comments.