HI Guys,,Since our cars came stock with a 68mm TB,now that you can put on a 74,75,76 and now a 82 on depending on your mod level>>This is my tech question for all you savvy fuel injection guys out there...
If you went from a 68TB to a 76TB with the same type of manifold,lets say stock type on a light to moderate build and had the fuel to support that level>> IF your build did not need the airflow from the 76mm and just was able to make the same power as with the 68mm one....Would you still use more fuel at WOT??
I would guess it would not because if it didnt make any more power from the additional size that the monitoring sensors would only give enough fuel to support what air that has flowed thru it that could be used, being the same amount as a 68mm since it couldnt make more power from that 76TB....
But I would guess also that it would use more fuel on part throttle settings??..
I know carbs and carb tuning but not this fuel injection stuff fully,,just want to learn more.....
THANKS for any input......

 

I am not sure about fuel use, but the consensus that I got when researching the TB upgrade, is that you don't really get any benefit until you go a little bigger in turbos, like a 24/20 or GT30.

I would not upgrade for 24/18s, but I could be wrong.

 

I can not believe I was told two different answers by two different Porsche Techs..One agrees with me, above post and the other doesnt..

 

datalogs show me above 1377 cfm 5volt is at the maf sensor....after this point the maf system cant read any more flow and you are at blind cablibration and you have a tuned fuel delivery from your tuner for your special turbosize

with k24/18 i estimate at 1,1 bar you are already over that point

stock k24 with 1 bar wastegates and 1,25bar are exact at 5volt at the maf

that is the weak point on stock mafs and real great turbos, because the system cant read any additional change in flow, and calculate with boost, rpm and intake temperature


i have made some logs 68mm and after installing a 75mm TB and it doesnt change afrs

for a 75mm tb for my understanding you dont need more fuel, but turbos can do his work more easy and tb responce is better....

hope my english isnt to bad for what i try to say

 

Yes many say this is wasted money unless you plan 650Hp plus

 

Hi ,Thanks but I was just asking about a fueling question witha TB switch..

 

Hi ,Thanks but I was just asking about a fueling question witha TB switch..

 

Not sure I fully understand the question John, but will take a stab. Your ECU will increase the fuel delivery for increased airflow as long as you dont need more fuel than the fuel system can deliver for the programmed mixture ratio. The question in my mind is, would increasing just the TB size without increasing plenum size result in any more air flow to the engine at WOT? My guess would be very little if at all. Now if you went to a 75mm plenum and TB you would increase airflow and fuel delivery significantly.

Hope that somewhat deals with your question...LOL!

 

Hi ,Thanks for taking that stab..The connection on the stock T plenum that go from each bank are 80mm ID. diameter from side to side,so they are already good sized,which is larger then the TB openings..I saw the 997.2 turbo plenum and that T section looked smaller then our turbos and the TB??.
I also have a Modified IPD plenum from TimNYC that has the complete splitter removed and a whole new back side on it,so its like a stock one now except for the bigger TB opening..It does still have a nice front short side radius unlike the sharp Vivid one.. I hope I can test that on the dyno also,,when i get there..LOL..
My original question was basically,If the motor combo can does not make more power with the larger TB over the 68mm TB will the fuel delivery be the same as the 68 because that larger TB air flow was not needed??
But are you saying also that the 'Stock Style' with the matching 74TB opening and the 80mm body wont flow more regardless??Thanks for the info......

 

sure you mean cfm? that would be too much. I think the limit is around 1400 m³/hour

above that limits (>80% WOT) the ecu calculated the charge throught closed loop lambda control, which obviously works quite fine.