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Direct injection
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EFI
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Carbon build up comes from lack of PI that helps clean the back of the valves.
If you car has PI, it doesn't have carbon build up. It has nothing to do with DI itself.
engineermike
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One of my favorites subjects. I’ve been experimenting and tuning the gdi system on mine for close to a year. A few points:
- The primary purpose is knock suppression. The direct injection vaporizes quicker in a larger volume so it cools the air, as opposed to the port and intake valve.
- There is a power advantage from gdi alone, even without higher compression. The rapid cooling of air in the cylinder during the intake stroke condenses it and helps draw in additional air.
- Particulate emissions are worse with gdi. I think this is the primary reason they kept port, distantly followed by valve-cleaning. (Fords di timing on the di-only Ecoboost works pretty well in keeping the valves acceptably clean.) They use mostly port injection at idle and light loads.
- You can’t just turn off the gdi injectors. Well, you can, but the injector will overheat and blow out. Some amount of fuel flow is maintained at al but the lightest of loads, in order to cool the direct injector tips.
- On the flip side, the port injectors are never phased out completely. I think this has to do with a delay. They will switch an injector off, which happens more than you think, then turn it back on. With port, the first squirt or two wets then port and valve so it doesn’t immediately reach the cylinder like direct. This would cause a temporary lean condition. Ford doesn’t command less than 10% port injector flow.
- Gdi injector timing and pump control is a fascinating subject for a nerd like me. It’s not really what the thread is about so I’ll reserve that for another discussion. I have modified my gdi pressure and found the limits of injector open and close timing. The speed and accuracy of control in the pump and injector is absolutely astounding.
- The primary purpose is knock suppression. The direct injection vaporizes quicker in a larger volume so it cools the air, as opposed to the port and intake valve.
- There is a power advantage from gdi alone, even without higher compression. The rapid cooling of air in the cylinder during the intake stroke condenses it and helps draw in additional air.
- Particulate emissions are worse with gdi. I think this is the primary reason they kept port, distantly followed by valve-cleaning. (Fords di timing on the di-only Ecoboost works pretty well in keeping the valves acceptably clean.) They use mostly port injection at idle and light loads.
- You can’t just turn off the gdi injectors. Well, you can, but the injector will overheat and blow out. Some amount of fuel flow is maintained at al but the lightest of loads, in order to cool the direct injector tips.
- On the flip side, the port injectors are never phased out completely. I think this has to do with a delay. They will switch an injector off, which happens more than you think, then turn it back on. With port, the first squirt or two wets then port and valve so it doesn’t immediately reach the cylinder like direct. This would cause a temporary lean condition. Ford doesn’t command less than 10% port injector flow.
- Gdi injector timing and pump control is a fascinating subject for a nerd like me. It’s not really what the thread is about so I’ll reserve that for another discussion. I have modified my gdi pressure and found the limits of injector open and close timing. The speed and accuracy of control in the pump and injector is absolutely astounding.
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mangosmoothie
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The carbon comes from some combination of combustion PCV and EGR. Port injectors wash the valves and carbon never has a chance to stick.
DI only has nothing washing the valves so the carbon sticks and builds up. DI is not the source of the carbon.
EFI
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Keep trying then, it's been explained to you by several people on here that DI itself does not cause carbon buildup on valves.
Strokerswild
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It's fairly well established that one point of compression is good for a 3-4% bump with all else the same....
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IPOGT
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Aww, just throw an Edelbrock intake and a Holley 650 on it with vacuum secondary’s and you’ll be fine. May have to change the throttle linkage a bit
adjust the power valve and re-jet though.
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EFI
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EGR is exhaust gas recirculation, where it takes some of the exhaust gases and passes them back into the intake manifold to be burned again. The Mustang doesn't have this.
PCV is positive crank ventilation, where it takes the excess pressure from the crank case and passes it back into the intake manifold. This is where oil vapors get dumped into the intake and without a catch can will settle on the intake manifold, runners and valves as carbon deposits. PI usually cleans the valves off this stuff that's why the Gen 3 doesn't have this issue.
engineermike
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Nah, the catch can craze spans all makes, models, and engine technologies.
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