I have been PMing Don from DMH who says that he will not program for injectors larger than 380s with the stock fuel pump.... Don said that Dinan and others agree.... this is the first I have heard of this as I have run 400s and now 440s and have to trim them back.... the term "pooling" is being used...... I asked Don if he wouldn't mind starting a discussion so we could here his views and and the views of others with experience......

 

Hmmmm, I don't have anything to add but this looks like another quality thread brought to you by spiderX... I hope this one goes the distance.

bump.

 

Oh great another new $$$ mod to worry about...! :-)

 

My 400s seemed to smooth out the acceleration curve.
Not sure what they have done to my lean or rich mixture.

Paul

 

Peace SpiderX,
I can't say much on this except I've run 400's without a problem. I think the problem has more to do with more than just the injectors. The folks who have tried to run straight turbo ran into problems with the fuel delivery system in general even with larger fuel pumps. Apparently the fuel delivery apparatus consists of a returnless system. On most cars the system is a loop which "returns". This has been the biggest obstacle for the go turbo only crowd. It has been addressed by adjusting the fuel pressure regulator which can only go so high no matter what size pump you use. Most twincharge and turbo kits use 500cc injectors with the stock pump because of this. Yes, Dinan does change the fuel pump, and they are the only folks i've seen doing it. Anyway, I'm no mechanic or expert, but this is what experts have explained.

 

Bob, I wonder if "pooling" is a reference to the spray pattern, like it's poorly atomized. I'm thinking with a bigger orifice you may need a bigger pump to get a decent level of atomization/spray pattern. Like a garden hose - tiny hole, it really sprays out of there. Wide open, it just runs out the end in a poorly atomized stream. I don't know much about it, other than that spray pattern is a factor in a good burn, just like good swirl etc in the airflow. I remember some film in a mechanical engineering class where they slowed a cylinder cycle down to the point you could watch the flame front burn across the chamber, and they discussed how this could be altered by various conditions such as airflow, injector spray pattern, spark plug location and quantity, etc.

 

the injectors are open much longer than the valve is. Something to think about.
I too got smoother operation in upgrading injectors, but I've also measured degraded flow in just one year of injector operation, so smoother with larger injectors may just be that they are clean and have better matched flow.
As far as having to upgrade fuel system components? I'd say there are lots of "existance proofs" that it's not required, even if benefits may be there to be had....

Matt