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With TBI the mixture is set before the runners, so it is consistent, leaving you only with charge volume issues.




That's assuming your intake provides good fuel distribution as well.



Perhaps I didn't explain that part very well. Because the fuel and air are mixed before the runners/distribution system, you will have very consistent mixture in a TBI. You may get more/less of that good mixture to each cylinder because of the runners, but it will all be the same mixture. This of course ignors other things like vacuum leaks or fuel drop out. In general, though, the TBI are not very good for performance as they do not atomize all that well, and put a lot of restriction to the airflow.

As Daytona says, it isn't really the single/dual plane that is the issue. It is the airflow balance over the entire rpm range. I like dual planes, because the (can) have much better matching of the runners (and longer runners) for better flow match. Other than that, there is no inherent benefit to a dual plane, as the other thing they do well is put a strong signal on the carb, which doesn't matter. If you do run a dual plane, you are actually better off to cut out the divider to pick up the top end.

I also have seen (one) single plane give suprising performance with a MPI setup. It was a street dominator on my 340. It gave fantastic response and power. Unforturnately, the bad distribution caused it to detonate under boost (turbo), foul some of the plugs, and get 2 mpg lower than the good dual planes.

I guess the net result is that you shouldn't get hung up on dual/single for any other reason than flow balance. You will find some very bad dual planes (Wieand 8007 for one), so just going dual plane is not the answer. I have not found any single plane that is close to the good dual planes.

Techinically, all the very well matched OEM stuff on new cars are single plane.

If you look at the other thead, there are a lot of pics and explanations that might make things clearer.