EFI... that looks like Webers?

[fkemmerer]

If you use the TWM manfold/injectors, I would recommend the modification. On an individual runner setup like the TWM, there is not way for the computer to control the amount of air going into the motor at idle to regulate the idle speed. The modifications involve running lines under the intake to a common resevior at the back of the intake manifold wher the IAC is mounted. Once the TWM manifold is installed, all of the plumbing is hidden underneath and you can easily change the IAC motor which will be at the back of the intake. If you decide to take the motor to an engine builder to install the EFI setup, they would most likely do the modification for you and then tune your motor on a dyno. If you want to do this yourself, you'll need to find a compent builder or machinist who is familar with EFI and they'll handle the modifications for you. Keith Craft did my manifold and they did a great job. Without the IAC, you loose a couple of important capabilities: 1) the computer will have a very limited capability to regulate idle speed (only ignition timing). To compensate for this, you'll have to mechanically set the idle speed fast enough to allow the motor to warm up when its cold which will probably create a faster warm idle speed then you'd want on the street and 2) you'll lost the "throttle follower" capability that most EFI system use. This has a number of impact on how well transient throttle action work which is important on the street. For example, if you accelerate hard and then completely lift off the throttle, most engine will tend to go lean and backfire because of the sudden high vacumn situation created in the intake. The IAC motor and the computer on a well tuned EFI setup will compensate for this by opening the IAC motor at full throttle and then closing it over a short period of time to avoid the high vacumn/backfire scenaio that I mentioned. Net is that you really want to run an IAC motor with a setup like the TWM on the street. Its a little extra trouble and $$ up front but you'll be glad you did once the motor is done.