RX-7's would run this a lot extra injector or 2 right at the intake elbow before entering the TB. You can control them with a piggy back designed for controling an extra injector. I "think" that HKS and Greddy had something for that but I have dumped most of my RX-7 memory after dumping my 7

 

Back in my Supra days I always used the GReddy Rebic. I'm not even sure it is still produced.

 

We ran a 5th injector on several Formula SAE cars I worked on in college. It has huge benefits with alcohol cars aka E85 and meth. With M85 on an average day in Texas, we determined that if you inject methanol 12" away from the combustion chamber, the charge air would be cooled to almost 32* in some cases. At idle we could actually produce frost on the intake runners some times. This was done on turbo charged 600cc honda engines. There are of course lots of variables, so the air is not always 32*, but it just gives an idea about the cooling power available with these fuels.

I have always planned on doing a 5th injector on my car as well. It would be great if there was a way to integrate this into the stock ecu. If that is not possible, I think it would be fairly simple to build a controller for it.... Something to look into.

 

more fuel for this fire......... http://www.rossmachineracing.com/dualinjassm.html