Q: I just finished rebuilding the 5.0L engine for my Fox Body Mustang. I made the following modifications:

I am reusing the stock 19 pound/hour fuel injectors and electric fuel pump. The engine doesn’t feel as strong as I think it should. I added a 140-amp alternator which helped a little. Would a Crane HI-6S ignition help? Should I upgrade to 24 pound/hour injectors? The engine has just 1,600 miles on it, so it’s barely broken in and I haven’t gotten on it hard yet.

Red Fox Body Mustang
(Image/OnAllCylinders – Nicole Kunar)

A: The modifications you’ve made are good ones. We’d start by adding a larger Ford Racing 190 liter/hour fuel pump and either the Crane HI-6S ignition or an MSD 6A ignition. We’d also adjust your fuel pressure with the BBK regulator. Adjust from one to three pounds more or less than the stock pressure (45 pounds), depending on what the engine likes—don’t go beyond this range. Take a look at the spark plugs as you do this (here’s a guide to reading spark plugs). The plugs will tell you if the engine is running rich or lean, although you can also use an air/fuel ratio gauge if you have access to one. You may very well need the bigger injectors.

This is another in a series of weekly Q&A Mailbag sessions with Summit Racing‘s tech department, in which there are hundreds more. Click here to see them all

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