I bought an S4 NA last fall that was pretty much stock engine-wise. A few months ago, it blew a coolant seal so it's time for a rebuild. I don't have any crazy power goals for car - all I'm looking for is a healthy engine that I won't have to worry about when I drive it on cruises, autox, track days, etc.

While I'm rebuilding the engine, I'm planning to get it street ported and I also have a full Racing Beat exhaust to throw on when the engine goes back in. I don't have any specific intake mods planned at the moment, but it's probably something that I'll look into down the line. My question is, will I have to worry about running lean and/or detonation from a street port and bolt on mods? I noticed that in the FAQ section it said that the stock NA fuel system can support up to 250 HP, so I probably won't have to worry, but I couldn't find any documentation to support that. Can anyone else confirm?

As part of routine maintenance, I do plan to change the fuel filter and send the injectors out to get cleaned while the engine gets rebuilt, but that's pretty much all I have planned as far as fuel system goes. Is there anything else I should look into while I'm rebuilding the engine?

 

I'd personally get a standalone computer to compensate for such, but people have been doing this decades on stock ECUs with no issues, if this was a turbo application I'd say otherwise but under atmospheric pressure I think you'll be fine.

 

Yeah a standalone will be nice but definitely a financial commitment there, I just want to be able to drive and enjoy the car for now. Nonetheless, thanks for the info!

 

its fine. i put a wideband on an S4 NA that was totally stock, and the AFR's Mazda chose are pretty good, its in the 12's from 4000-6500rpm. at some point you run into the AFM being wide open and the not rich stock mixture starts to go lean. there are many ways around it, the best being an ECU that isn't from 1986.

the best example is the S5, it runs the same 12.2:1 AFR at 4000rpm that the S4 does, but the S4 is 12.8:1 around 6000rpm, and the S5 is about 11:1, same pump, same size injectors, different ECU

 

I'm personally running a streetport on a stock S5 ECU. Using the pineapple racing 6port inserts and the aquarium pump VDI mod. Racing beat exhaust. I dynoed a reliable 165rwhp it's fun as hell. I track (autocross and road courses) and the occasional canyon/mtn ride.

 

That's good to know. What's the aquarium pump vdi mod?

 

Same as the lumbar pump mod(what I'm about to do). It's to replace the airpump(s5)/exhaust(s4) that controls the 6pi and vdi actuators. It can be used to add vdi to s4 intakes as well