Sooo, I'm definitely no tuning expert, but I was curious...

The car I'm picking up has 2 720cc (or 750cc?) injectors, and a (I believe) stock ECU.

The way the car was tuned for those injectors was by changing the fuel pressure with the SX Fuel Pressure Regulator.

Now, I'm kinda leery about that, but I know nothing about tuning like I said. Is this ok to do? Apparently it was tuned to be rich on the safe side, but I don't know much about it, any thoughts?

 

720's on the stock ECU without any tuning would already cause the car to run rich on boost, since the ECU would be driving them at the same injector pulsewidth as the stock 550's ... It's quite possible that the FPR could have been used to lower overall fuel pressure (so long as the stock FPR was removed), however this isn't probably the case, since you require a minimum pressure at idle to keep the car idling well .. If they used the FPR to raise fuel pressure, then you are certainly going to run pig rich .. You can't really tune a fuel curve with just an FPR (I'm going under the assumption the sx FPR is a 1:1 rising rate fpr)

 

wouldn't an aftermarket fuel pressure regulator not increase fuel pressure under boost like the stock FPR does? Or are they built specifically to do that?

And where's the stock FPR so I can see if it's there.

 

Yes, it will raise fuel pressure on boost.. depending on the type of FPR you have, it can raise boost 1:1, or 1:whatever you choose .. I belive the SX FPR is a 1:1.. The stock FPR is also a 1:1 unit..

The stock FPR is located at the firewallside of the stock secondary injector fuel rail.. it should also have a vacume nipple on it.... It shoudl be easily visible if you look at the back of the upper intake manifold.. If they removed it, they probably tapped the fuel rail to accept earls fittings..

However, I belive the issue is the fact that the larger secondary injectors would already run you rich when using the stock FPR.. installing an aftermarket FPR isn't going to tune the injectors down, but rather, probalby make you run even richer...