So, from what I understand, it's difficult to upgrade the injectors while utilizing the PFS Purple box. I've been told that it's possible if you upgrade the primaries and secondaries with the same 550/850 ratio. Why is it that you cant just get bored 850's and throw 'em in for a little more juice up top?

Because the stock ECU still believes it has 550cc injectors in the primary. Different sized injectors need different amounts of time for voltage applied. For instance 850cc injectors will need less time to open up for X amount of fuel vs. the smaller 550cc injector.

you can use the injectors but I dont recommend it. You have to pull full out insted of adding like you normally do. Also if you are using stock twins the stock fuel trim is fine with an upgraded pump.

Ok, good answer. It's not like I'm not shooting black soot and flames as it is, so I'll stay stock.

Like Rikki said your pulling fuel out, basically running the injectors at a percentage, or you'll dump too much fuel.



I dunno **** about the PFS though. Could you run an AFC with it?

It basically is an AFC.. The whole reason for this question is that last summer, I was running 15-12-15 on the stockers, and my crappy little Apex'i Turbo timer's AFR display would no longer peg at 10.0:1 - it floated around 11.8-12.2:1. Now, I know they're not accurate at all, but I'm used to seeing that thing peg full rich on boost.



So anyway, I'm thinking that if I should ever require more fuel, I'd likely just run this setup - bored 850's that flow 1000 cc's or something, and pull fuel at the top like was recommended. Although, at this altitude I could probably put 16PSI out of the stockers with an upgraded SMIC.. Hmmm..

Also a good trick is to raise fuel pressure! But I ran stock Fuel Pressure and did o.k. I did 354hp on stock fuel except a supra pump.

Yeah I know someone who ran a TD-06 turbo on the stock FD fuel system and upgraded fuel pump with raised fuel pressure.

Would it be false to say that an upgraded fuel pump (walbro 255) raises fuel pressure?

No the fuel pump just raise the rate of gallons or litres per hour!