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I decided to pull the 535 injectors out of my turbo car and stab the 325i nozzles back in. The way it was I had to crank the AFM so far up that it wasn't hella rich at low load, at the expense of driveability and economy. At the same time I was still maxing out the rate of gain on the RRFPR, as the AFM adjustment kept the duty cycle down under full load as well. The whole point of the injector swap was to rely less on elevated fuel pressure and more on injector flow. So anyway...

The question is how much fuel pressure can I get away with before I have to worry about blowing fuel lines off (or up)? In its current state of tune its making seven PSI of boost in the manifold. The RRFPR is still maxed out, and the fuel pressure at roughly atmospheric pressure is about 45 PSI. If its boosting fuel pressure by four for every one pound of boost, its making about 75 PSI. I'm thinking it'll be going back up to ten pounds of boost for the occasional Evo or STI. That'd push the fuel pressure up to a maximum pressure of about 90 PSI. Is this alright with stock BMW fuel lines and screw type clamps? The last thing I want is a gasoline + glowing turbine housing situation...

turbodan wrote:If its boosting fuel pressure by four for every one pound of boost, its making about 75 PSI. I'm thinking it'll be going back up to ten for the occasional Evo or STI. That'd be a maximum pressure of about 90 PSI. Is this alright with stock BMW fuel lines and screw type clamps?

NO...you are going to pressure lock your injectors. In other words, the pressure will be so high that the injector will either lock full open or shut, both are bad. I bet your fuel pump will not be able to deliver that much pressure if asked to anyway.

Where are you getting the 1 psi =’s 4x fuel pressure equation? From my understanding the RRFPR raises the fuel pressure 1 psi for every psi of boost.

A normal Fuel Pressure regulator will raise fuel pressure 1psi for every 1 pound of boost, to keep the Pressure differential from the fuel rail to the Intake manifold constant.

A Rising Rate FPR will allow you to add OVER 1 psi of Fuel Pressure per 1psi of boost. So that the pressure differential between the fuel rail and intake manifold increases as boost increases, therefore adding more fuel as boost increases..

The Cartech 2025 does more than 1 to 1. I'll have to look and see where I got the 4 to 1 number from. I might have just made it up and accepted it as a fact. Whatever its doing, its enough to work with the stock injectors. The question is, how much fuel pressure can I get away with without worrying about blowing the fuel lines off of the fuel rail or blowing up th lines themselves? I'm not really worried about pressure locking the injectors.

http://www.cartech.net/fmu2020instruc.htm

If Corky Bell isn't worried about it, thats good enough for me.

turbodan wrote: I'm not really worried about pressure locking the injectors.

Well, you should be. They will lock at about 95psi and your face will hit the steering wheel pretty hard. Why have you not installed 24lb injectors yet?

Todd

I tried some 535 injectors I had laying around. The only way it would run right was with the AFM cranked way tight. It wasn't quite right anywhere but between 4k and 6k under boost. And I still needed the max rate of gain on the RRFPR for the best power under boost. It was like it was using the larger injectors at a lower duty cycle than the smaller injectors. I dont doubt that it will run even worse on even larger injectors. I'm thinking about porting the AFM, but I dont know if I can cut enough metal out to make it run right down low. It just doesn't need a whole lot of fuel off boost down low.

Perhaps this is the difference between a draw through and a blow through AFM configuration. I'm not running the same setup as the TCD kit. I'm sure I can make it work, but its clear that it needs to be tuned differently. As long as I don't blow any fuel hoses up or off, I think it'll be alright. Maybe a custom chip is in order...

uhhmn, I havent checked the parts lists, but I was under the impression that 535i injectors and super eta injectors were the same P/N

You're thinking of 325i injectors. They are essentially the same flow rate, its just that the blue top 325i injectors operate at 3 bar, and the white top super eta injectors operate at 2.5 bar. its not that the super e white tops cant be used at 3 bar, but thats the only difference as far as I know. at the same pressure they flow the same rate. I think the 535i injectors are rated at about 18lb/hr while the 325i/super e injectors are 14.75. Whatever they are, they're bigger than the super e/325i injectors.