Hellmun wrote:wozzah1975 wrote:Hellmun wrote:NB8B has a different fuel rail to NB8A and before. The NB8B system doesn't have a fuel return so as you reach the end of the manifold you get pressure waves bouncing back and that leans cylinder #4 slightly. I've just secured the fuel lines/rail for an NB8A for this very reason for my turbo motor build. Wouldn't say that fuel rail was worth it for 200hp though like stated it's a little more buffer if you can afford it, or just keep the tune conservative. So whether it's a good idea depends on your budget and what you'd be sacrificing to have it.
I'm still curious to the method used to measure it if that is the case.
Woz
Just explaining the ratioale but you could prove it by drilling out the solid end of the rail and putting a fuel pressure sensor in, then have a tee'd pressure sensor on the inlet to the rail (as a reference source) as well to measure any deviances with a logger before/after a injector pulse. I bet you'd find the fuel pressure would spike a little and drop inbetween injector cycles at the end and the pressure is lower between the inlet sensor and the rail end sensor. Graph it and as long as you have sufficient resolution I'd expect to see a wave. It just makes sense to me talking fluid dynamics as when the injector opens the fuel expands out the hole from every direction until it closes but only one side is being fed and should have a moment where there is the pressure differential either side of the injector. More volume of fluid involved means less percentage drop in pressure it would have so the last injector would suffer the most and a dual feed should balance all injector feeds out as the pressure drops are acting on a much greater total volume of liquid (fuel from that injector to the fuel tank as opposed to just the rail). The refilling fluid force is higher as a percentage of the fuel remaining between the injector and fuel rail end so hence there should be a larger effect. Whether this has enough affect to lean things out enough for damage is not something I've seen proven. I don't personally have any benchmarks but an aftermarket fuel rail like the 949 is larger bore anyway so it provides other advantages along the same lines to reducing the pressure drops. It was recommended to me by an Mx5 race engine builder to get the NB8A rail and return line so I did. Didn't cost me anything and the logic made sense. If you want to go to the trouble to disprove returning fuel systems as having any advantages go for it... as far as mods go the rail is pretty cheap .
Drilling the solid end of the rail and fitting a gauge would effect this so called pulsing and bouncing being refered to in this topic if that is indeed the issue. For it to lean out injectors would have to be a fuel VOLUME issue. If you flow benched the fuel rail you would find that the VOLUME amount of fuel supplied to all the injectors would far exceed what is needed (probably x 100+ times), so the rail simply doesn't need to be any bigger anywhere. The diameter of the fuel rail is bigger than the fuel lines, so the fuel lines will run out of fuel volume well before the fuel rail does. Simple mathematics.
The only way to simulate it is simple. Set up the fuel rail with all the injectors fitted on a test bench with measuring flasks under all the injectors. Simulate the pulse at full duty cycle and measure how much fuel passes through each injector.
I would be quite happy for someone to send me a fuel rail and injectors to flow bench and simulate when time permits because I'd go as far to say that its a complete waste of time and money for 99% of vehicles. There would be exceptions where the volume of the fuel rail would become a problem, like on big horsepower methanol applictions. The chances of anyone chasing that sort of power here would be few and far between.
Woz
