Higher fuel pressure = better atomization?
 

An M.netter and I (POPSTOY) were having a discussion at the South Bay GTG last night. He mentioned that a higher fuel pressure not only provides more CC/min, but it also provides a better atomization and more power. Any truth to the matter? My current plan was to pick up some 550s and link them to a stock fuel pump with MS and a WB02, but I'm starting to think I may want to incorporate smaller injectors and an AFPR.

I tend to think that the higher pressure will give you better atomization, but there is probably a point of no further return. It would be nice to know what the vehicle that normally uses the 550's runs for fuel pressure when it is demanding 70-80% duty cycle. I am sure that running them at lower than their rated pressure to maintain an idle will reduce atomization.

Sure it does. That's one of the benefit of the current crop of direct-injected engines popping up on the market (VAG, BMW, Mazda, Mitsubishi, etc.).

Of course, the injectors on those engines are running at 1000-2000 PSI...a far cry from the 50 vs. 75psi that we're talking about here ;)

But, yeah, it will absolutely atomize better. As to what measurable benefit that might have in our applications, I'm not sure.

But it could go the other way too don't you think? Hit a certain point and due to the increased fuel pressure it starts to suffer. I've seen this with an airbrush (yes I know it's not the same thing, but similar).

Maybe there is a reason that most cars run ~50psi fuel pressure, the injectors are designed around it. Or at least you'd think so.

absolutely, couldn't have said it better myself.

I am shooting for 220rwhp. I honestly have no idea how much injector I actually need, but the plan was to use 550s just to be safe. I'm now considering using WRX injectors (420cc) since I have a couple of buddies who have them, but I'm not even sure if I'll need that much fuel. I wouldn't be shooting for the moon, just as much pressure as the stock fuel pump can provide, mabye 60-70psi.

um, id say get a bigger injector than you will need. Nothing too crazy, but something with a little headroom. Then use the stock 55psi fuel pressure and go with that (fuel pressure rises to about there w/ atmospheric pressure) you got megasquirt, you will be fine man.

Damn, i just looked at the stuff you got on there, im diggin your setup. I kinda wish i got the 6ul's now. On second thought, get the 550's so you can boost to 15psi and beyond when you feel the need. If you blow your motor, put another one in.

hey so you guys are in cali eh? Let me know next time you have a get together, id like to meet some of the people from this board.

They happen every week, check the California section over at Miata.net. It cycles between Union City, Daly City, Mountain View, and Milpitas, IIRC. If you want a ride sometime just let me know and we can meet up at a GTG and sling it around some onramps. Bring your turbo car, though. I still haven't actually ridden in a turbocharged Miata. :(

I don't think I'll ever feel the need for 15psi. This motor has to last me through college so I'm going to do 220rwhp or 12psi, whichever comes first. Looks like more fuel pressure isn't worth the hassle as well.

Anyone know how good that RC Engineering injector calculator is? The injector requirements seem abormally high. I'm still trying to figure out how much injector I'll need, 420cc vs. 550cc at stock fuel pressure.

A 460 injector should get you to you goals. For 220whp your after about 250hp at the crank give or take. A 460cc injecttor @50psi will get you there with a little bit of wiggle room.

I wonder if I saw you at any meets ~1.5+ yrs ago.... been to a couple in 'n out and kk meets close to the south bay.

actually for 220 whp, you dont need to go overboard with fuel injectors. 550s are about the most you'd want.