upgrade injectors and fuel system ?s
 

My car's in pieces and I'm thinking about upgrading my injectors. Right now I have 750cc injectors which work just fine but am considering swapping them out for 1200ccs. This would be to avoid having to redo my maps if I max out the injectors. Right now, my fuel system is stock with the exception of the injectors, Hydra, and Walboro 255HP. If I upgrade my injectors will I need to swap out anything else in the fueling system or would it just be PNP?

Some simple math says that you "may" not have enough fuel pump for 1200cc injectors.

80% duty cycle of 1200cc injectors gives you 3840 cc/min, if you convert that to l/hr you get 230.4

So the 255 lph walbro pump can only supply the needed fuel with less than 10% margin for error. Flow losses and head will probably be less than that so you should be okay.

Those injectors should support around 550 HP unless you are going to E85 then you could get to around 400 assuming 40% more fuel requirement.


How were your duty cycles on the 750s? A little real world observation trumps math any day of the week.

Thanks for the math help-- I wasn't sure how to get the flow capacity of the injectors but that's makes ez sense.

I think my duty cycles were down around 48% around 250whp.

Would I need to make any changes to the FPR?

Unless you are going for 400+ I wouldn't bother with bigger injectors.

I put an adjustable fuel pressure regulator on my car and raised the fuel line pressure from 43.5 to 60 psi making my 750cc injectors flow 880 ccs.

All the calculators for fuel injector are here.

Whose 1200cc injectors were you thinking of?

I would also think 1200cc injectors would lead to a piss poor idle. Dual fuel rail is another option. I can't remember if adding pressure increases or decreases effective atomization. I think it decreased it. Probably not a huge deal, but it's something to think about if you're planning on running crazy high pressure to get smaller injectors to put out what you need. Obviously 60psi isn't a problem for Chris. I personally would go with a dual rail at that flow rate. You could keep your 750's and put in a set of 550's and that should get you better control and better idle and allow you to save a bit of gas if you care.

With my current setup I'm going for 400-450whp (with 50% meth WI). I'd like to set myself up to be ready to upgrade my turbo and get north of 500whp in the future.

I was thinking of RC Engineering injectors.

One thing I don't understand: When I was messing around with the calculator at the bottom of the page, if I increase the pressure at the rail, my Lbs/hr drop. Does that make sense to anyone?

That calculator tells you what size injector you need to produce the target horsepower. If you raise the fuel pressure the injector will flow more, so you need a smaller injector at the higher pressure.

If you want to see what changing the pressure for your specific injector does, use the Find Fuel Flow After Pressure Change calculator above it.

You should check out the injector dynamics 1000cc injectors. They should get you to your goal and they seem to be pretty nice. Can't wait to get my own set.

Isnt it true that theres a better chance of an injector locking if it has more fuel forced through it than made for by a rising rate FPR. Not saying it will happen since it usually doesnt, but i've always heard that if a bigger injector can be had without forcing extra fuel through it to make it flow more than thats the way to go when making alot of power

Yowza. By RC's calculator, you could get 600-700whp with these injectors @ 100psi on our engines.

ID has a neat website: http://www.injectordynamics.com/badasses.html

I did about 10 minutes of research on them so far-- and the big selling point seems to be their ability to handle 100psi and their flow testing is better. By comparison, what can RC engineering's injectors handle?

In general, why doesn't everyone run humomngous injectors? Is it just because they won't be able to idle well?

Sorry for all the newb questions. I only just started to understand turbos.

Hadn't heard that but it seems reasonable that you wouldn't want to exceed the specifications for the injector.

Mine say

Pressure:
Min 30 PSIG / Max 70 PSIG

Saturated Injector SH4-0750D (Denso style top)

I think if I were going to go much bigger though I would seriously look at a dual injector setup. Stock or just a little bigger as primaries for idle/partial throttle, then my current 750s for secondaries when I wanted the extra fuel. The packaging for dual injectors and an ubercharger might get a little interesting though.

Injector Dynamics=Bosch, the 1000s are what I am putting in my build. My tuner swears by them, says they idle better than other make's smaller injectors, fwiw.

According to the DIY sticky in the useful saved posts on here, the 255lph pump will outflow the stock regulator, causing it to run at higher pressures than expected. I did some quick hydraulic math on the fuel lines and fittings, and the stock parts should be ok within the boundaries we are working with, ie, negligible pressure drop with the flows we are working with. I'm going with the 255 HP pump, and probably the m-tuned regulator, I'm expecting that regulator to be able to handle the 255lph pump.

Why are you going with the m-tuned regulator? Why not the BEGI or whatever brand FPR something like this-

Amazon.com: AEM 25-301R Red Adjustable Fuel Pressure Regulator: Automotive

When we increase the base fuel rail pressure (I'm learning ;)) do we need to go to a return-based fuel system? My 03 is returnless.

Sorry, FF, I was enjoying the sound of my own typing so much that I disregarded the fact that you are NB. There is a little blurb here about returnless: https://www.miataturbo.net/forum/t10821/. Looks like Begi might know what to do in your situation. I will probably just go with the best/most available/cheapest afpr.

Hmm why would I need an inline fuel pump? I already have a 255HP in-tank pump. If I went with the Bosch injectors, wouldn't I want two Walboro 255s to run lower psi to the FMU?