How far can I stretch the 1.8 injectors?
 

If using the 1.8 injectors on a boosted 1.6 how far can I go? Will be using mega squirt and upping the duty % but what power is usually achievable before you run out of head room and need to upgrade to larger injectors?

Thanks, Adam

not far enough

Somebody I know with a basic turbo set up, ie no management, FPR, 1.8 injectors with a 1.6 engine has 205hp at the fly. I was thinking maybe in the region of 230 hp was possible, am I way off?

Yes, you're way off.

You get 200 hp out of 1.8 injectors because your friend is using a rising rate fuel pressure regulator. The "rate" that you're rising is the fuel pressure. Injectors are rated at a certain amount of cc's per minute, at a certain psi.

So,
1.6 is 235cc/min @ 43psi
1.8 is 265cc/min @ 43psi
rx7 is 460cc/min @ 43psi
etc, etc.

Now I may be wrong on that set psi, it might be 60psi, but you get my point. With your friend's RRFPR, he's raising that base fuel pressure as boost increases, so you're turning a 265cc/min@80psi injector into a 350cc/min@100psi injector, or there about. It's why it's more important to change your fuel pump in a bandaid setup than it is with a MS setup, which keeps stock fuel pressure.

This is the one "downside" to using MS, you have you add larger injectors, unlike bandaid setup. However this ~$200 upgrade (used 460's and a clean/rebuild), is further justified with the above mentioned fuel pump upgrade some consider necessary with a bandaid setup, making the injector upgrade more like $100.

Bottom line: If your friend is getting 200hp out of 1.8 injectors and bandaids, you'll most likely only get 105-110hp, assuming your 1.6 is like most 1.6 engines, and running around 90hp currently.

I've seen values between 230 and 260cc/min for the '94-'97 tan-tops. If we take the larger value and do a little math over at the RC Engineering web site, assuming stock fuel pressure and 0.6 BSFC, those injectors would support about 135 bhp and just a hair under 150 bhp at 90% DC.

Obviously some folks are doing more than this- FM claims 180hp on the Voodoo II kit for the 1.8 NA on stock injectors, which seems optimistic. On my '92, my 440s were at about 75% DC making roughly 205 whp.

But the real answer is that there's no answer. Try it, keep an eyeball on your AFR and injector DC, and that'll tell you when you need to install a set of "real" injectors.

i maxed 305s at 7psi (i was around 170rwhp).

if you want to keep stock injectors, youll need an FMU in addition to the MS.

if you want to use the stock injectors, you need to rise the base pressure to increase the injector output over stock levels

base should be 43.5psi so with an adjustable FPR you could raise base fuel pressure to 50 or 60lbs to get more fueling out of them. Remember adding boost will increase pressure of the injectors as well, so if its stock at 43.5psi, and you are running a bar of boost ( 14.5psi ) the fuel pressure should go up to 58psi since its a 1:1 FPR

Keep that in mind because if you do want to up the base pressure you may need a fuel pump to keep up the pressure.

http://www.rceng.com/technical.aspx has a fuel flow pressure caulcator there

at that point it is better to just buy bigger injectors.

yup.

there's a bit of misinformation here.

injectors at flowed/rated at 43.5psi. that's it.

Our fuel rail 90-97 sits at ~35psi at idle and ~48-50psi at atmospheric. Yes, it is a 1:1 ratio, so at 15psi you'll be seeing ~65psi in the rail.

The fueling capacity of the injectors will be the same as the atmospheric regardless of boost, since the pressure inside the manifold also increases, the 1:1 ratio just mantains the capacity as the boost increases.

the NB fuels at 60psi static. at 15psi you'll be at 60psi of fuel. Fueling capacity decreases as the boost increases, because there's nothing to compensate for the pressure increase in front of the injectors.

Upping the static base pressure will only do so much, when we are talking small injectors, you really need to increase the fueling at at least a 2:1 ratio for there to be any real significant capacity out of them. Bumping from 50 to 60psi base pressure will only net your 265cc injectors ~7cc of extra capacity.

I'd want to see 265cc injectors run closer to 80psi or even 100psi in boost. that would give you the support of ~200rwhp and ~225rwhp repsectively.

Or drop in 460cc injectors, leave the stock rail, pump and fpr in place is support ~230rwhp right out of the gate.

Since I started this thread I've chucked together a 'band aid' turbo set up. No full management, just 1.8 injectors and a fuel pressure regulator. Any recommendations as to what I set this at @ idle?

[IMG]https://www.miataturbo.net/attachmen...ine=1313191872[/IMG]

Rough and ready :loser:

turn it to "on".

Set it to what your wideband says. Under 12:0 in boost or you'll blow it up. Best to back the timing off too, since you have no timing control.

If you don't have a wideband, you're in for a world of hurt here.

wtf is going on with that elbow at the compressor?

The elbow coming out of the turbo looks a little restrictive but seems to be flowing just fine. Ignition backed right off and wideband on order :-)

How far can you stretch it?



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