RX7 allnight

ok i have a 88 vert N/A. before i worked on my own car's.. i had a mech. worked on rotarys for over 30 years and raced them. really knew N/As well.

he offered me a upgrade which replaced my secondarys to the 1st gen gsl-se orange cap. 680 cc's. everyone and their friends says even the turbo 550 cc's are to big for a N/A with just a big street port. so why the heck did he upgrade to the orange 680cc injectors? stock n/a's run with 460 cc's

so this was like 5 years ago and ive still been running them. about to change and go with the stock reds..

RotaryRocket88

iTrader: (7)

There's no point in going bigger unless you have some huge ports & a manifold to match. 4x460cc injectors will flow more fuel than 90% of NAs will ever need.

RX7 allnight

he said they had more flow on the top end and would help. did he really not know what he was talking about or just trying to make an extra buck on me..i prolly wasted so much gas over the five year span its not even funnny

RotaryRocket88

iTrader: (7)

If anything, a stock NA needs to have fuel removed, not added.

stacher

When I had my N/A, I wanted more full. So I put 550cc on the secondary. It actually did worse. It didn't rev as quickly and was starting to flat out around 7000 rpm. In essence, it was getting to much fuel.

Stock injectors will do fine with a mild port.

RX7 allnight

yeah thats what i have always heard. im just wondering why he thought it did better. ive been driving my car like this for 5 years now so iam about to switch and iall update when i can

RX7 allnight

yeah i bought a safc-II never installed it though

calpatriot

I have an 86 NA with a street port, K&N intake, and a low restriction exhaust; everything else is stock including the injectors. My O2 sensor voltage indicates the mixture is rich of stoichiometric all the way up to redline rpm at full throttle. I cannot imagine that larger injectors would make enough of a difference to notice, and might also put you on the far (rich) side of the power peak.

RX7 allnight

ok heres why he thought they would be better this is from mazdatrix.

"note: For higher fuel flow in an 86-87 1/2 Turbo or Non-Turbo, the 84-85 injectors may be substituted in either the primary or secondary position (Not recommended in primary). The cutoff for 87 1/2 is June 1987 and splits at VIN # ending in 550168. The SE injectors will NOT work in engines after this VIN numbers."

RotorBalls

iTrader: (1)

I have the same setup, large street port with the 680cc on the secondaries, true duel exhaust. I want to put the stockers back on but I need to buy a pair first. It's running rich for sure and spit fire if I let off the throttle in high rpms. It really feels like I'm lacking power in the upper rpms where I was told I should be better.

rotarygod

iTrader: (1)

I'd actually like to see smaller fuel injectors than stock but with higher fuel pressures. Remapped too of course.

2slow4stock

iTrader: (18)

Also you need a wide to go with your safc ii. Or else it'd be a waste installing the safc.

calpatriot

I have a lot of respect for Mazdatrix, so I will never dismiss their opinion out of hand.

However, my 86 NA shows an O2 sensor voltage on the order of .56v to .7v throughout a full-throttle rev to redline with full throttle. I have read that the ideal mixture for maximum power occurs at an O2 sensor voltage of 0.82v ... assuming my voltmeter and grounding are perfect (not determined), it would seem that there might be a little advantage of richening the mixture slightly to get to 0.82 during acceleration. However, the sensor voltage does not vary lineraly with mixture, so the mixture difference to get to 0.82 would be very small. How small is another matter.

I think if you are really going to tweak things this close you will need a wideband O2 sensor (which is reportedly much more linear, and valid over a much larger range of air-fuel ratios.) Someone else on here will likely have more information on the characteristics of the wideband sensors.

The power vs. mixture slope is shallower on the rich side than it is on the lean, so there is not so much to be lost if you 'go over the top' of the peak in the curve (go too rich by installing injectors which are a bit too large), but if you do not really hit the peak of the curve, and instead roll over to the rich side, you are losing part or all of what you gained.

Of course, you could 'tweak' the mixture to max power using a dyno, but then you will need control over the injector duty cycle, and then you will need an aftermarket ECU (unless someone knows how to tweak it in the stock unit...)