joegallo13b

i was wondering if i could take out the stock na 460cc injectors and put T2 550cc in. will this make more power and will there be any problems?
87 gxl 5spd 80k miles
thanks

peejay

You'll make less power and it will run like crap. The factory tune is extremely rich, there are a lot of gains to be had in leaning it out.

For one example, a certain Improved Touring racer (must run stock computer, ports, and manifold) found that best power was had by tweaking the fuel pressure regulator to get pressure DOWN to 25psi. And that only because the regulator was unreliable at pressure lower than that. That's something like 25% LESS fuel than factory.

The stock 460s are more injector than anybody is going to need with the stock manifolding. If you run them out to static, they're good for roughly 330-340hp.

RotaryEvolution

iTrader: (30)

330-340hp if you use physics, unfortunately rotaries defy the laws of physics/mathematics and the injectors would never see anywhere near that power level in a rotary engine.

but yes, in a stock n/a car bigger injectors just waste fuel, kill the environment and make less power.

peejay

I'm running twin 680s and I'm making the theoretical max of 230hp, based on quarter mile trap speeds.

Yes, they hit static... but just at the crest of the power curve Bridge and peripheral ports have better full-throttle BSFC than side port engines. I was hitting static with my old street ported engine at lower power levels - around 210hp.

330 or 300hp, you'd not going to make that much power with a stock port/stock manifold engine. I do understand that the stock ECU is limited to about 70% duty cycle, but you're still going to be unlikely to run into that as a limiting factor.

Sgt.Stinkfist

iTrader: (6)

Actually from testing with my oscilloscope, my S4 NA pcm wont push anything further than ~65% DC, I can use an SAFC to try and add more fuel at the top end but the PCM just stopped adding anything more. With 4x reman'd 460cc injectors I was running out of fuel over 7k and had to drop in a pair of 560cc EVO9 injectors in the secondaries. hopefully ill soon be running a different manifold setup, my haltech E6k and a just a pair of denso 1000cc's


But I definitely agree, unless you have a ported engine that can breathe decently and a means of controlling fuel, do not just drop in some higher flow injectors. When I first swapped in my EVO injectors, I swapped in all 4 just because I figured that I already had the manifold off, so I may as well, and just to idle semi-decently, I had to use my SAFC to remove around 20% fuel. Also to stay in a decent A/F range, was correcting my fuel from between -25 to -17% throughout the whole powerband (I cant imagine what that was doin to my ignition timing running such heavy corrections)

RotaryEvolution

iTrader: (30)

the n/a cars can use a little more timing so lowering the load the ECU sees it would keep the timing higher, longer.

Sgt.Stinkfist

iTrader: (6)

Thats a interesting concept. If I was goin to stick with the stock computer and sensors, ide consider experimenting further with it. Unfortunately the factory S4 set up is so rudimentary that I would rather just go full standalone and set my fuel and ignition timing as I wish, as apposed to fooling the PCM's inputs to achieve a desired outcome

Luckily ive been able to dig up the factory timing tables for stock S4/S5 turbo and NA, as well as the maps for the Rx-8 so I have a little base info to play off of

RotaryEvolution

iTrader: (30)

that is always true, you just don't know what the stock ECU is putting out unless you load the car on a dyno and get actual timing measurements or tune the engine based on the torque curve.

to make hard adjustments requires sacrificing low end timing by adjusting the CAS from default, with a standalone you have full control. i've played around with the stock ECU but it was hardly a good investment of time with piggybacks, with timing advanced 20+ degrees at 10+psi the sacrifice was in backing off the low speed timing 10 degrees through a hard timing adjustment by retarding the CAS to make it safer. this was a high compression turbo engine which liked the advance, unfortunately i did not.

i was told the vert ECU timing maps were conservative, i found the reverse was in fact true. though it made the best power, it was far from safe. low speed drivability also suffered.

peejay

I was under the impression that the ECU only looked at the MAP sensor for ignition timing, not the air flow meter.

Sgt.Stinkfist

iTrader: (6)

Lol. The mysteries of FC pcm's are still a pleanty. I thought that the map sensor plays virtually no role in timing, but primarily for varying when the secondaries come online. And it was the AFM + RPM (and TPS to an extent on S4's) that dictated the majority of the timing

j9fd3s

iTrader: (3)

i have seen a logical explanation for this, on this era of EFI systems, like the bosch motronic 1.1/1.3, the 65% cap lets them have enough headroom for the coolant temp sensor corrections.

so its sized so it can be dead cold, WOT, and at high rpm.

anything newer than the S4, will have something that limits WOT power, like the double throttle thing, so then they don't need WOT high rpm AND the coolant corrections. it becomes WOT high rpm OR coolant correction.

i haven't tried it, but if you gave the S4 ecu the -32C coolant temp, and WOT and 7000rpm, you'd see more than 65% DC.

Sgt.Stinkfist

iTrader: (6)

I suppose I could either disconnect my CTS and/or just add an appropriate resistor, or rheostat in place of the sensor to mimic a ultra cold condition, and recheck the DC% on my scope...purely for experiments sake Ill have to dig through some of my FSM's for find the resistance charts for the CTS though.... again , purely just for ***** and giggles to test this theory

peejay

CTS is similar to the industry standard GM sensor, the resistance is not the same as GM but it's really close, like only 10 degrees off across the normal operating range. It's a negative temp. coefficient, unplugging it makes it peg cold and shorting it makes it peg hot.

mfishe12

Have any of you played with the rtek 2.1 mod?... it works great on my TII although with boost you are visibly limited to 8700 rpm and 16 psi.
I just finished a 6port NA half bridge on the lower secondary ports with a large center street using TII injectors...my ecu is on its way to rtek right now so I can actually tune it...on the stock map it is way to rich and will only start ( poorly ) at WOT. It does however have enough umph to pull on a rx-8 r3... pretty confident that if you were to use TII injectors with stock ports it would never start.

j9fd3s

iTrader: (3)

haven't used the Rtek, although i've done SAFC/haltech/carbs on NA before.

the ITS prep FC we raced back in the day was only running like 77% injector duty on the stock NA fuel system, so unless you're trying to get around some ECU limitation, or actually making power the 460s seem fine?

i think if/when i do this again i'd be really tempted to use an Ev14 injector, like maybe the Rx8, and then play with fuel pressure. i'm sure the gains are small, but it would be interesting to see if you could coax a slightly better bsfc out of the engine with better atomization

mfishe12

The rtek first step.is tell the ecu what size injectors your using. It will automatically compensate for the larger injector if you select 550 or 720, from there you can modify the cranking map idle then comes fuel and timing map/rpm
Also a 0-5 v can be input to at least one open pin at the ecu for an a/f sensor or other
For the price $450 its pretty nice and scca leagal..
I do agree that the stock 460 s are good for pretty much anything you want to do with the NA

mfishe12

Come to think I don't even know what size the rx8 injectors are

peejay

330 or 360 x6.

mfishe12

That is low! And there are people turboing 8s with stock injectors successfully. I guess that is because the duty cycle of the pump gives the pcm more control over volume while maintaining pressure.