Player0

I bought my car with stock injectors, an autothority maf, a k27-8 and 3 pound FPR. I run at 16# of boost and installed a air/fuel gauge. Everything seems okay and it's worked like this for years. But how can this work?

HP calculators for these injectors only put it in the 200+ range. I'd be surprised if I wasn't making over 300HP. With online calculators, it seems as though I should be running a 65-75 lb/hr injector.

I'd like to try 18-20# at boost at the track on race gas. But I'm pretty sure that's going to lean me out even worse.

How do I calculate my duty cycle? I assume I'm at 100%.

Can I just install larger injectors without worrying about a remap/new chip? I imagine the chip is tuned for stock injectors at 3bar and has the floodgates open. So a 65# injector might be too much fuel. But I can turn the FPR down to 2 or 2.5 bar which ought to help right?

I don't know much about tuning or if I can just take this to a shop here and have them map something. Not sure if that's specialty equipment or would interfere with the current chip/maf stuff.

Eric_Oz_S2

The stock turbo injectors are good for 280-300 hp. You are probably running near 100% duty. Along as your afr is measured at around 12 or less near peak revs, you should be ok.

If you use larger injectors you need to retune.

Player0

Okay, so I need to retune. Given my set up, what is the best way to do that? For the Evo I just bought a Cobb and took it to a shop.

On the 944, am I just going to need a buy a new chip from someone that might have the correct maps? Or is there a tuner I can get so I can bring it to the pros for something more custom?

Yeah AFR never drops below 12 as far as I can tell. I need to set up a gopro or something to record it under load though to be sure. I'm going by the corner of my eye and a quick glance usually.

It's the APR a/f gauge and it has a digital output. But I am not sure how to capture it's output. It'd be really nice to have a chart of what the wideband is actually doing.

Darwantae951

How much are you looking to spend? There are quite a few tunable set-ups out there. Rogue tuning seems to be pretty popular and Josh is very active on here. Also he is a very knowledgable, helpful person and stands behind his stuff.

http://www.roguetuning.com

Player0

Well my primary concern is not blowing the engine to pieces at track events. I have a 30 year old head gasket on there. I have no idea how the car is currently tuned and if it makes any sense for the performance mods on the engine.

Secondly, when the engine does blow the head gasket, I'm going to have the head reworked a bit to try and reduce some spool time on the k27-8. So ideally I'll need a tuning set up that will allow me to easily retune.

So I'm thinking I need slightly more than a preprogrammed chip. But I'm not looking to build a full race car either.

Willard Bridgham 3

Find out what your fuel pressure is now. Measure it with a calibrated gauge. Stock injectors can make a lot of Hp.

Darwantae951

There really isn't aot that people do with the turbo heads. Some have ported them, but with the ceramic liners in the exhaust ports I've seen more people mess with NA heads.

I'm running an NA head and so long as you swap over the turbo valves (I also did valve springs) it will work great and you can get them fairly inexpensively. The. You can have it ready to go on when you're ready to change it.

Player0

Fuel pressure I did adjust to a solid 3 bar and I have a gauge on there now. The injectors were all flowed by witchhunter the year before last so I assume everything is working pretty well. Just stock.

The rogue tuning datalogger is kind of nice and it'd attach to my wide band.

kev951

If anything, the injectors are working harder.. you could upgrade to 55Lb injectors from RC or seimens.

Willard Bridgham 3

You can change to a larger fuel pump and pick up fuel pressure with the stock injectors.

Jon Milledge, a legendary 944 turbo tuner, gave me a lecture about changing from stock injectors saying they were the best motorsport injectors available.

Keep track of the a/f ration either with your gauge or on a dyno.

blown 944

The rogue tuning software uses a MAF along with a map sensor. It is designed to be able to understand air volume and pressure to use the appropriate tuning cells.

So to answer your question, you won't need to retune up to some pretty high hp. He also sells a tuner/logger to get a supr fine tune. You could get that ahead of time and see where your IDC is at.

Personally I wouldn't run the stock injectors past 16 psi (unless still using a k26)

Player0

So update:

For giggles I increased the setting of the fuel pressure regulator. It's somewhere around 50PSI now at idle.

The car runs a lot richer. You can smell the fuel oozing out. It's getting way too much though. At idle, the AFR is about 13.0-13.5, and it reads 10.0 under full boost.

Before it was about 14.7 and 12.0 respectively.

Is it safer though running the engine super rich, or is this just stupid for other reasons. I need to go search more on air fuel ratios.

Player0

I guess my big question now is:

1. turn the AFR back down to run a bit less rich

2. adjust the maf piggyback to run less rich.

Not sure which is going to be happier with the map. Maybe they're both effectively the same thing. Tell it it has more air or give it less fuel.

I guess running rich can screw with turbo lag. On the other hand, I can probably add a whole lot of boost if I wanted without worrying about the injectors.

TurboTommy

You have to turn the fuel pressure back down to where you had it before (you said 3 bar; so pressure at idle should be around 35 - 36 psi at idle with vacuum line connected )
You cannot run it rich like that; it will cause cylinder wash and excess carbon buildup; bad for the engine.
If you have a wideband air/fuel gauge, you're over thinking this. Like somebody said, if your air/fuel gauge shows good air/fuel ratios, you're okay. At high RPMs, the engine is less sensitive to detonation so if air/fuel creeps up to 12.5 past 6,000 RPM, it's still acceptable. (providing you don't go above the moderate boost you're currently running)
That all being said, you probably are approaching 100% duty cycle and prolonged track driving will stress the injectors and computer. So if you're worried, you have no choice but to buy larger injectors and get the chip reprogrammed for said larger injectors; end of story.

Player0

3bar = 35-36PSI at idle? I thought 3 bar = about 43-44PSI? Do I really want it so low at idle? I read somewhere to set about 6PSI higher at idle to accomplish the correct PSI under load. So I thought 50PSI would give me the correct 44PSI under load which should be 3 bar.

Clearly its too rich though there.

I'd be super interested in getting that RogueTuning kit though that guy hasn't gotten back to me.

But yeah, it sounds like 12.5 is the target for high load, so I'll have to reduce it. I guess the 3 bar regulator can give a lot more than 3 bars.