jussnb

<ul><li><a href="https://forums.audiworld.com/a4/msgs/742942.phtml">Link to my post on the A4 forum</a></li></ul>

Audiboy

Looks really sweet. Like the headers.

jussnb

Thanks. It's an absolute BLAST to drive.

Audiboy

without worrying about ECU mod. You'll use a tad more gas depending on how heavy footed you are, but at cruising, the close loop system may manage and cut back on the duty cycle and still keep your system healthy. Just a thought. BTW, What exhaust did you use to bolt up to that header ( still infatuated with the headers I'll probably do the same, but waiting for Stasis to sell me stuff. Check them out next weekend at Laguna Seca.

scott12v@pghaudi

If our stock injectors are 200CC, they should be good for up to 240HP (calculations below). If we move up to 220CC injectors, then we are good up to 264HP. So by increasing injector size, we're not really adding any additional horepower, but rather are removing them as the limiting factor.

My primary question is: what are the downsides to sizing injectors larger than what you need. It appears to me that 220CC injectors will be able to handle the TDL mods, but what if forced induction is added to the equation (which would get HP over the 264HP that 220CC inj. could handle)?

In other words, if I someday plan on doing forced induction, would it be bad to go ahead and get 260CC (312HP) injectors now rather than getting 220CC now and later upgrading to something larger?

Thanks,
Scott


200CC/10.2 lbs/hr = 19.6 lbs/hr
19.6 * 2.04 = 40HP per injector
40HP * 6 Injectors = 240HP

220CC/10.2 lbs/hr = 21.6 lbs/hr
21.6 * 2.04 = 44HP per injector
44HP * 6 Injectors = 264HP


240CC/10.2 lbs/hr = 23.5 lbs/hr
23.5 * 2.04 = 47.94HP per injector
48HP * 6 Injectors = 288HP

Audiboy

psi of fuel and maybe 90% even 100% duty cycle. I happen to have had for a while a Fuel injector pulse meter and 02 sensor LED display dancing around my car since last year. You will be lucky to get it past 80% duty cycle at 6000rpm WOT, about 50-60% duty cycle around 4000, 5000 rpm. 02 indicates about 14, 13 maybe 12 stoich, but nothing richer. My meter corresponds to the VAG. And for most NA cars including Bosch, WOT programming is fixed, not listening to MAF or O2, just rpm, air and water temp for the most part.

Larger injectors just help give you a richer system to compensate for what I mentioned above. So while 200cc injectors are indeed good for 240hp, at say 90-100% duty cycle, the stock ECU isn't close to doing that.

All the mods that were done to his 12V are to increase flow efficiency, but nothing on the fuel side. Timing is good on these cars. I measured 20BTDC at one point, and the ECU just backs up from there. That just means that while he is adding more power, he is also going on the leaner end side of the 02:fuel scale, and significant hp drops off when on that lean side. Whereas on the rich side (10:1), power is on a flatter curve, you just increase your NOX and HC emissions - but at WOT, who cares. All cars fail emissions at WOT.


Going back to your question, you probably cannot jump up to 260. Your stock ECU will not have the bandwidth to compensate for that and you'll just run rich at all conditions. If you plan to have forced induction over an efficient plumbing (i.e. TDL mods) you really have to go to a new controller like Motec II and then 260, or 300cc injectors you can play with. However, if you are goig with that much power, keep an eye on the SpeedVision A4, because they are engineering the engine for high compression and you may need to get a few parts from them to get passed a 280hp number or so.

jussnb

the pressure up 5psi over stock to 45psi. Do you think just bumping up the fuel pressure will be enough to keep up with the rest of the mods?

I'm pretty well-educated on the mods I have had done, but some of this fuel stuff is pretty new to me. Thanks for any additional feedback you can give.

jussnb

Headers &gt; Y &gt; Cat &gt; Borla primary muffler &gt; Magnaflow secondary muffler.

Going the two-muffler route was the only way to keep the sound at a tolerable level.

And boy...does it sound sweeeeeeet.

Audiboy

with manifold vacuum in the regulator, and without as in WOT, it goes up another 0.5bar at 0 vacuum in the regulator, or about 58psi.

So, I don't know who told you 40 psi stock to 45 psi new, that sounds on the low side.

Also, do you know if they just swapped an adjustable pressure regulator that adjusts your pressure when there is vacuum in the regulator only? Because that would mean that you raise the base pressure but the WOT pressure is the same.

Anyway, lets just say that they mean 5psi above from base so your new pressure goes up 55psi. New flow rate is dependent on the square root of the pressure ratio. So, your new flow rate of stock 200cc injectors will be about 209cc at idle and cruise. If your WOT pressure also goes up assuming that you really have a fully modified not close to stock regulator, then 208cc at WOT - otherwise 200cc at WOT if only base pressure affected. So, it is better than stock, but you see why I like 220cc injectors right

scott12v@pghaudi

On page 24-12, it states that fuel pressure at idle, with the vacuum hose connected should be 3.2 - 3.8 bar (46 - 55 psi).

The Residual Pressure after 10 minutes is 2.2 - 3.0 bar (32 - 33 psi) depending on whether the engine is hot or cold.

I cannot determine whether or not that these pressures are measured before or after the regulator, but I must assume that they are after.

Justin - I'll show this info to Lloyd this weekend and find out the reason for the discrepency.

Scott