RedHardSupra

iTrader: (1)

at 6600rpm (normal upper limit of a stockish LS1) and 80% peak volumetric efficiency (average for unported 2 valve heads), you're pushing about 40lb/min of air. at 13.0afr you need about 29lb/min to supply enough fuel at 80% duty cycle. that's just about what z06s run, injectorwise. so i'd say about 400hp for safe operation with a healthy margin of error. which also agrees with some books which say you make about 9.5-10.5hp per 1lb/min of airflow (40lb/min*~10hp/lb/min= ~400hp) so that's all you should ever do with stock injectors.

DaveSchott

iTrader: (5)

When we first installed the incon on my car it had stock '00 injectors, which I relaize are different (believe 28lbs). On a mustang dyno we could only muster 400rwhp at maybe 4400rpm because the injectors ran out and the car was going lean.

Whoever pushes stock injectors to the max is playing roulette considering replacements are cheap and very easy to tune.

JakeY2KZ

iTrader: (9)

^^^^the reason why I just bought some svo 30#'s. Some good deals on Ebay for them.

dynocar

Vetronix's Tech II normally displays this only as "inj pulse width", but on some years/models vehicles it may not.

markp03

iTrader: (4)

i was around 360hp and my tuner suggested upgrading to soem 30 svo injecters which i did....now i want 60# hehe

white2001s10

iTrader: (4)

Running boost changes the rules, because once the intake is pressurized the injectors can no longer deliver the same amount of fuel unless the fuel pressure is increased to match.

It is accepted procedure for those running boost to have to increase injector size according to the boost pressure seen in the intake..

In NA or bottle applications it is not uncommon for pressure in the manifold to drop below atmospheric as the RPM increases, and of course injector output increases as well.

white2001s10

iTrader: (4)

Well the experiment is finally done and I don't have to worry about it anymore.

It turns out that the stock injectors on the 1998 C5 really don't do anything past 100% duty cycle. The DC's and PW's reported are accurate, and the actual AFR does slowly start going lean after 100% DC as the RPM continues to climb & DC increases further past 100%.

After seeing it happen I can see how easy it is to be fooled by the wideband data. It would've been plainly obvious in an M6 equipped car because the RPM would be in a high range for most of a test run.

The highway geared A4 that I tested is just the opposite. The RPM stays low for most of the run, and in fact in 3rd gear stays between 4000 and 4500 RPM for the entire last 1/8 mile of a run. On the bottle the high RPM's flash by rather quickly with a 200hp shot so there is little time to register a slight lean condition that is only momentary. It does show on the wideband but looked like a hiccup and was so small as to be ignored. Most of the run on the wideband was well down in the 10:1 AFR so there seemed little to worry about.

In actuality as the RPM climbs slowly (NA) at the end of second gear, there is time to clearly see an upward trend with the AFR after 100% reported DC. With the injectors static & working like a carburetor, there is still no evidence of a massive lean conditon. As RPM increases the need for fuel increases, yet the need for fuel per cycle gets smaller to an extent too cancelling part of the fuel deficit. The result is a smooth rise in AFR.

Here's the data:
RPM----DC-----PW-----AFR
5150--99%--20.850---10.89
5332-101%--21.232---11.16
5476-103%--21.582---11.30
5639-106%--21.963---11.42
6109-108%--23.013---11.63

I forced a commanded 10.75 - 10.61 AFR for the testing to see how much was left in the injectors.
At the lower RPM there is quite a bit left to easily drop down in the 9:1 AFR range or a little lower. In fact 90% of my test run averages about 10.97 AFR and only leaning out in very small areas where the RPM is the highest.
It's much more dependant on RPM than anything, which is why this C5 was able to digest a 200hp shot of N2O without a problem and put up 11.0 @127 MPH with stock fuel system/injectors and still have room left.

Conclusion: A highway geared A4 car that keeps the RPM down can get away with murder with stock injectors. 500 - 550hp is a piece of cake as long as you don't need to spin high RPM to make it... and the bottle don't need to do that.

If you have a M6 car that makes its power higher in the RPM range, then you're going to be sorry for not upgrading injectors before you put the bottle to it.

I said I would do the experiment and I did it. It all makes sense now, and there isn't any real trickery or mystery involved at all... happy ending.

john3daly

iTrader: (4)

I made 500.3 rwhp with a bone stock fuel system and the mods below. AFR was 12.5-13.0. Shut down the dyno at 5900rpms.

GuitsBoy

iTrader: (4)

Thats more believeable because the rpms were kept low. The same guy making 500 RWHP but turning 7400 with a t-rex, not so believeable.