MSCLCAR

Those dyno graphs are very interesting. So all that was changed was the injectors? Damn, that's a BIG difference! And the wiggly lines are due to the natural lean condition of an LS1? I gotta get me some bigger injectors & retune....BTW - my Predator dealer says he can write me a custome tune to compensate for them.

Team ZR-1

When the engine is too lean and there is knock timing then of course is being taken out and back in and shows up in the dyno graph ( if smoothing was not done by dyno operator)

Again though with PCM tuning most of the time a bit larger injector is not flowing any more fuel then as stock ones, meaning its not that more fuel is being consumed all the time, only when engine demand requires it so I try not to say larger injectors but injectors that have more ability to flow when required.

I use the C5R 42 lb injector and the engine idles just as well then with stock ones.
I used the SVO 30s for 1 1/2 years and was just fine except when racing the duty cycle would hit high 90s and induced knock, 42 lbs cured that but also allows well mannered engine at part throttle and idle conditions.

Rob98Z

Okay I have a friend who has a 02 Firehawk that we just did heads/cam. We dyno'd it this week and he's putting out right at 400rwhp. Now his car is running rich according to Autotap both on the street and on the dyno at WOT. Looking at your formula above, he needs at least 36lb injectors. By installing 36lbs injectors won't that make it run even richer or am I missing something here?
Thanks

MyLS1Hauls

iTrader: (2)

No, if you tune the PCM for larger injectors, it will not run any richer. I think thats one of the things Team-ZR1 is trying to get across. More fuel is only consumed when the engine needs it. A lot of the time, the motor doesnt necessarily receive any more fuel, it just receives it in a shorter amount of injector on time. Instead of the injector taking say 10ms to shoot in fuel, a bigger one would do it in say 8ms. There are only so many milliseconds when the intake valve is open at 6k+ rpm when the motor can even receive fuel. If the intake valve is only open for say 10 ms, and the injector needs 12ms to get all of the required fuel in, the A/F charge is lean.

Also, I wanted to thank John for explaining all of this as I've learned several things. John, have you noticed a difference in hp/tq by changing the injector offset with varying cams? or is the change not big enough? Since performance cams open the intake valves early, you could essentially start spraying fuel early right?

Team ZR-1

Brad,
my thoughts are if the injector is a Multech =II designed then the internal coil responds the same if its a bosch 26 or 42 lbs.

I have not seen any difference in leaving the stock offset values just where they are and have not seen any changes in different flashes that I have checked that were tuned by a supercharger vendor.
My concern is people making changes to offset that would change the correct timing as to when ign coil, injector coil and position of piston.

It is also interesting that the offset table via LS1edit for all this time was confusing as to MAP KPA or vaccum KPA and thus only the 1.29B version that table is now flipped by 180 degrees and thus how many people were makes changes to the wrong area they thought they were adjusting so for me the offset table should be left stock unless the injector being used is not a high impedance type for one of the changes to Multec II was fast response time from coil when it is commanded by PCM.

Rob98Z

Thanks that helps a lot - just what I needed to know and was kind of thinking it was something to do with how fast the injector can react.

CAT3

iTrader: (9)

Damn, my head hurts.
If I remember correctly John stated that when you push an injectors DC it will heat the fuel up and thus bring on Knock, that if the righ tinjector size was used would not be there? I am glad for people on sharing their experience.

MyLS1Hauls

iTrader: (2)

I have some Bosch C5R injectors,and according to Bosch, the offset needs to be adjusted slightly. I have the table straight from them and was suprised that they were different. Any thoughts on that? I am looking to put them in my buddy's car w/ S2 heads and a big cam.

99 Black Bird T/A

iTrader: (4)

John,

Thank you for the graph...very nice gain!

...but...

I'm a little confused...as I read this the car increased it's rwhp with the larger injectors...but the A/F has been leaned out more according to the graph. Why use a bigger injector and lean it out?

Or is the point the car can actually run leaner and make more power with less fuel?...provided the shot of fuel is delivered exactly when needed in the correct amount...which could actually mean less fuel if it's at the right time in the cycle.

Sorry for being obtuse...this area is new to me...thanks.

Team ZR-1

The use of the larger injector allows a nice wider tuning window to really clean up all trim cells so its averages are all around zero and thus no need to do radical tuning to be sure PE/WOT is too rich or lean and not having to lower timing to cure knock issues.
Leaner is better for HP, if there is no knock effecting timing and timing scale can be pretty flat instead of adding and removing timing within the RPM range.

Keep in mind on a dyno, the MAP KPA is high, only about 5 trim cells are used, and of about the 30 second dyno pull only about 10 seconds of that is in true WOT, so with the larger injector it allows you to solve the trim averages of all the other cells that were too lean, causing ill effects by the time you got to PE and WOT for those cells are controled by what 02 is reporting where PE is controled by the AFR value in the PE table for the RPM the engine is at.

The difference can be most people just use 1 value to scale across the whole RPM range of injector flow where I tune each trim cell to balance it so they are all about even in their trim average.

John,

Thank you for the graph...very nice gain!

...but...

I'm a little confused...as I read this the car increased it's rwhp with the larger injectors...but the A/F has been leaned out more according to the graph. Why use a bigger injector and lean it out?

Or is the point the car can actually run leaner and make more power with less fuel?...provided the shot of fuel is delivered exactly when needed in the correct amount...which could actually mean less fuel if it's at the right time in the cycle.

Sorry for being obtuse...this area is new to me...thanks.

NoGo

iTrader: (2)

Call me crazy, but it looks like the a/f ratio of the 2nd pull is about .5 a/f higher, from a 12:1 a/f to a 12.5:1 a/f. This much of a shift towards the optimal a/f is about a 5-10 HP gain.

I am going to rule against the injectors being out of shape and blame it on the car being too rich prior to the injector swap (which could be conscrewed as the stock injectors being plenty big enough to handle the task).

Not trying to stir the pot, but I simply disagree with this big push (as of late) for everybody to start swapping to bigger injectors for lightly modded cars. (yes, I know about IPW / 80% / DC / IO)

343 HP is *very* lightly modified.

JMO

JNorris

iTrader: (4)

John,

Did all the LS1s come with a Multech =II injectors? I was under the impression that the 97-98s were a Multech =I.



Thanks

John

99 Black Bird T/A

iTrader: (4)

NoGo, I think you and I are sort of asking the same question.

Team ZR-1

I think it was around 98 when the change from Multech I to II.

Multech I was designed to allow the fuel to pass through the internal cool to keep coil cooler but due to makeup of smog gas the fuel was eating the coating on coils windings and leaving deposits so Multech II the coil was moved out of the fuel flow.
Also the coil reacts much quicker when commanded on then Multech I does.

Team ZR-1

Changing injector size is not some new fad, it is no different then 30 years ago when I would replace the jets in my Holly carb.
I have used a bit larger injector in my own C5 for years now and have installed them in at least 200 others and not one has failed smog testing inlcuding here in Ca so they are not causing the powertrain to run richer.

As to the dyno AFR, that is useless to look at those and get any better results for IMHO using a wideband in a muffler tip is a joke,
thus you cannot look at those two graphs and know for sure exactly what the AFR was from one to the other, they were done a week apart and a simple change of wideband one time in right muffler and next time in left would give a different results.

As to the wavy lines, its clear that the one with smooth line, had better performance yet it has larger injector so if 1st dyno results with stock injectors were wavy then the 2nd dyno results should be worse.

The point totally missed, again if you install a bit larger injector in it now allows a much wider tuning window and end results is better performance, better fuel mileage, less load on injectors and PCM output drivers and is clearly considered by GM since the C5R uses a 42 lb injector.

People need to understand the 3 mSec average pulse width and instead of yanking the **** out of timing to solve knock, to tune in larger injector gets overall better tune and performance.

MSCLCAR

Hey John,

I installed 30lb injectors yesterday & went right out to the track (50+ miles away). The good news is the popping in 2nd gear was gone, the bad news is I was running 2/10's slower than last week, and no matter where I set the timing or fuel, all the way up or down, it didn't change. I made it change about 3/10's last week with minor tweaks.

So, do you think I needed to give the PCM more time to adjust (& should I have disconnected the battery) or do I need to get a wider (leaner) fuel adj window from the Predator folks? I have not monitored real time data, so I have no idea what my a/f is (via the O2s...915mV = 12.8 on my wideband dyno run)

Mark

NoGo

iTrader: (2)

Sorry John. I still disagree. Neither of your arguments are persuasive that larger injectors are needed for a 340 HP car. You still have a dyno graph above that shows the 2nd pull leaner than the first.

As for the wavy line argument.......come on.

Additionally, there was obviously some tuning between dyno 1 and dyno 2, because without tuning the car would have been noticeably richer had the injector table stayed the same with the new large injectors......

We don't need to 'yank the **** out of timing' when we use smaller injectors. If a timing table is done right, you don't need a rich condition to hide imperfections in the timing table.

The C5R motor uses 42 lb injectors because IT MAKES 600 HP AT THE FLYWHEEL!!!!!!!! not because you and GM are on the same page.

MSCLCAR

I just took some real time data after the inj swap. I have my fuel set to max lean, and the timing bumped just a tad. (derived from where the car ran best at the track last night) The numbers are certainly different now. There is good news, and bad.

First the good news. My car now has 31.9 deg of timing at 5800rpm in 2nd gear (@ 3rd gear shift. It was running 27 degrees (note I added 1 degree via the Predator from where it was set). And it's dead nuts solid, no falling off as the rpms climb (like it used to). Absolutely 0 KR. No blips, no 3.9 readings, nothing like it used to.

Now the bad news. It is pretty rich. The LTFT's are running -11.7 & -12.2 @ 70mph in 4th gear (2000rpm) and -12.7 & -14.1 @ 70mph in 3rd gear (3000rpm). The O2's are in the hi 600 to low 700mV range at that point. When I go to WOT my O2s read 935, which according to my dyno run should = ~ 12.6.

So, will the PCM adjust for this much richness? Or do I need new fuel tables for my Predator? Or should I ask JR Granatelli to re-tune my MAF (again)? I think this setup will make the car faster, certainly safer for the motor, but how is the best way to tune it?

Mark

CAT3

iTrader: (9)

Mark, MSCLCAR, get with your vendor and have them scale the injectors for you. If not, your never going to get it right.

98z28hispanic

hey man from the School of Automotive Machinest they said that you can run stock injectors till 10 secs and im gonna lisen to them cuz they got some fast n/a ls1's.