750cc Injectors Maxing out-18psi

[GSXlaunch]

I just installed an SCM-61 turbo, along with 750cc injectors and a GM Maft. Last night I let it build boost and noticed that my injectors were already reaching their limit. This is a quick log thru 3rg gear...boost very breifly touched on 20lbs but 90% of this run boost was at about 15-17lbs and throttle position never reached 80%. It did sputter a little at about the 6500rpm mark. Possibly rich sputter? How can these injectors be running out of fuel already? I am running a stock ecu and am using both the maft ver. 2.01 and safc (old 5 knob type) to tune.

RPM-Knock-Timing-O2 Trim-Airflow Hz-Inj. Duty Cyc.-Throttle Pos.
4468-0-30-.80-623-25%-60%
5062-0-27-.84-1026-47%-66%
5500-0-25-.84-1442-68%-79%
6187-0-21-.80-1606-93%-77%
6312-0-20-.80-1606-95%-66%
6562-0-18-.80-1606-51%-10%

How can I be at a little further then half throttle and be maxing out 750cc injectors? I should mention these injectors were purchased used and had "H-75" stamped on them which I was told meant 75lb/hr. If you do the math, then these are actually closer to 788cc injectors!! These were used on an EVO that ran 30psi of boost with a frank turbo at 103% duty cycle. My afc settings are as follows:

800rpm: -12%
2400rpm: -10%
4000rpm: -8%
5600rpm: -6%
7200rpm: -6%

I've got the maft set up to read 450cc injectors as the car idled much better with this setting.

If I am running overly rich will this cause the injectors to reach their limits much quicker? Any and all suggestions/help is appreciated.

 

[karbon]

As long as you're not knocking you always have a little margin where you can lean it out bit by bit. Your knocksums are non-existent, so lean it out a little, log for knock, and watch your IDC go down. Also I think I remember someone else tlaking about very high IDC and someone suggested that they logged IPW instead and calculate the IDC theirselves at various points and compare them to make sure it's correct.

 

[GSXlaunch]

Wow! thanks for replying so fast. Basically I should log for knock and timing...? I will try it. The other thing is that the car did not pull very hard at all. It pulled okay, but my old set up (EVOIII and 650cc's, 2G Mass) seemed to pull much harder...again I was only at 79% throttle so i guess that had something to do with it. I guess running rich robs the car of a lot of power. I was really expecting to blown away at 20psi with this turbo.

 

[karbon]

Well, just log for knock. Timing is variable on basis of how much knock you have. Your timing will start going down above 5 counts of knock, so as long as it's 0 - 5, your timing will not be pulled. 20 psi should feel pretty damn strong on that turbo. Keep leaning it out. Watch your EGTs, and watch the knock count. 1 to 3 counts of knock on some RPM bands won't hurt you any, but tuning for 0 knock is always best. It should be running strong in no time.

 

[doug]

1 to 3 counts of knock on some RPM bands won't hurt you any, but tuning for 0 knock is always best.

Agreed. Even a few counts of knock will cause your timing to dip a little (each count of knock retards timing 0.35 degrees), but it's nothing to worry about that much.

 

[GSXlaunch]

Its all in the tuning...which I come to find is much more difficult with both a maft and safc. I will try leaning it out to -12% from 4k+. I guess for being partial throttle it pulled okay...it was a very quick run. If I had really put my foot into it I think boost would have jumped to 27-30psi!! I'll have to regulate that. So will running rich cause the car to feel like it has no power>? Thanks again fellas.

 

[desolateboosted]

I have the same turbo but I'm on 880s. I'm running 20psi on pump right now and my dutycycle is at around 92-93%.

 

[Car Cannibal]

Whats your fuel pressure?

Running 750's and the mafts on 450 seems odd. That would mean you are running more pulsewidth at idle and should be running really fat.

I would set the maft base knob for 750's, run 45 psi line off and then tune with afc to get it in check. The higher base fuel pressure will help out on the high end if you are running out of injector and you can pull more pulse width out down low with the afc.

The scanmaster is really helpful with getting the low/mid/high trims in check.

 

[GSXlaunch]

Finally did a wot in 1st-3rd gears. I can say the turbo did pull much harder but that is likely due to the high boost level. I tried to shift right at 7k but can definitely say it needs more rpm to get the full benefit. One main difference I can feel between this turbo and the evo3 is that the scm does not drop off at 6500rpm...it seems around this rpm it is just getting into its "hard pull" stange (for lack of better wording). Anyhow here is the log...much better, but I still have a long way to go. Still not getting any knock whatsoever so I'll leave that part out.

Second Gear:
RPM-Timing-O2v-Air Flow-Injec DC %-Throttle %
5062-26-.84-1058-50%-100%
5375-25-.84-1247-59%-100%
5593-24-.82-1455-71%-100%
5843-23-.82-1606-81%-100%
6062-21-.80-1606-90%-100%
6375-20-.80-1606-92%-100%
6718-18-.80-1606-93%-100%
7000-17-.80-1606-31%-10%

Third Gear:
4937-25-.84-1052-49%-78%
5406-21-.82-1549-75%-100%
5562-21-.82-1606-82%-100%
5906-22-.80-1606-94%-100%
6125-21-.80-1606-92%-100%
6250-21-.80-1606-40%-10% <----- Had to let off. Too much traffic

My afc settings are:
800 -14%
2400 -14%
4000 -10%
5600 -10%
7200 -8%

I saw it touch on 25psi but had to keep an eye on revs so it may have gone higher. Seat of the pants feel was good. It did feel stronger than my evo3 for a brief moment. Not too bad considering the tune. I am sure it can hit 30psi with the current set up but I doubt It'd be effecient. I can still take fuel out; add the afpr and try it again. Now, there is absolutely no doubt that I need cams. FP2's are next on the list!!!!!

I do have a question...how can I be at 25psi on this insane turbo and a) I have zero knock with pump gas and b) it still hardly pulls much harder than my evo3?

 

[doug]

How could you have no knock but have your timing keep falling off as RPMs increase? Is that normal?

 

[DSM90AWD]

How could you have no knock but have your timing keep falling off as RPMs increase? Is that normal?

The ECU has a timing MAP that lowers timing as airflow increases.

Note that by subtracting airflow via the S-AFC you indirectly increase the timing values as the ECU "sees" less airflow.

 

[GSXlaunch]

Not sure...it isnt falling off nearly as fast as when I do see knock. Technically, I had "1" count of knock at about 5300rpm but I dont even think I was at full boost yet. I think I am gonna have to run close to 30psi to get the full benefit of this turbo and my set up. I want the cams so I feel more comfortable shifting at 7500-7600rpm.

 

[DSM90AWD]

Big turbos are for making power in the Higher RPMs.

FYI.. I also just put a new turbo (50-Trim) on my '90.. and looking at the HP/Trk figures against my old 16G the only gains were > 6K RPMs.. with peak power comming at ~6800 (+43HP with same tuning)

 

[doug]

The ECU has a timing MAP that lowers timing as airflow increases.

Is this true only for '90s? I'd heard that the '90 ECU had less aggressive timing maps. My timing doesn't drop like that, but increases slightly as RPMs go up as long as I have no knock, of course.

 

[DSM90AWD]

Is this true only for '90s? I'd heard that the '90 ECU had less aggressive timing maps. My timing doesn't drop like that, but increases slightly as RPMs go up as long as I have no knock, of course.

I'm using a '91 ECU w/ Stg3 EPROM (91-94 maps/trims).

Just for reference check out Kyle Tarry's Timing Graph . You are likely on the lowest line on the top graph (2.06g/rev airflow).

Note how the timing decreases after 6K which is independant of the ECU's reaction to Knock > 6counts.

 

[doug]

Good info-- thanks. And sorry for dragging the thread off-topic a bit.

 

[GSXlaunch]

I agree, good info...does that graph mean I need an upgraded ecu?

 

[DSM90AWD]

I agree, good info...does that graph mean I need an upgraded ecu?

Maybe. As Kyle explains the stock maps in the ECU are capped at an airflow that you'd be able to reach with a 16G (the bottom line of the top graph). That being the case the EPROM-burners (JeffO..etc) have the option of the extended maps at the cost of resolution (the bottom graph).

Another great benefit of the EPROM mod is that big injectors can be compensated for at the ECU level.. not tricking it via (-) correction on a piggyback (S-AFC).

By coding it at the ECU the airflow it sees is true airflow so the timing maps it uses in response are the ones optimized for the airflow.

Sorry if I lured you off topic.. was searching for Injector Duty cycle and came across this thead. BTW.. mine is now 123% at 6500 RPM with my 50-trim and 550s

 

[GSXlaunch]

Sorry if I lured you off topic.. was searching for Injector Duty cycle and came across this thead. BTW.. mine is now 123% at 6500 RPM with my 50-trim and 550s

Good info...I guess I'll have to look into getting an eprom ecu. How can I tell if my ecu is socketed?? BTW, are you looking to upgrade your injectors any time soon?

 

[DSM90AWD]

Check out DSMChips FAQ for more info on EPROMs.

Yes.. I'm now looking at 650 FICs.

These "inexpensive" turbos sure do cost alot when you add up all the supporting mods