1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
-1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
-2002 Cavalier, Tuned with HP Tuners
-1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)
Last edited by 96lt4c4; 07-06-2012 at 03:25 PM.
-1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
-2002 Cavalier, Tuned with HP Tuners
-1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)
I do have another question though, why is it the stock tune shows the injectors as 60 PPH and they are known as 55 PPH? I always called them 60's because thats what the stock tune shows.
I just recalculated using one of the other sheets and it shows I need to run the 60's at 25 psi.
Last edited by 96lt4c4; 07-06-2012 at 03:35 PM.
-1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
-2002 Cavalier, Tuned with HP Tuners
-1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)
Once an internet rumor is started it can never be taken back!
Your 55PPH and 60 PPH are 61PPH...
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
I was waiting for that!I just recalculated using one of the other sheets and it shows I need to run the 60's at 25 psi.
This also brings on many more tuning issues as the pressure is way outside of what the injector was designed for, can be done but way to much work.
But your 80PPH injectors, at 85% Duty Cycle and .5 BSFC and 17 PSI (more realistic) will support 311 HP, now the key to get a good tune with this spreadsheet is the BPW is 102. Or at 16 PSI = 302 HP and BPW 105.5. I er to a little bigger, easy to take away fuel in tune, hard to add if it was never there... VE numbers can come down but can only go to 100 and should really never pass 95, but having WOT only need 85 is sweet....
This is really KEY to tuning a modified engine with old 160 Baud ECM.
Now you probably have a newer 16197427 and it can be fudged a little after this calculation by changing injector size, smaller = more fuel and larger = less fuel, but you still need enough fuel to feed the beast at WOT or all your idle and drive ability tuning has been a waste of time. This fudging will only work so far and you'll be able to tune in low end or high end, usually you end up short at high end and injector duty cycle goes 100% or static... so only fudge a little after calibration.
I like to calibrate a tune correctly to start. If it does not have enough fuel to support WOT High RPM, then why start?
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
Yes, its a 94 Truck so it has the 7427 in it. I have done what you are talking about, fudging the the injector constant while datalogging, and emulating. I watch the BLMs and fudge the consant to get it close in real time. Seems to work OK most of the time. So it looks like I may be keeping the 80;s in there and just doing some more tuning.
-1999 Hugger Orange SS, LS2 402 T56, 9 inch Ford 3.90 gears, Tuned with HP Tuners
-2002 Cavalier, Tuned with HP Tuners
-1994 Full Size Blazer ,383 TBI 4L60E, 4.10's, Tuned with Tunerpro RT (Where it all began)
If you get the injector size correct then no BPW in that PCM... so it's a matter of building a smooth VE table to work with. Like 85 at WOT stuff down to little lower then stock at idle area with cam.
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
You need to be careful with the 255lph walbro pump. I have been running a walbro high volume AND high pressure pump ( there are 2 255lph pumps available, a standard pressure and a high pressure) on my '89 Firebird Formula for ~3 years now and have had to deal with excessive fuel pressure ever since. The car was originally running the stock 5.0l L03 TBI and 1228746 ECM, but is now running an L31 5.7 and 16197427 PCM. All the while, I have been running the stock 305 injectors and an O.E. style billet aluminum adjustable FPR with an added vacuum reference port. With the original regulator modified to be adjustable and the spring tension backed off as far as possible, the fuel pressure was still running in the mid-20's due to the flow of the pump exceeding the demands of the injectors and the capacity of the return passages in the throttle body. I then installed the billet FPR and set a base pressure of 30psi and when referenced to intake vacuum it would drop to ~21psi at idle. Even with the 350, the fuel demands aren't enough to allow for a lower fuel pressure. I know that your engine will definitely have a higher fuel demand, but it probably won't be significant at idle. I don't have any known tuning issues with that fuel pressure, but it can cause problems and most guys on here don't recommend more than 21psi on TBI injectors.
Now, you do have options that would allow for use of this pump with your current configuration and also have lots of room for any future upgrades. You can always use a block off plate in place of the stock regulator and use an external regulator that will allow for the use of just about any injection & fuel pump combo. I would have done this myself a long time ago, but there's always something more important I need to buy. I'm a little surprised that you haven't had any issues with a vortec application fuel pump, but I don't know the flow rating of them either. Anyhow, I just wanted to give you a heads up before you install the walbro. There's nothing wrong with them, they just put out a little more than a typical TBI system can handle without some accompanying mods/hardware.
So instead of starting a new thread I'm digging this one up because this is an issue I'm faced with at the moment. I have two sets of injectors (61&80pph) and need to decide which to use. Either set I'll need to run at higher than stock pressure and I will be sending the injectors off to be cleaned and flow rated as well as having witch hunter measure latency.
My engine setup should hopefully be close to 400 hp and assuming 0.45 BSFC and at 85% DC I'd need to run the 61pph and 80pph injectors at 35 psi and 21 psi respectively to give the engine the required fuel. So larger injectors/lower pressure or smaller injectors/higher pressure? What are the pros and cons of each?
I'm running a vortec EP281 pump so higher fuel pressure is not an issue with respect to fuel supply.
Whatcha guys think?
95 ecsb vortec 357 10.44:1 scr LT4 hot cam single plane TBI 7427 $0D
Bigger injectors at lower pressure! Pro is they work fine at that pressure, Con at higher pressure is they open slow and casue issues, no need for latency on TBI injectors, just a service.
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
The only drawback that I can think of with running so much fuel through only two injectors is the pulsewidth at idle, it may be difficult for the PCM to get it to idle as lean as it should. I have found that the smallest pulsewidth I can run is around 0.488msec, which barely gets it down to stoich at a warm idle.
1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
1981 Camaro Z-28 Clone, T-Tops, 350/TH350
1981 Camaro Berlinetta, V-6, 3spd
1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s
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