Tuning a 93 3.4 Firebird

[tkoforpresident]

that's what i'm talking about. when you got WOT or when the engine is stopped but the pump still supplies pressure/flow, it goes to full pressure but at idle and other areas of high vacuum(like at 4K RPM with no throttle for some engine brakeing), it will lower the pressure.

obviously it does, so

as long as you don't run into any issues, keep going higher until you feel there is no benefit.

but if you get to a point that it wants to idle strange due to the injector being commanded on for such a short peiod of time that it doesn't give the required fuel mass due to the injector not opening and closing intantaneously, then you'll need to drop some pressure, but that situation usually happends with injectors that are WAY too large for the application, so i don't think you'll have to worry about it with those 19lb/hr pieces.

well like i said, it never seemed to affect driveability (running at max psi) so i guess i'll shoot for low 50's then or something along those lines. I definitely want to run higher psi than stock (43-47 psi, i mean who really wants to do anything stock? )

but i don't want to compromise anything. Once i hammer out the #'s again maybe you can double check it and then i'll load it onto the .bin and use it in my first chip burn. I WILL however have to remember to actually set my fuel pressure with the holley fpr and autometer gauge, otherwise I will run into fueling issues. I didn't know until now just how important fuel pressure is in messing up/affecting the BPC. My car must have run UBER rich when i was at 60 psi before, even with stock injectors.

Thanks for the input Robert. I'll be back on tomorrow, i'm going to bed.

[robertisaar]

that's what i'm talking about. when you got WOT or when the engine is stopped but the pump still supplies pressure/flow, it goes to full pressure but at idle and other areas of high vacuum(like at 4K RPM with no throttle for some engine brakeing), it will lower the pressure.

obviously it does, so

as long as you don't run into any issues, keep going higher until you feel there is no benefit.

but if you get to a point that it wants to idle strange due to the injector being commanded on for such a short peiod of time that it doesn't give the required fuel mass due to the injector not opening and closing intantaneously, then you'll need to drop some pressure, but that situation usually happends with injectors that are WAY too large for the application, so i don't think you'll have to worry about it with those 19lb/hr pieces.

[tkoforpresident]

now you got your numbers right.

what pressure: IDK, what's the highest you can run and still be able to get a decent idle? it's going to have to be something you'll determine on your own, but if you can hit 60 psi without either locking them, blowing fuses out, or other issues, i don't see why not...

that holley does drop the pressure at low MAP, right? if so, do you know by how much?

Umm, i don't know what you mean by low MAP (sorry.. noob)

but i do know that when you set fuel pressure (say to 47) and then start the car and let it idle, the psi will drop down to about 42 on the gauge.

For the record, I've run 60 psi before without issues, though i didn't notice MUCH of a performance gain (seat of the pants) by going up from 47 to 60. I've dialed it up to 60 while idling and the engine will change its noise/sound a little bit but never runs any worse.

[robertisaar]

now you got your numbers right.

what pressure: IDK, what's the highest you can run and still be able to get a decent idle? it's going to have to be something you'll determine on your own, but if you can hit 60 psi without either locking them, blowing fuses out, or other issues, i don't see why not...

that holley does drop the pressure at low MAP, right? if so, do you know by how much?

[tkoforpresident]

slight flaw there: a 3.5% increase in psi, is not a 3.5% increase in flow...

use the witchhunter calc to see what it would equate to and try again.

and in most cases, more pressure will give a better spray pattern, which helps with power, economy and emissions. as long as you don't get to a high enough pressure to hydraulically lock the injectors closed due to too much pressure and the coil not being powerful enough to open it correctly. you could also run into injector fuse popping issues at that point.

lol my bad....


So what the 3.5% increase in psi does is essentially change the injector size to:

19.7495 Lb/HR

which added into isaac's equation (as i have decided to call it)

= 202 BPC with 19lb injectors at 47psi !! (way off from 193)

Now that i have the equation right.... I can decide which psi to run...

what's your opinion Robert? I can run anywhere from 43.5 psi all the way up to 60 with the holley afpr. I'm thinking somewhere around 50 should do.

[robertisaar]

slight flaw there: a 3.5% increase in psi, is not a 3.5% increase in flow...

use the witchhunter calc to see what it would equate to and try again.

and in most cases, more pressure will give a better spray pattern, which helps with power, economy and emissions. as long as you don't get to a high enough pressure to hydraulically lock the injectors closed due to too much pressure and the coil not being powerful enough to open it correctly. you could also run into injector fuse popping issues at that point.

[tkoforpresident]

as a little test: what % change do you expect to make for using 19lb/hr injectors at 47psi?

well let's see. the difference from 43.5 to 47 is 3.5 or .080459770... % change.

therfore my BPC of 210 would decrease by .080459770% or 16.896...

essentially turning my BPC with 19lb injectors @ 47psi into (210-16.896)

~ 193.0


using this method (assuming it's correct and logical) i can change my BPC any time i decide to change my fuel pressure, right?

I've also heard from certain circles that the higher the psi, the better the injector spray and the finer the mist, making for more power potential (maybe someone can confirm this)

but what i don't know is whether or not running stock psi (43.5) or a higher psi (43.5 - 60 psi) would be helpful in any way.

thoughts?

[tkoforpresident]

will do, thanks!

[robertisaar]

considering the specific issue, yeah, not a bad plan.

[tkoforpresident]

depends why it stalls... what is the "Minimum IAC Position" saying when its parked/put in drive/whenever? if it's too low, that would be a major issue, since the motor is not getting the air it needs.

for comparison, my wife's dead stock 90 GP 3.1 likes around 27 Steps to idle perfectly.

luckily we can change the initial value that the ECU starts at, so instead of doing idle relearns, we just set the value and forget about it until there is a change to the motor drastic enough to warrant changing it.

if it's a fuel issue, that's just as easily fixed. wha do the BLM and INT look like when you throw it in drive?

spark: if those two, don't fix it, time to play with it.

ok... so datalog first

[tkoforpresident]

The tune I sent you is a stock 3.4 OBD1.5 that was converted to OBD1. Magnaflow cat back was all

see what i mean? not really geared towards my vehicle at all.

especially since i have a flowmaster =p

[ForcedFirebird]

The tune I sent you is a stock 3.4 OBD1.5 that was converted to OBD1. Magnaflow cat back was all

[robertisaar]

depends why it stalls... what is the "Minimum IAC Position" saying when its parked/put in drive/whenever? if it's too low, that would be a major issue, since the motor is not getting the air it needs.

for comparison, my wife's dead stock 90 GP 3.1 likes around 27 Steps to idle perfectly.

luckily we can change the initial value that the ECU starts at, so instead of doing idle relearns, we just set the value and forget about it until there is a change to the motor drastic enough to warrant changing it.

if it's a fuel issue, that's just as easily fixed. wha do the BLM and INT look like when you throw it in drive?

spark: if those two, don't fix it, time to play with it.

[tkoforpresident]

educated guess meaning, i can still hear that cam loping

it's probably going to be a bit rich in the low RPM ranges due to the loss of VE there because of the cam, but the upper RPMs should be somewhat close.

always better to be rich than lean...

and we all develop our own methods of what we think should be done first, how much, and why.

honestly, john sent you one that SHOULD be good to go, if you feel the need to modify it later, do so then. for now, get it running and get a feel for it.

but

i like to smooth out the spark tables before i start anything, since some of the GM ones look very odd, depending on the application.

you say the tune John sent me is "good to go" but i mean my car STALLS OUT when i put it in drive lol. I'm not sure his tune is setup for that

Can you help me "smooth out" my spark table?

[robertisaar]

educated guess meaning, i can still hear that cam loping

it's probably going to be a bit rich in the low RPM ranges due to the loss of VE there because of the cam, but the upper RPMs should be somewhat close.

always better to be rich than lean...

and we all develop our own methods of what we think should be done first, how much, and why.

honestly, john sent you one that SHOULD be good to go, if you feel the need to modify it later, do so then. for now, get it running and get a feel for it.

but

i like to smooth out the spark tables before i start anything, since some of the GM ones look very odd, depending on the application.