F.I. Timing map

[SSpdDmon]

So, I made this as a starter high octane timing map for a stock internals '99 running ~7psi through a D1SC. Thought I'd share. Any feedback is welcome. :)

[Redline Motorsports]

Looks a bit aggressive for a 10 psig motor on pump gas. You can run a decent amount of timing down low at WOT as enough boost hasn't built yet but it needs to taper a bit as you head towards peak hp.

I think timing should be closer to 20-21 max at peak.

Howard

[SSpdDmon]

7psi on 93 - stock internals. Aggressive as in too much or too little timing?

[Redline Motorsports]

7psi on 93 - stock internals. Aggressive as in too much or too little timing?

I think its a bit too much timing. Since a centrifigal supercharger builds boost linear to rpm, you don't have as much boost in the lower rpms. Because of this you can be more aggressive at lower loads but need to ramp back the timing as boost increases.

When we do PC Z06's, they don't really make any measurable boost until about 4K. I use a NA timing (our timing table :)) until we hit 4K and then start toning it back. We only use about 14 degrees on 5 psig on these motors but run as much as 28 down low.

Howard

[SSpdDmon]

Hmmm...I really need to get on a dyno.

[Redline Motorsports]

Hmmm...I really need to get on a dyno.

Send me a e-mail and I can send you a file of a timing table we have used on many PC cars. Of course every car is a bit different but you can get the general idea.

[SSpdDmon]

PM'd email...

Next issue = fuel pressure drops to ~50psi under WOT and a low of ~48psi at 6Krpm. Fudging the fuel tables, I can keep the afr at 11.8~12.0 until about 5800rpm. Then, it'll hit mid 12's. The paperwork from the previous owner indicates a Walbro 355 pump & hotwire kit was installed (I believe it's the Racetronix plug & play system). My lights flicker under any throttle and occasionally at idle. Thoughts? I can't seem to find this electrical gremlin. :confused:

[Redline Motorsports]

PM'd email...

Next issue = fuel pressure drops to ~50psi under WOT and a low of ~48psi at 6Krpm. Fudging the fuel tables, I can keep the afr at 11.8~12.0 until about 5800rpm. Then, it'll hit mid 12's. The paperwork from the previous owner indicates a Walbro 355 pump & hotwire kit was installed (I believe it's the Racetronix plug & play system). My lights flicker under any throttle and occasionally at idle. Thoughts? I can't seem to find this electrical gremlin. :confused:

Varying fuel pressure definately needs to be addressed! A stock engine on 7 psig shouldn't be running out of fuel with that pump unless the pump is bad or the hot wire kit isn't working. Maybe the alternater is on the way out.

[SSpdDmon]

Varying fuel pressure definately needs to be addressed! A stock engine on 7 psig shouldn't be running out of fuel with that pump unless the pump is bad or the hot wire kit isn't working. Maybe the alternater is on the way out.
Logged GM.VOLTS and it bounces around between 13.6 and 14.2 volts. I'm wondering if the hotwire kit isn't working right.?.?.?

[SSpdDmon]

Hmmm...someone just made an interesting point. If you boost your intake say 7psi, doesn't that mean you're effectively reducing your fuel pressure by that much because the fuel now fights that pressure....thinking along the same lines of why the IFR table is slanted, where additional vacuum actually improves the flow of the injectors???? Maybe my pressure drop is normal for a stock fuel system with an upgraded pump and injectors only???

[joecar]

Jeff,

MAP (boost) is applied to the bottom of each injector;
rail pressure is applied to the top;

the injector's flow rate is propotional to the squareroot of the pressure difference ("delta") across the injector (rail pressure minus MAP)...

On a returnless fuel system (like your F-body), MAP has no influence on rail pressure...
delta varies inversely with MAP, so the IFR table has to be sloped... but because the IFR table starts at 0 kPa MANVAC it fails to specify the IFR for boost (negative MANVAC)... (I beleive the PCM just uses the value at 0 kPa MANVAC, and I don't know if it extrapolates using the same slope).

On a return system (like various trucks and early Y-body LS1), MAP increases rail pressure propotionally as MAP increases... the FPR adds MAP to the rail pressure which keeps delta constant... these FPR's have a MAP reference hose connecting the FPR to the intake manifold... (this type of system is ideal for boost).

In either case, rail pressure should/does not drop as MAP increases...

any pressure drop greater than 5% is pointing to some problem (pump voltage/ground, pump motor, filter, obstruction, leaky regulator, insufficient pump capacity...).

Cheers,
Joe

:book:

[SSpdDmon]

Jeff,

MAP (boost) is applied to the bottom of each injector;
rail pressure is applied to the top;

the injector's flow rate is propotional to the squareroot of the pressure difference ("delta") across the injector (rail pressure minus MAP)...

On a returnless fuel system (like your F-body), MAP has no influence on rail pressure...
delta varies inversely with MAP, so the IFR table has to be sloped... but because the IFR table starts at 0 kPa MANVAC it fails to specify the IFR for boost (negative MANVAC)... (I beleive the PCM just uses the value at 0 kPa MANVAC, and I don't know if it extrapolates using the same slope).

On a return system (like various trucks and early Y-body LS1), MAP increases rail pressure propotionally as MAP increases... the FPR adds MAP to the rail pressure which keeps delta constant... these FPR's have a MAP reference hose connecting the FPR to the intake manifold... (this type of system is ideal for boost).

In either case, rail pressure should/does not drop as MAP increases...

any pressure drop greater than 5% is pointing to some problem (pump voltage/ground, pump motor, filter, obstruction, leaky regulator, insufficient pump capacity...).

Cheers,
Joe

:book:
:frown: But I don't wanna replace the fuel pump...

[joecar]

Change the filter, check voltage drops on pump power/ground circuits.

[SSpdDmon]

Change the filter, check voltage drops on pump power/ground circuits.
Suggestions for doing this while under boost (only time pressure drops)???

[joecar]

Jeff,

I know, in tank fuel pump is a PITA to work with... :bangin:


Hook up a DMM/voltmeter and fuel pressure gauge, put in visible place...
voltmeter has to be as close to the fuel pump as possible...
lift and secure car rear, and power brake (you have M6... this is easier on A4)...


If you had access to an oscilloscope, you could instead do a throttle WOT snap, that should give you boost momentarily and the scope would have recorded the voltage.


Could also use DMM extenstion leads and duct tape and place DMM in your lap, and drive car on street to get into boost...


The thing is... need to see what voltage is at the pump, and if it is not correct work forward (toward front of car) from there...
- is fuel pump relay and/or fuse(s) dropping more than 0.1V...?
- is power wiring from battery to pump droping too much voltage...?
- is ground wiring from pump to battery dropping too much voltage...?
- is fuel filter obstructing flow (it usually flows ok until large flow is demanded)...?
- is pump able to keep up (it may be ok until high demand)...?
- is pump electric motor worn...?
- is pump "hydraulic" mechanism worn/leaky...?
- is integeral regulator weak/leaky (if it was, you would probably see pressure dropped all the time).


An oscilloscope would allow you to capture voltage waveform on pump... looks like a ripple (one ripple for each commutator segment in the pump electric motor)... this would show if the pump motor was bad (missing ripples), and allows you to measure pump rpm to see if it is suffering... but access to a scope may not be possible.


Dropping fuel pressure means that the fuel pump is not able to push fuel due to either a [partial] obstruction or the pump being maxed out (which can bedue to electrical or hydraulic problems).


There's a whole art/science to fuel pumps...

Regards
Joe
:book:

[SSpdDmon]

:wallbash:

[joecar]

How many miles on the car...?

[SSpdDmon]

51k - I'm just frustrated because I just got it back from the shop on Thursday thinking, "Ok, now all of the mechanical issues are resolved..." Then, I found this fueling issue. I really hope it's something stupid like a fuel filter or even the battery (optima redtop).

[white01ss]

So what ever happened? I have the Racetronix pump and wiring kit and my pressure drop from 62 @ cruise to 58 @ WOT. That's a 6% drop. Wondering if I need one of those voltage booster devices like KB boost-a-pump or something.

[SSpdDmon]

So what ever happened? I have the Racetronix pump and wiring kit and my pressure drop from 62 @ cruise to 58 @ WOT. That's a 6% drop. Wondering if I need one of those voltage booster devices like KB boost-a-pump or something.
Sent the sending unit off to lonnies performance for a twin in-tank upgrade. Going to a vacuum/boost referenced regulator. There should be no excuses for fuel pressure drops after this... LOL

And to keep with the "twin" scheme, it's getting a twin disc ram clutch as well... :D