24 lb in a speed density?

[87lxmustang]

I.ve been kicking this around for a while about trying 24lb
injectors in my speed density combo. Like I said in my last thread,
my air/fuel ratio was spot on at 12.5/1 on the dyno,but I,m
running 52psi fuel pressure on the 19lb'ers. Would it be possible
to install 24's and cut back the fuel pressure?? I know my computer reads airflow on pre programed perimeters so the injector pulse width is set. But it makes sense that it could be dialed in with fuel pressure because I have to be close to the limit of the19's. I'm installing a typhoon intake in place of my ported stock lower and comp box upper and i'm anticipating more air flow (hopefully) and i'm not sure how far I can push the fuel pressure on the 19's. Has anyone tried this or know of anyone
who has?? The driveability is great now and it gets about 23mpg
on the highway and runs 12.70's at the track.

Any info would be great

I.m currently running out of the box TW heads-70mm throttlebody
190lph fuel pump and the usual bolt ons with 3.55's out back.

[theduckylittle]

The should work out fine. My computer works on about the same principle and swapping up to 42 lbr's doesn't really effect much so long as you dial back the fuel pressure.

-Duck

[87lxmustang]

Duck,
I,m not familiar with what your running.Svo turbo?
Speed density?? What size injectors were stock?

Tim

[theduckylittle]

Originally posted by 87lxmustang
Duck,
I,m not familiar with what your running.Svo turbo?
Speed density?? What size injectors were stock?

Tim

It's a 2.3 SVO Turbo engine. (More or less.)

The computer is a Vane-air Metering type that's really quite stupid for various reasons. In any case, factory injectors are 35 lbrs. (Low Impedence) but both a speed density and a VAM style make the same assumptions about fuel pressure and injector size. So long as you provide approximately the same amount of fuel per injection it really don't care what injector you've installed.

It only really becomes problematic when you start installing injectors that are so large that the car won't idle properly.

-Duck

[Macs Stang]

Adjusting the Fuel pressure with the 24's would probably help like we were talking about today. Did you also adjust your ignition timing?

I know that Tim was asking if you could use a Tweecer on a speed density car, is that possible? I am sure it would be, my guess is that if you choose to stay with speed density then you would have to shut off the mass air meter in the program. Not totaly sure, but I am certain that some people will chime in and answer the question correctly.

[87lxmustang]

Yes, i've played with the ignition timing. Currently i'm getting
away with 18 degrees of timing running 93 octane pump gas
with no problems. My 285hp dyno run was with 15 degrees
timing but my 12.79@109.9 was with 18 degrees,short belt and
fan removed,on drag radials.

[theduckylittle]

twEECer is for MAF only vehicles. However, there is a version of the FMS (the old school piggy backer) that runs with it (if I remember correctly). I've heard that helps. So long as you're not changing the vacuum characteristics of the car there really shouldn't be any problems.

-Duck

[wiplash]

There's a couple of guys running the tweecer on speed density cars, seems to be working pretty well for them too.