SAFC tuning fuel press Q's

[kikdurazz]

I'm planning on heading back to the dyno in a few weeks.

Mods for the car:
LEx afm/SAFC
550 RC's
walbro
Areomotive AFPR
CT26 60-1
Spearco and 2.5 mandrels
3in mandrel exhaust
etc etc.

So that last time out I boosted 18psi, AFR 11.4-11.7-1 throught the power band. My ct has lasted a miraculous 4 years at this level.

I wanna get a little more out it up to the 20psi range. When we attempted this the last time on the dyno I was hitting fuelcut as soon as we jumped the extra 2psi even though the A/f were hovering around the same mark

Base pressure is around 32 if I recall and my SAFC setting I can't remember off the top of my head but I believe in the -10-15% range on the upper rpm limits.

If we added a little more fuel pressure and took out a bit more with the SAFC would that help with fuel cut or have I maximized on this setup?

My only concern is that I have nothing to monitor timing so I am wondering if this would advance the timing to much? (Timing right now is set to stock)

Thanks for the input let me know if you need more info I can grab the safc setting if needed right now at work and can grab the fuel press if needed this is with the vac line on.

 

[bountykilla0118]

have you adjusted the screw thats hidden within the AFM?

 

[sethron71]

I am running a pretty similar setup and have the exact same problem. 18psi all day 19.6psi fuel cut. I have a FCD just not hooked up. When I go to dyno next time I am going to hook it up. I only have a 57 trim but made 350rwhp(minor technical difficulty with my boost controller) but shooting for 375 at 18psi and 440ish at 25psi. But as mentioned adjust the AFM screw all the way out, make sure it is still tight enough that it does not fall out though.

What did you dyno numbers wise?

HTH,
Seth

 

[azsuprasm]

Wow. I'm running pretty much the same mods in Sarah, my 90T/Auto (7m with all that and some 7-series NGK Iridiums), but with the stocker 440's benched to 455 @ 100%.

I was peaking my STOCK CT at 305/350 with an even safer A/F Ratio at 15 lbs, but as you guessed, even with full hardpipes & Spearco IC, it drops down to ~12 lbs from 4000-6000 rpm.

I've since added the 57-trim CT, and I've referrenced some of the old SOGI stuff for the Lexus/Hall info...

...so to answer the original question about fuel pressure, the answer is YES!
With 440's or 550's, you need to adjust your base pressure 1 lb more for every additional lb of boost you add...over stock (38 lbs FP, 8lbs Boost), watching that you do not exceed your injector capacity (too much!).

Now there's more to the calculations for this, but in a nutshell, if you want to run 25 lbs of boost, you'll need to increase your base FP by 17 lbs:
17+38 = 55 lbs.

Pull the vac hose off of your AFPR, and at idle you should be at a solid 38-40. Unlock the hex adjuster off the top and dial it up (at idle) to 55, lock it down.

If you can't get to 55, then consider bridging the fuel pump voltage regulator (left side under the hood on the passenger fender well, finned alum: Paper clip to bridge the wire). This supplies 12V constant to your pump instead of 9v at lower RPM and 12v above xxx. If you still can't get to 55-60 lbs, you either need to get rid of a fuel restriction or break down and buy a Walbro!:icon_bigg

As suggested earlier, you also really need to allow whatever air you can through that auxilliary slot that the Lexus AFM offers, so back out that screw AFAP.

...and then tune the snot outta it on a good dyno with a wideband & maybe an EGT (for insurance).

My goal for SILV'08 is about the same as you guys: 375 RWHP, 450 RWTQ.
...and if I have to sacrifice anymore of my low-end TQ, I'm tempted to put back the pea-shooter. :nono:

All of this came from way back to the OG SOGI folks...Reg Reimer, Dave Hall, Arlene Lanman, Rich in N.Illinois.

Old School MkIII HP.

 

[Rennat]

are you sure about the 55psi at an idle if your going to run 25psi of boost?... thats 80psi at full boost...

 

[azsuprasm]

are you sure about the 55psi at an idle if your going to run 25psi of boost?... thats 80psi at full boost...

Am I absolutely sure?...No. Like I said, there's alot more to these calculations that needs to be considered. But you also must assume that you'll be creating full boost at well below red-line RPM's. The key here is to consider all the variables when calculating the correct FP to your Boost & HP goals, along with the capacity of both your turbo and your injectors. Remember, FP only allows your injectors to flow more when they need it...which is both at Boost and higher RPM's.

Let's say you've got your base FP (0 vac) set at 40lbs. Granted, your FP should advance to 60 lbs @ 20 lbs of boost...theoretically, but you'd have to be in test mode or on a dyno to see just how your FP is affected by boost. You may find that 20lbs of boost may only give you ~55 lbs of FP, and that may have lead to FC, even with your S-AFC tuned for safety.

There's a ton of additional information out there in the archives, but other than the few pages I have printed out, I'd recommend your fav. search engine to see what else is out there. Post here if you are able to find a more definitive formula or explanation of FP vs. Boost vs. RPM vs. HP calculations.
I'll post if I can find it sooner.

 

[4U2QUIK]

are you sure about the 55psi at an idle if your going to run 25psi of boost?... thats 80psi at full boost...

it does seem a bit much. I'm running about 10psi boost and I'm only runnin about 38-39 psi fuel pressure with good afr's all around.

 

[grimreaper]

you set idle pressure for idle, ONLY. the fuel regulator should be a 1/1 meaning as vac decreases and boost increases, fuel pressure will rise. no adjustment needed other then tweaking your setup to adjust the fuel through out the entire rpm band,

 

[teamslow]

leave everything alone just back out the screw a little bit on the lex afm. and that should help with the fuel cut.

 

[kikdurazz]

you set idle pressure for idle, ONLY. the fuel regulator should be a 1/1 meaning as vac decreases and boost increases, fuel pressure will rise. no adjustment needed other then tweaking your setup to adjust the fuel through out the entire rpm band,

So leave the FP as is at stock, back out the Lex screw as far as possible and clean things up with the Safc.

Whatever I get is what the setup is meant to do. Just curious why some on the exact same setup can run 20+. But I am running into issues? I know cars are different but seems odd that 2 psi makes that much difference.

Ahh well guess time for turbo upgrade and go from there.

 

[grimreaper]

your going to have to raise fuel pressure accordingly if you run out of room with the safc, or if you start to run lean. there is not a one size fits all ( i assume you know this, just double checking) stock would be a good starting point, the high side of stock though to be safe. i think you got it, just take baby steps. its a hard learned lesson how in an instant the motor is gone due to a tuning error.

my understanding: tune the fuel pressure so that your on the rich side at wot, then you can remove fuel by telling the ecu that there is less air then there really is. this in turn raises fuel cut. soo max out AFM screw, adjust fp, then pull some out with the safc to a certain limit. if you find you have to pull more then 20% (seems to be the limit on the 7m for safety) then drop the fp a psi or two and start over with the safc

 

[kikdurazz]

your going to have to raise fuel pressure accordingly if you run out of room with the safc, or if you start to run lean. there is not a one size fits all ( i assume you know this, just double checking) stock would be a good starting point, the high side of stock though to be safe. i think you got it, just take baby steps. its a hard learned lesson how in an instant the motor is gone due to a tuning error.

my understanding: tune the fuel pressure so that your on the rich side at wot, then you can remove fuel by telling the ecu that there is less air then there really is. this in turn raises fuel cut. soo max out AFM screw, adjust fp, then pull some out with the safc to a certain limit. if you find you have to pull more then 20% (seems to be the limit on the 7m for safety) then drop the fp a psi or two and start over with the safc

Thanks that clears it up in my head. That is what I thought I had to do, but was getting confused. Puts me on the right track to getting it tuned. I'm not looking for miracles just a little better with this setup. Hopefully my next post isn't, "So blew my car on the dyno"

Thanks for the info. Will when I go to my dyno guy.

By the way what is your car putting down with the SP61GT. I'm at a toss up between that and a Boss 550 TO4E 58 stage 5.

 

[grimreaper]

not a clue, haven had time to dyno between fixing all the seals on the front, work, school and the lake . might see what its got thursday. guys with a ported exhaust and safc have laid down 440 or so at 18-19psi, im at 14psi running rich as hell.