Tuning Help

[SJ1g]

I was reading up on a few boards...and i came across a few topics...about 750cc's being too big for an afc..and ive also heard that you can make them work with a Maf-t set up which i already have...Now when it comes to tuning i have no clue..So my questions are,How true is this?Does anybody here had this experience?..What are my options?

Any help would be greatly apprettiated.
Thanks.

Merry X-mas

[BigT]

750's aren't just too big for an AFC, but all piggyback computers which includes your MAFT. You need something to either internally adjust the injector setting in the ecu(dsmchip or dsmlink) or a standalone.

[blcknspo0ln]

Just to give you a clue of how SAFC's work. On my 660's @ 24.5psi, my injector duty cycle was close to 90% and I had to adjust my HI settings at -43% to compensate for the injectors. The max adjustment on an SAFC is -50%. Not only will 720's be too large for just an SAFC to lean out, it also makes your stock ECU use a more aggressive timing map because you'll be hitting 24+* of timing. This is a no no. Again, as T put it, you need to get some sort of injector calibration before you put these injectors in. Either with DSMLink, standalone, or chipped ECU.

[faithless]

You can also lower your fuel pressure and take out a lot of fuel across, which will make you not subtract so much fuel on the SAFC.

[BigT]

You can also lower your fuel pressure and take out a lot of fuel across, which will make you not subtract so much fuel on the SAFC.


Why would you want to lie more to the ECU? It expects a certain amount of base fuel pressure. Leave it to a DSMer do it half ass. :roll:

[atc250r]

I don't think that's that much of a half ass way to do it. The ECU isn't going to know that you lowered the fuel pressure so you'll compensate without screwing up your timing tables. Of course if you do that your 750's will not flow 750cc anymore so you'd be giving up some of that larger injector you paid for.

John

[Nate Crisman]

You can also lower your fuel pressure and take out a lot of fuel across, which will make you not subtract so much fuel on the SAFC.


Why would you want to lie more to the ECU? It expects a certain amount of base fuel pressure. Leave it to a DSMer do it half ass. :roll:

Whoa. Lowering fuel pressure corrects for the larger injectors WITHOUT screwing with the ecu and pulling you off the right timing table. How exactly is this half ass? Correcting for larger injectors with an AFC by giving the ecu an incorrect MAF reading and screwing up the timing has a shit side effect.

IMHO you have it backwards. The AFC is the more half ass method of the 2.

Why lie to the ECU with the AFC? It expects a certain airflow signal to run the ignition timing. Changing fuel injectors is a mechanical change. might as well correct a mechanical change with an inverse mechanical change in a lowered fuel pressure and not even get the ECU involved.

But, realistly, it's not happening. you can't go from 450 to 720 and correct with fuel pressure alone.

[Nate Crisman]

I don't think that's that much of a half ass way to do it. The ECU isn't going to know that you lowered the fuel pressure so you'll compensate without screwing up your timing tables. Of course if you do that your 750's will not flow 750cc anymore so you'd be giving up some of that larger injector you paid for.

John

If you need to back the fuel pressure down, or pull fuel out with the AFC, then you really didn't even need those 750cc injectors you paid for either. :lol:

[atc250r]

True. It's kind of a compromise of half assedness!!! :lol:

[90goldtsiawd]

If you need to back the fuel pressure down, or pull fuel out with the AFC, then you really didn't even need those 750cc injectors you paid for either. :lol:

+1 I wanna know what turbo this guy's running to begin with.

[BigT]

Thats exactly my point. Why offset a piggyback with lowering base pressure to offset something else? Sure you can work your way around it, but why? A 1g ecu does expect the 38psi or whatever it is just like a 2g is expecting 43.5. By altering this, you need to make changes to all of the fuel maps. I know closed loop will probably stay the same given you dont take away too much pressure but your open loop fueling will be off. Again my point, why?

And yea, I think its pretty half ass regardless.

[BigT]

Of course if you do that your 750's will not flow 750cc anymore so you'd be giving up some of that larger injector you paid for.


Ding ding ding! You are the winner, claim your prize.

[Nate Crisman]

Thats exactly my point. Why offset a piggyback with lowering base pressure to offset something else? Sure you can work your way around it, but why? A 1g ecu does expect the 38psi or whatever it is just like a 2g is expecting 43.5. By altering this, you need to make changes to all of the fuel maps. I know closed loop will probably stay the same given you dont take away too much pressure but your open loop fueling will be off. Again my point, why?

And yea, I think its pretty half ass regardless.
Why offset a piggyback with lowering base fuel pressure? Because it's the best way to get the result you want.
Lowering the base pressure is the better way to offset larger injectors becuase it does not have a negative side effect.

And AFC is MORE HALF ASS HACK than lowering the fuel pressure.

Lowering the fuel pressure makes the AFC needs to lie less to the ecu keeping the ignition timing where it should be. It's simply another tuning variable that should be used if available to get better results vs cranking the AFC to -50% and dealing with 42 counts of knock as soon as you touch the throttle.

Iv only been doing this for like 8 years, what the fuck do I know.

[blcknspo0ln]

meh, either way sucks. Why not do it the right way and get a compensated ECU or a tuning program?

[Nate Crisman]

meh, either way sucks. Why not do it the right way and get a compensated ECU or a tuning program?

Of course a ECU chipped with the correct map for the injectors would obviously be a better solution. And a standalone the best.

Im just saying that lowering the fuel pressure is better than airflow signal hackery. Unfortunatly you only have so much wiggle room with fuel pressure.

[BigT]

meh, either way sucks. Why not do it the right way and get a compensated ECU or a tuning program?

This is exactly my point.

And nate, i'm not trying to raise your blood pressure man. Relax. :lol:

I was just in a bad mood last night and i guess my posts reflects my attitude. Everything you have been saying is exactly what i have ,with a larger explanation. Yes, you can lower base pressure, within "wiggly" room. But now your stealing from your injector. Yes AFC's throw off your airflow tables. Its a double negative. Its just my opinion that its pretty backwards working.

[Nate Crisman]

:lol: Merry Christmas :lol:

[SJ1g]

Well am running a 20g...the only reason i bought the injectors..is because i thought 550cc were a lil small for a 20g plus i had my eyes on a 60 trim but i kindda ran out of $$......also i still have my old set of 550's...i can use for now till i get the dsm link...either way i have to get the car tuned..wich i don't have a clue how to do.

Mods are:
Crower stage 2 cams
aem cam gears
gasket matched head on exhaust side
mitsu m/h/g
arp studs
stock bottom end
20g turbo pretty sure is clipped and ported
ported 2g exhaust mani
aeromotive fpr
rx4speed/slowboy 2g fmic custom fitted for 1g
Greddy bov
safc2
gm maf-t
act 2600

egt gauge/boost/a/f
I think that's it.

Thanx alot for your help so far.

[gtluke]

what are your cam gears set at?

[SJ1g]

To tell you the truth i don't know...i bought the car with most of the stuff it has on it .And i had a buddy of mine help me putting everything back together but hes kindda mia right now...And again when it comes to timing/tuning..i have no clue..ive been reading here and there trying to teach my self but am just terrified of tuching anything of the sort.

[SJ1g]

Am not making anything easier for you guys am i.. :lol:

[BigT]

what are your cam gears set at?


:lol: :lol: :lol: :lol: :lol: :lol: How is that question helping this thread?

[Nate Crisman]

Put the 550's in, they are fine. 550s were enough for DSM's to run 10's back in the day when 650 and large were not available.

I had 550s in my 20g setup back in like 1999-2000 and they were fine for about 22psi on pumpgas and about 28psi on racegas. (vpc/afc tuned without a wideband or dyno). No chip or ecu mods available back then either.

WHen you get the dsmlink, then think about putting the 720's in and retuning the whole thing. No need to make it any harder on yourself now with them.

[SJ1g]

Cool...ill throw them in today if i have some time...so where should my setting be at..for afc/maf-t and fuel press...ball park figure.?
Again thanx for the help!

[iboostdoyou]

if your sticking with the 550's, dont touch the fuel pressure. Every car is different, but find the manual online for the maf-t and turn the appropriate knobs to compensate for the 550's, it's quite straight forward. If it's bogging afterwards or blowin smoke, lean it out a few % on the safc. Just be careful you dont run it too lean and blow anything up. I'd suggest in a Wideband, makes even the dumbest tuner look like a pro.

[Nate Crisman]

if your sticking with the 550's, dont touch the fuel pressure. Every car is different, but find the manual online for the maf-t and turn the appropriate knobs to compensate for the 550's, it's quite straight forward. If it's bogging afterwards or blowin smoke, lean it out a few % on the safc. Just be careful you dont run it too lean and blow anything up. I'd suggest in a Wideband, makes even the dumbest tuner look like a pro.

Agreed. Set the MAFT for 550 injectors per the manual (there are different versions of MAFT that some work backwards, so make sure to read YOUR manual).

Then do your tuning on the AFC.

[atc250r]

If you're planning on keeping the car and continuing to mod it I'd say you really need to start tuning it yourself. It isn't that hard, especially now that you can buy a wideband for under $300 and easily interface it with the stock ECU so you can log the wideband's readings along with all the other info. Then after you do a pull you can just look at the log you took and see where you need to adjust your fuel settings. Otherwise you'll have to pay someone to re-tune it every time you change something and that can get expensive really quick.

John

[SJ1g]

I don't have the manual for the maf-t..but ill search online for it...another thing..i have a after market fpr..where should i have the Fuel pressure at?
And after reading everybodys expert advices.. :wink: ..am def. getting a wideband for my next upgrade..What do you guys recommend?

I appreciate the help guys.

[iboostdoyou]

I believe stock 1g is 38-39psi, and stock 2g is 43-44psi. Both are approximate, I'm not 100% sure though.
And yes, a wideband is absolutely the way to go. I had the AEM UEGO which worked well, but the sensors go bad fairly quickly, apparently. Whichever you can find the best deal on, go for it; just make sure it has a .5v output on it so that you can log it on the dsmlink when you get it.

[atc250r]

I would fool with the fuel pressure and find what pressure in the 30psi-40psi range will give you an acceptable AFR while doing a WOT pull with the least amount of SAFC correction. That way you're not fooling too much with the air flow and messing up your timing tables. That being said, the stock fuel maps are way too rich for a performance application so you'll probably have to fool with both pressure and SAFC to get the top end right. If you're going to try to make the most of your 550's then you might want to try running a high base pressure (around 45psi is fine) and then pull fuel as needed with the SAFC. That will make the injectors act like they are bigger than they would with a 38psi base but won't push the pressures too high under boost.

John

[1gnasty]

Put the 550's in, they are fine. 550s were enough for DSM's to run 10's back in the day when 650 and large were not available.

I had 550s in my 20g setup back in like 1999-2000 and they were fine for about 22psi on pumpgas and about 28psi on racegas. (vpc/afc tuned without a wideband or dyno). No chip or ecu mods available back then either.

WHen you get the dsmlink, then think about putting the 720's in and retuning the whole thing. No need to make it any harder on yourself now with them.i dont know how the heck u always get away with the crasiest set up and u always come out fine 8)

[SJ1g]

Got it..ok i didnt have time to swap the injectors yet...i drive trucks so i put in alot of hours.Plus the change in time/weather does not help..Specially when am working on it outside...but am def. doing it before the new years(hopefully)...ill post some pics soon.

Again..thanx for the help.