Turbo Tuning Advice

[njp98]

Hey Guys, I'm a noob to HP Tuners and computer tuning in general. I have a turbocharged 3.8L Firebird mod list here: www.cardomain.com/id/njp98 . I looked around at these forums fo a while, but most of the stuff is for NA applications or blowers. The car runs good now with only a rough idle and its rich on the top end.

Currently I'm using a Vortech S-FMU to boost reference the fuel , if I want to remove that and run only the computer how would I go about this?

Also, I often wonder about if the rough idle is cause by my tuning or the turbo piping that curves before the TB (you can see it in the website). I saw a post about removing the MAF screen can leave a lip that cause turbulence, could this also be the cause of the rough idle?

LTFT tuning - I looked about at the process of unpluging the MAF to adjust the VE table, would this work on a turbo application and if so how does this differ from running a pure speed density setup. Would running SD have any advantages?

Sorry for all the noob questions. I'd really appreciate your help.

-Nick

[arthansen]

Welcome.

Most of your issues are the same as Supercharger issues. There are a lot of posts about this. Perticularly, look at the info on 2 bar and 3 bar MAP sensors. Many are waiting for this support and I think this will be the main thing you need to address your issues. This includes SD tuning, LTFT, idle issues, MAF, and VE tuning. Untill the 2 bar is supported, you will continue to have issues.

Good luck.

[phoenix64]

I'm running 43lb injectors HPtuner, and no FMU with a wideband, what kind of informantion are you looking for?

[phoenix64]

Just checked out your site, very nice headers. I noticed your runing the FMU and 43lb injectors. I have way more than enough fuel with just the 43lb injectors in my car, and I've been over 12psi of boost. Really all you need to do is just enter the correct injector flowrates, which for me has been 51lbs at the low end, and about 46lbs at the top, and set the PE to start at your boost threshold, for me 25-40% throttle depending on rpm, instead of 75%, and the MAF will add all the fuel you need, at least thats what has worked for me. The rough running is probably the big injectors, if you just take the stock injector flowrate tables, and change them from 22lb to 43lbs, you will be rich. The stockers flow more like 19, and the 43's flow more like 49 with the fuel pressure we run. Hope that helps.

[Missing2]

that was some solid advice pheonix..

I may have a few questions for you when i get my injectors..

[TDZ16]

Hey Phoenix, I'm working on getting my turbo setup together right now and have some questions as far as tuning issues I'll run into also. You know how the injector flow rate vs. KPa Vacuum chart only goes to 100KPa or 14.7PSI(atmospheric pressure)? I want to run 10 lbs of boost, what should i tune that chart to with the 44 lb. injectors i'm gonna run? You mentioned something about 51 lbs. around idle and 46 up top? I don't understand that if your injectors are only go up to 43. Also, how come we're putting in our max values here, is the computer always gonna be dumping this much fuel in? At idle, stock, don't injectors just put out as much fuel is needed? I just don't understand why that chart seems to be maximums? Maybe you could clear some of this stuff up for me.

Also, you know how we can swap in a 2 BAR from a gtp, this would split the injector graph in half leaving the bottom half for vacuum and the top half for boost. We lose some resolution but this could be helpful, but what other graphs do we then have to chop in half? I'm so confusedededed....haha....
~Tom

[phoenix64]

What I was talking about with 51lbs, is that our fuel system holds about 49psi, the injectors I bought were rated at 42.5lb per hour, but thats at 43psi, so at our fuel pressure they flow more like 49-51lb's.

As you can see from the table in hptuners the injector flowrates go down as the manifold pressure rises, thats because pressure in the manifold reduces the flow of the injectors. So what I did was played around with the flowrates till I got the right mixture at low throttle, which was around 51lbs at the far right of the table, the whole time I maintaied the stock curve of the table, every time I changed it I multiplied the whole table by whatever factor I was using.

For the 0kpa value which is what the computer sees while under boost, I entered the flowrate that the engine would need at full boost. It makes it run a little rich when you are at low boost, but without a 2bar its all you can do.

For an example of how to calculate this, if your flow rate changes from 51lbs to 48lbs, from 100-0 kpa then you know an increase of 14.7psi reduced the flowrates 3lbs, so if your going to run 15psi of boost, then you would lower the last value in the table 3lbs more.

The value you enter in the table is not the amount of fuel the computer adds, those are the values the computer enters into its fuel calculations, so the larger the number the less fuel it will add.

As far as a 2bar swap I tried it, but the only sensor avaliable around town didn't read right so I gave up, and went back to a 1bar. If you search in this forum there are a couple good posts about it.

I'm a little rusty with the exact values, I haven't been near my car in over a month, but I hope that helped. And as a disclaimer this is just the way I have done it, it doesn't mean its the right way, good luck.

[TDZ16]

Hey, thanks for the advice, I still need a tiny bit more clarification though, i'm sorry.

So, when i looked at the chart, i misinterpreted it and thought that 100kpa was open throttle. But that is actually not 14.7 PSI atmospheric, but that is 14.7 PSI vacuum, aka closed throttle, which would make WOT 0 PSI/kpa vacuum. Then theoretically farther left on the table would be boost pressure. If this is right, then, 'i gotcha'.

Also, you say that "our fuel pump" can flow 50+ lph, but I'm going to be running a walbro 255, how does this come into the mix of things, what does it change while entering those values?

And finally, I didn't quite get what you meant about the higher the values, the less fuel it will add. Could you explain that to me possibly?

I'm going to say something now that may be right and make you think I can figure out the rest on my own but if you could please still answer my questions, you'd be my best friend.....Am I misinterpreting that chart as what the injector sprays into the intake and i should be thinking of it as how much fuel the pump is going to send to the fuel rail at that manifold pressure instead? I think everything would seem to make more sense if this was the case, but i'm not sure. Now i'm thinking that the LTFT and STFT values are more what I would use to tune the actual injector pulse rates. I'm sorry for the length of this, but this stuff really keeps me awake at night. I have trouble sleeping or doing anything else when this stuff is on my mind....haha.....Thanks so much. Where are you btw?, that you haven't been near the car?

~Tom

[phoenix64]

I was talking psi, The fuelpump can flow all the fuel it wants, the regulator should still hold 49psi at the rail. The walbro shouldn't effect it too much unless your flowing more than the return line can handle. But I'm runing the stock pump still so I'm not sure.

All those tables effect are injectors pulse widths Fuel flow and fuesl pressure are both regulated mechanicaly.

The way it works, is the computer has a formula that it uses to calculate the injector pulse width. As I understand it at a given RPM, manifold pressure, and MAF frequency the engine says I need so much fuel. Say its 1lb of fuel. So the computer goes to the injector flowrate tables, and it sees that at 14.7psi, the injectors will deliver 49lbs of fuel per hour, so it then calculates the length of injector pulse width required to deliver1lb of fuel, and then it holds the injector open for that amount of time, regardless of the actual flow rate.

To show another example if you leave the tables alone, and install 49lb injectors, the computer thinks the injectors flow 22lbs, so it will hold the injectors open for the length of time required for 22lbs, but becuase the 49lbers flow more fuel you will be pig rich.

I seems like you might be over thinking this, but I hope that clarifed it. I don't mind answering questions, I just hope that peoplle can benifit from all the stupid mistakes I have made.

I'm up at school in Duluth MN, 5 days left. Can't wait to get back and get the car dynoed.

Do you have any details on your setup yet? What kind of turbo your going to be running? Custom, headers, or an under the crossmember pipe?

[TDZ16]

ok, so i get you, that if you leave the table alone, it'll use the pulse width for 22lb injectors, which at WOT could be pretty large....and then if you actually have 44pounders in there, it will think to use the same pulse width and make u as rich as i am poor....haha. So is that why i see a lot of people just putting their injector sizes in there instead of actually figuring out a nice number like you did? Either way, i getcha now, you're awesome. I really think you're right, i'm thinking way too much on this, i should just get the stuff together, get it running, then deal with it as necessary. You know how you say the computer has that formula for knowing how much fuel to add, how does it know there is boost pressure if our MAPs only go to 1 bar though? Is this where you would just have it go to PE then tune as necessary from a wideband looking at LTFT and STFT?

As for my setup, I have right now a huge project on my hands, but very managable in time. I have a 1994 camaro 3.4L A4. I hate automatics, and there is no performance parts for the 3.4L, so by a stroke of pure luck i found a kid with a 97 firebird 3.8L M5 that had just gotten into a pretty rough accident as far as the body was concerned. He let me come up to him (he was in connecticut, i'm on long island), and strip the ENTIRE car of like EVERYTHING, plus a z28 rear end (1,000 miles on rebuild, 4.10 richmond gears, new posi unit, and girdle style cover) all for $1400 bucks. By the way the engine was a 39k mile engine that was just put in a month or two before the accident by chevy. So yeah, basically his car is sitting in my garage. I know your probably thinking, "but HP tuners is OBD2" so yes, i took the entire engine and chassis harness from his car too, even the dash and all. So i'm going to swap in the dash and whatnot too.

As for the turbo, I got 2000 tubular manifolds seeing as I was anticipating doing the under the k-member method, but I now think it might be better for supporting the turbos weight if i had forward swept manifolds/headers. I say manifolds/headers, because i think what i'm going to do is make up my own flanges from 3/8" steel, then weld some upward/forward bends from v8 headers i have to them, but keep them really short, and weld each of them into the side of a piece of 2 1/2 " exhaust tube. I'll block off the back of the pipe and put a flange at the front and realistically have my own manifold of sorts, then i'll make a y-pipe kinda like yours for the front of the engine. As for parts, so far I have the turbo (.50 compressor a/r, .63 turbine a/r), wastegate (35mm 4psi spring), BOV(greddy universal type s), hp tuners, 255lph fuel pump, RX-7 intercooler(lil guy but it'll work for now..only gonna run 10psi max i think to start), and i feel like there is other stuff, but i have no idea right now, i've just been spending money left and right. Hopefully this break will gimme a lot of time to get it all ready. My girlfriend is coming home so money will be really short if i wanna treat her right, which goes without saying. What's your SN on aim? Mine is ataris1618. Drop me a line.
~Tom

[phoenix64]

Yeah with the 1bar map, speed density is pretty much imposible. Thats why I use power enrichment mode. When the car goes into PE is uses the MAF, which is the only sensor we have that can "see" boost. Right now I'm using the RPM enrichment table and the injector flowrates to tune it. You'll defintly need a wideband, the stock o2's are useless for anything but fuel economy.

One note about the o2's, in theory they should compensate for larger injectors to a certain extent. Thats why you can just enter a close guess, and the fuel trims will just pull fuel, till the base is back to lean. I had a problem with a defective 02 sensor I think, and found that my engine ran better with the O2's deleted. I don't recomend it though. I'm still not sure why my car idled so rough with the O2's still in the system, but it sounds like NJP98 is having the same problems I had.

Sounds like a sweet setup, that thing is gonna spool like crazy. I would definitly recomend the header route. Keep us updated, and if you have anymore questions feel free to ask, my AIM is dtrg88, but I'm not on much.