1991tsi

iTrader: (2)

I've been reading and learning, but if you know the answer to these it shouldn't take a second to answer:

Is it true that ~4psi can be run (safely) without any fuel management? Anyone done this?

If the answer is no, which i suspect it probably is, how does one go about choosing the fmu boost/press ratio, other than trial and error tuning?

Thanks!

1991tsi

iTrader: (2)

to clarify, i'm referring to a mild non-intercooled turbo setup. can proper AFR be achieved by tuning with a bleeder on any FMU ratio, 6:1 to 12:1?

Redmax

iTrader: (20)

at 4psi on a turbo you will just need an fmu and a better fuel pump

hlh0501

iTrader: (1)

at 4psi you do not need a new fuel pump,
atleast from my personal experience the factory one was fine at that point

and some will debate on if you even need a fmu at all.

subs1000w

i would think the stock MAF would be able to meter 4psi and tell the stock injectors to flow more but i wouldnt go above 4 or 5 psi

it would be simalare to when you go to a z32 MAF and Z32 370cc injectors

this is just my opinon dont listen to me and mess up your motor

1991tsi

iTrader: (2)

are you saying z32 maf and injectors on a vq30 would handle 4psi without other management?

Mishap

He's saying the factory setup can handle ~4 psi w/o any changes. Though I don't know if that's correct. The Z32 MAF/370 combo works by tricking the ECU into thinking less air is flowing than there actually is. This works in combination w/ the larger injectors b/c the computer thinks its running the regular injectors and runs them at a lower flow rate. Doing this setup costs more than a Cartech/BEGI fuel pressure riser which all that's necessary for the car.

On Shadow's and Sadler's cars the Cartech FMU is rough at best in tuning A/F. It's default set to run pretty rich out of the box and w/ tuning you can get the car to run close enough to 12:1 that you can drive but you'll want an AFC to do further fine tuning to flatten out the curve. Since it's boost dependent, there's a big dip into extremely rich as boost hits before the turbo really starts flowing. We'll be using a Greddy Emanage on Shadow's car to fine tune his car. To get A/F correct, it's best to run the car on the dyno w/ a wideband O2 sensor plugged into the downpipe. The shop can slowly tune the bleeder to get close to stoich at least in the high end but can't get the dip out.

As for the extra fuel pump, I'd get one just to be safe since they are ~$80. Don't see the factory one being outrun at 4psi but it's cheap insurance.

A 4 psi non-intercooled setup seems kind of a waste. So much money and time to install an extremely complex system to be mostly bypassed. To me it seems a SC w/ a stock or slightly smaller pulley would probably be better since it's far more plug and play than any turbo setup. Don't get the same low end power but a full turbo system with most of the exhaust gases vented seems pointless.

1991tsi

iTrader: (2)

Thanks for the info mishap. from the posts I've read, 4psi should net about 230whp... that doesn't seem too pointless. I don't see this as too big a project either, going to have the uppipe made for me starting with a budget y-pipe, using a z31 300zx O2 sensor housing, and possibly part of a 300z downpipe to fabricate the exhaust end of things, right back to the budget flex section. my only concern was simple fuel management, which I'll probably just tune with an a/f gauge like I did on my talon, and making a custom home depot intake.