90-irocdx3

iTrader: (4)

Well i dropped off my car to get it dynoed a few days ago and the car was doing fine until it went into boost at which point it runs to lean and we can't achieve any added horsepower. the mechanic is suggesting this may be due in part to the stock gm computer. Also, i now have a blown headgasket on the #7 cylinder. Any thoughts on what may have blown the headgasket, and any thoughts on how to correct the lack of fuel flow?

engine specs:
zz 383 crate motor
forged 4340 crankshaft
forged rods
hypercautic pistons
.41 thicker head gaskets, previous compression was 9.6 to 1 before i put these gaskets on.
fast burn heads with 1.5 rockers
msd distrubtor and wires, colder plugs
super ram intake with 52mm throttle body
stewart stage II water pump
hooker 2055 headers
42lb svo injectors
1.1 procharger fmu
d-1sc procharger
stock computer
inline fuel pump
222/230 and 509/528 cam 112

AmorgetRS

iTrader: (6)

Right now do you have anything to up the fuel level when you get into boost, like a FMU? Are you retarding the timing at all?

90-irocdx3

iTrader: (4)

yes i have a 1:1 procharger fmu, and yes the timming is retarded.

AmorgetRS

iTrader: (6)

Ah, sorry, missed that in the list. It may be the 1:1 isn't enough. By stock computer I assume you also mean a stock tune?

TraviZ

iTrader: (2)

I agree I dont think 1psi/fuel per 1psi/boost is enough to compensate for the ecm only dumping enough for for what it is assuming an N/A engine. was the afr linear once it hit boost or did it continually get leaner?

90-irocdx3

iTrader: (4)

well it has a custom burned chip but stock computer. the dyno guy says the computer has added as much fuel as it can. i am kind of suprised cause the injectors are rated at 670hp but he said i may possibly need a 8:1 or 12:1 fmu.

90-irocdx3

iTrader: (4)

it was leaner as the boost went up.

AmorgetRS

iTrader: (6)

Sounds like you either need a higher ratio FMU or a boost referenced tune.

TraviZ

iTrader: (2)

with a stock ecm, I think a higher boost referenced FMU is the route to go imo. Go 12:1 and if its to much, you can take it out via ecm at least.

WheelsUp84z

iTrader: (2)

what pump are you running, might try to step up to an A1000 or magnafuel pump, maybe twin 255lph walbro's. Do you have a dyno chart? Hows the AFR?

askulte

The stock fuel pressure regulator is a 1:1, so having an additional 1:1 FMU should really do anything. My Walbro pump (with 55 lb injectors at around 50 psi base) hit a wall around 500 hp, where the pressure drops like a rock after 3000 rpms. The single pump just can't keep up.

Is your pressure dropping, or does it keep rising with boost (like it should with a 1:1)?

90-irocdx3

iTrader: (4)

well i found the problem, the head has a dip on the #7 cylinder head next to spark plug. the headgasket never blew it looked fine. so it sounds like a defect in the head. i will update what happens after i get this head situation fixed.


yes the pressure was dropping when it went to boost.

xpndbl3

iTrader: (5)

that's not the "problem" though if pressure is dropping when you hit boost. you need a bigger fuel system without a doubt.

90-irocdx3

iTrader: (4)

so do you think a 12:1 fmu would make it ok, i am running the supplied procharger inline fuel pump. i guess will go ahead and put a high flow fuel filter in it to.

JoBy

An 1:1 regulator is what the stock one is. With that the fuel pressure (on a gauge) rises with boost, 1 psi for each psi boost.

If pressure is dropping with boost, then the pump can't deliver enough fuel and that is problem #1.

KS91Z28

I agree. The fuel pump is the first problem you need to overcome.

86Z

iTrader: (4)

Do you have a fuel pressure gauge? i was seeing 90psi of pressure at 9lbs of boost and 30# injectors on my 305, i've now ditched the fmu and added 42lb injectors with a 3 bar map and code $59 now i see 45psi at 11psi of boost on a side note, with my stock $8d chip and the procharger supplied fmu and 30# injectors i was going lean, i had to add more fuel via the chip.