smooth1990

What are you guys running for a fuel system?

I have a aeromotive 340 pump and 63 lb siemens injectors and I think my car is running out of fuel at 4700 rpm or so!! (10 psi of boost)

I have a built 383 with a D1SC. Im not 100% certain if its fuel or ignition but at 4700 RPM it has a bad studder. My A/f is 11.5 across the board! My fuel gauge is set at 45 psi at idle and under load it goes to 50 psi. at about 4300 rpm my fuel gauge starts to fall off and by 4700 its down to 44 psi I did a datalog and ofcourse it doesnt show me anything.

Kinda stuck at the moment. I dont think its the ignition system...but idk for sure!!!. I have NGK tr6 plugs gapped at 35.

any ideas or help would be great!

cudamax

IMO u have to high of a C/R with no Intercoolers. I think it's Detonation that's ur problem and u need to have the Ignition timing backed off when u come on the Boost and it needs to be running richer for a cooling effect above 4000 to 4500 rpm than 11.5 Try backing off Inital timing alot and go to the Air-port or a Road Ranger and try and get some real high octane gas The Pink Stuff and give it a shot but I think ur tune is going to be best for backing off that Deadly **** when high boost levels r coming on.
As a rule of thumb for Intercooled EFI/TPI applications with low compression ratios (less than 9.5:1), often high boost levels (14-17 psi) can be safely run with full timing on pump gas, and will produce horsepower gains of 75-100% (depending on boost level and the motor specs). For low compression EFI/TPI applications without an intercooler, boost levels above 5 psi will require the use of ignition/timing retard if you wish to run pump gas, and will produce lower horsepower gains (35-45%) than capable with an intercooler system. To decrease the risk of detonation, High boost levels (above 12 psi) should generally be avoided even with racing fuel on a low compression motor. As a general rule lower compression motors are capable of handling higher boost, and higher compression motors should run less boost. Most preassembled supercharger kits for street applications are designed for use with pump gas at full timing and will not negatively affect daily drivability.

For carbureted motors, the rules are slightly different. Carbureted motors can generally handle more boost than a comparable EFI/TPI motor because carburetors deliver most of the fuel to the engine in a liquid state. As this raw fuel atomizes from liquid to gas, an endothermic chemical state change actually occurs. This reaction draws heat and cools the incoming air. For low compression carbureted engines (9:1 or less) and average boost levels in the 8-14 psi range, pump gasoline works very well. Higher compression ratios (10:1 or greater) require lower boost levels, a higher octane fuel, intercooling, or some combination of these. Extremely low compression ratios (7or 8:1 range) can usually handle 12-20 psi on pump gasoline.

cudamax

follow these rules as a starting point:

* less than 10psi: 12:1 Air Fuel Ratio
* up to 16psi: 11:1 Air Fuel Ratio
* 9.5:1 compression or less: 1 degree retard/#boost
* above 9.5:1 compression at least 1.25 degrees per psi

smooth1990

I am running an intercooler. My compression is only 10.1. and its falling off at 10 psi of boost. I dont think its detonating.

I will bring the A/f down to 10.1 above 4 grand and Ill throw some 110 in it but it doesnt feel like its detonating. I think my opti is taking a dump. If you look at my dyno graph from last week when I had the car on the dyno naturally aspirated it was falling off at 5500 rpm. I didnt feel it alot in the pedal but it wasnt making alot of power either.

dizwiz24

you need to talk to greg@blowerworks. He has lots of different pump combo test results of actual fuel flow rates, under boost, thru c4 corvette fuel lines.

I have a gsl392 feeding a walbro 340 255 l/hr intank pump. Racetronix relay harness also.

60 lb/hr injectors.

No fuel issues.

9.7:1 compression(achieved by putting bigger chamber 61cc afr 195 comp port heads), 12 psi boost at 6000rpm, meth/water inj. Stock bottom end. No worries. 520 rwhp

smooth1990

I have been working with greg. Im sure i will talk to him in the morning.

cudamax

New opti couldn't hurt and backing the **** out of the base timing and going for a blast don't take much time to see. Just say-in

smooth1990

I agree. I pulled 5* out after 60 kpa and 4500 rpms all the way to 100 kpa and 7k. I am running a 2 bar map... That will be the tell tale sign I guess.

smooth1990

Diz- What does your main spark advance up top look like?

smooth1990

Ok so I pulled 5* of timing out and it made zero difference. Its still falling off at 5000 rpm. I have zero ideas besides the OPTI. Guess I can run the car NA tomorrow and see if the problem persists.

If it was running out of fuel, I would see a big dip on the fuel gauge and in my AFR gauge I would think.

God I hate LT1 cars.

cudamax

Sorry Man I still think it's Knock-in and ur running to much Advance. Like the other guy said What is it programmed for or set up at for full advance up top? If you really don't think it's an advance problem Disconnect the knock senors and run a big gamble on beating the **** out of everything
http://forums.corvetteforum.com/c4-t...-location.html
or I would bet maybe talk with ur tuner and see if he was under the Impression that u were going to come right back, right a way after u had ur pro-charger Installed and for ur first tune set up full advance around 32-36 total to come in around somewhere from 3800rpm to 4000rpm then later for ur motor boosted he'd just back it off total assuming u'd be at maybe 16-20psi of boost 24-32 total all the way up to 6000rpm

cudamax

Really any motor thats running full advance on some heavy boost will destroy itself. It will beat the pins out of the piston/destroy and crack piston skirts Hammer the crap out of the cyl head guides/valves=valve seats/bearings
I think the only thing that save-in-ya is the knock sensors and thats whats going on. If its starving for fuel I feel the pressure should fall on its face/Tank or at least loose half the pressure at high rpm and cause more knock from a lean-out.

cudamax

O.K. Why don't u just see what total advance u have built in to that thing. Hopefully u got a dial back timing light. Hook it up and just buzz it up to 4000 rpm and start adding degrees to the timing head to u start seeing 0/TDC on the balancer?
I'd really like to see from 2000 rpm al the way up to around 4500 rpm in 500 rpm increments to see what has been dialed in to ur motor.
This way will put to rest a knock problem or not and maybe u take a ride out to ur tuner or just end up screwing with an opti for the day.

bjankuski

I suspect you are loosing spark, try tightening the spark plug gap to .025 and see what happens. Another possibility could be valve float. Your NA dyno sheet shows it breaking up at 5500 RPM (Possible valve float), with 10 PSI of boost the valves will float earlier, is this a possibility?

tequilaboy

You are running out of fuel. If it idles at 45 psi, it should rise to about 52 psi at wot out of boost. As boost builds, fuel pressure should continue to increase. You should see fuel pressure of approx 62 psi with 10 pounds of boost to maintain the pressure differential across the injector.

This doesn't rule out other issues as already discussed, but its a clear indication that the fuel system is not keeping up with the demand.

smooth1990

LOL! I already said my timing has been cut way back! At 5000 RPM when the car starts to break up It is at a total of 20 degrees timing!!! asa the rpm goes higher, and i build more boost, I cut timing.! Stock timing at 5000 rpm is 40*....Last night I cut 5 more degrees just to seee if that was a possibility. It not detonating...

I think it is either spark (opti) or fuel loss. You can see on my dyno graph where it started to break up at 5500+ . Thats pretty typical for optis. Its definately not valve float. I have PAC springs with awesome seat and open pressure. I use to run this thing to 7200 RPM with zero issues.

That was my other concertn! Fuelk pressure should not drop off at all under boost. It will rise to 50-52 under WOT. after it builds boost it will start to fall off. It could be my pump. I do not have the racetronix harness. I would think if that was the case, wouldnt I see it in my A/f gauge tho?

smooth1990

Ok I have a couple issues going on! Its running out of fuel. No question about that! I have ordered a whole new fuel system! Hopefully I will have it in the car this weekend!

I am going to take the belt off the blower, pull the intercooler and run it back on my NA tune and see if the high rpm stumble persists. Im pretty sure the opti is failing also!

Stay tuned! more to come. I cant wait to get this thing buttoned up! The power is incredible at 4500 rpm and below. Its way faster than my 560 WHP Z06 at low rpm. I cant imagine what its going to feel like at 6500 rpm and 20 lbs of boost!

dizwiz24

21 degrees from 4500 rpm and up.

A couple more degrees down low, but i discovered less timing down low = more power down low, with my afr heads.

Sometimes an extra 1 degree of timing can mean the difference between starting to get knock retard (and sapping the power) or not.

dizwiz24

I had issues with plugs gapped that tight. Id get misfires/vibrations during low rpm high gear highway driving with gaps < .030"

.038ish " works best for me

cudamax

Their ya go I didn't know it should be up in the 60's Someone send Tequila boy 10 bucks Via pay-pal to buy himself a drink