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THRAMP-master
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3,473 Posts
Discussion Starter #1
At the drag strip, THRAMP's engine is "breaking up" just before 6000 rpm. I suspect lack of fuel. How to tell if it's--
a) Not enough fuel pump (190 lph, 24-lb injectors, 5 lbs boost)?
b) Inaccurate AutoMeter tach, and it's really the ECU shutting down the party at 6250 rpm? (Seems unlikely, as I don't remember it doing this before installing the supercharger.)
c) Other fuel-related issue?

Or, could it be lack of spark? Higher cylinder pressures are "extinguishing" the spark? (On another car, nitrous used to do that until I put a hotter coil on it.) I have plugs set at .035" gap.
 

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Moderator Ad Nauseum
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18,585 Posts
I cannna gi ya anymore power. She's gonna blow I tell ya!

I'm betting on spark blow-out Tim since you just stuck that huffer on it.
First step is to make sure everything in the ig system is up to snuff so it'll deliver the higher voltage the plugs now need. In other words, a hotter coil won't help if the wires are breaking down.
You can "read" the plugs to tell if it's a mixture issue but I'm betting it's spark.

d



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Moderator
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You might want to check the inlet of the fuel pump to see if the sock is still on and that no debris has started to accumulate on the inlet screen of the pump restricting flow. This can easily happen to a car equipped with a fuel cell that has been on the road for a few years and the foam material starts to deteriorate.
 

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Moderator
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7,237 Posts
I'm betting fuel. Are you running an FMU? If so, the required fuel pressure at 5-6 PSI of boost could drop the capacity of that 190lph pump down low enough that you're short on fuel. If you're not running an FMU, the 24's are probably not large enough to support the HP your car makes.

Another less likely possibility is your tach isn't terribly accurate and you're hitting the factory rev limiter. Either way, it's bad news to lose fuel under boost!
 

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Mid Ohio Loopster
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1,980 Posts
Wasn't your car running about 370rwhp at the Fling? My guess is not enough fuel also. You really need to feed these things when you boost them.

Scott
 

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FFCobra Fanatic
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427 Posts
Bwana50 -

Check your fuel pressure at the fuel rail. You didn't mention whether you are using a regulator or not. It may be as easy as stepping up the pressure at the rail. I agree that it sounds like a fuel issue.

Ken
 

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922 Posts
I vote for timing too far advanced. I only say this because it just happened to me. My 392 was breaking up when I got close to 5k. I retarded the timing on the MSD dial and it went up to 6k without missing a beat. So, I ordered an MSD distributor and will set up the curve correctly when I get it.
 

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THRAMP-master
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3,473 Posts
Discussion Starter #9
I do have an FMU, 12:1 gain. I may try a 10:1 gain, since the dyno indicated it's running too rich at high rpm. Eventually I may put in larger injectors and ditch the FMU, but between the Fling, the supercharger, and new pipes, I'd be pressing my luck too far with CINC (House) to put any more money in it right now. Octane should be OK, as I was running premium gas and octane booster - although we have that cruddy methanol-mix gas out here.

I'll check all the basics, see what I find (fuel pump inlet, plug gap & appearance, timing, etc.)

Drive on!
 

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Moderator
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w/ a 12:1 FMU, you're likely up in the 80-100 PSI fuel pressure range under boost. I would recommend selling the 190 pump and replacing it w/ a GS340 high pressure 255 lph pump. The 190's flow will fall off quite dramatically at that high pressure. The 12:1 disk is better suited to 19# injectors. You'll probably want a 10:1 or 8:1.
 

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3,427 Posts
My turbo charged Mitsubishi had this problem, and it drove me nuts. Ended up being a bad plug wire. You would of never known by the resistance in the wire both hot and cold. Finally change it out of frustration and it cured the problem. I realised that the problem started after a plug change. The car would buck like hell a full throttle and high loads. Fuel starvation has a very similar symptom, both are deadly to a pressurized motor.
Mike
 

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Charter Member
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7,902 Posts
My engine is not blown, but I would think it might be worth looking at getting a chip and tuning it on the dyno. I am considering getting a SCT chip and tuning it on the dyno - that might help with concerns about detonation etc.

Just a thought.

Howard
 
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