SBC 383 missing a lot of power

Old 07-17-2009, 03:06 PM
  #1  
lmccoll
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Default SBC 383 missing a lot of power

We have a new 383, 12.5:1 compression, Brodix racerite heads ( flow about 270 CFM at 0.6 lift) , a solid roller cam with 0.6 lift, 292 total duration, Victor Jr intake and a Holley 750 double pumper. Headers are some used ones I had that are 1 5/8" tubes. Open exhaust. Ignition is a MSD distributor with a high RPM module, all new plug wires etc.

Total timing is set at 35 degrees at about 3500 RPM and up. We run 110 race gas.

Based on our ET's, I am only making about 410 horsepower. The engine was professionally built by someone that has built race engines for about 20 years. They said it should make near 550 HP. The only info they didn't have was the size of the headers.

I have rechecked the timing and it is still at 35 degrees. Going down the track, it pops in the exhaust some, indicating it is running really lean. I don't have a air/fuel monitor to check it. Fuel pressure at idle or reveving up the engine is about 6 lbs.

One thing I don't know is if the fuel pressure is holding going down the track. I have 1/2" tubing all the way from a fuel cell. The tank is vented ok. The fuel pump is new, it is a JEGS 130 GPH pump.

Any ideas would be greatly appreciated.

The only thing I can think of is the fuel pump is not pumping as much as it should.
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Old 07-17-2009, 04:32 PM
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TS1955
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Look at your spark plugs. If they are extremely white & the ground electrode is blue, then start with jetting. Also you need to see what your fuel pressure is going down track. If jetting helps, keep going bigger until you MPH starts dropping off, then back the jets down one size. That should get you pretty close on jetting. Hope this helps.

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Old 07-17-2009, 04:41 PM
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kwkracing
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Is the distr. locked or unlocked? How are you setting the timing? What kind of balancer is on the motor and was the timing mark checkd to see that 0 degrees was at tdc on the piston?
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Old 07-17-2009, 06:16 PM
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lmccoll
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Default SBC losing power

Spark plugs are white looking for sure. I may get a electronic fuel gauge so I can measure fuel pressure going downt the track.

On the timing, I have the vacuum advance disconnected and plugged. The initial timing is set to about 15 degrees and by changing the springs in te distributor, I have about 35 degrees total. It is all in at about 3000 RPM. My stall convertor is a 3500. Trans is TH350 with quick shift kit and rear end is a spooled 4:11. Traction seems ok.
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Old 07-17-2009, 07:46 PM
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edbrgolf
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My 383 likes the timing around 40 to 41 deg. just my 2 cent.
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Old 07-17-2009, 08:38 PM
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kwkracing
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What kind of carb system are you running? Sounds like your timings off or your not getting enough fuel
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Old 07-17-2009, 11:14 PM
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cepx111
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X3 on the timing and jetting.

Go to 40 degrees on the total timing and fatten the carb up.
Cp
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Old 07-18-2009, 11:31 PM
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OneBadGMC
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If the plugs are white now, add fuel before you start adding more timing.

Adding more timing will require more fuel. It's silly to add more timing until you get the right amount of fuel in it for the timing you have now.
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Old 07-19-2009, 11:08 AM
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TS1955
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Originally Posted by OneBadGMC
If the plugs are white now, add fuel before you start adding more timing.

Adding more timing will require more fuel. It's silly to add more timing until you get the right amount of fuel in it for the timing you have now.
I agree. Do one thing at a time.

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Old 07-30-2009, 12:09 PM
  #10  
mopar1962
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Try to get your total advance in by 1200,.......
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