SBC 383 missing a lot of power
07-17-2009, 02:06 PM
#1
Member
MASTER JOURNEYMAN
Thread Starter
Join Date: Jan 2007
Posts: 36
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.
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.
07-17-2009, 03:32 PM
#2
Senior Member
DYNO OPERATOR
Join Date: Aug 2007
Location: Lost Creek, WV
Posts: 533
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.
TS1955
TS1955
07-17-2009, 05:16 PM
#4
Member
MASTER JOURNEYMAN
Thread Starter
Join Date: Jan 2007
Posts: 36
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.
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.
07-18-2009, 10:31 PM
#8
Senior Member
RACING JUNKIE
Join Date: Sep 2007
Location: Belleville, IL
Posts: 658
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.
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.
07-19-2009, 10:08 AM
#9
Senior Member
DYNO OPERATOR
Join Date: Aug 2007
Location: Lost Creek, WV
Posts: 533
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.
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.
TS1955
