70 duster with 1/8 mile problems

I have a duster with a 340 .030 10.85 comp.ratio .484 284 mopar cam mildly ported J heads an old LD4B intake with a 780 holley
727 trans with a 3000 stall con. 4.57 gears and it only ran 9.09 @ 76.7 MPH. any help would be greatly appreciated!!!

Some questions first....What are you shifting at,what is the trap rpm,what size tires on the back,are they street tires,how does the car come out of the hole??? Is this a race only car??

Thanks for writing. I shift at 5900 rpm. for 1st and 6100 for 2nd I have M/T ET drag slicks 10 wide and 26 tall. The car hooks pretty good my best 60 foot time is 1.84 but it feels like it falls flat at half track. I dont understand why my mph is slow. I wanted the car to go low 8s or high 7s. I drive the car some but not much because the stiff gears . thanks

I don't know if you have the Mopar super Stock springs on your car, but if not I'd put them on.It sounds like you may have a fuel delivery problem to me,you should have a electric pump and fuel pressure set to around 6.5 psi.Your carb may need a little tuning also,you may need to experiment with shooter and jet size.Also I assume you have a vacuum secondary carb and you'll need to try the Holley spring kit and try the various springs for the secondary opening rate.What shooter is in it now and what jets are you running??? And what is your trap rpm??

I have the super stock springs and a snubber set at about 3/4 inch from the floor. The holley has #76 in the front and #80s in the rear. Im not sure about the shooter size because the guy who had it before me said that it was drilled out. I wish I Knew but I dont think its the problem because it doesnt bog. I had one guy tell me that he thought it was my intake. He said that I need an LD340 instead of my LD4B. When I got the intake I inlarged the ports to match the 340 so I thought it would work well. My trap speed was around 4800 to 4900 rpm. Is this to low?? I was wondering if i changed from an orange box to chrome would help.

My main reason for asking is the 60ft times,I feel that you should have a 1.65-1.70 which tells me the car isn't leaving hard enough and that intake may be the problem.I'd really go with a single plane intake such as the Mopar M-1 or a Holley strip dominator that you may find used.Your trap rpm says the car is laying down at half track or before.I also NEVER drill out shooters,It's so easy to buy and keep some for tuning at the track and by keeping a log book,you can plot your results.I run the same cam as you in a 383 Dart,have 60ft times that range from 1.55-1.58 even when we had 4.56's and a 10.5x29.0 M/T on it.(now we have 12.25x31.25 Firestones and a 5.12 gear) so I suspect the manifold and some carb tuning.It should be pulling more trap rpm than 4800-4900.You can switch to the chrome box,but this wont solve your problem.

Make sure you have good enough fuel flow and delivery. I ran 1/2" line to a carter mechanical pump on the motor no problems yet. The combination you are running should be in the 8.0 to 8.20 range at about 83 to 86 mph. Try shifting the car at 5500 you may be streching it to high for what is needed . How much does the car wheigh?
We need some more info on the car.

Andy, car sounds like it could be a good 1/4 mile car but may need lower rearend gears. Sheeesh. . .do they even make a 5.13. You say you have a 3000 rpm stall converter. I'm assuming you have a 10 3/4" verter. Stall speed depends on the rate of "power" put into the verter -- so it may not be really 3000 rpm. Christopher has the right idea: try short shifting at 4000 rpm then gradually increase the shift point. U should go thru the traps at about max rpm. My 64 Ply 383 - 330 (E/SA class in early 70s) usta shift at 5200 and hit the traps at 6500 (1/4 mile strip). Most first time drag racers like to shift at max rpm and then wonder why it doesn't e.t. very well. Max rpm is usually well beyond the torque peak and therefore yur engine "slows down" in it's rate of increase in rpm. Oh well, getting too long -- keep trying shift points before you pull the intake and change carb settings. Good luck.

I agree with the other guys, check you fuel delivery. run 1/2" line and a good electric pump. The best way to find out if it is a fuel problem is to run a fuel pressure guage and try and keep an eye on the guage as you are running the car and where you think the car is "falling flat" on the track. You want to keep the fuel pressure between 5-7 lbs throughout the whole run.

Had this same problem with my 383 Duster, it would launch pretty hard then fall off and then appear to pick back up again. What I discovered was one the fuel pressure was way low, except it was ok sitting on flat ground. The problem is in you fuel system but I would vote more for pickup problems than anything else. They others guys are correct you need 1/2 line and en electric pump, but I would vote for installing a fuel cell with rear mounted pickup while you are doing it. Most likely when you launch the gears are steep enough to cause the fuel to slosh to the back of the tank and its not picking up enough fuel. It this is the case then the your 60ft will be slower than they should be which someone mentioned earlier.