Fuel pressure drops today from 9 to 5 at wide open throttle (WOT) on highway. Then you can see it rising back to 9 when I let off the gas. From 2000 to 4500 rpm. Cruises at around 9 pounds. The other factor with any pump is flow rate, which I cannot measure. Pressure is only part of the equation. I'm still going to get rid of that 3/16" pea hole at the inlet when I convert to -6AN and see if things change. Measurements are from a tee that's on the fuel filter which is immediately downstream of the fuel pump. https://vimeo.com/176545104 Another run: https://vimeo.com/176546878
I suspect your pressure transducer is mounted prior to the inlet, so the 3/16" orifice isn't the problem. Well it isn't "that" problem. Personally I suspect you can overlook that issue. Sounds like you are working toward a solution, though! -BC
Ya, I'm slowly figuring things out! The pressure could still be high with a small orifice at the carb base and after the gauge, yet the flow rate could be low as the pea hole might limit flow. One thing about pumps is that although pressure and flow rate are related, they need to be talked about independently. Sent from my iPhone using Tapatalk
When you replace that fitting with this one, https://static.summitracing.com/global/images/prod/large/rus-640340_w.jpg?rep=False that pea hole will be history
Yep, got one. It's a beaut!!!! There's a local place in town that manufactures race car parts. They are giving me a sweet deal on -AN parts. Sent from my iPhone using Tapatalk
Stage 1 fuel pump added. A little more constant pressure from 2000 to 4500 rpm. Drops from 8 to 6 psi at WOT. Nothing else changed yet. https://vimeo.com/176869003 Stage 1 pump on the left: Other than finding out that somebody stripped the threads nearest the front and my car overheating, it was a great morning......
If you have 6 psi at wide open throttle you have plenty to get the job done.... My Monte drops to 4 and still does the 1/4 with out drying up. If your car still does not perform better start looking else where. Jim J D
Thank you, I have to agree. I do believe that pressure runs a little more even (just a little bit) with the stage 1 pump. But I'm not noticing a power increase. I also drilled out the brass fitting on the carb inlet from 3/16" to 1/4" and that doesn't seem to make much difference. I would have went bigger but realized I didn't have a bigger metal drill bit at the time. Still, going from 3/16" to 1/4" is an increase in surface area of 1.8, almost double, so I don't think it's a fuel delivery issue downstream of the pump. I did check the secondary air flaps and the tension on them is just enough to get them to close, so they are not too tight. I messed around with the set screw and tension screen and couldn't improve that at all. Sent from my iPhone using Tapatalk
I'm wondering if maybe there isn't an issue with the secondary plates, throttle linkage or secondary lockout. Sent from my iPhone using Tapatalk
Are you in any car groups in your area or guys that might have an extra carb to try on your car? That would be the best way to try and find the issues... I would still go back to carb and timing issues. Distributor not advancing correctly etc. Jim J D
Unfortunately no, and it's a smaller town. There's one or two guys I can ask. I had it at the track this year and last with a different distributor each year. I'm thinking carb at this point. I think I have the timing nailed down. Sent from my iPhone using Tapatalk
Looks like somebody put some washers on the accelerator cable to tighten it up. I'll have to get a friend to see if the carb is opening all the way up when the pedal is pushed all the way down. https://vimeo.com/177223905 Sent from my iPhone using Tapatalk
IIRC A small block car's throttle cable is different from a big block car's throttle cable, IIRC your car is a small block car so good catch opting to check if you're getting WOT when you put it to the floor. If that is good or you fix it, I'm curious to see some results from a compression test to see if every cylinder is close to the same PSI. If that checks out decent then you could have a weak ignition system or a bad or wrong plug(s) or 2 or a bad wire or 2? Not sure if you're running points or electronic ignition, but when I swapped my points distributor for an electronic one I went a whole second faster in the QM when I still had the 283(from mid 17s to mid 16s) in in my '65 Impala still with the original powerglide trans. Like Larry said, you should be running much better then the times you posted, something is a miss, hopefully its something easy.(I have my fingers crossed for you) GL Derek
Thanks Derek. The car was originally a 400; now has a 455. Plug wires are new this year, low resistance. Distributor is newly rebuilt. I did have someone push on the gas pedal tonight. Secondaries aren't opening very much at all! https://vimeo.com/177329539 Sent from my iPhone using Tapatalk
wow... THAT IS NOT GOOD AT ALL. gOT TO GET THAT SOLVED. might have the wrong throttle cable and reason for all those washers etc. At least your checking things that do not cost money. Jim
It turns out the throttle cable had too much slack so I put three washers on the cable temporarily and she opens up full now. How to get 40 horsepower for 18 cents. New cable and bracket are in the mail. Sent from my iPhone using Tapatalk
New throttle cable and bracket installed. I'm getting about 85% on the secondaries now with the gas pedal to the floor. I still need a bit more as I can move the carb linkage by hand and get it 100% open. I'm going to bend the gas pedal bracket to gain 1/2", and the secondaries will be open 100% New cable on top: Sent from my iPhone using Tapatalk
Compression test results. Cylinder number with compression written next to it. Sent from my iPhone using Tapatalk
