Well thanks everyone for the input here. I got my fuel pressure gauge installed and made two runs. Fuel pressure plummeted to 2 psi as I passed 5k in 2nd gear. The fuel pump is on its way to RobbMc for an upgrade and I’ll also have to install a regulator. Hopefully this cures the issue and it’s not related to the issues Cliff brought up. Im taking recommendations on the best regulator with 1/2” inlet/outlet
Good job on finding and correcting this, before you hurt the motor. I recommend this regulator- 3/8 NPT inlet is effectively 1/2".. use steel fittings for the largest internal fitting diameters. http://www.jegs.com/i/Aeromotive/02...MI1sbC5Jb41gIVCo5pCh1CmAOGEAQYAyABEgJytvD_BwE JW
I had to do some research to remember how AN and NPT threads differ. Seems like 3/8 NPT is smaller than -8 fitting, but turns out they are equivalent and thus this regulator won’t be a restriction in my -8 fuel system. There’s a great Tech Bulletin about it here: http://aeromotiveinc.com/wp-content/uploads/2014/12/TB_901_AN_and_NPT_02.pdf Thanks Jim
From what I've seen with this topic over the years the worst electric pump mounted behind a sumped tank or fuel cell is better than the very best mechanical pump sucking on 14' or so of fuel lines of any diameter. The faster your car is and harder it launches the more troubles you will see trying to use an engine mounted mechanical pump in that scenario. I know, I know, tons of folks post perfect success with that deal, but in all the years and countless testing I've done here with a wide variety of vehicles that are drag raced and capable of running sub 1.6 60' times and well into the 11's or quicker, we've had PERFECT success with rear mounted electric pumps and at least 8AN lines/fittings everyplace. Success with engine mounted mechanical pumps trying to do the same thing has been "hit and miss", and NONE of our cars running deep into the 10's and quicker will use any sort of mechanical fuel pump........FWIW.......Cliff
As far as NPT threads vs AN, the good news is that most aftermarket stuff, fuel pumps, filter housings, regulators, etc, will have NPT threads, 3/8 NPT is very common there. This makes it super-easy to put together a fuel system especially if you use "push-loc" type hose/fittings. I like Aeroquip FC-498 or equivalent, tough as alligator hide and fine for all modern fuel blends. Armed with a hand full of 3/8" NPT to -8 fittings one can put together a fuel system in minutes using AN push-loc swivel fittings. Just eat your Wheaties that day, and use some lubricant on the push-loc fittings to get the hoses in place. We use hose good for at least 150psi in that configuration, so fine for any type of fuel system you are putting together. I set mine up way back around 1999-2000 and it's still in perfect shape. The only issue I've had is one set of brushes in the Comp 140gph pump and a couple of rebuilds of the Holley regulator (torn diaphragms).........Cliff
Well the results are in. I had the RobbMc pump upgraded to the 1100hp version, installed the Aeromotive regulator Jim recommended above, -8 Aeroquip pushlock hose and fittings all the way from the RobbMc 1/2" pickup through the high flow filter to carb. I've got 11.5 lbs of pressure at the pump, 7 lbs coming out of regulator. I've installed pressure gauge to measure pressure right in front of carb inlet. A couple full throttle runs resulted in same thing....pressure crashes quickly to 2-3lbs above 5k in second gear, engine stumbles and I quickly get out of it. Looks like I may be in for constructing the fuel system Cliff has described, which is frustrating because this is a street car with a once per year run down the track. But I need it to be right. Any other suggestions here before I start down Cliff's road? Is it worth upping the pressures at pump and perhaps up to 8-9psi coming out of regulator? And lastly, I recall someone saying the little filter in the carb could possibly cause the issue. Worth removing that filter and try a run? Thanks all for the help.
My CV pump makes a constant 8-9 psi at idle. The QJ doesn’t seem to mind it at all. I have seen it at 10 occasionally. I would up the regulator to 9 and try again. I do not use the filter in the carburetor. I removed the entire filter housing and use a Russell fitting with a -6AN male. There is a billet filter in line between the pump and carburetor. I have a billet filter in the frame rail before the pump as well.
The later Q-jets will EASILY handle higher fuel pressures. I run 7.5 psi on mine (1977 model) and flawless now for decades. I use a .145" seat as well. I'd add here that I"ve had my 1977 carb on the dyno back to back against just about every type of full "race" carb out there, and backed up the dyno numbers at the track. To date it has outran every Holley, Demon, Quick Fuel, Edelbrock AFB/AVS (clone) and TQ we've tested it against. This simply happens because I've been fine tuning it for my application almost 30 years now, so it is "spot-on" in all areas and nothing else is going to work as well, at least not without the same amount of effort put into it. Kind of a neat story if you don't mind the rant, but we did some testing for Popular Hot Roddings "Engine Masters" edition a few years back. The representative from Popular Hot Rodding who covered the dyno testing and the track testing that followed a couple of days later actually grabbed a custom Holley "dyno mule" carb in the dyno room between pulls and asked us to do some testing with it for additional magazine coverage. I was reluctant to complicate the already very labor intensive event (and you never know if you are going to get your ars handed to you as well) but agreed to the additional pulls. I remember his words almost exactly, "now let's see how much power this engine will really make", or something very close to that. So we bolted down the big Holley which that shop used for a LOT of their dyno testing with engines very similar to mine. The big Holley LOST about 1-2 HP over the Q-jet, and a few days later backed up the numbers by running .02-.03 seconds slower and about .5 less MPH.......so I dodged a bullet there. I'd also mention that NONE of that testing got any magazine coverage, my first lesson in the "politics" of magazines and "high performance" aftermarket parts....FWIW Anyhow, for most outings I replace my stock fuel filter housing and filter with a housing tapped for an 8AN fitting. I have forgot to swap them out a few times and it doesn't make any difference at all at the track. I've had some customers swear that just removing the stock filter and installing a large in-line filter cured all of their fuel delivery issues, so hit and miss with that sort of thing. What I do know for sure when it comes to this topic is that PERFECT traction and really quick 60' times tax a mechanical fuel pump set-up pretty hard, even with big fuel lines and well located sump/inlet. As I covered here in detail ALL of my fuel issues immediately went away FOREVER when I sumped the stock tank, moved the Comp 140gph electric pump behind the tank, and went 8AN lines/fittings everywhere. For sure I've seen folks run quicker than I am with LESS of everything, but all I know is what has worked for us here, and ALL of our cars that are capable of sub-12 second runs and 1.6 or quicker 60' times use either a fuel cell or sumped tank, electric pump behind the tank, and 8AN (or larger) lines/fittings everyplace. Once this is done we go onto worry about other things, as doing this will immediately solve any and all fuel delivery issues no matter what type of carb you are using. Even with that said we've still not able to get those POS Edelbrock AFB clones to run well on race days no matter how much heavy metal we add to the weighted air flaps.........FWIW......Cliff
How about just adding an electric in-line pusher pump near the tank, then a small "surge tank" just after the pump?
Well I've done a couple more things...upped the fuel pressure to 9psi and went to remove carb filter but it didn't have one. Made a test run and same thing....pressure crashed above 5k. Jim suggested I test the fuel tank venting system and it was functioning perfectly. I'll double check that my pump pre-filter isn't clogged, but that would surprise me. So I'm beginning investigations into in-tank electric setups. Initially I like Rickstanks new "Restomod" stamped steel tank: http://rickstanks.com/products/tanks/restomod/ Fits like OEM but can accept a number of different pump options, and has a neat pickup system so it doesn't need a sump. Anyone have experience with these? They also sell a kit for in-tank electric pump in a stock tank but I think you'd have to shim tank for plumbing to clear trunk floor, etc.
An in tank electric pump (with baffles to keep in covered on hard runs) would be the very best system. This eliminates any suction lines, which from what I've seen are a negative for cars that leave really hard. During the improvements made to my car to completely eliminate fuel delivery issues at one point I made an oversize pick-up line and located it pretty far back in the tank then put the same Comp 140gph pump I'm using now in front of the tank. Ran 8AN lines/fittings all the way to the regulator then on to the nose of the carb. Initial testing on the street showed zero issues, so I thought I had it beat. The first track run with traction was going really well till about 5000rpms where the engine started to go "flat" and loose power.......bummer. The next step was to weld a CE sump on the stock tank, move the Comp 140 pump behind the tank, and hook up to the same 8AN lines used from the old pump location to the regulator and carburetor. There were no other changes done, just installed the sump and moved the pump behind the tank and put a high flow race type filter back there with it. That did the trick, never to date have had the first hint of a fuel delivery issue and I've went on to install a more powerful engine that took the car from mid to high 11's to nearly into the 10's. To this day I'm not sure why all this happens, as I see folks getting to do more with less when it comes to this topic. For sure I can't get away with it! If I had to do it over again I'd get a new tank with an in tank pump, provided the tank was baffled for fuel control on hard runs......FWIW......Cliff
How much fuel did you have in the tank? If it wasn't full, I would fill it and try again. Stock type picks are very susceptible to fuel level.
Yes, a full tank makes no difference. Still researching in-tank options. The restomod tank referenced above has no option for a carbureted returnless system. I really don't want to run a return line other than perhaps using the stock 1/4" return line, but I know that's not adequate. Aeromotive makes a returnless setup for carbs, but I'd have to stick it in their gigantic 25 gallon tank. Not sure how they get away with calling it a replica OEM yet it holds 8 more gallons than my factory tank.
The tank we put in one of our cars couple years ago was a regular ole spectra premium, but I noticed it had weld marks on the outside, looked inside and it was baffled , haven't ordered another one since then as I simply haven't needed one but will here soon as I get closer on 70 X, maybe they have made an attempt at addressing this issue,... hopefully that's the case anyway
What sending unit in ur tank do u have? With all this long winded discussion it should all come down to the basics. Disconnect ur fuel line at the carb, aim it into a bucket hit your pump with 14 volts. If after 12 seconds u don't have enough fuel in the bucket u have a fuel restriction. Your problem will be before the carb.
How much fuel should be in that bucket after 12 seconds to keep up with the current power level and vehicle performance?
According to the 1971 Buick chassis manual, one pint of fuel should be pumped in 30 seconds or less. Fuel pressure at the carburetor should be 4.5 psi minimum for the 455. Both tests conducted at normal slow idle speed. We all know that the stock fuel pump can't keep up once you get serious with modifications (above 450 HP)
