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#1
08-21-2021, 08:30 PM
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Checking fuel pressure with mechanical pump.
Do you check the pressure at idle or at higher rpm’s ?
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#2
08-21-2021, 08:36 PM
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BOTH at idle and at 2k+ RPMs.
Verify that is is correct at idle and that is doesn't change when at higher RPMs.
You do NOT want to see cavitation - that's where the needle flutters excessively, rather than coming up to the factory pressure and staying there. We've seen some mechanical pumps' pressure drop off when revved up and others go too high. Good luck! |
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#3
08-22-2021, 06:35 AM
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Even at slow driving speeds I once found out what the minimum fuel pressure is for a Q-jet .
At 3 psi the motor would idle fine and on level ground with light throttle openings you could do between 25 to 30 mph in a 3700 lb car before it would buck/ sputter and have no response to the throttle. At this point in time the car was fitted with a big Holley can type filter so pressure loss was likely minimal.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#4
08-22-2021, 10:54 AM
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Set it at idle and then check it at all rpms. Best to have one you can see inside the car, obviously.
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Chris D 69 GTO Liberty Blue/dark blue 467, 850 Holley, T2, Edelbrock Dport 310cfm w Ram Air manifolds, HFT 245/251D .561/.594L, T400, 9" w 3.50s 3905lbs 11.59@ 114, 1.57/ 60' |
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#5
08-22-2021, 12:11 PM
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What kind of fitting is being used? tough to put on a QJet with steel fuel line.
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1968 Firebird 400 RAII M21, 3.31 12 bolt, Mayfair Maize. 1977 Trans Am W72 400, TH350, 3.23 T Top Everyone you will ever meet knows something you don't. Bill Nye. |
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#6
08-22-2021, 12:55 PM
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It is tuff with a steel line because unless you want to splice in a short length of hose out of the pump all you can do is loosen the line so it dangles out at the pump end.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#7
08-22-2021, 02:04 PM
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Or just get some extra steel line to cut a section out for some rubber while you check the pump's pressure.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#8
08-22-2021, 11:23 PM
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If you are wondering whether or not it can supply adequate fuel volume for the hp you are making, you check pressure at WOT in the upper rpms.
Sent from my SM-G991U using Tapatalk |
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#9
08-23-2021, 08:22 AM
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As stated need to test at all rpm and loads . Many posts over the yrs about running out of fuel etc car nosing over at higher speeds. I made a steel test line with a tee so I could attach a hose with a gauge. Now have AN line with a fitting but same concept. Ran it up to the cowl zip tied it to the wiper arm . I ran the car hard and verified psi at all speeds etc. It’s not pretty but safe. A friend just picked it up couple days ago. Nice diagnostic tool.
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#10
08-23-2021, 09:25 AM
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My GTO (mild 455 with headers, Q-Jet) noses over or rather flattens out at top of 1st gear, shifting at 4800. It has stock type fuel pump. (whatever a 69 automatic GTO was supposed to have). Other wise runs fine. Is there some volume test that can be run? Say I run a rubber line to the carb with gas and then start the car, how much fuel is supposed to come out of the pump in how much time?
I have a buddy with a very mild 350 '73 Corvette, he says it runs well except it flattens out at 3000. After reading other posts about junk fuel pumps here, I wonder if both of us have bad fuel pumps. I have the Carter pump recommended here but I'll have to cut my steel fuel line and splice with some rubber hose to use it, plus block the return line. The Carter pump doesn't use one. |
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