does a semi crushed fuel line mater much?

Grumpy · Sep 6, 2016

mr. S said:
Found this while installing new springs on my 55 the other day. Looks like it got partially crushed by a lift at some point. Think it could have caused fuel delivery issues, or not so much?
it's 5/16" metal fuel line, I would think still enough for a 400hp 350.It looks like the line was squished by careless lift pad placement at some time in the past

The cross sectional area of a typical 5/16" fuel line, will allow the typical chevy manual fuel pump too fill a carburetors fuel bowls just fine under general driving conditions,
but if you put the gas petal to the floor, and hold it there for several seconds , it will have a hard time maintaining the full fuel level, thus under full throttle, the cars likely to run ok through first and maybe second gear then fall on its face, or develop what feels like a bad ignition miss, as the fuel bowls level drops and the fuel flow can,t keep up with demand,
many guys will think its an ignition related issue , or maybe "VALVE FLOAT" as it kicks in only as the engine rpm levels exceed about 5000 rpm plus , or blame the intermittent miss on valve float, but the truth is your suddenly running very lean and it cures itself once the demand drops off as you let the rpms fall back into the range where the fuel pump and line restriction allow enough fuel to flow to refill the carbs fuel bowls.
if your building a serious performance fuel system on a street car Id suggest you look at this diagram and carefully read the links posted below.
fuel line size does mater, and just installing a performance fuel pump rated at 80 GPH-to- 130 GPH, will generally help but certainly won,t cure every fuel starvation issue, that the typical stock 45-60 GPH manual fuel pump may be contributing too.

https://www.summitracing.com/parts/anm-cp7838

and rev the engine a few times and watch the fuel pressure it should in theory remain in the 38 psi-42 psi range for most TPI and TUNED PORT efi

If you cut the fuel flow by even 15% on that 5/16" fuel line flow rate at 7 psi by internal cross sectional area, it would reduce the flow to a state where maintaining more than about 275 hp would be rather difficult, and thats assuming the fittings and fuel filter are negligible flow restrictions and the fuel system was working at nearly ideal capacity.
on anything over 350 hp but under 450hp, youll generally want a minimum of 3/8" feed and a 5/16" return line from a fuel pressure regulator
any thing north of 450 hp but under 600 hp would be best handled with a minimum of a 1/2" or AN#8 feed and a 3/8" or AN#6 return line as you always have flow restrictions in filters and line fittings, this chart shows you only need about 45 GPH to provide fuel for a 500 hp engine , but thats the required fuel flow at the carbs inlet port and it assumes thats provided at about 7 psi, at wide open throttle, inertial loads ,filter restrictions and internal fuel fitting restrictions generally reduce flow from the fuel pump by 35%-60% of what left the fuel pump by the time it arrives at the carbs inlet port.
a fuel pump that is rated at 50-60 gph would almost never be used on a 500 hp engine under real world conditions as its almost sure to prove woefully inadequate

NOT A TA · Sep 8, 2016

Fixed a fuel line last week. Car fell flat on it's face a hundred or so feet before the finish line at 1/4 mile drags. New rubber section of fuel line had been put in when new steel lines installed by someone years ago. Dunno if the rubber kinked immediately or as rubber aged from pressure of the lines themselves. I bent the lines to line up better and replaced hose with higher quality fuel injection hose and FI clamps. Car really needs new custom bent fuel line with better curves as you can see there's still a slight kink in the steel line in the lower pic. I know it's a lot more time consuming to make custom lines but I've rarely seen "reproduction" lines fit properly and folks force them into place "just a little" and end up with slight kinks like the one in the steel line shown below.
GET A FUEL PRESSURE GAUGE AND MEASURE DON,T GUESS
how can you possibly set up your fuel system unless you know the pressure and flow rates required and what currently exist's

READ LINKS

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

http://garage.grumpysperformance.com/index.php?threads/how-big-a-fuel-pump-do-you-need.1939/

http://garage.grumpysperformance.co...ss-fuel-pressure-regulators.12776/#post-65998

Grumpy · Sep 8, 2016

great pictures! yeah I find a great many tuning issues are really related to inadequate fuel delivery due to crappy or non-existent fuel system design or thought going into its parts selection,one of my favorite stories was related to a guy who had a 1966 pontiac lemans he installed a 540 big block chevy and a turbo 400 transmission in, along with a ford 9" differential, the car originally had a 6 cylinder engine and he installed 1/2" fuel lines and a bigger fuel pump, but used a brass reducer fitting with a 1/4" internal passage size, to connect those larger lines to the original fuel lines at the tank, effectively making the larger line size meaningless

If your current fuel tank or fuel lines can,t keep up with the engines demands, can you remove the current plate and fittings and drill and soldier in a larger dual fuel fittings

http://www.tanksinc.com/index.cfm/p...t_id=100/category_id=167/mode=prod/prd100.htm

http://www.jegs.com/c/Fuel-Carbs-Intakes_Fuel-Cells-Fuel-Tanks/10297/10002/-1

http://garage.grumpysperformance.co...es-restrict-fuel-flow-rates.12859/#post-66683

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

http://garage.grumpysperformance.com/index.php?threads/how-big-a-fuel-pump-do-you-need.1939/

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

http://garage.grumpysperformance.co...ss-fuel-pressure-regulators.12776/#post-65958

http://garage.grumpysperformance.com/index.php?threads/input-on-electric-fuel-pump-selection.10664/

http://garage.grumpysperformance.com/index.php?threads/fuel-line-sizing-return-vs-feed.3067/

NOT A TA · Sep 9, 2016

I tell guys the same thing about these fire bomb fuel filters. Even though they're made for 3/*" line they only flow through 1/4" because the plastic wall of the tube where the hose attaches is thick.

GLHS60 · Sep 9, 2016

I had the same issue many years ago when I bought my now sold 1967 Pontiac Strato Chief, 2 dr sedan, 427 automatic.

It was not running and after I rebuilt it and got it running it had a fuel delivery issue.

Very hard to find in my case as the steel line was crushed behind a frame retaining clamp.

The line was perfect before and after the clamp, I can't imagine how it got crushed in this exact spot.

Good reminder thread!!

Thanks
Randy

Grumpy · Sep 9, 2016

yes those type inline plastic semi transparent 3/8" fuel line, fuel filters are very common, but they are also very well know potential restrictions and fire hazards

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

Grumpy · Sep 9, 2016

mr. S said:
Had it out today to get the alignment done after installing new springs. Even with the patched section replacing that bad spot, it's pulling hard every time. It had to be causing an issue.

does a semi crushed fuel line mater much?

Grumpy

The Grumpy Grease Monkey mechanical engineer.

NOT A TA

reliable source of info

Grumpy

The Grumpy Grease Monkey mechanical engineer.

NOT A TA

reliable source of info

GLHS60

Well-Known Member

Grumpy

The Grumpy Grease Monkey mechanical engineer.

Grumpy

The Grumpy Grease Monkey mechanical engineer.