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1974 350 4 speed. Original cap was not vented. We did FITech EFI and a new in tank high pressure fuel pump. We used the original fuel neck. i stay with NOT vented correct. Thanks. Tom
The original cap was not vented because the venting occurred through the evaporative charcoal canister. You need to vent the tank in some way to prevent pressure build up and more importantly gas tank collapse. The use of a vented cap either way adds another potential venting devise.
NEVER allow full manifold vac to be applied to the fuel tank, even with a vented cap......
that suck line always goes to the PORTED vac witch is above the throttle blades, /just after the air cleaner if you will.......
The original cap was not vented because the venting occurred through the evaporative charcoal canister. You need to vent the tank in some way to prevent pressure build up and more importantly gas tank collapse. The use of a vented cap either way adds another potential venting devise.
Yep- need to vent it- however I don't think the cap will let it breath enough with a fuel injection system...plus depends on whether you are running a return or return-less system.
When I went with fuel injection set up- I added a vent/roll over valve and a charcoal canister for it to breathe through so I did not get gas fumes/smell.
Not sure why you worry about vented gas caps. The one I bought yesterday has a one way check valve so it pulls air in when the gas is consumed but no vapors or fuel will escape out. Balkamp brand $7.00 or so.
Not sure why you worry about vented gas caps. The one I bought yesterday has a one way check valve so it pulls air in when the gas is consumed but no vapors or fuel will escape out. Balkamp brand $7.00 or so.
What happens when your car is sitting in the sun and the gas expands?
Reshound, that's SAD, that pix.....I not 100% sure as to earlier vettes but my '72/up has a vent valve on the left upper edge of tank, supplied with a hose from tank to that black plastic valve, it has a float in it to catch raw gas from sloshing into the hose going forward when tank is full enough to toss fuel down that vent tube/hole.....
that other hose it's keeping the fuel from, is there with slight vacuum like I said previously, to suck fumes from tank into the carb/injection with LO sucking pounds as it's before the throttle blades, but after the air cleaner.....
This followup note is directed to MelWff and also all who posted their remarks:
Most interesting post....I just had my 78 tans/sending unit etc installed and so far so good as in no visible leaks but wifey tells me the garage always smells from gas and my usual response is that most vintage cars that are garage kept will almost always have some fragrance.......
However, the PO had removed the OE vapor canister and the installer did connect the top left side of the tank fitting and did run the hose..somewhere???
That being said do I still need to have a vented gas cap installed???
The key to your question is to find the other end of that hose, start in the area of where the canister was originally mounted.
Yup, replace that canister and put the other hose up to the ported vac like I said before......the valve on my canister WAS vac operated on full mani vac...but the valve failed in the open position of all things, and so it's just connected with the two main lines, one to that float valve at the tank, other to the carb as described.....and I have a locking vented cap, no fumes, and I recommend a cap with vent both ways, because I been there with the pressure/heat build up, really easy in FLORIDUH......especially is you drive it a bit and circulate that gas back to the tank when full, and that float valve can close with pressure holding it closed.....I went to take the cap off, and all sorts of pressure relief, I just glad it didn't mess up the tank....
What happens when your car is sitting in the sun and the gas expands?
Pressure, volume and temperature...How much fuel volume is displaced by a temperature change? Is it more than a cup or two??? The volume of fuel changes a little and the air in the tank is compressed slightly by the small increase in fuel volume. You will loose more fuel volume than that on the drive home from the gas station. If the drive is short and you are paranoid you might not want to top it off all the way. Did they warn us of this danger in the owners manual? Did GM design a fatal flaw in the fuel system all these years ago?
High pressure fuel pump was installed in the fuel tank
If you are running a return- you definitely need to vent correctly.
At idle 98% of the HEATED fuel is returning to the tank- that'll creates a lot of vapor.
Your Hyperfuel in-tank looks like a knock off the the Aeromotive Phantom I am running.
I have a non-vented cap- and from what I have read just changing over to a vented cap (designed for a carbs) cause venting issues- not to mention that gas smell.
The vent on the Aeromotive Phantom Pump - manual said the vent should be 6" above the tank and use a roll over valve. In a Vette to do this the vent would have to be a couple of inches above the rear deck!!!
So I added a roll over valve- connected it to a charcoal canister ( used in GM cars for the brake vacuum line) and then a vent used in marine applications placed in the antenna hole. I also ended up going w/ Russel Synthetic rubber hoses to hopefully stop the permeation of the ethanol in the gas - and gas smells.
roll over valve
Vent for boat hulls-
Vent in the antenna hole-
The other thing I did was putting a fuel cooler on the return -a few OEM new cars have it- can't imagine it would hurt ...
So my thoughts- no gas smell- have a roll over valve if I am ever unfortunate to roll the car. I also adding a Ford inertia switch to shut the fuel pump from an impact. Has a reset and mounted it in the battery compartment -for easy access.
From: Las Vegas - Just stop perpetuating myths please.
Yes as Richard mentions when you add a full functional return line you need an effective tank vent. I learned the hard way when I plumbed in a constant return all the way from the carb. You would (or at least I did) expect the overflow check valve to protect the charcoal canister but it didn't. Just a normal right turn with a full tank and the tank became pressurized! The exit vent now became the vent on the charcoal canister and fuel was flowing onto the frame right next to the exhaust header! I don't know why I didn't become a news story that day but it didn't start on fire.
So now I run a vented gas cap along with a new check valve on the tank vent. Not very professional but works until I can install better. And this reminds me now that I'm going to replace the fuel tank due to chemical corrosion.
I really think Richard got it right and something to take note of.
Vented or not vented gas cap
