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    1. #1
      Join Date
      Jan 2008

      EFI Fuel Venting using Vaporworx GM Module and IIMuch

      I have an older Datsun Roadster that I am upgrading with modern everything and for the fuel system I plan on running E85 since the Autech engine I have is almost 12:1 compression. I have already purchased the SS ring from vaporworx to mount a Camaro V6 Fuel Module, which should both be able to handle the E85 and also support the HP rqmts (~200RWHP). The tank will sit a bit more than 1" down from the trunk floor, so I don't need to build a recess in the tank and I'm following the rough shape of the stock tank which gives me ~ 11 gallons. I will be cutting out the section for Carl's SS ring as seen by the sharpie mark. My question is how to handle the venting on this tank. I wanted to go with the IIMuch system, even though they don't warrant for E85, but their detailed install instructions say that you have to have a domed portion of the tank to allow expansion--a dome which I don't have (and most tanks I see others building online for EFI don't have as well). Other installs just put the vent port on the top part of the tank somewhere. The stock tank cap is vented, but I know I at least need a nipple or something when fuel is added to relieve the pressure. I'd like to minimize gas smells, which is another reason I was considering the IIMuch system. What's the real requirement for venting? If I can't get the domed part of the tank (not happening in my application), what's the next best solution if I can't go with the IIMuch system? Does it matter where the venting will be as long as it's on the top (i.e., is it better to be near the filler)? Thanks for your recco's.
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    2. #2
      Join Date
      Nov 2006
      Mountain Springs, Texas
      Country Flag: United States
      Based on my experience I would put the vent on the filler neck. The higher the better imho.

      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain

    3. #3
      Join Date
      Mar 2015
      Country Flag: United States
      From what I've been told the vent should be higher than the fill.

    4. #4
      Join Date
      Sep 2010
      Orange County, CA
      Quote Originally Posted by showdog75 View Post
      From what I've been told the vent should be higher than the fill.
      The filler neck will be the highest part of the tank, thats where you’ll tap in for the vent. Then you run a line from the filler neck to the actual vent which will be located as high as possible under the car or in the trunk which would then be vented to the outside.

    5. #5
      Join Date
      Aug 2004
      Two ports are better, if you have just the one on the filler neck you'll probably have problems when you fill it. I'd suggest one port at the base of the filler and another one on the tank as high as possible mounted on the side as far away from the filler neck as possible. You'll then T the two together, and from the T run a line up hill to the II MUCH vent. If the tank is properly vented you only need to mount the IIMUCH vent as high as required to prevent fuel from getting trapped in the vent line -- look under your kitchen sink, for an example of a P trap. P trap is bad for venting. These are general guidelines, and are based on experience with other customers, if you have additional questions I'm happy to discuss at whatever length is required for you to achieve a safe and effective solution (888-216-6033). Regarding E-85, I am very conservative on any possible failure mode of the product. if you choose to use E-85 every portion of your fuel system should be inspected on a regular basis especially if you don't drain during storage.
      Installation instructions for the two different II MUCH brand products are located here


      Last edited by JohnUlaszek; 02-21-2021 at 04:35 PM.