Gas leak -- very puzzling

[Steve C]

Jack,Richard,,

Jack,

Why do you think > 70mph air is entering the roof vent, what is causing the low pressure in the cabin?

Have you tried this with the NACA duct servo open (switch NOT on recirc) that should bring air into the cabin and exhausting through the roof vent or cracked toll windows...if not enough air volume with just the NACA duct open what about with blower on high (all that air coming just from the NACA duct has to go somewhere...where does the majority of it go if not out the roof vent unless the toll windows cracked? Are you and Dennis sure your NACA servo wiring isn't reversed (MINE WAS, I was in recirc when I thought I was bringing outside air in).

Richard,

Looking at some of your earlier pics in this thread see where the fuel tank vent lines run up to the upper filler assembly that bolts to the mono...what Jack and I are saying is that the sponsoon area around the mounted tank is all open and that this open space continues around the vent lines and the main fill tubing vertically (so the sponsoon area is in fact a big L....down from AROUND the fill pipe and then horozontally where the tanks mount). Question is wheather the vertical void is in fact not sealed from the cabin. As Jack explains: there are lightning holes in cabin side mono panels. I'm OK with this as long as there is a positive pressure in the cabin during forward motion or with the blower on high with the NACA ducting open to outside as I wrote above because with a positive pressure (if it does exist) it will push some air through the sponsoons and out a rear sponsoon vent if installed therby purging the void.

Thoughts??

Steve

[Richard]

Well Spielberg I’m not, my attempt at making a video was a total bust. I did however take some additional pictures which should clear thing up. Pictures are as follows.

1. “Fake” old style gas cap, besides being decretive its only use is to contain and then dump any overflow fuel out of the bottom of the car through one of the three vent lines.

2. Real gas cap and filler neck that may or may not work as expected. Two vent lines that come up from the tank enter the filler neck just below the cap.

3. The tank end of the filler neck as it enters the sponson.

4. This is the important one. It shows the area where the filler neck and vent lines pass through. As you can see it’s sealed at the bottom to the top of the sponson and at the top to the gas cap thus separating it from the remaining A pillar support and dash area. It’s kind of like a stove pipe stuck onto the front of the sponson.

5. This picture shows the outside of this “pipe” as it passes through the A pillar support. I stuck my shop light into the area behind the dash and as you can see the light comes out the holes in the side of the A pillar but more importantly it shows the cover (pipe) around the filler neck and should prove that that area is separate from the dash area.

I'll include the rest of the pictures I took just in case it helps.

[Steve C]

Hi richard,

After your pics above I get it. The "stovepipe" really describes it.

I havent pulled my inspection cover off yet to inspect but, I looked at a pic I posted in the SPF forum under P2125...on page 3 showing new inspection plate gaskets and it looks like I do have a base of what might be the "stovepipe" like yours.

If I'm like you with the stovepipe and closed off sponsoon to the void where the large holes are plugged it won't help to drill holes in the plugs as Lynn has; we need another opening into the forward end of the sponsoon. Where do you think would be a good place that won't let water or debris enter?
Over next few days I'll try to inspect.

Still wondering about Jack's comment re the roof vent and wondering what he thinks about my question about positive cabin pressure.

Steve 2125

[Jack Houpe]

Richard,I DO NOT have this stove pipe, but wish I did, I see that SPF has made more my changes to in order to keep these fumes from entering the car. I retract my statement about the holes going to the cab. I see that our cars are 33 apart, so I wonder when they started making the change? Your pipe has solve many of the problems I have been trying to fix. I hope to see and meet many of you on this form at Road America, it will be good to compare cars and notes.

Steve, Dennis told me he has done a slip stream test with small streamers taped to the car, the slip stream changes as speed increases, creating vortices's. That is why the air starts coming in rather than going out at speed. Having the vent open for positive pressure of the cabin should work but if your trying to cool your car on a 95 degree day it defeats the purpose of AC don't you think?

[Richard]

It would be helpful to have some pictures of an early car.

[Steve C]

Jack/Rich,

Still haven't had the nose clip off to make sure but, I think like Jack I have the pre stovepipe design.

Was able to look into the area with 3 plastic plugs and see that Olthoff drilled relief holes in the larger plug (holes drilled in the plug sidewall not face on).

I bought some fittings from Boat US used to vent fuel tanks (similar to the fitting Lynn constructed) and will install these where SPF now installs the rear sponsoon vents (like Richard shows).

I'll be happy with this set up (actually I'm OK now...had full fuel tanks over the winter w/o any fuel smell in cabin...had the car out over last wk a few times and don't notice any fumes so with the added rear vents I'll install I'll feel even better and will use them to "sniff" occassionaly as another precautionary PM.

Steve P2125

[Richard]

Steve, I hope Laurent doesn’t think we hijacked his thread because I think this is all pertained to the understanding of the SPF GT40s fuel system. We could still use some input from Laurent to see if he’s found out anything.

At this point I’ve crawled through just about every square inch of the car in an attempt to fix a few inherent problems that comes with trying to drive a race car on the street. It will also help me if something breaks as I’ll have a better chance of fixing it myself.

I’m worried that the early cars just have a hole at the top front of the sponson where the filler neck comes through that opens into the A pillar support and the interior of the car. Granted if for some reason any part of the fuel system were to leak we would all be in trouble. However on the early cars I’m worried that fuel would have a better chance of getting into the cabin area in the event of an accident.

I would think we could come up with a retrofit that would segregate the two areas that wouldn’t be that hard to install.

Just my $.02.

[Steve C]

Richard,

With your excellent picture taking skills and with your car partially disassembled would you be able to show the location you refer to: (" that opens into the A pillar support and the interior of the car?").

Steve

[Richard]

Steve
So you’re resorting to flattery, OK that works for me. I’ll have to work on my movie making skills as I see it as the best way to show how everything is connected. I’ll see if I can barrow a friend’s POV camera (point of view) which should allow me to get some A pillar support interior shots. It will be next week as I have to travel to Boise to watch my oldest son graduate from college this weekend!

[Steve C]

See pics below of vents I added today to the R & L rear sponsoons (similar to what SPF is now doing as shown by Richard above):

This post before and pivc of vent components (vent is a chrome plated brass thru hull vent purchased form "West Marine" store.

[Steve C]

Below see hole location and completed R & L sides:

[Laurent Gauthier]

Hi All,

Here's a quick update on that apparent leak. I checked the crossover line and it looked fine, so that was not the issue. So I took out the plastic joints on the caps. I drove 400 miles with full tanks, empty tanks, in between and I had not problem. I think that was it, somehow the caps were sealing too much.

One think I experienced however driving under a massive rainstorm: I essentially took a shower.

Thank you all again for your advice last month, I would not have figured out the problem myself!

Laurent

[Jack Houpe]

Originally Posted by LOG

Hi All,



One think I experienced however driving under a massive rainstorm: I essentially took a shower.


Laurent

If you ever figure out where this water comes in from, let the world know.