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1725 Flame Trap

Discussion in '"Stock" Alpine' started by Durhamguy, Aug 17, 2021.

  1. Durhamguy

    Durhamguy Platinum Level Sponsor

    I know this topic has been discussed before but would appreciate some input. My S4 came out of the shop this week with repaired floors, a positive safety check and is ready to be run - yippee. Apparently, it is the first time it has had a Ministry safety check in 20 years according to the previous owner who was a mechanic/dealer. It is a 1725 Rapier block, Alpine heads, crank and rebuilt 5,000 miles ago, again per previous owner. The Rapier engine block # is B022008680 H(?) LSX.

    The engine does not have a flame trap (see pictures) and based on previous posts, I assume that it should. Am I incorrect?

    Attached Files:

  2. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    From your pictures it is a bit hard to tell how you are plumbed.

    On a stock Alpine 1725, the hose from the tappet cover would be connected to the PCV valve on the Strombergs intake manifold. I don't see that in your pictures. No PCV valve?

    There would be a fresh air hose from the Strombergs to the flame trap and then to the oil filler neck. It looks like you have a remote air filter supplying air to the Strombergs. What is connected to the oil filler neck?



  3. Durhamguy

    Durhamguy Platinum Level Sponsor

    There is a rubber hose on the Stromberg side of the oil filler neck. That hose loops around against the bulkhead to the passenger side and (see 3rd picture) is connected to the lower engine block below the spark plus wire in the picture. The guy I bought it from was old school, he fixed what needed to be done and told me when he rebuilt the engine he set up as they did in the UK . Yes, the air supply to the Strombergs is not like anything I have seen on this forum. I have not located a pvc value yet. See extra picture of air supply set up plus a better picture of the hose connecting back to the block.

    Attached Files:

  4. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    I see a plug in the port where the PCV valve normally is.

    I expect the custom air filter arrangement was created because the series 4 brake master reservoir interfered with the normal 1725 air filters that sit on the Strombergs.

    I don't think you want the tappet cover vent connected to the oil filler neck. Nasty air getting re-fed back into the top end of the motor. Maybe someone else can provide the details for why that arrangement is not desirable.

    So you could try to source a PCV valve and connect the tappet cover vent to the PCV valve. Original PCV valves seem hard to find. I think a standard motor V100 PCV valve will work well enough as a replacement for the stock PCV valve. I have run both the stock PCV valve and the SMP-V100 and did not notice a difference.

    I think Tim R doesn't run with a PCV valve and he vents the tappet cover vent open to the ground. I think he still has fresh air coming into the oil filler neck through a flame trap, though.

  5. Durhamguy

    Durhamguy Platinum Level Sponsor

    Thanks Mike, I am going to think on that and do more research. It makes sense that looping the gases from the tappet to the oil filler neck is a problem. Initial thoughts are that venting the tappet to the road and installing a K&N filter to the oil filler might be the preferred solution. Would you be aware of th K&N filter folks use on the oil filler?

    Again, thank for your valuable input.
  6. rixter

    rixter Platinum Level Sponsor

    I can't see where you would getting any venting at all. You have a closed connection from the valve cover to the side tappet cover. Unless I am missing something, there is no provision for exit of gasses or entry of fresh air to chambers that would have crankcase gases. This should be resulting in how engines were even before the draft/road tubes on the tappet cover.... and my understanding is that this would be increased contamination of the oil and increased possibility of oil leaks at gaskets. A flame trap inserted into this connection hose wouldn't serve any purpose if there is no connection to the carbs/manifolds.

  7. Durhamguy

    Durhamguy Platinum Level Sponsor

    Based on your input and Mike's, I would agree. Venting is the issue. Thanks David
  8. Tim R

    Tim R Silver Level Sponsor


    We vent both the filler neck and tappet chest direct to atmosphere. We turned the filler neck round and run a pipe straight down. When this is parallel with the metal pipe coming out of the tappet chest we clip the two rubber pipes together, run them down and back and vent them under the car. We do not use a PCV or flame trap. We have no fumes and no problems running it this way.

    Tim R
  9. Kristian Jonsson

    Kristian Jonsson Donation Time

    I always threw these flame trap jars in the dustbin.

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