Danger To Manifold - Stupid Aux Blockoff Mistake
 

When I originally did my turbo in my underground I made the decision to not bother with aux ports for simplicity. I wanted to remove that part of the intake because it makes taking off the upper part way quicker and it was on and off a lot when i was making stuff. So I made plates out of 3\16" Aluminum so the ones on the lower intake wouldn't potentially react with the existing cast lower. The 2 ones on the lower intake see no pressure ever and have tapped holes into the aluminum so overkill mounting strength. The plastic upper has those 2 brass sleeves with through holes because the tapped holes are in the inserts on the aux part of the intake.

I thought those brass sleeves were ribbed into the plastic and would not move. I was wrong. I used an M6 bolt with a nut but no washer because I thought the brass was locked in there. The nut was barely larger than the diameter of the brass sleeve. This worked for a long time at low boost pressure (.4 bar/6psi). Recently I got a boost control solenoid and now running .9bar/13psi this happened.


https://cimg4.ibsrv.net/gimg/www.rx8...04789c71b7.jpg

Fortunately this happened on the highway near my house. The car starting accelerating on its own and would rev to like 6k when out of gear. The haltech was seeing atmospheric pressure and was fueling accordingly. Exacerbated by the fact I haven't tuned that part of my map so there was tons of fuel there to make it rev. Had to stand on the brakes to make it the 3 blocks through my neighbourhood.

The solution is some nice bog washers on the top side.


https://cimg5.ibsrv.net/gimg/www.rx8...88aa5b2fd4.jpg

It was an alarming situation so I wanted to post it up.

Cheers

not too surprising because when it’s bolted to the actual manifold piece that insert is supported by it, but not supported when you have a plate on it like that. So take the ID of the hole the plate is covering and calculate the square inches of area and then multiply that by the boost. I’m going to guess it’s about 2.5” ID or so, approx. 5 sq in x 13 psi = 65 lbs of force trying to push away and deflect that plate. You may even want to consider making it thicker to be sure it can’t deflect the plate enough to possibly leak some under full boost.

I used to work in Japan, building intake manifolds. All the sleeves and nuts were smooth, and we could do what you did and just hammer them on or off to save the part, if it was worth saving.

well again, the mating part that’s no longer there has the threaded sleeve fixed in it. In the original NA application it only has vacuum pressure working on it. So when you’re bolting it down the bolt is pulling and sandwiching the the two together. Also, with that mating part the cavity is open then rather than having a flat surface area for any pressure force to be applied to. So while a full manifold for an FI application has the positive pressure inside and working against the internal surfaces, it’s not the same as that plate.

People have blown apart UIMs before having those pull out. Which for FI is then transmitting the force of the new flat surface area directly on the sleeves that way. So the washer does assist in that regard, but the force on the plate still exists. If the plate is not thick enough it could potentially lift-twist enough around the middle areas of the gasket surface and leak depending on the material and thickness. However, even with a full manifold it probably makes sense to use washers like that on all those joints just to be sure and minimize any potential leaks. So it seems to be a good point and a worthy thread for FI owners.

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Interesting ...not something you would think about normally ...but obviously needed to be addressed with sound engineering.