Making Fiberglass Velocity Stacks

[SBell]

Last year I made a set of fiberglass velocity stacks for my 2.7 MFI motor and a few pelicans who have seen them asked what the process was like so I figured I would just start a thread in case anyone else wanted to try to make something similar. I'll preface this with an acknowledgment that I used some tools that most people probably don't have.

[SBell]

First task was to make the trumpet shape. I largely copied the dimensions of a factory S stack since my engine is essentially an RS spec motor. I did make some modifications based on some intake flow papers I read and to make them easier to lay up.

They were done with a wet layup on a 3D-printed mold. I used fiberglass tubing so I didn't have an seams. Getting fiberglass parts off of round molds is a challenge even with mold release. I tried a bunch of methods and ended up greasing the printed mold and then shrink-wrapping the entire mold before laying up on the shrink wrap.* The mold has to be printed from ABS or another more heat-tolerant plastic because the heat from shrink wrapping will warp* plastics like PLA. I 3D printed lathe fixtures to trim the top and bottom to get relatively consistently sized stacks.


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[SBell]

I made some vacuum bagged fiberglass flanges bonded to each stack to hold the air filters. I again 3D printed some fixtures to use my CNC router to trim out the holes consistently.

I had SendCutSend laser cut the air filter plates and lower TB flanges. Both sets of flanges were bonded using a methyl methacrylate based structural adhesive from Permabond.

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[stownsen914]

Nice work. Like many nice things, sounds like substantial effort. With a nice looking outcome.

[PeteKz]

Why not 3D print the trumpets, instead of printing the molds to make them out of hand-laid fiberglass?

[SBell]

Originally Posted by PeteKz

Why not 3D print the trumpets, instead of printing the molds to make them out of hand-laid fiberglass?

I thought this would be more fun. I also wanted the more period look of the fiberglass stacks like on the 908, 910 racecars.

I'm very comfortable with CAD and 3D printing so that wouldn't have really been anything new for me. I'm also not in any rush since I haven't found a car to put this engine in yet. Projects like this help me scratch the Porsche itch while I'm away at school.

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[r lane]

We like the challenge of designing and making things, I definitely get it. I just fashioned a set of dies to form fender louvers. a

[r lane]

Amazed at your system and final product. Gotta ask, but is fire not a concern. I know the factory used them and I assume with good results. The trumpets on the early "Ts" had issues. Had to inquire. Bob

[SBell]

Originally Posted by r lane

Amazed at your system and final product. Gotta ask, but is fire not a concern. I know the factory used them and I assume with good results. The trumpets on the early "Ts" had issues. Had to inquire. Bob

Thanks man, the process took a while to work out. I haven't run the engine yet so I can't say it won't be a problem but I used the most heat resistant resin I could find that would cure without an oven so hopefully it'll be ok.

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[PeteKz]

Originally Posted by SBell

I thought this would be more fun. I also wanted the more period look of the fiberglass stacks like on the 908, 910 racecars.

I'm very comfortable with CAD and 3D printing so that wouldn't have really been anything new for me. I'm also not in any rush since I haven't found a car to put this engine in yet. Projects like this help me scratch the Porsche itch while I'm away at school.

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Got it. Makes perfect sense to car guys.

[JoeMag]

Nice work SBell... Sometime's it's just nice to be a "craftsman" and have something to be proud of along with being functional.

How is the trumpet connected to the black part that holds it onto the throttles?

I think you'll be okay on temp... When the car is running the throttles are actually not that hot (say below 100F because of all the air flowing through them). At idle and after you turn car off is when they get hot (up around 200F). I did a test by putting a thermal couple between these printed parts and my throttles to gather this data (readings to my AIM dash).

[SBell]

Originally Posted by JoeMag

Nice work SBell... Sometime's it's just nice to be a "craftsman" and have something to be proud of along with being functional.



How is the trumpet connected to the black part that holds it onto the throttles?



I think you'll be okay on temp... When the car is running the throttles are actually not that hot (say below 100F because of all the air flowing through them). At idle and after you turn car off is when they get hot (up around 200F). I did a test by putting a thermal couple between these printed parts and my throttles to gather this data (readings to my AIM dash).

Thanks, as a bonus, even with the waste from R&D I still came out ahead of buying T stacks and boring them out.

Those black flanges are cerakoted aluminum that are bonded on using a methyl methacrylate structural adhesive from Permabond. I could dig up the specific number if you're interested. The datasheet showed pretty good bond strength specifically for aluminum-fiberglass and fiberglass-fiberglass and it is clear which was especially nice for bonding on the upper fiberglass flanges.

The resin I used is good to I think 220F and I believe to adhesive is about the same so hopefully I should be ok.

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