Automotive Intake Manifold – Boss 302 Independent Runner

Discussion in 'Lost foam casting' started by Al2O3, Apr 24, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Ok, instead of an intake manifold lids, let’s make the whole darn intake! It’s an independent runner Boss 302 intake for a pair of Inline Autolite Carbs. Easily my most ambitious project yet. The design aspects were more challenging than cutting the foam. Had to do some fairly extreme things to get it packaged properly. The goal was a long runner intake that would fit under the hood of a street car without a hood scoop. The carbs were developed for TransAm racing but never met the homologation rules. The intake is intended to have features of similar racing intakes of the 1969-1970 TransAm racing era.

    The flanges were easy.

    1 Flanges.JPG

    The runners were a bit tedious but all-in-all not too bad. There were eight of them and six pieces in each assembly. I built them similarly to how I make my water necks but they have a rectangular cross section with radiused corners. I used a pin-wheel jig which is basically just drilling a hole in a piece of foam and spinning it under the cutter on the pin router. These were fast and easy.

    2 Toroids.JPG

    Then a right- and left-hand template for the rest of the runner to make each half.

    3 Runner Halves.JPG

    Then hot-wired the bend segments and glued the halves together.

    4 Runners and Bends.JPG

    Then started piecing it all together on an assembly fixture.

    5 Piecing Together.JPG

    I fit everything up with tape and two-sided tape, did some fine tuning, and glued it all together. It’s starting to look like an intake now.

    6 Flange Runners.JPG 7 Flange Runners.JPG 8 Asssembled.JPG 9 Front View.JPG

    Glued the runner assembly to the flanges with fast grab tacky glue and weighted it to dry overnight.

    10 Glued-Weighted.JPG

    -More to come.

    BattyZ, Peedee, Rocketman and 8 others like this.
  2. What can I say, it's a work of industrial art.
    Nick Lazenby likes this.
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    Now that's just friggin cool :cool:
  4. Jason

    Jason Gold

    You must go through some serious pink stuff! Please tell me all this work produces another couple hundred ponies and it's not available off the shelf???

    I'm with you, I hate hood scoops. I like sleepers.
  5. GTS225

    GTS225 Silver

    Heck of a project, you actually possess a pair of these ultra-rare, in-line 4-barrel carbs?

    Yes, I'm aware of their existence, but have only seen a pic, probably 25 years ago.

  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Mark. I may have to stare at the pattern for a while after it's complete and before it gets evaporated. It's going to be a 3-Candle pour ;)

    Going to have to go to my big furnace for this one. With a conservative feed system, an A20 wont do it. My next biggest crucible is my A60 :eek:

    Yah most of it turns into fluff into the dust collector.

    A couple hundred? They're only 302 cubic inch engines but like anything else, in the hands of the right individual, can produce some impressive results.......definitely won't find another one like it.

    THOMAS A BEASLEY likes this.
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks for the likes fellas. The XPS foam continues to impress me. In the post above, I had it weighted with 45lbs and it was still quite solid, yet the pattern is feather light. It should be a very stiff intake when it becomes aluminum. I didn’t have much time to work on the intake today but I did make and attach the carb flanges.

    11 Carb Flanges.JPG 12 Carb Flanges.JPG 13 Carb Flanges.JPG

    Much easier to port and blend foam than aluminum

    14 Blend Flange.JPG

    Next I’ll start walling off the openings so the space between the bottom of the runners and engine valley can be sealed with a plate and used as a vacuum plenum……..

    15 Plenum.JPG

  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Weather has been great the last couple days so I’ve been enjoying the great outdoors. I like it when projects get to this point because there are lots of little details I can do an hour at a time, like walling in the lower plenum and adding mounting bosses.

    To wall in the lower plenum, I just cut a template from thin foam and then used it to reproduce the others, carving and fitting with a razor knife where needed, then installing them in the windows and applying fillet.

    16 Windows Closed.JPG 17 Window Close Up.JPG

    Because of the layout of the intake, four of the mounting bolts need to be installed inside the runner through the carb openings. I don’t like the idea of hardware inside an induction system, but it was common on intakes with similar layout because there is just no way to otherwise accommodate the mounting hardware. In this case the bolts are long enough they are captive should they ever come loose but it does mean after the initial installation the carbs must be removed to re-torque the intake mounting hardware. I made a fixture out of some recycled MDF to position the intake at the 22.5 degree angle of the boss/bolt holes, and transferred the centerline position of the bosses to the fixture.

    18 Fixture.JPG

    I clamped the fixture in place on the drill press with the target location directly under the drill press center. Then I could just align the pattern on the fixture to bore each hole.

    19 Pattern On Fixture.JPG
    20 Pattern Aligned.JPG

    There was a little pucker factor boring that first hole in the pattern so just to be sure, I chucked up a long 1/8” diameter drill to insure it was properly aligned and hit the target location marked on the pattern. Then the Forstener bit was used to bore the hole for the boss. Bullseye!

    21 Bullseye.JPG 22 Bullseye.JPG

    This worked very well. The bosses were made with a plug cutter. The resulting joint has a complex intersection with the runner wall but the method produced a very nice fit. This is an example of the design freedom enabled by evaporative pattern casting. It would be very difficult if not totally impractical to try produce such detail in a cored sand casting. With lost foam, it’s just cut and paste.

    23 Boss Installed.JPG

    I then used a round nose router bit in my die grinder to blend it back to the internal runner surface.

    24 Blended.JPG

    When the casting is machined, the bolt hole will be counterbored to recess the bolt head below the runner surface to minimize any disruption to flow.

    I’ve done quite a bit of detailing. It’s almost done. I just want to announce I now own the world record for the number of feet of wax fillet applied to single foam pattern!

    25 Detailed.JPG 26 Detailed.JPG 27 Detailed.JPG 28 Detailed.JPG 29 Detailed.JPG 30 With Carbs.JPG

  10. DavidF

    DavidF Administrator Staff Member Banner Member

    Just remember to recite the magic words when you go to pour it.....
  11. Jason

    Jason Gold

    Sacrificing a chicken works for me.
  12. Three candle pour?, that's gotta be a five candle pour at least!:D.
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I usually wait until just before the pour to say this but given the stakes,..........this is never going to work.............:):)!

  14. Melterskelter

    Melterskelter Gold Banner Member

    Maybe don’t pour it. A little silver paint from a shaker can... Who’s to know? Yowzers, you are putting a time investment on the line.

  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Won't work, it's 1.3% oversize.......:D:D

    With the pattern completed, my thoughts have moved onto to gating and pouring. As I was making the pattern, I developed a pretty good idea on how I was going to gate it. I’ll make a separate post in this thread on that subject shortly.

    This casting will be a number of firsts for me, which has me a bit nervous. It’s my largest and most complex lost foam pattern to date by far. That's a lot of foam to evaporate. The raw casting will probably be around 25lbs but the feed system and a generous pouring cup could easily add another 10lbs. Pouring short would be a disaster so also should have a little buffer for spillage or burpage out of the cup.

    Obviously my A20 and smaller furnace won’t do it. My next largest crucible is an A60. It’s a beast. My larger furnace was intended to be fuel fired but does have electric insert. I built a shank for the A60 a long time ago. It was always intended to be used on a pouring cart or with lifting equipment so I wasn’t too concerned about weight. The shank weighs 55 lbs. The crucible alone weighs 33lbs. So with 35 lbs+ of metal, that means >123 lbs. There was a time when I might have had thoughts about pouring it by hand but that time as given way to age and wisdom.

    I’ll mold this in my larger flask (30 gallon drum) and molding rig which means the pouring height will be at least 36”. I think a gantry crane and hoist makes much more sense to safely handle this and future pours. So I’ll have to tackle that before the pour………more on that later.

    Given the size of the pour, I think it also requires a larger pouring cup. A bigger pouring target and larger buffer of metal volume to help ensure a continuous pour can’t hurt. Seems like a good opportunity to use a different construction method for that cup. -More on this later as well.

    I plan on plenty of future parts in this size range so the handling equipment for larger pours will be a good investment of time but I have some work to do before I pour this part.

  16. Kelly,
    This is an amazing thread to follow I now see what you were talking about in the picture of the Inline B carbs on top of the intake. that looks like 15 pounds of stuff in a 10 pound bag! the 351C would definitely have more working room.
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks John, it's been akin to building two large houses on a small lot.........but I think I'm getting there.

  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I got the pattern prepped with the feed system. In lost foam the lines between gates and runners can tend to blur. Here’s the pattern with feed system.

    31 Intake Gated.JPG 32 Intake Gated.JPG

    I’ll pack this in my large molding rig flask (30 gallon drum). It will be oriented vertically and slightly angled with the top of the intake facing downward. This seemed to promote better filling of the intake runners.

    I'll position it with the water snouts at the bottom. I actually wanted them at the top so they would see the hottest metal, but there is a cavity in the lower plenum that would not fill/pack well unless it was oriented in this manner.

    I wanted a long contact area the length of the part, contacting the more massive locations, and preferably centralizing or minimizing the total molten metal travel distance to any location on the part. Ease of de-gating was also a factor. The base of the flange was the obvious location for a pair of gates on the bottom. The bosses in the center of the tunable vacuum plenum on the top side of the pattern looked like an open invitation to feed metal. The sprue is 1 ¼" square.

    I was trying to get a good estimate of part/pour weight. I got a surprisingly wide range of results and tortured myself with the following dribble.

    Since I knew the foam density, I thought I’d just weigh the pattern and use that to estimate weight. So I weighed the pattern on a triple beam scale. It weighed 174 grams or .383 lb. The foam is supposed to be 1.3lbs/ft3. When I used that density to calculate the volume of foam for this pattern weight I got 509 in3, and since aluminum is about .1lb/in3, that meant 51lbs! Wow!!! way is that correct.

    33 Weight Estimate.jpg

    Then, as a check, I cut a block of foam, calculated the volume, weighed it, and this suggested the foam density was actually 1.5 lb/ft3. The Foamular 150 is supposed to be 1.3lb/ft3! Arghh! What the heck? So if I recalculate above at that foam density, I get 44lbs……still no way that is accurate.

    The big error was induced by the wax fillet on the pattern. It is very dense by comparison to the foam. Problem is I didn’t count how many sticks I used, but I figure at least 20 strips at 24” long. So I weighed 10 strips of wax. The weight of 10 strips of wax is equivalent to 7.8 in3 of foam or nearly 8 lbs estimating error in aluminum casting weight. If I used 20 sticks of wax, that would overstate the estimated casting weight by 15.6lbs. So this further reduces the estimated weight to 28.4 lbs.

    I decided weighing the entire pattern is not a very good method for estimating casting weight, but for grins, I weighed the leftover basic building blocks of the pattern….no wax in these parts, just a little glue and estimated the remaining volume using basic geometric shapes. This method suggested 28lbs without feed system.

    I have an several intake manifolds that are reasonable proxies for this intake and they range from 21-28lbs……no feed system of course. Estimating the weight of the feed system was more straight forward. 6 lbs plus whatever is in the cup which could be 5-10lbs. The other factor is spillage or burpage.

    Anyway for those keeping score, if I use the 28 lb estimated casting weight, with gating and cup, I get 44lb pour, with no spillage, boil-over or belch. I’ve got a feeling that is a bit conservative but pouring short would be a disaster. There is a lot of buffer in a 10 lb pouring cup so it will take something circa a 45lb pour.

  19. DavidF

    DavidF Administrator Staff Member Banner Member

    Getting close to pouring??
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Have to complete the gantry crane/hoist and build a bigger pouring cup and then will be ready. Got few other domestic projects to take care of first though.


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