Twin-carb blow-through

I'm almost done building the plenum box for my setup.

I have two Weber 36-36 carbs off 1985-ish Masterati Biturbos on ...

... a Clifford dual-quad intake with...

...home-made adaptors.

The plenum box ended up being about 1100 cubic inches to fit both carbs inside. Corky Bell recommends that the plenum be about 110%-120% of engine volume, meaning that my plenum is much larger than it should be.

Does anyone have any experience / recommendations on this subject?

I'm thinking that once I'm done, I'll find some pieces of foam or wood to put inside the plenum box to reduce its volume. What do you think?

You would need to find something like Nitrophyl foam that would not collapse under boost. As big as your box is you might want to reinforce it in areas. I seem to remember someone running a homemade sheet metal intake with a turbo in a inline six van and the intake cracked. I could see something similar happening if you have large surface area for your plenum. IIRC the reason for cracking was in the un-reinforced area the sheet metal was flexing and cracked from metal fatigue.

Thanks for the feedback.

Reinforcement sounds like a good idea to stave off a problem I would not have foreseen.

As for my foam filler pieces, I'm trying the pink insulation foam you can get at Home Depot. I'm going to subject a piece to some heat and see how it holds up. I'm pretty sure it'll hold up to pressure.

Might want to expose some of that foam to gasoline to see how it acts. Wouldn't be surprised if it melts. Nitrophyl is a trademark name for material designed for use in petroleum environment.

Instead of foam or something similar why not just separate the plenum into two smaller plenums and connect them with a piece of tube or something like that. That would get your plenum size down and would also make it stronger.

I wouldn't sweat the volume, oversize won't be as much a problem as undersize. Can you share a picture of your plenum?

As for the foam, I am going to assume that we are discussing the carb floats and not the actual plenum. Hollow carb floats collapse under boost. I would hesitate to put ANYTHING into a carb plenum- ever seen an engine inhale something solid? Or pieces of foam pulled through a carb...

I did some experimenting with my pink insulation foam.

When exposed to heat, the foam melts like ice cream.

When exposed to gasoline, it gets all gooey.

I'm thinking of turning to some kind of lightweight wood at this point.

The experiment continues....