Hilborn MFI

[liqu]

Hi, I am building a manifold to mount a Hilborn 4 port on my engine, I have chosen to make it from lexan with a clear epoxy coating on the inside (stops clouding of the runners from the fuel), my question, how much vacuum will the manifold see at the end of a quarter mile? (8,000 RPM, 320 inches, foot off the gas)

Thanks

[user-23911]

All of it.

[MadBill]

Yes, expect total barometric pressure acting on it, zero absolute manifold pressure; that will give a small margin of safety. [By "320 inches" do you mean 320" H2O barometric pressure? if so I'd design for 100" more, JIC you ever come down off your mountain to race in Siberia. (at 32" Hg., highest baro on Earth.)]
Also, assuming your construct has some flat surfaces, count on severe 'oil-canning' due to pressure pulsations.

[liqu]

Hi, I'm worried about the manifold imploding when I let of the gas, I have a pop off valve for a back fire, but nothing for excess vacuum, yes some flat surfaces, I just don't how much vacuum I might experience.

PS the engine is 320 inches

[Belgian1979]

Almost complete vacuum

[Newold1]

Why are you building an intake manifold out of lexan?? Is this for flow testing or something. I definitly would not run something like this in a car or such with fuel and fuel vapor. Lexan PLASTIC BURNS !! Not a safe material for an intake on an engine on or in a vehicle and actuaaly not real safe even on a dyno for that matter.

[stealth]

Post up pics when done...

[LCaverly]

Make sure its lexan!!!! Customer brought 535 pontiac to be dynoed had tunnel ram with 1/2 inch top that I thought was lexan , engine coughed while trying to start and I spotted the carb leaving the premises .Turns out it was plexi sure looked impressive both on engine and in mid air.
Len C

[tresi]

A total vacuum is going to be 29-32" hg depending where you are. Test your manifold by sealing it up and hooking up an air conditioning vacuum pump and pump it down.

[MadBill]

Fun fact: At the bottom of the deepest mines, baro can be >45".

[englertracing]

I think I have seen pictures of plywood tunnel ram tops