I have a 8.1-8.8L EFI marine motor to Turbo for a boat. The OE manifolds for these suck, they have really long runners and much restriction, I have chewed at an oem manifold but Im not keen to finish it. There is but one aftermarket choice for this cathedral port tall deck BBC by Dart.

So, I bought it, dual-plane manifold with plans to convert it to EFI. The manifold has bosses to drill for injectors - nitrous I think but FIs maybe, some bosses are a little small. This carb manifold is much lower profile and with an elbow I think it helps the overall fitment of the Turbos, Intercooler and TB. It is an enclosed engine bay but lots of room behind engine just not height.

Do I need to mill out the plenum divider and make it more of a single plane, will that even work? It will have and elbow or an Intercooled hat directly on the manifold.

Other than that? line it up on the mill and make some holes perpendicular to the bosses or do I need angled bosses and weld them on?

See attached PDF for a better picture of the situation. Thanks

Glenn

 

Dual plane isn't optimal, but it isn't just the divider that causes problems. Just mill out the top 1/4" of the divider to allow good signal transfer and go. Watch your plugs for a while when you get it running, pull a full bank at a time and check for lean/rich conditions. It seems like it should be easy to do plug chops on a boat.

 

Agreed, its not optimal but it is the best available without being a custom $$$$ creation, I think..

Not exactly sure what you mean by signal transfer, this is not carbed. I think I would machine out the divider completely and make a selection of various heights to play with, that way the intake is not hacked up if I wish to sell it.

It is a 4.5"B x 4.5"S engine using log driven Twins. It has an O2 sensor on each bank, but obviously that doesn't account for mixture balance between cylinders.

Induction thoughts

option 1: 92mmTB Tee'd to the comp. inlets with the outlets direct to a w/c inter-cooler hat that bolts directly to carb flange.

option 2: comp inlets open/filtered and outlets to w/c inter-cooler mounted vertically behind engine feeding forward through the TB and through a 90deg elbow into carb flange. Maybe smoother air with this one and room for a BOV?

option3: mess with oe manifold and win or eventually pay someone to make a nicer one.