Intake Options + Adapter plate for a Weber 32/36 DGEV on a 7K

[zorartic]

Hey everyone!

I have a rebuilt 7K motor, which runs like a charm apart from the carb. I managed to get my hands on a 32/36 Weber DGEV but not on an adapter so I've been working on designing and manufacturing that myself.

The problem is that I had managed to find extractors for the 4K, which is something very rare in my location. And unfortunately, they don't fit with the intake that the 7K came with, it has a set of intake + regular exhaust manifold that needs to go together due to a bolt pattern, so I stuck with the 4K intake + extractors on the 7K engine upon the advice of a couple of people.

Now, when I'll be upgrading to a 32/36, I was told the adapter plate doesn't provide enough of a taper for optimum airflow and should look into porting the intake runners a bit, so

1. How much would the flow potential be restricted by the 28/28 runners on the 4K intake 
2. What's better? A 4k intake matched to the 32/36 bores + extractors OR a 7k intake matched to the 32/36 bores + a regular exhaust manifold. While port matching, what measurements should I be aiming for in the runners, and then the adapter plate side?
3. How tall should the adapter plate be? What's a good height to allow a smooth enough taper for the air to feed into the intake with minimal turbulence?

Moreover, what about port matching the 4k intake to the 7k head, how necessary is that? How much does turbulence kill power gains from the bigger carb?

Apologies for all the questions, there aren't a lot of experts on this topic around my area, and I wanna learn as much as I can myself.

Cheers

[altezzaclub]

Well, the 7K is a long-stroke engine so you don't need to be aiming for lots of rpm. Bluntly, any vertical carb manifold is crap, turning the air through 90deg is never a good idea, but without going to a side-draft system, its what you are stuck with.

So widening the ports anywhere is not a big deal if you're stuck with that 90deg bend. That means smaller intake diameters are not as important as in building a 4K race motor. I'd say the thing to eliminate would be any steps in the intake system, from carb to valves. You can step up in diameter as the air moves in, but any step down needs to be turned into a cone. Ideally you would taper any steps in both directions.

The turbulence may add power from swirl as it fills a cylinder, you'll never know.

Make sure the carefully shaped ports you make actually line up when the manifold goes on the head, you may have to drill pins in to keep it in exactly the right place.

I'd go for a 7K inlet and stock exhaust  manifold myself. Don't get too fussed about smooth flow through the adapter plate, the air is about to get turned 90deg just after that.  Make the manifold and adapter fit the carb throats and leave it at that. Cone the manifold out under the adapter plate so the air has a curve to follow rather than a square edge.

Get a flappy disc drum and use an electric drill to smooth out any casting debris in the head ports and inlet, although now you're looking at taking the head off.

You might find a bit of useful stuff in here-

 

[zorartic]

Hey,

That makes sense, thanks alot for your response.

I'll check out the post and update when I've got her up and running : )

P.S. casting debris in the head ports and inlets were already taken care of during the rebuilt, hoping that wont be an issue

Best

Edited September 30, 2025 by zorartic