Porting intake

Bob Legere Intake Photos

I recently tried some of Bob's suggestions on my intake manifold, but I have to admit that it hasn't turned out quite as nice as the pictures. I just concentrated on smoothing out some of the square edges and ensuring that the opening matched the carb. I haven't had the nerve (yet) to try the more radical changes, such as grinding right through the mounting bosses and then welding them up. But I am considering adding the "pent-roof" to the base (to improve low end response by reducing the volume). But I will probably get it professionally welded, as I haven't yet learned the art of aluminum welding with my MIG welder. As for power improvement, I am at least a few months from having it back on the road.

I recently saw pictures somewhere of a CIH engine that had a very nice manifold modification, where he actually cut out the square corners (along side the carb mount) and then MIG welded in angled plates to make the airflow smoother into the side runners. If I can find the picture, I'll post it as well.

I have the .zip file of a bunch of pictures of Bob's (now Charles Goin) intake manifold, but it is too big to post. So here is one select photo (at reduced resolution), and I will see if Gary can post the .zip file somewhere.

Cannon intakes flow like crap. They're the worst of the sidedraft intakes I've flowed. However, they really respond to being professionally ported. They need to be welded first, on the inner radius just after the mounting flange where the carb mounts. I end up grinding about 3/8" of material away here, and it breaks through the casting. The results are incredible, one person who's using a pair of Cannon intakes I ported gained 500 rpms in top gear at Daytona in his Opel Kadett, with no other changes.

His cylinder head flowed 128 cfm through the bare intake port. With the standard Cannon intake bolted in place, the airflow dropped to 117 cfm. After porting the intakes the airflow increased to 132 cfm, so it actually improved arirflow over the bare port because the intake runner straightens the airflow prior to it entering the port. Opels have turbulent intake ports.

Screen in the intake port? It'll choke down the airflow. Not worth it. Properly sized chokes and a well set-up engine will atomize the air/fuel just fine.

Bob

Ported intake

Keith

if your refering to my intake the welder built up the outside more than i asked and it is all solid weld... the inside is radiused just like bob posted in his full race proted intake article

as far as polishing the outside.... i would suggest doing the grinding yourself and taking it to your local polishing place and have them do it.... mine only cost $40 and if you do it yourself it is time consuming and not worth it to me.

The expensive part of getting the manifold ready to port is getting it ready to port by welding.... it is necessary to build a jig to bolt it to to keep the warping to a minimum.... also the easyest way to weld the wedge in the bottom was to cut the bottom out weld the ramp in and then weld the bottom back on. i also had 1/4" alluminum rods installed in the old intake to exaust bolt holes and welded in so i diddnt port into this void (as bob suggested)

both of the mounting surfaces (carb mounting surface and manifold to head surface) warped, i had to have them machined flat again.... this machining also lead to having the bolting suface on the exaust manifold milled down to mach the bolting surface thickness on the intake so everything matched.