230 2bbl mod for weber 38x38

Posted by: 70Nova

230 2bbl mod for weber 38x38 - 11/05/17 03:45 PM

Long story short....

Hogged out stock intake hole, went clear through the wall and into the exhaust heat cavity behind.

Made a steel sleeve to slip inside to make a solid wall again

Brazed the sleeve in place, drilled and tapped the 4 surrounding casting bumps, and had a machine shop mill the surfaces flat and to the exact same height

Made skinny barrel nuts for the studs, the two bigger ones were Porsche 911 exhaust nuts, drilled and tapped to different thread size and reduced OD. They have a convenient 6-point Allen head at the end. The 4 smaller barrel nuts were brake line flare nuts, drilled and tapped and hex reduced to 10mm for extra clearance.

Got a block of aluminum to make a carb adapter out of, for the Weber 38/38 clone

bolted the sucka on with the recessed nuts

sandblasted the manifolds

Painted them too


and replaced all studs with new. Currently waiting to find time to hang them on the car. Left a piece of aluminum sticking out of the adapter for now, in case I need to use it to fabricate a throttle cable bracket or something. Haven't thought that far yet, I'll burn that bridge when I get to it I guess.

Factory carb hole on the intake grew surface area by 46%, roughly the same amount the carb bore grew going from stock single barrel to two 38mm. The carb is a true 2bbl, butterflies open simultaneously.

I suspect this engine will make much more exhaust heat than needed to heat the intake, so I will be using the block-off LPG gasket between the exhaust and intake, and rely on conducted heat only.

Next step would be headers so this is not permanent.
Posted by: stock49

Re: 230 2bbl mod for weber 38x38 - 11/05/17 05:50 PM

I like the fab work. It's nice when modifications look like they belong there. The allowance for the linkage is thinking ahead. Prevents a second iteration on the fab. Once the linkage is sorted I would bolt the carb to the adapter and trace around the base with a sharpie. You should be able to lose the excess metal from the adapter and make it look like the manifold was cast as as a two barrel.

If you decide to go for headers - a heat plate can always be added.
Posted by: 70Nova

Re: 230 2bbl mod for weber 38x38 - 11/05/17 06:00 PM

I plan to do the sharpie trace and cut it down, yes. I wanted to leave a little extra all over, in case I need it.... much harder to put it back on later laugh Headers may be on the to-do list next summer. For now I just want to see how it runs like this.
Posted by: 70Nova

Re: 230 2bbl mod for weber 38x38 - 11/08/17 10:45 AM

If memory serves, hole went from 45mm to 55mm. If anyone was wondering.

38mm area = 1134mm2 x 2 =2268mm2

45mm area = 1590mm2

55mm area = 2375mm2

hope I got that right laugh
Posted by: moregrip

Re: 230 2bbl mod for weber 38x38 - 02/16/18 06:29 AM

70Nova, awesome idea! how is this coming along? How do you like that carb?
Posted by: Beater of the Pack

Re: 230 2bbl mod for weber 38x38 - 02/17/18 10:17 AM

I Like this. You just have to respect guys who work on mods like this and share it in detail and freely with others. Thanks! smile
Posted by: 70Nova

Re: 230 2bbl mod for weber 38x38 - 02/17/18 11:54 AM

worked great, better response, idle, and power all through the rpm range. Easy to control throttle, the way I have the linkage set up, there's a lot of range of movement in the pedal. The only think I will change is add an extra return spring, the pedal is a whole lot lighter to push. too light for my taste. Now I feel my bottle neck is the stock soda straw exhaust smile

I bought an aftermarket round chrome air cleaner housing and made an adapter for it, sits nice after some trimming, hood closes, everything looks ok.