Jeff20B

I've hit a wall with my carb-on-a-20B idea.



I see four possibilities.

1) get an Atkins SC manifold and add an aluminum plate with a carb spacer for an Edelbrock or Holley four bbl. Sounds easy enough.



2)Attatch my dellorto 48DHLA to the 20B UIM while leaving enough room for the oil filler tube and brake master cylinder. Not to mention hood clearance.



3)Cut UIM and LIM and weld back together closer to the engine after rotating the UIM 90º so the intake is straight up. The Edelbrock's secondaries match the secondary ports in the UIM. Only the primaries will flow into a single port. Or I could simply widen the primary port to accept both carb barels.



4)Go FI with a megasquirt, custom shortened secondary injector rail, inline high pressure fuel pump with some sort of return line, and a stock throttle body. This would clear the hood.



I know the FI guys will tell me to go injected. It's also th most expensive option. The easiest option is to get an Atkins 9" SC manifold. I thought of doing this last year, but wanted to give the stock manifolds one last try.



I think I figured out something about the SC manifold. All my previous ideas revolved around having a tall carb spacer to help with flow or to bring the carb up to the height it would be at with an SC. I kept having a problem where the front rotor would go lean under heavy acceleration. I now think I know why those ideas were flawed; the carb's distance from the manifold was the problem. If I could mount the carb directly to the aluminum plate (with a 1" carb spacer to allow linkage movement), the dynamic pulsing of the engine would take care of the AF mixture problem under acceleration. It's the same thing that happens inside the UIM's dynamic chamber, only there won't be tuned-length runners to take advantage of.



Dragon told me that I ought to at least have the LIM shortened to bring the torque curve up in RPM as much as possible. Well, the SC manifold has super short runners. The Edelbrock flows best on a plenum manifold, which this setup will be.



I hate this aspect of working on cars, but I also love it.

j9fd3s

yeah sounds like the s/c manifold is the best solution here

Jeff20B

This frees up the dellorto to go onto a 13B. (I've been one carb short since rebuilding the 13B in the GLC).



I've noticed sometimes there seems to be a great deal of "writer's block" when it comes to doing car projects. I've gotten really familier with it lately since taking on this 20B project. I've changed my mind about things many times so far. Sometimes, certain things just seem to flow like the compact header (no pun), dizzy, oil pan etc. This intake stuff has been a whole 'nother animal unto itself though. It's the only reason why my 20B isn't running right now.



Thanks for the advice, Mike. I guess seeing one of those manifolds in real life last week finally clicked this morning. Ok, I'll save up and get one as soon as I can.

Jeff20B

Here is what the dellorto on the 20B UIM sort of looks like. Horrible port mismatch.



It's Santa Clause in a ski mask!

Jeff20B

I test ran the 20B for a short amount of time yesterday. The dellorto is not a good carb to use. Or at least my particular dellorto and the crappy carb adaptor together allowed the engine to idle, but as soon as I'd touch the throttle, it would stall just like snapping one's fingers. Besides, the upper parts of the dellorto would hit the hood. Scratch option 2.



I think I'll scratch option 3 as well because by the time it was all said and done, the cost of all that TIG welding would probably be the same as option 4, but with horrible AF mixture distribution. I noticed. Only the front and middle exhuast ports had any fresh carbon coating after removing the header. The rear looked as if it wasn't getting any gas. That's odd because all three leading plugs looked similar. Actually, the front plug looked like it had the most run time. The middle and rear looked identical, which is odd because the rear exhaust port looked like it did before the test run. In other words, I'm sorta stumped, but now think it's a bad idea to try to force an AF mixture through the upper manifold and expect it to be stoich on all three rotors. Scratch option 3.



Option 4 is fuel injection. I'll keep the stock manifolds as they are (no cutting and welding) for the possibility of going fuel injected some day. Option 4 is still on the list, but it's getting beaten by option 1 due to money and lack of knowledge of FI type stuff. Nobody nearby knows it either. Gotta go with option 1.



Yep, I'm going with option 1 (the Atkins SC manifold) for reasons such as already have the carb, adaptor, uh well that's it so far. It should be very easy to set up and only requires a couple parts. It might be tough fitting it in the car, but I'm prepared to mod anything in the engine bay to allow it to fit. It also means I could go with a supercharger some day (who knows?)

j9fd3s

yeah same here. sometimes its pretty easy to see a solution, but you intake just doesnt present an easy one.





oOOoo go super old shool and put a log and an up draft on it!

Jeff20B

Is that what SU carbs are?

j9fd3s

i think they have su updrafts?

Jeff20B

Heh, I have no clue when it comes to SUs.

j9fd3s

i only know about my tr3 ones and the later mgb ones. the really really old stuff might be updrafts, it was all the rage in the 30's