I started a similar thread on this subject, but I aborted the project.......
....so now I'm starting a new thread for the benefit of 2 of our members who recently contacted me about their plans to ditch their downdrafts and go with a single side draft carb and manifold instead. The reason for their switch? Both are seeking a more reliable, more stable, more power, set up.
To get things started, there are two main things that will need to be changed with the jetting and carb set up, as compared to the well-known DUAL side draft set up jetting scenarios. First, you have to put the largest fuel bowl inlet valve in the carb, second, you will likely need to increase the Main jet size by 30-40.
Another set of things that will need to be addressed, is how are you going to actuate the carb, air horn length, air horn filters/screens or an air box with filter, and what to do about the PCV function of the big hose to the valve cover.
Air horns look cool. Looooong air horns look even cooler. But you have a GT, so looooong air horns are pretty much out of the question. From my personal, non-racing, casual, weekend fun, experience, air horn length means absolutely nothing. I noticed no difference whatsoever between 60mm, 40mm, 25mm, and no horns at all an air box and a big K+N filter. I'll just leave it at that. That's my experience and that's all I have to say.
Air filtration and what to do about the PCV hose from the valve cover go hand-in-hand. You guys can refer to my 2.4 with SSD threads and my Gordo's GTX threads to look at all the different horn length and filter screen and big hose experiments I have tried. If you go with just screens on the horns, stuff will get into your carb. Not much, but some. If you get the dual-horn screen I tried and install the big hose in it, it will work great. Or you can go the air/oil separator route I'm currently using. Or you can run the hose out the bottom of the car and feel guilty that you're a filthy, dirty, polluter who is coating his car's underside with oil vapor. I researched the concept of maximizing air flow and minimizing restriction in a suction system and came to the conclusion that suction is not linear, but instead draws air relatively equally from all directions. Forced or blown air IS linear and tends to blow in a straight line. Therefore, to maximize air flow to your side draft, you want there to be a lot of room, in all directions, around the vicinity of your air horns. My experimental solution was to build the biggest air box I could fit into the area, cold air intake tubing, and a K+N filter on the front side of the radiator. My big hose goes to the air box(after passing through my air/oil separator). My current system is the best, cleanest, highest air flowing, no fuss and bother system I have come up with so far. This is what I have observed over my many experiments, if you disagree with my conclusions, feel free to comment. I started this thread so that folks going or gone the SSD route could choose various options or tell us about their set ups, opinions, and jetting scenarios on their single side draft set ups.
Actuating the carb can be done with the oem solid linkage or via a cable throttle mod. OGTS/Splendid offer a special length, adjustable, linkage rod that goes from the firewall to the carb. It is ONLY for the Midikit style of SSD manifold, it will not work on the new Steinmetz SSD manifold. You'll have to come up with a cool solid linkage mod(like I did ) to operate the carb on a Steinmetz manifold or go with cable throttle. There are many threads and ways to go to make a cable throttle, I can't help your there very much. You could buy a Mangoletsi gizmo to handle the carb end of things, but you'll need to come up with a mod to connect the cable to the gas pedal or early part of the solid linkage. Or you can look into aftermarket cable throttle/gas pedal systems.
That's it for now, later I'll post some jetting scenarios and tips for setting up the carb.
If you have a 40DCOE SSD on a 2.0 set up on your Opel, please tell us how you have your carb set up and your basic adjustments!