Basically it just means that all the primary tubes are the same length before coming together at the collector. These are pretty much the norm for extractor and merged style exhausts. Since the collector is towards the front of the engine, the primary tubes coming from the rear 1 and 3 have to be long to reach. However the primaries from 2 and 4 don't HAVE to be long since they are right there... Equal length tubing means all four are same length, look at some pics and you'll see how the front two tubes bend around and back so they can be longer. The idea is for the the exhaust pulses to hit the collector in a timed sequential manner. With tubing that is different lengths the timing can be such that pulses are fighting each other, not helping. Think harmonic reinforcement. --Ryan
And such things as clearance. Sometimes you have to sacrifice to get what you want.
CENTERMOUNT 2BBL SYSTEMS
PROGRESSIVE carburetors used on VW's are mechanical secondary carburetors. A mechanical secondary carburetor opens in relation to throttle position. The Progressive set-up uses a small primary barrel, allowing for excellent drivability and mileage. These also offer a larger secondary barrel for more power when you open the throttle. These carburetor kits can take a lot of time - up to 8 hours - to dial in for your particular car. This is partly because they are supplied from the factory with generic jetting often not suited for the VW engine, and also partly because the jets can be difficult to access. A good kit won't be too far off straight out of the box, but even a close one will need some tweaking before it is perfect! The center-mount progressive is a fantastic carburetor once it's jetted properly (but remember that it's no small task). Most are also available with an electric choke, making it easier to start and drive when the engine is cold and when air temperatures are colder. Most stock carburetors came with electric chokes, and they definitely made life easier for the driver of a vehicle with a center-mount set-up. The Progressive set-up is an excellent combination of performance, drivability, and economy. The main downfall of this system is the time it takes to get it set up properly.
Not worried about convincing anyone. Price was right. $299. If and when I get the extra cash I'll prob go with the dual 1bbl. if for nothing else the separate carbs just look good. This is also the first bug that I owned that didn't have a stock engine. Actually its the first bug I owned that has a dual port. I even had a 1500 single in my 75 super. Benefits of growing up in the middle of a salvage yard. Used to get paid to haul these things away.
Planning on painting car the same color as engine.
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