Their primary's are small so they work great with small engines and the secondary's are vacuum operated so if you have a small engine pulling on it the secondary's may not open all the way so in essence they only flow 850 when used on an engine that's big enough to pull the secondary's wide open. They are rebuildable but they have quite a few more small parts compared to a Holley so some guys like Holley's better. As long as it's jetted reasonably close to what your engine needs and you know what your doing their easier to fine tune than a Holley. Just my .02
