FX Off-Road Manifold 3.5cc - Short-Medium FX Royal Racing Engines short-medium radius off-road manifold. Fits all mufflers. For maximum performance and reliability, use only original FX manifolds.There are different types of FX manifolds, each designed for particular track conditions and for particular engines. These recommended manifolds will help optimize performance for the majority of track conditions. However, some specific track conditions or fine tuning of engine settings may require changes to the manifold (as desired).Pipe + Manifold combinations:Top Speed: • 659501 - Muffler 3.5cc EFRA 2100 Tuned Muffler + • 659700 - Short Manifold, Small Radius • 659701 - Medium Manifold, Small Radius • 659702 - Long Manifold, Small RadiusBottom End: • 659502 - Muffler 3.5cc EFRA 2108 FX 2108 Tuned Muffler + • 659704 – Short-Medium ManifoldManifold recommendations:Short Manifold (659700): Recommended for tracks with long main straights to achieve the highest RPM, but has reduced bottom-end performance in the low RPM range. Medium Manifold (659701): Recommended for medium (“standard”) sized tracks. Short-Medium Manifold (659704): Perfect combination of Short and Medium Manifold which makes it more universal and compatible with the majority of tracks. The manifold was developed & designed to work well with mufflers 2131 and 2068. Long Manifold (659702): Recommended for short tracks where bottom-end, lower-RPM performance is required.