Stage 1 1-5/8" headers are race headers for aftermarket aluminum heads. Low or high compression engines. Comes with 2-3/8 crossover tube. With our unique design we do not have to pie cut the number two cylinder,  if you noticed how other manufacturers make Buick turbo headers. Grand Nationals was our first cars to make turbo headers in the 90's . With years of experience, so we know what works and secret for fast spooling without pressure reversion into the cylinders.