I could use mandrel bends, but then the exhaust will be just like everybody else's. As far as flow is concerned, I wouldn't do a pie cut turbo manifold or a pie cut headers for a high strung tuned n/a engine. These are for Harley's, most Harley's are good with a little bit of back pressure. The pie cuts don't cause much disruption of flow though, I make them at real shallow angles depending on what my centerline radius needs to be and I back purge everything. I've done a lot of pie cut exhaust's before and haven't had a weld fail yet.