I Come To Seek Advice

I Have A 1978 Datsun 280z With A 1983 Datsun 280zx Motor Swap
Right Now. I Have No Exhaust System, An I Know Thats Lowers My Compressions Cause Its Not Making Enought Backpresser, But The Motor Run Good Intill 4000 Prm Then It Does Not Make Anymore Prower, It Starts To Sputter And Backfire. I'm Thinking Its The Exhaust System But Anybody Has Any Ideals Or Helpfully Tips Please Help Me Out Cause I Know Thats Motor Make Good Prower An I Want To Feel It.

Thank My Fella Zheads