Ad0911

I have search the forum for threads regarding the benefits of headers vs the regular manifolds. My 4.5L 1978 of course has the cast-iron manifolds, that does not have equal length exhaust pipes. I read that the 85/86 manifolds are better but to my humble opinion the only advantage is reduced weight. Proper headers should have equal length exhaustpipes (thats why the old heatexchangers on classic 911 engines are better than the later style ones for 3.2 L engines). The 85/86 manifold doesn't have equal length exhausts. Could the 4.5L engine benefit from equal length exhaust headers in any way? Perhaps only at high RPM?

James Bailey

The most common headers , MSDS, are not equal length so there is little real data.

IcemanG17

Other OB owners have had great results with custom exhausts using MSDS headers, no cats into some type of high flow setup (single or dual).....typically around 200-220whp with an otherwise stock OB motor that is only rated at 219 crank HP....