Oh geeez;
Slap stick! My man.....
Plus the Magnums have 3" exhaust.
Off the exhaust manifolds, the BEST was 2-1/4 IIRC, possibly slightly larger. All exhaust & tail pipes I have crossed after the “Y” pipe merges is 2-1/2 inch.
On a older 318, thee Bauer system can be copied quite closely if desired but headers into a dual exhaust @ 2-1/4 would be excellent.
Then the cams are different plus the throttle body is huge compared to the little Carter.
And a larger opening will gulp more air requiring more fuel. AKA Worse fuel mileage. The roller cam is fatter (larger under the curve) and will use more fuel due to that fact.
By comparison the 318s in my 72 and 73 Chargers were rated at 150 hp net. My 92 318 is rated at 230 net.
Earlier 318’s are also rated at 230 hp.
If the OE poster needed a rebuild, I’d suggest a high ratio for more bang for and from the buck. Compression is power. Octane limited though. A big bummer for the 91 max guys, but yet, not the end of the world. Not by a long shot.
Don’t kid yourself or anyone else. They make the same HP.
Missing from the diced quite is the mention of free-er flowing heads. This lends itself to more power as well as more fuel consumption at anything other than cruise. Which is t exactly true but to small to split hairs on because of the second missing item not quoted....
The F.I. System is Calibrated for the vehicle it came in and will require a recalibration in order to do everything better than a older carbed engine.
Once dialed in, the fuel and ignition should be optimized and perform with superior excellence.
Id go there!
