Join Date: Jan 2000
Location: madison, AL, usa
If the motor is truly bone stock, the 1 3/4 headers and assumed suitably flow capable exhaust system are going to be too large (for the engine combination in that state). They are not too big because of any relationship to the stock 5.0, or any sort of hp capability; I dont subscribe to that thinking, its all about valve events, flows, crosssections, rpm, and displaced cylinder volume.
They are too big because the valve events are just not right to effectively use that much flow capability and cross-sectional area on the exhaust side. the exhaust lobe positioning is too early, even with the cam installed at the typical 115/115 positioning, its just not good.
Retarding it seems to be a possible avenue, but it will kill the intake side even more. Retarding it is not going to be productive unless you were to go up to some huge rocker (like 1.8 or something). The motor will respond favorably to a lot more inlet valve activity, then delay, and possibly shorten, the exhaust activity (narrower LSA) and things will begin to turn around pretty nicely.
As it sits, the exhaust activity is just way too early. The cylinder pressure is lower, the motor will be a little sluggish and just not provide a good mid range response, and it will likely hamper the upper end as well. You will also notice that this scenario is the typical report experienced when too large of exhaust is added. the difference is I provided some reasoning, and its not really the exhaust's fault, its the overall combination.
If the intent is to assemble for future growth (and there is no harm in that), then atleast make some changes so the larger exhaust doesn't hurt it too bad. I assume the intent is not to open up the motor, or spend money on cams. So at least try to recoupe some of the relationship by adding 1.7 rockers on the intake side only. (possibly borrow from a friend). Also on the exhaust side, leave current the exhaust system in place. Install the 1 3/4 headers but let the collector neck down (albeit smoothly) to your current exhaust system. these sort of items will enable the early exhaust to be absorbed a little better.
Then later on when changes are made, you can do the rest of the exhaust, for example.
A lot could be said for a huge headed 5.0 Ford motor, with stock hyd roller cam, and a seriously flow capable exhaust. they can be quite impressive.
Last edited by buddy rawls; 09-25-2013 at 05:38 PM.