Quote:
Originally Posted by chiphead
Are those 6X-4 or 6X-8 heads? I think 6X-8 was stock on standard-perf 400s. The 6X-4 were used on P350s and high-perf 400s. The -4s have smaller chambers and the compression is higher with them.
That cam is marginal for 6X-4 and way too big for 6X-8 heads. You may be able to tune it and get it to run better. What you describe is typical behavior for an engine with entirely too much cam. The late intake closing event bleeds off cylinder pressure and kills the low-RPM power. The tight 108LSA causes low idle vacuum which causes a a rough idle.
I bet your power brakes suck due to low manifold vacuum.
Usually you have to add a lot of fuel through the carb's idle and off-idle circuits to provide a rich enough mixture to the weak vacuum signal. You also have to increase base timing to 15-18* to increase idle vacuum and give the mixture time to burn. The fuel burns less efficiently in a low-compression engine so you've got to give more spark advance. Stock HEIs have a lazy and short advance curve. Start reading up on how to re-curve an HEI.
These tuning methods are a crutch to get a mis-matched combination to run. A summit 2801 cam would be a much better choice. A swap to a set of milled 6X-4s with 88 CC chambers would really wake that combination up. The rest of the list of parts sounds pretty good.
|
I just figured a 4.15 bore, 3.75" stroke, 93cc chambers with 8cc flat tops .010" in the hole and got 8.38:1scr!!!!! Not good!!! for any cam in my world but certainly not good for that cam!!!!! It would only have 6.3:1dcr.............
Cut those heads all the way down to 87cc and get 8.80:1scr still way too low!
Karl
