Originally Posted by vinniekq2
toddalin said,,,and a dynojet dyno usually reads lower than a mustang chasis dyno. 12.8-12.9 af is great for the street.It would make more power with open exhaust and a little richer. so lets say your engine is 400 ish hp. for sure a good guideline to build 400 hp. My favourite carb for small v-8s like 327s is a 4777 with 4781 base plate and a few tweek
s like replaceable air bleeds and minor contouring etc.
Its a great share offering your parts list and actual dyno figures.
In this other set of dyno runs that include A/F ratios, in every case the leaner pull made more power at any point on the RPM band
. That's why I went 1 jet leaner on the secondaries.
Initially I tried 2 jets leaner on the primaries, but that created a lean surge while cruising. I returned the primary jets and it cleared right up, so took 1 jet size from the secondaries. Taking it from the secondaries also "squares up" the mixture better as it enters the manifold.
Also, this clearly illustrates that the "bog" is created by an over-rich condition (note that the A/F drops to ~10:1 at the point of bog), rather than a lean spot as most infer. The PO of the carb was trying to chase the bog and, based on conventional wisdom
, put in the 28 squirter in the secondaries. The 25 in the primaries is standard. When I changed to the 21s the bog went away, though I've not done another dyno run to see where the A/F now is at this point. But the SOP, says much
improved. Note how smooth the A/F ratio
is past this point.
I recognize that the dyno is NOT THE STREET and most jet a bit richer for the street to account for unknown variables and load factors that come into play. But, my A/F ratio is still safe, and a slightly leaner mixture also typically improves gas mileage and throttle response.