Patriyacht wrote:Jetting comes staggered from Mercruiser. Apparently they think it gives better mixture distribution.
gasman5.0 wrote:Patriyacht wrote:Jetting comes staggered from Mercruiser. Apparently they think it gives better mixture distribution.
I can't imagine this true, Unless Merc was to dyno tune each motor. All three carbs had the same jets and staggred the same.
How does pri 82/sec 90 with 4.5PV sound as a starting point?
Ranken Tech wrote:Here's how I do it.
600hp=about 300lb/hr fuel
300lb/hr fuel=3510 cc/min fuel
3150cc/min fuel divided by 4 jets=787.5 cc/min per jet
My jet flow chart says that a 83 jet flows 780cc/min on the low side 795cc/min on the average and 811cc/min on the high side
So, that would be 83 square. But, you want this thing to idle and cruise leaner than that so you add a PV.
A PV is worth around 6-8 jet sizes so that would give me approximately 76 fronts with the Pv and 83 rears .This would be for something around a 12.5 afr Boats may want to run richer than that. (according to the original jetting, I would assume so)
A 93 jet flows 1250cc/min according to Holley, so your original jetting is equal to 350lb/hr fuel and firstname.lastname@example.org
If you go with an afr around 11.7:1 you need about 360 lb/hr fuel. This would explain the original jetting numbers and spread.
A clean idle and low cruise(76 fronts) yet extremely safe rich afr(93rears) when duty calls and you need to show off for the girls.
If you want a happy medium 325lb/hr go with something around 78 fronts and 90-91 rears.
F-BIRD'88 wrote:If so, what worked for the stock 502-502 dual plane manifold will not work with the racey single plane manifold. Dial it in on a dyno with a proven dyno carb and then make the marine 850 carbs run the same.