BBC 502 600hp jetting recommendations

[Troy Patterson]

The 850 will only provide some 1.69 cfm per cubic inch displacement to a 502 cid. Let's say the 850's are milled and flow more, say as much as 950 that's still only 1.89 cfm per cubic inch displacement. That's less than a stock 350 sbc with cast iron exhaust manifolds and 3.25 rear end ratio was provided more cfm (2.03 - 2.14 p/cid) from the factory than those engine's will get with those carbs.

Trouble with small carbs on a performance engine is it's not possible to get a good fuel curve and balance between main jet and high speed air bleeds to allow the engine to take full advantage of all the various upgrades done to the engine as the calibration requires a greater degree of compromise than necessary.

Also, cool engines prefer more atomization than a down leg booster - assuming the carbs have down leg boosters. They'd make more torque, horsepower and you'd see more top end RPM on the lake / ocean therefore more speed Not all annular boosters are created equal

Troy Patterson blog tmpcarbs.blogspot website TMPCarbs.net Engine Professionals Magazine's TMP Tuning article, pg. 44

[gasman5.0]

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.

The Merc HP500's came with a Dart Single Plane intake manifold.

As Patriyacht mentioned the carbs come with staggered jetting.
By my notes they came with the following:
Starboard Primary = .082" = #75 Jet
Starboard Secondary = .105" = #93 Jet

Port Primary = .093" = #81 Jet
Port Secondary = .104" = #89 Jet

My buddy said the motors had a single plane. When he called me asking about jetting he only had two of three carbs apart and those two had {Pri-75/78}{Sec-89/93}.I did question the air bleeds but he didn't know what are where they were. Not to bad mouth my buddy ...He a good wrench and a pretty sharp general auto repair mechanic but he really is waaay... outside of his realm. I would like to help but I haven't been asked and I'm very.. very apprehensive at this point. These guy's are itching to fire them up.

[gasman5.0]

The 850 will only provide some 1.69 cfm per cubic inch displacement to a 502 cid. Let's say the 850's are milled and flow more, say as much as 950 that's still only 1.89 cfm per cubic inch displacement. That's less than a stock 350 sbc with cast iron exhaust manifolds and 3.25 rear end ratio was provided more cfm (2.03 - 2.14 p/cid) from the factory than those engine's will get with those carbs.

Trouble with small carbs on a performance engine is it's not possible to get a good fuel curve and balance between main jet and high speed air bleeds to allow the engine to take full advantage of all the various upgrades done to the engine as the calibration requires a greater degree of compromise than necessary.

Also, cool engines prefer more atomization than a down leg booster - assuming the carbs have down leg boosters. They'd make more torque, horsepower and you'd see more top end RPM on the lake / ocean therefore more speed Not all annular boosters are created equal

Troy Patterson blog tmpcarbs.blogspot website TMPCarbs.net Engine Professionals Magazine's TMP Tuning article, pg. 44

From what I've heard these are the stock carbs that came on the motors from mercury/factory in the boat.

[Troy Patterson]

The 850 will only provide some 1.69 cfm per cubic inch displacement to a 502 cid. Let's say the 850's are milled and flow more, say as much as 950 that's still only 1.89 cfm per cubic inch displacement. That's less than a stock 350 sbc with cast iron exhaust manifolds and 3.25 rear end ratio was provided more cfm (2.03 - 2.14 p/cid) from the factory than those engine's will get with those carbs.

Trouble with small carbs on a performance engine is it's not possible to get a good fuel curve and balance between main jet and high speed air bleeds to allow the engine to take full advantage of all the various upgrades done to the engine as the calibration requires a greater degree of compromise than necessary.

Also, cool engines prefer more atomization than a down leg booster - assuming the carbs have down leg boosters. They'd make more torque, horsepower and you'd see more top end RPM on the lake / ocean therefore more speed Not all annular boosters are created equal

Troy Patterson blog tmpcarbs.blogspot website TMPCarbs.net Engine Professionals Magazine's TMP Tuning article, pg. 44

From what I've heard these are the stock carbs that came on the motors from mercury/factory in the boat.

Ya, if making some more power is the goal, I'd recommend a bigger, better carburetor for sure.

Troy Patterson blog tmpcarbs.blogspot website TMPCarbs.net Engine Professionals Magazine's TMP Tuning article, pg. 44