Shafiroff 540 ci dyno results....
05-29-2007, 09:08 PM
#22
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Member Since: Apr 2006
Location: Southern California
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540 cubes here as well.
I agree with you on the air fuel. We ended up jetting up to 90 for the primaries and 92 for the secondaries just to get us to 13.0. Car was stumbling a bit at cruising speed because of the large jets so we have to do a bit of work on the carb before hitting the dyno again. My goal is a 12.5 air fuel as well.
I plan to hit the dyno again late next week with the carb dialed in (dropping back down to 87/89 jets) and playing with the timing a bit more.
Any more direction you would offer up?
B.
I agree with you on the air fuel. We ended up jetting up to 90 for the primaries and 92 for the secondaries just to get us to 13.0. Car was stumbling a bit at cruising speed because of the large jets so we have to do a bit of work on the carb before hitting the dyno again. My goal is a 12.5 air fuel as well.
I plan to hit the dyno again late next week with the carb dialed in (dropping back down to 87/89 jets) and playing with the timing a bit more.
Any more direction you would offer up?
B.
You had 13.0:1 A/F ratio with 90/92, but bad driveability. If you ran say 86/96, you'd have much improved driveability but still have 13.0:1 A/F ratio, since you went up 4 jets in back and down 4 jets in front, so overall no real change. Doing that would put you half way there, because then you would have good driveability without going leaner than where you left off. But you're still not at the 12.5:1 A/F ratio you're looking for. Considering that changing a pair of jets 1 size, changes A/F ratio approximately .1, the obvious thing is to fatten up the secondaries even more. Running 86/100 jetting would put you approximately in the 12.6:1 A/F ratio range, just where you wanted to be, but still with good driveability. I know it sounds rather unbalanced, but you need what you need. This idea would work best with a single plane intake so that the air and fuel have more of an opportunity to become a homogenious mixture, which would largely eliminate the concern about unbalanced jetting. Adding a carb spacer will help even more. If you start there, you'll be darn close to start out, then you can fine tune the bleeds, power valves, etc from there without running that new 540 dangerously lean while trying to sort things out. And you might even like things just fine right there. Give it some thought, it might make life much easier on you.
Last edited by 540 RAT; 05-29-2007 at 09:13 PM.
05-29-2007, 10:53 PM
#25
Racer
Thread Starter
I understand your desire to have essentially balanced primary/secondary jetting, but as you found out, fattening up both ends wrecks your cruising mixture. So if you go back to the 87/89 to clean up the cruise, you'll be dangerously lean at WFO throttle. You said you wanted to end up at 12.5:1 A/F ratio, so that would be going in the wrong direction. I suggest you bite the bullet and setup unbalanced primary/secondary jetting. That idea might not give you the warm fuzzies, but it'll get you where you want to go. Consider the following:
You had 13.0:1 A/F ratio with 90/92, but bad driveability. If you ran say 86/96, you'd have much improved driveability but still have 13.0:1 A/F ratio, since you went up 4 jets in back and down 4 jets in front, so overall no real change. Doing that would put you half way there, because then you would have good driveability without going leaner than where you left off. But you're still not at the 12.5:1 A/F ratio you're looking for. Considering that changing a pair of jets 1 size, changes A/F ratio approximately .1, the obvious thing is to fatten up the secondaries even more. Running 86/100 jetting would put you approximately in the 12.6:1 A/F ratio range, just where you wanted to be, but still with good driveability. I know it sounds rather unbalanced, but you need what you need. This idea would work best with a single plane intake so that the air and fuel have more of an opportunity to become a homogenious mixture, which would largely eliminate the concern about unbalanced jetting. Adding a carb spacer will help even more. If you start there, you'll be darn close to start out, then you can fine tune the bleeds, power valves, etc from there without running that new 540 dangerously lean while trying to sort things out. And you might even like things just fine right there. Give it some thought, it might make life much easier on you.
You had 13.0:1 A/F ratio with 90/92, but bad driveability. If you ran say 86/96, you'd have much improved driveability but still have 13.0:1 A/F ratio, since you went up 4 jets in back and down 4 jets in front, so overall no real change. Doing that would put you half way there, because then you would have good driveability without going leaner than where you left off. But you're still not at the 12.5:1 A/F ratio you're looking for. Considering that changing a pair of jets 1 size, changes A/F ratio approximately .1, the obvious thing is to fatten up the secondaries even more. Running 86/100 jetting would put you approximately in the 12.6:1 A/F ratio range, just where you wanted to be, but still with good driveability. I know it sounds rather unbalanced, but you need what you need. This idea would work best with a single plane intake so that the air and fuel have more of an opportunity to become a homogenious mixture, which would largely eliminate the concern about unbalanced jetting. Adding a carb spacer will help even more. If you start there, you'll be darn close to start out, then you can fine tune the bleeds, power valves, etc from there without running that new 540 dangerously lean while trying to sort things out. And you might even like things just fine right there. Give it some thought, it might make life much easier on you.
I had Bernard Mondello (Jim Mondello's son) build this carb for my motor. He wants us to use 'reamers' on the power restriction holes behind the primary and secondary power valves to .078 on the primary and .073 on the secondary and THEN install the #87 primary jets and #89 secondary jets. By his calculations, we will have the same (or better) A/F that we now have with all of the drivability. I plan on giving this a shot either this Friday or early next week.
As a side note, I KNOW we need to make a change as I installed a new set of plugs this weekend, drove about 30 miles and then rechecked the plugs.....they were hammered with fuel. Way, way too rich.
Thanks for all of the feedback.
My best,
Bryan
