Will putting richer pri. jets in give you more power with just that change alone? Or is it when you put the richer jets in that it helps stop detonation and allows you to add a couple more degrees spark advance that gives you more power? I just usually don’t see guys that care about performance with jet sizes in the #60's with a single four-barrel, is there a reason for that? I have a 3310 and I figure since pretty much all the fuel that goes through the motor when just cruising goes through those jets I mine as well go as small as I can without causing detonation for max mileage. So I am at #69 right now, if I were to go to the track would it be worth sticking say a #76 in? I know each motor is different, but I’m just talking in general. Also, I was wondering if the jets have anything at all to do with the idle characteristics on a Holley or is that JUST the transfer slots? If this were true richer jets are just going to foul plugs easier. Thanks!

Originally posted by 19Nova72:
Will putting richer pri. jets in give you more power with just that change alone? Depends on where you are on the A/F ratio curve. If say, you are already at 12.5:1 @ WOT, then richen the mixture up by going to 12.0:1, you will see no change in your power.

Or is it when you put the richer jets in that it helps stop detonation and allows you to add a couple more degrees spark advance that gives you more power? No, it's not that simple. The name of the game is that you want enough fuel so that all the oxygen is used up in the combustion process. If the engine was detonating because it was too lean, then yes, the larger jets will allow you to run more advance and bring more power. On the other hand, there are just as many situations where a richer mixture is needed but no detonation exists. Similarly, you can have an ideal A/F ratio and have detonation if your spark is advanced too far. For this reason the fuel is dialed in on the dyno before the spark.

The other questions you ask are due to the fact that many people automatically think that richer is better coupled with the fact that the average racer usually isn't concerned about MPG.

That's the beauty of a 4bbl, especialy a Qj. You can tune lean for cruise without giving up any WOT performance.

Mike

In some cases, "leaner is meaner". Use the plugs as a guide to whether the motor is lean or rich.

Hmmmmm, I guess I'll just have to experiment tongue.gif I sorta regret painting my carb. because everytime I take the bowls off the gas spills out on the paint and messes it up. Doh

And on the primaries of a Holley, the main jets are for cruising anyway. For power, you want the extra fuel to come from the power valve and the PV restriction. So...Jet for economy, Power valve and restriction for power.

more fuel doesn't equal more power unless you're lean. read your plugs to figure out where you are with your a/f ratio. power is found when you reach the optimum mixture, which is different per application.

anyone have a site that shows plug reading basics for non WOT runs? I know Pat Kelley has some pics for WOT runs but is there any readings you can make off of cruising conditions?

I actually welded an O2 sensor into my collector when I had my headers off. I tried useing it once and couldnt figure out how to set up the volt meter to read it, I got frustrated and gave up hehe. I should prolly figure that out and get close to a perfect air/fuel ratio when cruising, well as close as I can get with a carb'd engine.