I've got a relatively mild 402BB, and I switched from 2" primaries to 1-3/4" primaries on my headers. I'm curious as to whether I should change my jetting, and if so in what direction? I'm thinking the carb should get a stronger signal with hopefully increased exhaust velocity, but I'm not sure how that plays out on the jetting side.

I've got a 3310 Holley, vacuum secondaries.

Any comments would be appreciated, TIA.

What jets do you have in it now?

I have an adjust-a-jet now, dyno tuned to the previous headers. Supposed to equate to about 72-74, but I have the ability to make minor changes with the kit.

I'm running 74's in my 3310..454,small tube headers(1 3/4")
Secondaries still have the stock metering plate.

The only way to really know is to read your plugs.

Chris, given your combo vs mine, that's real good information, thanks.

Gasgzlr, I agree but was worried about running too lean before I got to the point of checking the plugs. Looks like that's not an issue, plus I'm not the best at reading plugs anyway.

Ok, I just came across a great page on Pat Kelley's website here at Team Chevelle:

http://members.uia.net/pkelley2/sparkplugreading.html

It's a great pictorial and explanation of reading spark plugs - if anyone hasn't seen it yet, it's definitely worth a look.

Pats page is very informative, here's taking it a step futher.

I posted a response from an email I received from someone who is extremly knowledgeable on fuel delivery and ignitions.

What he does is cut the plugs at the seat on a lathe and removes the threaded section , I used a 4" grinder with a cutoff wheel with the spark plug in a vise. Very easy to do, 30 sec. per plug. You dont have to shut the engine off at WOT. You can drive back to the pits and bring it home and do it.

After the plug is cut, clean the porcelin off real good with carb cleaner or ???

He ultimitly is looking for a ring where the porcelin steps, the furthest point that would see combustion. The ring should be .020" - .040" wide.

I had two rings. hence his responce, does provide more info though.
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-Two distinct rings with one about 1/2 way up the porcelain is quite common on an engine that has part throttle fuel problems.
-When the ring is 1/2 way up then that has to do with part throttle like in a burnout and when it's too rich it shows up there.
-the ring at the base should be clear down to the gasket line and that ring is fine at .050".
-The darkness of the ring will be real dark when you make serious power, lighter colored when the engine isn't grunting it's nuts off.
-If the ring is definetly away from the gasket diameter a ways I'd be checking for there throttle to not be wide open during the run.
-The throttle may be wide open sitting in the shop but the body twist etc may be doing something to you under the power and twist of the chassis.