I own an 84 TA with the LG4 305 4bbl. I am upgrading to a '92 L98 350 (keeping the 84's ECM) with TES headers and eventually a cat back system. The increase in displacement will obviously cause a lean condition. I went to Jett Performance for a chip, and they said all I have to do is recalibrate the carb. I would like to know:

1) Does this mean all I have to do is change the jets and mess with the mixture? I ask this because I thought the mixture was controlled by the fuel mixture solinoid, and messing with jet size and mixture doesn't do much. Please correct me if I'm wrong.

2) Would this be all I have to do, or would a chip be absolutely necessary?

Thanks for any help.

 

It's easier than you think. First off, carbs are about 80% self-calibrating to begin with. Unlike FI where you have to actually map out the entire fuel curve like a ginat spreadsheet, computer controlled carbs are much simpler. All the ECM does really is "trim" the fuel curve a bit, always shooting for a 14.7:1 A/F mix at idle through part throttle based on O2 readings. I have found that the stock carb and stock chip do a great job in 95% of the 350 swaps I have done or been a part of. The ECM and Mixture Control solenoid have enough range in them to handle the increase in displacement just fine.

The only part of the fuel curve you really need to worry about is at WOT where the carb basically goes into open loop and works jsut like a non-computer controlled carb at that point. Fortunately that's pretty easy to tune for since that's where the secondary side of the carbs comes into play. Just get some richer secondary rods and hanger and drop 'em in. I'd recommend a set of DR rods and a "B" hanger. If you want to be on the safe side then get an even richer set of DA rods and use those. Either way I promise it'll be in the ballpark.

 

You may want to get the L69 carb kit, it has larger main jets and metering rods and it also has the DR secondary rods, I don't remember which hanger it has, I think a B, but I've forgotten.

 

Thanks a lot for the info... it was a big help.