Matching CArbs to an Engine

[340_6pak]

If you have an engine that works well with a given carb, say a single 4 barrel, that would tell me that the carb was delivering enough fuel to satisfy the engine's demand. If you adjust the carb to give more fuel, you then have a 'rich' condition.

So if you wanted to add another carb for a dual carb setup, it would seem that you would not want one that is identical to the one that works well, you would want two that were slightly smaller, all else being equal. (Yes/No?). Or does the additional carb supply enough additional air?

What I really want to know is what sort of adjustments (bigger cam, etc), I need to be prepared to make to an engine to allow it to use the extra fuel and air that and additional carb will provide. And most importantly, how do I calculate the size of the carbs I need?

 

Thanks;

[nivvy]

I ran a dual quad setup with dual eddy 600's on my motor... both were the same I also had a progressive linkage to the second....... didnt open at WOT  as the first carb until   

Barry grants formula is cubes X shift point / 3456


440X5500/3456  is 700

LM1 wideband is best for tuning A/F ratios....

[MEK-Dangerfield]

I wouldn't consider dual carbs unless you are really getting radical here with the engine. I would try a bigger 4-barrel carb if you want to experiment.   


  Mike

[Chryco Psycho]

it depends a lot on the combination . more gear & looser converter is more forgiving , also how the carbs are opened , all at once is hard but progressively works better , at least 2x the CI is the starting point ,again depending on the air flow through the engine head flow RPM & Ci etc

[72hemi]

I'm running 2 625 Carter's on a small block with Edelbrock progressive linkage and it is way too much carburation on the low end. At the upper end of the rpm range it seems to be okay. Oh and I for some reason I am able to pull 15 mpg on the highway with a 3.23 gear.

[340_6pak]

Thanks guys, this is just an idea I have been kicking around, but I really do not know enough to do it right. The formulas for calculating carb size are great. I knew there had to be a way to figure that out.

[nqkjw]

When running multiple carbs your jetting will have to be much greater than what would seem correct.
This is due to the vacuum available being shared by more than just one carb resulting in poor vacuum signal to each carb hence the requirement for much bigger jet to compensate.

If that makes sense

[340_6pak]

It does make sense. Thats why I was thinking that a bigger cam might be needed.