Can anyone tell me how the A/F mixture will be affected going from a 48mm to a 58mm or vise versa?

Going from a 58 back to a 48, will it make the A/F richer, leaner or no difference?

 

No difference.

 

The ECM will determine the A/F ratio, so I don't think the 58mm TB will be a difference. And the stock 48mm TB will flow more than enough air for not only a stock motor, but also for modded motors.

The stock TB can be increased in size to a 52mm with some machining. A 58mm is really overkill and you most likely won't see any real improvement unless there is something in the stockk unit that requires replacing it.

 

The new engine is a mildly built 383 and when I built it I installed a 58mm which was included on the original startup tune. I have another thread here where I'm fighting a rich condition. I'm not as concerned about performance at this time as I am just getting the engine running correctly. Aftermarket throttle bodies can present their own set of complications so I'm going to put the stocker back on to eliminate them. Once I get the tune dialed in and running properly then I'll either have the stocker rebuilt and resized or put one of the other ones I have back on. We are in the process of working on the VE tables now to address the rich condition and I didn't know how drastic it would affect our progress.

Thanks for the help

 

Your on the correct path, the ve table needs to be addressed to solve your rich condition. The throttle body is not the issue.

 

The 58mm will work fine with your 383. Just need to get your tuning corrected.

 

Good Question. In my experience, the 58mm will cause the A/F ratio to lean spike upon opening. The air/fuel ratio will fluctuate up and down until it settles back down. This mainly happens during quick opening and closing of the throttle.

You can correct for this by changing the tables that control transient fueling. IE accelleration enrichment.

I removed my 58mm and found the car to be much more driveable and responsive on two different LT1's.

 

Sorry I forgot to mention that one of the issues I'm having is split BLMs. The idle air inlets on many aftermarket TB's need to be modified to eliminate split BLMs.