More on plenum volume, this time from Darin Morgan back in '05, currently Ford's Pro Stock engine designer:
Re: Plenum Volume
Postby Darin Morgan ยป Sat Mar 05, 2005 11:37 am
BRENT FAY wrote:
Plenum volume- what would be a good starting point as to know if you have enough? Measure volume of intake tract and divide the plenum by 4 (single 4 single plane intake or even tunnel ram) to end up with at least the volume of one cyl. or more if VE is say 110%? Or would you want a certain distance to the center opening of intake tract to throttle plates to keep fuel hitting plenum floor? Or you just keep adding carb spacers until carb loses it signal strength. Has anyone put a window in the side of plenum or int. tract near the opening to observe the A/F flow (Bill Jones?) on a running engine. On the intakes Jean Dittmer did for me he said to add a 1/2 in. spacer to make up for volume after reworking plenum floor. Or should one take a bunch spacers to track and do A B A B B C B C test. I dont have a dyno.... Just wondering, Brent
Plenum volume is interrelated to so many other variables such as, Engine size and rpm. Engines indented use such as Drag Racing, oval track, truck tractor pulling, boat racing, off shore boat racing and does it have an automatic transmission or five speed. These are all questions that need to be asked before deciding on how large the carbs and plenum should be. Its also the questions I ask when designing the manifold itself. If your asking for a magic number or formulas for any given engine, it does not exist. Its one of the last tuning factors we explore on the dyno. Its also very easy to get the plenum to large when chasing power numbers on the dyno! You can get a plenum way to big if you just look at power numbers on the dyno. Then, when you take it to the track the engine wont recover on the shifts and wont accelerate very well. An AED competition eliminator engine is good example. They have a sheet metal single four barrel manifold. On the dyno you can just keep stacking vertical spacers under the carb and the engine will continue to make more power. I have seen 7 one inch spacers make a lot of power on the dyno but the engine would lay on the converter and not recover. The farther you get the carbs from the runners, the more the signal suffers. There is a magic spot on every manifold as far as carb height goes. The track has the final word on that.
Darin Morgan
-Induction Research and Development
-EFI Calibration and Tuning
Reher Morrison Racing Engines
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