Technical Discussion

[Torque Junkie]

A chevy 350 V8 at 5000 RPMS only creates roughly 500 CFM of volumetric flow, explained in detail below:

 

Roughly 350 Cubic Inches of Displacement

Multiply by 1728 (12^3) to convert to Cubic Feet

Divide 5000 rpms by 2 because it's a 4 stroke engine and the intake stroke is only on half of the rotations.

 

350/1728=0.20255 Cubic Feet

0.20255x2500=506 Cubic Feet per Minute, or ~500CFM at 5000 rpms, roughly 600 at 6000 rpms, etc.

 

What I want to discuss, is your scientific opinions and experience with having bigger-than-necessary carbs or throttle bodies on engines.   For example, my truck has a 600 CFM Edelbrock, and at 5000 rpms (which it never sees) the engine is only requiring around 500 cfms.   What would putting a 750 CFM carb on there do to performance?  Increase it? Decrease it? Not affect it one way or another?  Or are there other variables like valve size, cam duration & lift that affect this?

 

My opinion and educated guess is that putting a carb bigger than the engine "needs" is going to not affect performance one way or another, because the engine doesn't demand what the carb is capable of flowing, the carb isn't working 100%, if you get where I'm going.   It might, also, reduce the performance because it would be running the engine a little too rich at WOT.

 

Also, what is your opinion of what would happen to the flow speed of having a carb capable of flowing more air?  Keeping the flow rate the same (keeping it on the same engine and at the same RPM), increasing the size of the 'pipe' is going to effectively slow down the flow, just as reducing the size will speed it up?  

 

Thoughts, input, opinions, educated guesses, scientific analysis, and experience-based deductions all welcomed.

 

-Mike

[CMNTMXR81]

Well, no scientific documentation to back it up, but from experience putting too big a carb (such as a 750) on a stock low to moderate compression, stock cammed, etc, etc 350 would actually hurt it's performance because you'd still be dumping in more fuel than can be atomized as the amount of fuel is the only variable increased here. Air flow coming in would remain the same no matter what simply because the engine itself can only inhale so much due to internals.

 

Now if you have a head and cammed 350, different story, but then you've increased it's volumetric efficiency.

 

Once again, no scientific data to back me up other than bolting them up and surmising why they ran like crap afterwards even after setting back jets and metering rods, etc, etc.