You took an engine that was already limited by airflow. The heads were at their max. A stock LSx is not at it's peak or limited by airlfow. When it's not limited, the bigger displacement can make more power.

Why are we dancing around the obvious and something I noted a long time ago?

 

They're both limited by airflow, that's why there is a peak torque value. If the engine wasn't limited by airflow, it would just climb in power forever.

How can you say that a 346ci LSx with stock heads is not limited by airflow, but a 347ci LSx with AFR heads is limited by airflow?

 

Because the one with AFR heads has a **** ton of other mods like a cam to take advantage of more heads.

Airflow isn't binary It's not just "restricted" or "not restricted."

I hate to be the one to break this to you, but there are times when a greater pressure differential (in this case, more vacuum) will draw more air.


"A little bit of knowledge can be very dangerous."

 

Just wonderring. Those tests were done over 5 yrs ago. Has anything changed parts wise or setup wise that would make the 383 make more power with the same setup as 346?

I could not see the graphs but you picked up 40 ftlbs of tq over the 346. Was tq picked up throughout the power band?

 

The cam doesn't matter in this case. The peak numbers would still stay the same had the engine started with a stock cam or a 224/228 cam. It could have had stock heads instead of AFR heads. These variables you're trying to say matter actually don't. If you add displacement and keep the induction package the same (all stock or all aftermarket), the peak HP number will be the same.

You're the one that was talking about restriction with your '86 TBI example. Just as there are instances when greater pressure delta increases the airflow rate, there are instances when a greater pressure delta doesn't increase airflow. What is it that you think happens when the TQ peaks and then falls off?

You still have yet to come up with any evidence at all to support your claim. Maybe you should dig up a real world example first before trying to aimlessly argue the validity of Tony Mamo's test that I used, or make any more smartass quotes about knowledge.

 

You know that's pretty much physically impossible, right? Flowrate is governed by pressure differential (assuming cross section is constant).

Torque is basically volumetric efficiency at a given RPM, less friction.

When the restriction is very high, a greater pressure differential isn't going to do much. If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much. If you have a moderate flow of air through a hole and double the pressure differential, the airflow will increase significantly.

 

Are you sure about that?

"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed."

Click and learn

 

I'm already aware of that. Are you aware that you're agreeing with me and disagreeing with yourself? Also, are you aware that choked flow generally only at issue when we're talking about super-sonic/near super sonic air? Just wondering. It's when you have a convergent-divergent nozzle to accelerate air to the throat, make it go supersonic, then accelerate it after the throat.
Air velocity can't increase anymore because (in short) it is at its max speed without a divergent nozzle.

I spent about 1/3 of my fluid dynamics class studying compressible flow and about a year at Pratt & Whitney developing convergent and divergent nozzles for military aircraft.


Nevertheless, you're agreeing with me and disagreeing with yourself.

Read what you posted:

"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure "

"If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much."

Fluid dynamics isn't a topic that is generally intuitive, but this isn't that hard to picture. Think about it from a common sense point of view. You have a 6 hole you're sucking fluid though. Apply a little vacuum and little fluid goes through. Apply moderate amount of vacuum and even more fluid goes through. Apply a huge amount of vacuum and even more air goes through. Double that huge vacuum and maybe a bit more fluid goes through. Double that again and you get virtually no gain.



But I'll tell you what- when you figure out a way to increase flow by decreasing the pressure drop (by decreasing the pressure at one end without changing the restriction/cross section), you give me a call. I'll help you patent it.

 

I'm not agreeing with you. Read what YOU posted:

It looks to me like you were trying to say that it was "physically impossible" that an increase in the pressure differential wouldn't yield an increase in airflow...that is unless you have a different definition of "physically impossible" than the rest of the world.

LOL, where did this come from? Why would you even think that I was entertaining the thought of that being possible? I already recognized the opposite concept to be true (ie Bernoulli's work).

BTW, still waiting on you to provide evidence regarding the original topic...

 

As for this ninja edit, that is exactly what I was referring to before you said that that was "physically impossible". Maybe you misunderstood.

 

Unless you develop a system which will literally do the impossible- run PERFECTLY at the limit of compressible flow, there will some marginal increase in airflow with an increase in negative pressure (relative). For what it's worth, that's impossible. There will always be a very very very marginal increase. There is no sense in arguing with you. If I'm technically correct, you say I'm not correct in practicality. If I'm right in practicality, your cite supersonic compressible flow.

Like I said, a little bit of knowledge can be a very dangerous thing. In this case, you have a little bit of knowledge. If you'd like to discuss this in advanced tech, I'd be happy to do so. Please PM me if you decide to take it there. I'm not really interested in debating this with you any further over here.

 

I really don't have any interest in a discussion in gas dynamics since it seems it's just to distract from the original topic in which you have failed miserably to argue successfully or convincingly. Just go ahead and post some evidence to support your argument (which I've asked for several times now) and we can continue that discussion, or you can save some face and admit you may be mistaken. Until then, you should probably consider who it is that really only has a little bit of knowledge.

 

little chevy, i have a very similar setup as you but i used the eagle rotating assembly with the prc 5.3 stage 2 heads, ms4, fast 92 and 1 3/4 headers. i made 460/430 to the wheels through a 6 speed and the clutch was slipping. also ran 125mph in the 1/4. i might be selling the heads/cam if your interesed

 

good to know thanks for the reply man