Port Cross Section and Torque Peak RPM

-

Ivoryk3ys78

Well-Known Member
Joined
Jul 5, 2018
Messages
210
Reaction score
93
Location
Oregon
I was reading in Andy F's book on stroking the big block mopar about port cross sectional area and that it largely determines where the torque peak will sit. I think its the Mcpherson formula. I was just reading a book Practical Engine Airflow (very good book) and it goes into that as well as port velocity etc a lot as well.

I had always thought of the camshaft setting the torque peak rpm but my take away is that the camshaft can broaden the torque curve and therefore extend the peak rpm out further but the torque peak would largely stay the same.

My question is are these cross sectional measurements written down anywhere so one could polug them into one of these formulas? My engine has a Strip Dominator and Trickflow powerport 190s. The engine is already together. My Dynosim puts my torque peak with my camshaft at around 4700 but I did not have the option in my simulator to put in cross section info and wouldn't know it if it did.

Anyway.. always nice learning new things.
 
WHile they work together, you aren't wrong.

A wider LSA will push the torque peak to a higher RPM.
 
my basic understanding of it is that port cross section with directly effect port velocity and it will gernally dictate that a certain rpm is going to be most efficient and you can work to widen the torque curve with good matching of components. I know the cam duration / overlap and LSA and centerline can have an effect as well as intake manifold.


I really do wish I knew the cross section of the strip dominator and Trickflow 190s to do some of the math on my 408.

In Andy Fs book on big block strokers I can't recall exactly but he said your peak rpm will be about 5500 because the torque peak would be around 4k I think he said unless you used raised port heads when building a 500 cubic inch stroker.
 
While I'm sure some head guys will have those actual measurements for a Mopar combo, I don't and I'd wager not too many will want to share much in terms of that level of detail for free.
In terms of what you're reading... The port is the potential, the cam is the amount of potential that the engine will access. That's why the cam choice can be so critical. IMO basing the value or quality of a port strictly on the cross section is a real simplification, because size does matter, but not in the same vein as "bigger is best". I can, however understand why Andy might choose to keep it generic and word it that way. The torque curve is the empirical measurement of the cam's efficiency with the port. Not the port size with the displacement.
 
Thanks for that Moper. Yeah it is not critical that I get it by any means. I do like learning and having a deeper understanding of things though. Like guitar or keyboard or most other things the rabbit hole just goes and goes and goes with performance engine design.
 
I get you. I get into it, then get a headache from it, then go back again when the pain subsides...lol. There's a lot to read up on and it will never hurt one to keep an open mind and learn. Regardless of the subject matter.
 
my basic understanding of it is that port cross section with directly effect port velocity and it will gernally dictate that a certain rpm is going to be most efficient and you can work to widen the torque curve with good matching of components. I know the cam duration / overlap and LSA and centerline can have an effect as well as intake manifold.


I really do wish I knew the cross section of the strip dominator and Trickflow 190s to do some of the math on my 408.

In Andy Fs book on big block strokers I can't recall exactly but he said your peak rpm will be about 5500 because the torque peak would be around 4k I think he said unless you used raised port heads when building a 500 cubic inch stroker.


You don’t have a SD to measure?
 
I bought mine from someone on here. I am no expert on this stuff but I think some work on it. It seemed to be gasket matched a little ways in and pretty much perfectly matched the gasket.



Well, that’s a bit hard to measure then. Bummer is I just sold a virgin SD or I could have measured mine for you. The other one I have is ported.
 
-
Back
Top