Rod Ratio

[Challenger340]

Anybody want to talk Rod Ratio, Pro's & Cons ? 

Just curious about differing opinions good or bad, why longer is better, or worse ?

Seems to be lots of guys building, or contemplating strokers on here, just thought it might be informative ?

Anybody ?   Any thoughts ?

[Bandit72]

http://www.dodgecharger.com/forum/index.php/topic,20375.0.html

[firefighter3931]

I'd be interested in hearing your thoughts. Especially concerning rod ratio vs cylinder head flow and Port cross section volume. I have my own ideas as to what works better with each configuration.


Ron

[Challenger340]

RON,

I was more curious what other guys have been finding !

We've done some "playing" from time to time. I know what I think, but, hesitant, to get into wars !
Everytime I think I know something, and have it "aced", it only opens up 10 more questions for me !
We've been able to "carry" relatively small heads with long rods, and done very well.
Surprised in fact !
Getting 894 H.P. out of a 540 inch with 2.19" valves, was GREAT we thought. We found out what it "likes". But now I'm gonna have to go back, and find out what "IT DOESN'T LIKE" to prove it.

I'm stuck on "how the engine breathes", or rather "plotting" accel & decel times per degree of crank rotation, on different ratios.
I'm NOT argueing that a two 540's @ 6500, DON'T need "X" amount of air for 100% V.E., just the "way" in which the port can "keep up" to provide excess Volumetric Efficiency(above 100%), in the Cam sweetspot. I know I'm heading into a scfm arguement with myself mentally !
Flowbenchs AREN'T dyno's ! The ratio must be the "kicker" from the flow #'s.

That making any sense ?

[firefighter3931]

That making any sense ?

Yep, makes a lot of sense.  And just to throw a wrench in the spokes, look at the power stockers make with OEM heads. Just goes to show the big flow numbers aren't allways the answer.  I've seen a few disapponted folks wh threw the "big" head on a good running combo, only to slow down. My thinking is that for a heavy street car a smallish port with big velocity with a long rod works well. My next build will be a 4.25 stroke combo and will put that theory to the test. 


Ron

[Challenger340]

I used to think of port velocity in relation, strictly, to torque when thinking power. It was simple.
I always attributed it to A/F speed, better mixture, better burn, WITHOUT punching up the turbulence in the chamber with a dome(remix).

Problem with Drag stuff, is too often we fall into "That penis thing" and go for broke port-wise, trying to work 'em like heck with shorter rod  stuff.

Now, I'm starting to think more in terms of "peak" A/F speed, and "ram effect", continued as the Valve starts to shut down(close ramp).

Far better with as small a port as possible for the application, but "just enough" port, efficient, and carry it with the longer ratio.

Like exhaust scavenging in reverse.

I'm seeing higher power numbers than "accepted" flow should produce. Thought the dyno was off ! But, I'm also seeing the mph/weight to back it up ?  The guy has been taking advantage of it with a powerglide trans.
Very confused !

Gonna be REAL curious about your 4.25" ! How big a Rod on the big arm ?

Am I still making any sense here ? I'm gonna keep sleeping on it for some more weeks. LOL !

[firefighter3931]

Now, I'm starting to think more in terms of "peak" A/F speed, and "ram effect", continued as the Valve starts to shut down(close ramp).

Far better with as small a port as possible for the application, but "just enough" port, efficient, and carry it with the longer ratio.

Yep, that's what i'm thinking too.  Sometimes the big port makes a nice peak number but if the car isn't geared for it the torque hit just flat out hurts the ET. I've seen it a few times and lots of head scratching going on. 


I'm thinking a 7.1 rod with the 4.25 arm which clears the stock internal pickup. E-heads at 300-310 cfm with a mild solid roller (endurance grind), single plane and 1000cfm 4150 style carb. Shift at 6500 max and geared accordingly. Should be the ticket for a 4000lb b-body. 


Nice flat torque curve to get all that mass moving and hopefully carry the tq long enough to keep it from nosing over too early. 


Still undecided on the LSA though....been seeing some strong running combo's with wide splits (112*) which is interesting.




Ron

[Todd Wilson]

http://victorylibrary.com/mopar/rod-tech-c.htm

[Nacho-RT74]

GOOD LINK!!! THANKS...

[Todd Wilson]

I
Now, I'm starting to think more in terms of "peak" A/F speed, and "ram effect", continued as the Valve starts to shut down(close ramp).

Far better with as small a port as possible for the application, but "just enough" port, efficient, and carry it with the longer ratio.

318 heads?     



Todd