rod ratio vers eng acceleration

[Daniel Haught]

Originally Posted by rookie

I personally try to stay away from combo’s where the pin ends up in the oil ring pack.
I don’t have a lot of experience with them, it just seams to me like with ring seal and oil control so important it would be best to avoid if possible.

Unfortunately on most of the real stroker sbc engines and others with low deck heights thats hard to avoid but it doesn't seem to cause a problem if you get your rings and rails from a good manufacturer. I've used pistons like that on lots of different builds and I've never had a problem yet

[DavidHarsay]

Another endorsement for Larry's PipeMax software... I wouldn't build an engine with out it!

[Stan Weiss]

This shows the velocity and acceleration of an engine with
Bore = 4.0, Stroke = 3.0 RPM = 6500 and two different Rod Lengths 5 and 6 inches

[MilesTugoh]

Larry Widmer, Smokey, and other accomplished engine masters have written on these subjects .. Larry suggests 1.75 is optimum, Smokey liked as much as the dimensions would allow .. I find myself constrained by the available, and affordable, rod lengths offered in BBC size or Mopar size.

I am currently using 7.1" BBC rods on my offset ground to 4.15" stroke (1.71 r/s) and the same rod on a 4.3" stroke (1.65 r/s). High $$$ rods are available to 7.6", then they become $$$$$$ rods

I look forward to DV's, and the memberships, writings on this subject.

[Stan Weiss]

Unless you are building for a ci/weight class or have $$$$$ to spend the best thing is to get the pin and ring package / piston the best they can be and let the rod length fall where it will.

[Cammer]

Rod length means very little!

Pins intruding on rings affects nothing!

See how easy this is?

_____________________

[MilesTugoh]

Stan Weiss ... I believe your approach and mine are identical .. I optimized my piston package (custom forged), optimized my rod choice (7.1" BBC), and optimized my stroke to fit the deck height (10.810").

Cammer ... When I'm havin fun its always easy !

Hate to be contrary to popular opinion, but depending on application, I don't mind very short R/S ratios at all. All this stems from multiple years of running the same engine in a very successfull Baja 1000 type application. 6000 lb. truck, 37 inch tires, 5.43 or 5.00 gears. T-400 trans with 3600 stall converter. SBC, original build 9.325 deck, 4 inch stroke, 6.200 rod, 1.45 venturi gas carb. Ran for several years this way, won lots of races including season points championships. 700 hp, 600 lb ft. but always had a little tip in issues when totally hauled down in deep, heavy terrain having to pull back up from closed or low throttle positions. Nothing major, just irritating. Changed up combo to 6 inch rods, actually added 15cc runner volume, same carb etc. Made no difference on the dyno, made a wonderfull difference in driveability. Any load, any throttle position, didn't matter. Totally smooth climb in power, you would swear it had a well worked out fuel injection setup. Even with bigger port volume, attribute improvement to better airspeed through carb. Would not make any difference with fuel injection, but if you have a high load at low rpm application with a carb ( sounds like a recipe for street cars ), short rods are the stuff for me. By the way, peak rpm was 7000-7200 rpm.

[MilesTugoh]

Certainly can't deny your successful development of your engine .. however, I do not believe you can conclude that last improvement was due entirely to the 0.200" shorter rod .. other important contributing changes were added at the same time .. happily the new combination is working and thats what its all about, a winning combination.

[Stan Weiss]

The trend in drag racing has been to shorter rod. Way back the hot setup was a 4" bore 3" stoke 5.7" rod 302 CI 1.9 R/S. Small block Pro Stocker 4.06" bore 3.25" stoke 6.0" rod 337 CI 1.846 R/S. Small block Pro Stock Truck 4.19" bore 3.245" stoke 5.58" rod 357 CI 1.722 R/S. Each step along the RPM's went up and head flow has gone way up.