I began to dig through some of my archieved paper and found a few thoughts on
rod ratios. One in particular is from Super Ford, April 1994. They begin with
all of the usual caveats about how it makes better power and torque, increases
dwell time at TDC and BDC thus increasing time for combustion. They did indeed
build a 5.0 engine using the 5.4 inch rods and J&E pistons to keep everything
within the fixed deck height. The standard rod has a rod ratio of 1.697 (or
nearly ideal per some folks) vs 1.80 for the long rod. SF dwells at some
length on the theory but does not provide any math to back up any of their
claims. They took their engine (motor? - another rant?) to the dyno and made
some pulls.
The following paragraph paraphrases the results: " Our 5.0 liter engine showed
a ton of torque and a mountain of horsepower. The '94 Mustang 5.0 produces a
peak of 285 ft/lbs (sic) of torque and 215 horsepower. Our long rod 5.0 liter
engine started it's torque at 285 ft/lbs and rose to 338 at the peak. As for
horsepower, we were 98 ponies ahead of the stock engine, rising to 313. Best
of all our 5.0 liter was a completely street legal engine, using all EPA
exemped parts. Even with the good heads and maybe a touch of camming this is
an excellent figure."
So what is wrong with this? Well, they mentioned only in passing that they
used Ebok heads with large valves, and a mild streetable cam, and a holley
4barrel carb. So even the experts do it. They compared their results to a
completly stock 5.0 but couldn't resist the urge to add three extra parameters
to the equation: heads, cam, and carb. They did howeve, provide some
interesting data in the form of volumetric efficiencies. In trying to read a
chart that is 2 inches by 4 inches I find that their data shows:
RPM Eff. SHort Rod Eff Long Rod
4250 100 100
4500 102 103
4750 103 104
5000 104 106
5250 105 105
5500 ------- No Sig Diff -------
5750 ------- No Sig Diff -------
6000 ------- No Sig Diff -------
6250 ------- No Sig Diff -------
6500 ------- No Sig Diff -------
6750 ------- No Sig Diff -------
7000 ------- No Sig Diff -------
7250 ------- No Sig Diff -------
So I give thought to this. Even with the Ebok heads, cam and carb, efficiency
is still the same for all practical cases. More info is available in the
October 1996 issue of SF.
Hot Rod has had mant article in the past but one come to hand from March 1992.
They made an even worse comparison by using a 400 ci short rod motor and
comparing it to a 350 ci long rod motor. Just about everything else was
different also, but thats they way they tested.
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