Long Rod, Short Piston www.ocpanteras.com
February 2008
Rod Ratios is a topic that some of you know has me “pre-occupied”. My Chevy experiences lead me to believe that the best combination for the olden days was the lowly 327. It had enough low-end grunt while giving me a very quick run to redline. The larger displacement small blocks yielded tons of torque but were just lazy reaching top end as a truck motor like the 454.
I was told that the performance difference is mostly based on the magical thing called rod ratio. Divide the rod length by the stroke to get this metric. Many agree that the 302 Z28 is a zinger with a ratio of 1.90:1. 1.70 is the ratio of Ford’s famous 302 (5.09”/ 3”). My stock 327 pushed 5.7 / 3.25 numbers for 1.75. Ubiquitous SBC 350 and its 400ci successor are 1.64 and 1.48 respectively. Most endurance racers today run with a range of 1.9 to 2.2. Chevy’s new NASCAR 358ci R07 engine has 3.25 stroke and varies the rod from 6 to 6.2” based on the track. It yields ratios of 1.85 to 1.91 to generate 9,300 to 9,600 rpm.
The theory goes something like this. Short piston rod length has a quicker turn
around at both top and bottom dead center.
Longer connecting rods stay a bit longer at the extremes and reduce the
side loads thus less friction and wear because of a better angle to the crank
also giving it more leverage. The delay
allows slightly more time at the top leading to a more complete
combustion. Better combustion translates
to less detonation through less timing and permits a slightly higher
compression ratio. Peak velocity is
delayed somewhat for more filling on intake, grants longer overlap timing, but
lowers scavenging of the exhaust gases at low rpm. Higher pin height improves the piston center making it more
stable. You can also use shorter skirts
therefore lighter pistons. Tensile
loading is also lower as the speed is reduced at TDC.
Chevy started its 265 in 1955 with a ratio of 1.9 as
a favorite of hot rodders. Drag strip
“Screamers” were the 283. It reigned
from 1957 through the mid 60s used the same 5.7 rod / 3 stroke as the early Z28
and the 265. Not all big blocks are
dogs. 1958 348 had a 1.89 ratio. Mighty fine 409 had 1.71 but both the 454
and 502 slipped to a stump pulling 1.53.
Ford started out quick too. I remember Dad’s 62 stick shift Fairlane
with the 221ci small block, predecessor of the 260W, whose ratio was 1.80. The 260 and 289 had ratios of 1.79
(5.15/2.87) then they produced the 302 and 351W at 1.70. Alan Foster’s race winning Mustang uses a
351W stock rod ratio (5.95/3.5) but is highly modified for head flow and is
internally balanced with a light rotating assembly. It screams down the straights at 7,200rpm and redlines well above
8,000. Our 351C (5.78/3.5) is fair at
1.65. Some of us have switched to a 6’’
rod to get back to 1.71. Tom Todak runs
his 380C with those Chevy 6” rods on 3.75 crank for 1.60 ratio. His objective is a reliable mid range torque
machine able to take the taller gears in his ZF. Art Stephens’ old 377C engine had no trouble getting the revs up
quickly with its 6.125/3.7 for 1.66.
But I eagerly await his new 408C engine with a 6/4 1.50 ratio. His right foot is about to test the heavily
laden 4 bolt with all the right Australian BOSS goodies. The typical 427W uses 4.17 stroke and a
6.125” rod for 1.47 ratio: our
Cleveland based 427 at 6.125/4.154 has a 1.485 ratio. Bill Wright lucks out by running one of these big cubes in a
super light GT40. I wonder how fast it
propels the car to 7500rpm? 911
Porsches are designed for 1.7 to 1.8 ratios.
Remember that Viper does prove that even truck engines can deliver fast
cars in the right combo.
The key seems to be the intake, exhaust, head, cam,
valve train, and rotating assembly selected.
The choices determine the flow possibilities so vital to extracting the
desired response from the engine. Each
designer chooses his own way to propel a car down the road. Horsepower is calculated by torque numbers,
so, do you want big booms or lots of little booms? Unfortunately, I don’t know what is best. I only hope that you will tell me of your
experiences and preferences. I, with
your help, can then plan the rebuild of my engine.
Reminders:
from rkunishige@hotmail.com. Please email needed corrections/additions to
me.
Mar 1-2 Willow Springs Open Track
sponsored by Jim Saxton 626 285-2024.
West Coast Racing invites you to run all makes & models at speed on
the Willow Springs road course in Rosamond, just north of Lancaster. Jim and Cherie Saxton host both Pantera and
Ferrari clubs for this two day event twice a year. TPOC helps registration Saturday as a fundraiser. So, bring your car and experience the
fastest track in the west (often the site of new car testing as seen on Speed
TV). The cars are divided into 4
classes based on your skill level from pro to novice (instructors provided) and
car preparation. Or, come and make the
TPOC treasury grow by helping with the registration and enjoy watching some
very fast, expensive cars race. Be sure
to offer a ride to the guy holding a helmet labeled with “ROD”.
Mar 2 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
Mar 12 TPOC
Mtg 7pm Mel’s Drive-in 12241 Seal Bch Blvd, Seal
Beach.
Mar 22 March
Field Air Museum 8am dash from
Donut Derelicts to Riverside to view our heritage & lunch. Make
reservations w/Cindy Harris at skylife@verizon.net
- $10 admission & 15.95 lunch.
Apr 9 TPOC
Mtg
Apr 13 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
Apr 18-20 Long
Beach Grand Prix.
Apr 30-5/3 Las
Vegas Fun Rally & Track Event Register early. See your POCA
Newsletter.
May 4 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
May 14 TPOC
Mtg
Jun 8 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
Jun 11 TPOC
Mtg
Jun 14? TPOC
Swap Meet at Bud Williams’ garage 9am-2pm. Bring your stuff to sell or bring cash to
carry goodies purchased. Sandwiches and
sodas provided. See Bud’s complete
collection. It goes well beyond that
shown in POCA’s article. I want a ride in the Sunbeam Tiger.
Jul 6 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
Jul 9 TPOC
Mtg
Aug 10 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
Aug 13 TPOC
Mtg
Aug 15-17 Monterey
Concorso Itialiano Black
Horse Golf check with PI. Sign up
now. Rooms are limited.
Sep Belmont
Shore
Sep 10 TPOC
Mtg
Sep 14 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
Oct 08 TPOC
Mtg
Oct 12 LB
Swap Meet at Long Beach Veterans’ Stadium 6am-1pm.
Nov 12 TPOC
Mtg
Nov Willow
Springs Open Track sponsored by Jim Saxton 626 285-2024.
Dec Christmas
Party
Dec 27 Gondola Ride
March Air Museum admission includes a simulator ride, 71
aircrafts, interactive exhibits even see some future technologies. Be sure to ask Bill Wright which plane he
flew. www.marchfield,org for more info.
Las Vegas is once again upon us. So, look
at your POCA newsletter for further details and plan to participate. Bring your car to show at the Fremont
Display or track it at the Speed Trials.
Willow Springs hosted by Jim & Cherie Saxton’s West Coast Racing in conjunction
with both Pantera and Ferrari clubs give you the chance to take your car on the
world famous high speed track. Street
cars abound as the Novice group makes full use of the free instructors to show
the best line to take on each corner.
They also advise you on the techniques to gain full control of your car
while extracting the most from its features.
Remember that there are four run groups based on your experience and two
days packed with lessons to help understand your car’s limits and at the same
time improve your driving skills. Come
out to participate or watch the excitement.
(Cherie prepares a free lunch for TPOC members.)
Events are an essential part of the club’s wellbeing. Please consider hosting one of your
choosing. The key is to bring
like-minded people together for some fun.
Contact Dave with your idea and let’s schedule it up for this year. It would be a special treat if some of the
ladies would come up with an idea or more.
I know that I sometimes get stuck in a rut and can’t seem to get those
wheels in my mind spinning in a new direction.
Simply, I am asking you, ladies, for directions.
Meeting Site Sought that will draw more members to attend. If
you know of a place that can accommodate us, please speak up. Our intent is to have easy parking, good
food, separate room to conduct the meeting, individual billing to free up those
who need to leave early and a locale better suited for the majority of
members. Talk to Dave.