5.7 vs 6.0 Rods

General engine tech -- Drag Racing to Circle Track

Moderator: Team

petiepye
New Member
New Member
Posts: 20
Joined: Wed May 14, 2008 9:48 pm
Location: Independence, Mo

5.7 vs 6.0 Rods

Post by petiepye »

I have a good 010 350 block and I plan to build a drag race only bracket engine. Planning the bottom end, and when considering cranks, the rod length comes up.
What are the pros and cons of the different rod lengths?
All opinions and explanations will be appreciated.
Thanks in advance, Pete.
bigjoe1
Show Guest
Show Guest
Posts: 6199
Joined: Thu Aug 24, 2006 8:16 pm
Location: santa ana calif-92703
Contact:

Post by bigjoe1 »

Here is a true story-- I build quite a few 383 Chevy engines, I usually use 6 inch rods because I like the light pistons. But, once when there were no 6 inch rods available, I put my regular 383 combo togeter with the shorter 5.7 rods. The engine was down everywhere about 15 to 20 HP, and 15 to 20 pounds of torque. That was the only time I used the 5.7 rods, and after that, I will never use them again.


JOE SHERMAN RACING ENGINES
petiepye
New Member
New Member
Posts: 20
Joined: Wed May 14, 2008 9:48 pm
Location: Independence, Mo

Post by petiepye »

Joe, that is a powerful recommendation. I forgot to mention that, indeed, I am building a 383.
1989TransAm
Guru
Guru
Posts: 15481
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

Post by 1989TransAm »

I was going to say with the long rods you get a lighter rotating assembly. However Joe's story is very interesting and compelling for the longer rods.
levisnteeshirt
Guru
Guru
Posts: 1912
Joined: Tue Aug 18, 2009 2:53 pm
Location:
Contact:

hey

Post by levisnteeshirt »

Big Joe , fan since 1979 ( '79 PHR 355 in Nova running 10.60's first read )

First , whats ur opinion of using a 6.125 rod in a 355 using a 383 piston for a 6.0 rod ?? ,

read one of your articles about a 406 , comparison between 5.565 rod and 5.7 ,, 5.565 down about 15 hp , then you put a dominator on it and got the difference almost back ,,,
bigjoe1
Show Guest
Show Guest
Posts: 6199
Joined: Thu Aug 24, 2006 8:16 pm
Location: santa ana calif-92703
Contact:

Post by bigjoe1 »

Once the engine is together and running, you cant really tell any differance. I have done a few of those things like 6.125 rods, and it NEVER paid off. It is not worth the cost or trouble, unless you allready have the parts to use.Ihave had racers tell me things like their big speed secret was short rods, but I have never seen it happen. Again, I just like the lighter pistons


JOE SHERMAN RACING ENGINES
randy331
Guru
Guru
Posts: 3337
Joined: Mon Dec 04, 2006 7:30 pm
Location: N.W. MO.

Post by randy331 »

As long as the rod is long enough to get the piston close to the head at TDC, yet short enough that it doesn't hit the head at TDC, or fail to keep the piston conected to the crank, and damage the head,(where the focus should have been) then the length is perfect.

Randy
Sprinter99
Member
Member
Posts: 57
Joined: Sun Feb 25, 2007 10:23 pm
Location: Forney, Tx.

Post by Sprinter99 »

Over the last few years i've had 5.85 ,6.0 and 6.125 rods in 355s and the longest rod made the MOST power on the dyno but was SLOWEST on the track, the 5.85 made LESS peak power than both the other two but was MUCH faster off the corners than the 6.125. A big example of we dont race dynos.
Kurt Summers
trmnatr

Post by trmnatr »

Sprinter99 wrote:Over the last few years i've had 5.85 ,6.0 and 6.125 rods in 355s and the longest rod made the MOST power on the dyno but was SLOWEST on the track, the 5.85 made LESS peak power than both the other two but was MUCH faster off the corners than the 6.125. A big example of we dont race dynos.
On a circle track car or street car i could see that
maxracesoftware
Vendor
Posts: 3627
Joined: Sat Feb 14, 2004 4:04 pm
Location: Abbeville, LA
Contact:

Post by maxracesoftware »

bigjoe1 wrote:Here is a true story-- I build quite a few 383 Chevy engines, I usually use 6 inch rods because I like the light pistons. But, once when there were no 6 inch rods available, I put my regular 383 combo togeter with the shorter 5.7 rods. The engine was down everywhere about 15 to 20 HP, and 15 to 20 pounds of torque. That was the only time I used the 5.7 rods, and after that, I will never use them again.


JOE SHERMAN RACING ENGINES

another true story->

around 1991 to 1993+ time period
i Ported different pairs of SBC #041x castings 165 CC Legal limit
with varying Port velocities (epoxy shapes)
for a SS/I 4-speed Camaro

unknown to me,
they used a 6.250 C-C rod with the 1st pair i Ported.
The Pitot Probe velocity was fast , and i was experimenting with
how fast you could push port speeds in various locations.
Port CC's were between 160 to 162 cc well safe of 165 Limit

the SS/I Car ran as fast as 9.69 ET around 18 years ago
and always between low 9.70's to low 9.80's w/6.250 Rod
set the SS/I Record like it was

since he was very fast for its time,
they decided to make it 100% Legal switching to 5.7" Rods C-C
..from that point it slowed down a solid Tenth ET or more
it became a high 9.80's to high 9.90's Car

i ported another pair with barely any epoxy in Ports
slowing velocity as much as i could,
kept Port volume on ragged edge of 165 CC limit ( 164 to 165)
with a Class A Burette
ran a few high 9.70's to low 9.80's

after 2years, NHRA reset Record...slower,
so he set the SS/I Record , but to a slower ET

i think he reset the record a 3rd time in SS/I later on

won Class at Indy 1993

its interesting that the 2009 SS/I Record is only a 9.93 :)

never again did it run any 9.69 or any low 9.70's !
like it did with 6.250 C-C Rod
this was approx 575 HP @ 7300 w/6.250
556's HP @ 7200-7300 with 5.7 Rods

down the DragStrip, since this was a 4-speed manual Trans
with 5.83 gears 3.08 1st
the RPM/SEC acceleration rates were approx->
1st Gear= 4300 RPM/SEC Avg
2nd Gear= 2000 RPM/SEC Avg
3rd Gear= 1070 RPM/SEC Avg
4th Gear= 560 RPM/SEC Avg

as you can see, the RPM/SEC rate is very fast,
coupled with small port volume head that was edge of too fast,
seemed to respond a lot to Rod Length changes.

--------------------------

if that were a 2-spd Powerglide Car, the avg RPM/SEC would have been
a bunch overall slower and not tax the Rod Length / Head CC combination


likewise if there were no 165 Cc rule and
you just built the same CID shortblock with a modern head
the Rod length effects becomes less
to where some say Rod Length doesn't matter at all !

then you look at Smokey's Era where you used
old Double-Camel_Hump Heads and old #292 Turbo Heads
with relatively small port volumes and possible very hi , too fast
local velocities causing CHOKE situations,
then you can see why Smokey preached long rods all day long !
MaxRace Software
PipeMax and ET_Analyst for DragRacers
https://www.maxracesoftwares.com
LoneRanger
Member
Member
Posts: 118
Joined: Mon Apr 28, 2008 7:29 pm
Location:

Post by LoneRanger »

a few years ago we used longer rods in our Ford straight six stock class circle track car, it was a good season with with consistant 1st, 2nd, 3thd, placings & one of the leading teams in points in our local area, the engine ran very strong, however the next season they changed the rules in regards to using different length rods etc & it was a slow start but made gains in other areas later trying various exhaust, manifold & cam changes
CNC BLOCKS
Guru
Guru
Posts: 4653
Joined: Thu Jul 01, 2004 6:34 am
Location: NORTHEAST
Contact:

Post by CNC BLOCKS »

Sprinter99 wrote:Over the last few years i've had 5.85 ,6.0 and 6.125 rods in 355s and the longest rod made the MOST power on the dyno but was SLOWEST on the track, the 5.85 made LESS peak power than both the other two but was MUCH faster off the corners than the 6.125. A big example of we dont race dynos.
Hopefully your not using the same cam for a short and long rod engines!
Website is up and running
http://hinksonautomotive-cncblocks.com/
Machine shop tour
http://hinksonautomotive-cncblocks.com/shop-tour/
Monthly Specials
http://hinksonautomotive-cncblocks.com/specials/
55MM babbit cam bearings with 1 hole
Old School
Pro
Pro
Posts: 461
Joined: Sun Feb 13, 2005 11:27 am
Location:

Post by Old School »

CNC BLOCKS wrote:
Sprinter99 wrote:Over the last few years i've had 5.85 ,6.0 and 6.125 rods in 355s and the longest rod made the MOST power on the dyno but was SLOWEST on the track, the 5.85 made LESS peak power than both the other two but was MUCH faster off the corners than the 6.125. A big example of we dont race dynos.
Hopefully your not using the same cam for a short and long rod engines!
What are the differences in the cams you use for a 5.7 rod compared to the 6 inch rod?
jmwsb2
New Member
New Member
Posts: 32
Joined: Tue Jan 20, 2009 4:18 pm
Location: Florida

ROD LENGTH

Post by jmwsb2 »

I am a fan of Big Joe.s also but I remember when he did a comparison of a stock length of a 400 ci small block and a 5.7 length rod. If my memory is correct the 5.56 length rd made more torque and power than the 5.7 rod until 6250 rpmon the dyno.

I also built a 6 inch rod 406 sbc and the car slowed down about 3 tenths.I discussed this with Bo of BLP and he stated had built a 6 inch rod sbc and was unable to get it to run as fast as the 5.7 tha it replaced. He stated tried for a year to get the combination to equal the 5.7 but eventually put 5.7's in the engine and picked up the time. This was also in a fairly heavy car. I questioned him in what would happen if I changed various components. His answer was that I would wind up taking the engine out.

After replacing the rear gears, coverter, cam carb and a lot of tuning and trying to blow it up I wound up giving the eng. to my son for his dragster and it picked up time over his 5.7 rod eng.

I built another 5.7 rod eng for my car and gained back the 3 tenths I had lost. This was many years ago.

I now have an engine with 6.2 rods and the other with 6.125. both are very close in horsepower.

I think you have to look at all aspects of the package, not just one aspect. We also don't race the dyno even though it is a great tuning instrument.

John
CNC BLOCKS
Guru
Guru
Posts: 4653
Joined: Thu Jul 01, 2004 6:34 am
Location: NORTHEAST
Contact:

Post by CNC BLOCKS »

Old School wrote:What are the differences in the cams you use for a 5.7 rod compared to the 6 inch rod?
It depends on the combination but rememeber that going from a 5.7 to 6.250 the engines is going to breath differently!!! And to optimize you can't run the same cam for both rod lenths.
Website is up and running
http://hinksonautomotive-cncblocks.com/
Machine shop tour
http://hinksonautomotive-cncblocks.com/shop-tour/
Monthly Specials
http://hinksonautomotive-cncblocks.com/specials/
55MM babbit cam bearings with 1 hole
Post Reply