When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
After going down a rabbit hole on modern pistons and rings, I’ve decided to pivot my engine build away from stock pistons.
I’m considering a 7.100" rod with custom pistons (shorter compression height). On paper, this setup improves the rod ratio (1.58 → 1.67), drops about 100–150 grams per piston/pin compared to a stock-style combo, and should reduce side loading.
I see the potential advantages as:
Reduced piston side loading → less cylinder wall wear, friction, and thrust.
Lighter reciprocating mass (~150 g savings) → better balance, higher RPM potential, quicker revving.
Longer piston dwell at TDC → improved breathing, combustion efficiency, and high-RPM power.
Flatter or slightly higher-shifted torque curve → more usable mid-to-upper RPM torque.
Increased durability at high RPM → less stress on rods, bearings, and bolts.
Better resistance to detonation.
What I’m curious about is real-world feedback:
Has anyone here actually run a 7.100" rod in a 455?
Did you notice any change in how the engine pulled — torque curve shift, smoother revs, or extended RPM range?
Any durability pros/cons compared to sticking with stock-length rods and a good forging?
Are there any other potential cons I might not have considered?
I really appreciate any input from those of you who’ve been down this road before — the collective knowledge on this forum is second to none, and I’d value your feedback.
What are you planning to do with the engine ? i think that unless you are looking at a unique racing class where you need every extra bit of power, or if you just have money to throw away and like to experiment, you will probably not notice any improvement in day to day operation.
If you want to reduce weight you can do it with stock dimension parts. Get a set of custom pistons with lightweight pins and you can probably save just as much as you will with the long rod combination.
It really is hard to improve on the factory engineering for a typical stock to mild performance engine.
I have 7.2 BME 426 series rods in my 468 with CP Bullet "496" pistons (designed for 4.5 crank, 060 over). Never had it on a dyno, though. I'm pretty sure Engine Masters has an episode on this very debate, and the differences were negligible.
I do believe Smokey Yunick said "stick the longest rod you can in it", if I recall correctly.
Smokey Yunick was indeed an interesting character. During the era he was involved in stock car racing, his statements may or may not have worked to gain an edge. Smokey also was known to circumvent the rules (cheat).
I do believe Smokey Yunick said "stick the longest rod you can in it", if I recall correctly.
Originally Posted by cutlassefi
Yes, that was his m.o.
But Warren Johnson said the opposite, “just stick whatever rod you have in it”. Both were successful so…….
"I think" we have to look at the type of racing and the different era's.
Smokey was "roundy round" racing in a narrow power band. Warren Johnson was pure power. The other thing to consider was the weight of the pistons in each era. In the "Smokey era" pistons were considerably heavier, including aftermarket racing pistons. Later manufactured pistons use thinner and shorter piston skirts which reduced weight. The "longer rod theory" probably reduced a lot of piston weight and added a little to rod weight.
Piston manufacturing equipment and processes have changed. A few years ago, I worked a job in a Federal-Mogul plant and the chance to see "centrifugal piston casting" machinery. It wasn't hard to see the higher productivity from the old "pattern and sand casting method".
.....Just my two cents worth.
Thanks for all the feedback! I found the Engine Masters vid very informative.
Yep, and it totally debunked the internet didn’t it.
Like I said, Warren Johnson always contended “just stick whatever rod you can in it”. Seems like he may have known what he was doing.
Yes, that was his m.o.
But Warren Johnson said the opposite, “just stick whatever rod you have in it”. Both were successful so…….
no, he didn’t say the opposite. if he did, then that would mean he said stick the shortest rod in it.
Johnsons comments were taken out of context by so many, including you. After that interview, the rod length internet gurus went nuts…just google it and you’ll see what I mean.
nobody in their right mind would build an engine on purpose with severe rod angularity which cause excessive side load on the cyl walls. look at any pro stock from his era and you’ll see an extremely short piston comp height and the longest rod they could fit, with a tiny ring pack.
Does anyone know why Olds engineers went with shorter rods when they increased the stroke on the big blocks starting in 68, yet over the years of the small block, they kept rod length and rod ratio the same all the way through its production run?
why didn’t they just use the 7” rod in the 400G and 455 from the beginning?
and why didn’t they just increase the bore on the 425? that would have been easier and less costly.
So the only change was the stroke? No other changes between the two, ie cam, heads, intake etc.?
THE EXACT same cam, heads, manifold, carb, headers, etc
The pistons were different of course, but the compression really didn’t change. 10.76:1 vs. 10.78:1 if I remember correctly?
THE EXACT same cam, heads, manifold, carb, headers, etc
The pistons were different of course, but the compression really didn’t change. 10.76:1 vs. 10.78:1 if I remember correctly?
This is a stock stroke and rod length (4.25/6.735) vs a stroker with a 4.5 stroke and 7.100 rod correct? Sorry for questions, just trying get accurate info.
Last edited by cutlassefi; Sep 15, 2025 at 01:41 PM.
Does anyone know why Olds engineers went with shorter rods when they increased the stroke on the big blocks starting in 68, yet over the years of the small block, they kept rod length and rod ratio the same all the way through its production run?
why didn’t they just use the 7” rod in the 400G and 455 from the beginning?
and why didn’t they just increase the bore on the 425? that would have been easier and less costly.
I have some theories.
First of all, they never changed the stroke on any small block so why would they change the rod?
Secondly, I’ll bet it was easier and cheaper to change the crank on a big block, vs making the block casting large enough to handle a 4.25 or so bore.
And Warren Johnson‘s point was, don’t fret over Rod length. If you have to stick a shorter rod in it because that’s all that will work, then just do that, and don’t lose any sleep over it.
Finally, any idea what the rod ratio is in the 632ci, 1000hp GM Crate engines, or virtually any 4 digit hp 632? A measly 1.41. Pretty tight. And the GM crate engines come with a warranty, go figure.
Last edited by cutlassefi; Sep 15, 2025 at 01:54 PM.
no, he didn’t say the opposite. if he did, then that would mean he said stick the shortest rod in it.
Johnsons comments were taken out of context by so many, including you. After that interview, the rod length internet gurus went nuts…just google it and you’ll see what I mean.
nobody in their right mind would build an engine on purpose with severe rod angularity which cause excessive side load on the cyl walls. look at any pro stock from his era and you’ll see an extremely short piston comp height and the longest rod they could fit, with a tiny ring pack.
I'll be over @ WJs in a few weeks and I'll ask him in person.
I'll be over @ WJs in a few weeks and I'll ask him in person.
good. I’ll bet he would say something different if asked again.
ask him specifically what’s better in a big block 455 olds performance engine.. the short 6.735 factory rod with 1.765 compression height pistons , or a 7” rod with 1.5” ch pistons ?
heck, if rod length and angularity don’t mean ***** ask if a 6.135” bb chev rod is ok?
considering it’s in a 50 plus year old thin wall factory block.
I'll be over @ WJs in a few weeks and I'll ask him in person.
Have you ever gotten engine building advice from WJ for one of your builds?
I heard him a few times comment in interviews, that he found NHRA stock class cars interesting.
Have you ever gotten engine building advice from WJ for one of your builds?
I heard him a few times comment in interviews, that he found NHRA stock class cars interesting.
Define "interesting".
I recall WJ coming from the Minneapolis area, many, many years ago. He was running a "Rat motored" Camaro in Super Stock or higher class. WJ has never run a true "Olds" engine, unless I missed it. Its always been Chebbie or the DRCE Olds (Chebbie based) stuff. I was surprised Oldsmobile recruited WJ. People that knew him said he was smart.
Have you ever gotten engine building advice from WJ for one of your builds?
I heard him a few times comment in interviews, that he found NHRA stock class cars interesting.
No, I've never had an engine build other than stock type for me to ask about that. Our conversations were 25% racing and 75% current affairs. Me talking to WJ about engines is a non starter.
I recall WJ coming from the Minneapolis area, many, many years ago. He was running a "Rat motored" Camaro in Super Stock or higher class. WJ has never run a true "Olds" engine, unless I missed it. Its always been Chebbie or the DRCE Olds (Chebbie based) stuff. I was surprised Oldsmobile recruited WJ. People that knew him said he was smart.
In my opinion the way he talked about the class it seemed that he had respect for the class, and would have had interest in the class if he was not already at the pinnacle of the sport.
Does anyone know why Olds engineers went with shorter rods when they increased the stroke on the big blocks starting in 68, yet over the years of the small block, they kept rod length and rod ratio the same all the way through its production run?
why didn’t they just use the 7” rod in the 400G and 455 from the beginning?
and why didn’t they just increase the bore on the 425? that would have been easier and less costly.
I have some theories.
Dale what are your thoughts on why they went to a shorter rod with the 400G and 455 when they increased the stroke?
In my opinion the way he talked about the class it seemed that he had respect for the class, and would have had interest in the class if he was not already at the pinnacle of the sport.
When I first saw WJ was in the late 60's. That would have been a prime time to run Oldsmobile's. I'm guessing he wasn't known outside of NHRA Division 5, far from the pinnacle.
At the time, Gary Ostrich and John Hagen were running the first Hemi Barracuda's and Richard Charbeneau was big with a 427 Ford Fairlane station wagon. Greg Murnane and his '67 GTO briefly held the NHRA MPH record in the same class as 442's ran.
I have 7.1” rods in a 4.060” bore 400 E block with 4.25” Scat stroker. Runs super. No problems. Used Molnar rods with BBC journals and Autotech pistons.
Dale what are your thoughts on why they went to a shorter rod with the 400G and 455 when they increased the stroke?
first I’ll say which ever engineer made that decision should have been canned on the spot and demoted to the Chev division.
they already had a beautiful design in the 425 where they could have simply upped the bore to 4.250+ to get their 455 while using the same rods, same compression height pistons and stroke. they could have used a cast crank instead of forged if it was about saving money. they upped the small block bore to 4.351” easy enough.
Buick engineers did it right when they went from 400” to 455” with same stroke and just a bore increase.
look at all the early big and small blocks, 330, 350, 400 and 425…even the 403,, they all used the same compression height pistons. so why not stay with the same CH design pistons and use a rod that’s around 6.88” for the 4.25” stroke increase?
why purposely use an even shorter rod with a longer stroke that increases rod angularity and requires a piston with increased CH?
the only reason I can come up with is because they knew car size and weights were increasing. the 455 only went into those big heavy cars. buyers wanted dead smooth quiet rides and silent low rpm engines. the lower the rpm, gear ratios were also getting deeper into the 2 series range for lower rpm’s
when an engine is designed for high TQ and very low rpm, piston skirt area needs to be increased , or scuffing happens and it’ll kill it. look at low rpm diesels, they have huge CH pistons to handle the piston loading at low rpm’s.
the 400G was a sorry by product of the 455’s low rpm design and GM self imposed 400” limit.
so in my opinion they went with the maximum skirt area for low rpm longevity where rpm’s would rarely go over 3k. the 6.735” rod used makes it so the bottom of the piston skirt bosses barely clear the crank counterweights.. it’s so close , if it spins a rod bearing bad enough, the piston bosses whack the crank
Last edited by CANADIANOLDS; Sep 24, 2025 at 12:11 PM.
first I’ll say which ever engineer made that decision should have been canned on the spot and demoted to the Chev division.
they already had a beautiful design in the 425 where they could have simply upped the bore to 4.250+ to get their 455 while using the same rods, same compression height pistons and stroke. they could have used a cast crank instead of forged if it was about saving money. they upped the small block bore to 4.351” easy enough.
Buick engineers did it right when they went from 400” to 455” with same stroke and just a bore increase.
look at all the early big and small blocks, 330, 350, 400 and 425…even the 403,, they all used the same compression height pistons. so why not stay with the same CH design pistons and use a rod that’s around 6.88” for the 4.25” stroke increase?
why purposely use an even shorter rod with a longer stroke that increases rod angularity and requires a piston with increased CH?
the only reason I can come up with is because they knew car size and weights were increasing. the 455 only went into those big heavy cars. buyers wanted dead smooth quiet rides and silent low rpm engines. the lower the rpm, gear ratios were also getting deeper into the 2 series range for lower rpm’s
when an engine is designed for high TQ and very low rpm, piston skirt area needs to be increased , or scuffing happens and it’ll kill it. look at low rpm diesels, they have huge CH pistons to handle the piston loading at low rpm’s.
the 400G was a sorry by product of the 455’s low rpm design and GM self imposed 400” limit.
so in my opinion they went with the maximum skirt area for low rpm longevity where rpm’s would rarely go over 3k. the 6.735” rod used makes it so the bottom of the piston skirt bosseby Chevys barely clear the crank counterweights.. it’s so close , if it spins a rod bearing bad enough, the piston bosses whack the crank
Thanks for the reply Dale.
I always felt they went backwards with the 400G and that it was not necessary. The 455 Buick is always faster than the 455 Oldsmobile in Stock class racing. You just have to look at how many big block Buicks are running in NHRA stock/ Stock class/ Fast Class etc. Its a very popular engine in a world dominated by Chevy's, Mopar's and Fords.
The 455 Buick is always faster than the 455 Oldsmobile in Stock class racing. You just have to look at how many big block Buicks are running in NHRA stock/ Stock class/ Fast Class etc. It’s a very popular engine in a world dominated by Chevy's, Mopar's and Fords.
So are you contending that the reason for the Buick‘s success is due to the rod length/ratio?
You don’t think the fact that the Buick’s bore is almost .200 bigger than an Oldsmobile, helping it breathe better, doesn’t have any effect on it?
And then what’s your explanation on why 454 Chevys are so successful, and make so much power comparatively speaking? Their rod ratio is less than a 455 Olds.
And isn’t it ironic that the factory rated torque king of the 70s muscle car era was in fact a Buick, not an Oldsmobile? The Buick had the shortest stroke of all of them, yet made the most factory rated tq in stock trim. I’ll bet the bore size, which is even bigger than a 454 Chevy, had something to do with it.
The rod ratio thing is mostly crap, but some people just won’t let it go. There are so many variables, you really can’t pin it on one thing.
