View Poll Results: Length matters
5.7"
2
10.53%
6.0"
12
63.16%
longer than 6.0
5
26.32%
shorter than 5.7
0
0%
Voters: 19. You may not vote on this poll
Longer is better Rod length?
Thread Starter
Race Director
Joined: Jan 2005
Posts: 10,641
Likes: 13
From: Slidell Louisiana
Longer is better Rod length?
For a high reving SBC which is the better choice 5.7" or 6.0" and why.
Please stick to engines with a stroke between 3.10" and 3.88"
I went with 6.0" with stock stroke.
I chose the 6.0s because it was a proven combination recommended by some people I trust.
I was planning on a 396 but was told that this 355 combo would do everything I want and rev too!!!
Mike
Please stick to engines with a stroke between 3.10" and 3.88"
I went with 6.0" with stock stroke.
I chose the 6.0s because it was a proven combination recommended by some people I trust.
I was planning on a 396 but was told that this 355 combo would do everything I want and rev too!!!
Mike
Last edited by aboatguy; Jun 16, 2007 at 12:35 PM. Reason: options!
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
How about this combination: 400 small block equates to a 4.125" bore, use a 327 crankshaft or equal which is a 3.25 stroke if my memory serves me correctly. Couple the pistons with a 6.375" rod, AFR heads, flat top pistons for a static compression ratio of 11:1. This engine with a very mild camshaft will make just a tad over 400hp and tons of torque. And will run on 87 octane! And it will rev to the moon as well.
The engine was featured in a hot rod magazine article a few years back. The rods they used were out of a Ford straight 6, they had to be machined to fit a SBC and special JE Pistons were used for the correct compression height but any manufacturer can make them. Just goes to show what a excellent rod lenght to stroke ratio can do for you. Smokey Yunick always said to put the longest rods in that you can! A longer rod puts the piston at TDC for a longer period of time (dwell) thus offsetting detonation. Less or no detonation equates to more timing you can add (to a point) which means more power. Also running a tight squish promotes better combustion which also means better mixing in the chamber and more power and less prone to detonation.
The engine was featured in a hot rod magazine article a few years back. The rods they used were out of a Ford straight 6, they had to be machined to fit a SBC and special JE Pistons were used for the correct compression height but any manufacturer can make them. Just goes to show what a excellent rod lenght to stroke ratio can do for you. Smokey Yunick always said to put the longest rods in that you can! A longer rod puts the piston at TDC for a longer period of time (dwell) thus offsetting detonation. Less or no detonation equates to more timing you can add (to a point) which means more power. Also running a tight squish promotes better combustion which also means better mixing in the chamber and more power and less prone to detonation.
Last edited by tjwong; Jun 16, 2007 at 12:26 PM.
Large Impressive Member
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
I, as did my hero Smokey mentioned above, also believe in longer rods. As you know Mike, I used 6" rods in my 388.
Just how long of course depends on practical and other considerations for a given combination and the end use of it. Within these reasonable limits, there are really no downsides to using them, IMO. Do the benefits justify the higher cost? That's for the guy footing the bill to decide. I was going with all lightweight aftermarket H-beams and pistons anyway, so why not use the longer rods?
Just how long of course depends on practical and other considerations for a given combination and the end use of it. Within these reasonable limits, there are really no downsides to using them, IMO. Do the benefits justify the higher cost? That's for the guy footing the bill to decide. I was going with all lightweight aftermarket H-beams and pistons anyway, so why not use the longer rods?
Team Owner
Joined: Feb 2006
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From: sw Ohio
How about this combination: 400 small block equates to a 4.125" bore, use a 327 crankshaft or equal which is a 3.25 stroke if my memory serves me correctly. Couple the pistons with a 6.375" rod, AFR heads, flat top pistons for a static compression ratio of 11:1. This engine with a very mild camshaft will make just a tad over 400hp and tons of torque. And will run on 87 octane! And it will rev to the moon as well.
Team Owner
Joined: Sep 2001
Posts: 62,153
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From: Athens AL
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I dont think for a street engine that it would make a big difference, but I would still say 6.0" for a higher-revving engine that sees some track use.
Melting Slicks
Joined: May 2007
Posts: 2,382
Likes: 2
From: Kathleen FL
I saw an article about the destroked 400 somewhere. I think it was called "The 350 Chevy GM should have made," or something along those terms. I never knew you could run 87 octane gas in an 11:1 static compression motor, until I read that article....
Instructor
Joined: Nov 2004
Posts: 110
Likes: 0
From: Texas
rod length
Depends on what you are trying to accomplish. Acceleration,longivity, peak power. Lighter rotating components (rods) will accelerate from A to B quicker, and recover from shift points faster. Longer rods will dwell at TDC longer. Some NHRA comp eliminator motors are using shorter rods than normal. Some people dont like the wrist pin up in the oil ring package,some piston brands for the same given stroke will not have the piston pin up in the ring package, etc.
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Large Impressive Member
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Short answer? Extremely good combustion efficiency. This is where all of the many nice little design features, such as piston dwell, quench, chamber and piston design, coatings for heat retention, good overall volumetric efficiency and other things pay their dividends. Air in, air out and good burn.....
Large Impressive Member
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Here's an interesting side note on this subject. Not too long ago I was looking into small block Mopar specs to give a little insight to someone who is planning a build of one. The 340 Mopar was always a strong runner and for it's day, had a rather broad torque curve and pulled well throughout it's range. But it has a much shorter stroke than even a stock 350 Chevy, so how can this be? In fact, the 273, the 318 (both the early 318s and the more modern small block versions) and the 340 all have the same stroke. Well due to this short stroke, the 340 was able to use a rod of about 6.125" This tells me that a longer rod plays more than a bit part in contributing to torque. I always was extremely impressed with 340s having owned a couple over the years. Now I more fully understand why they worked so well. 
The highest factory HP rating ever given to one was 275, except for the rare 6-pack versions in '70-'71. Trust me, that was quite under-rated.
One more quick example. Smokey Yunich always liked long rods for oval track engines where corner speeds were reduced to the point that coming off the corner, the engine was starting low in it's power range again. In other words tracks with long straights and tight corners such as a Martinsville for example. Makes sense now, doesn't it?
The highest factory HP rating ever given to one was 275, except for the rare 6-pack versions in '70-'71. Trust me, that was quite under-rated.One more quick example. Smokey Yunich always liked long rods for oval track engines where corner speeds were reduced to the point that coming off the corner, the engine was starting low in it's power range again. In other words tracks with long straights and tight corners such as a Martinsville for example. Makes sense now, doesn't it?
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by Corvette Kid
Well due to this short stroke, the 340 was able to use a rod of about 6.125" This tells me that a longer rod plays more than a bit part in contributing to torque. I always was extremely impressed with 340s having owned a couple over the years. Now I more fully understand why they worked so well.
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Large Impressive Member
Joined: Jul 2003
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Don't discount the bore/stroke ratio and the piston speed when looking at reasons for good performance from the 340. I prefer the longer rods, too, but I think within a reasonable length range there will be only minimal gains in performance due only to rod length. Except for maybe in a dedicated race engine, I would use the longest rod available for a given engine combination that didn't add much to the cost. For instance, If I had 5.7" rods on hand, I wouldn't go out and buy 6.0" rods, just for their length. if I were starting with a clean sheet of paper, with no parts on hand, I would build around 6.0" or even possible longer rods.
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Large Impressive Member
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
You're right. I checked it out and everything except the 400 used the 5.7 rod. I will say this though. Give me a 350 Chevy and a 340 Mopar with as equal of heads, cam, etc. as possible and I'd put my money on the 340 every time.
Melting Slicks
Joined: May 2007
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From: Kathleen FL
I know the 400s used a much shorter 5.56" rod. Correct me if I'm wrong, but GM never intended the 400s to be revved high. Block production lasted only for 10 years, 1970-1980.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by hooblyboobly
I know the 400s used a much shorter 5.56" rod. Correct me if I'm wrong, but GM never intended the 400s to be revved high. Block production lasted only for 10 years, 1970-1980.
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Le Mans Master
Joined: Aug 2000
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From: Australia
Instructor
Joined: Sep 2006
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From: Yorkville IL
We've debated this a lot over at the firstgen camaro site, we build a lot of small blocks there.
For a street car, it doesn't make much difference (in power) at all.
The 400 used short rods to keep the piston compression height where Chevy wanted it to be.
A 6" rod and a 3.75" stroke in a 9" deck ht SBC puts the wrist pin right through the oil ring, not something an OEM would ever do.
When I built the 383 for my camaro, I used 6" rods and SRP forged pistons. I did it because:
It didn't cost any more.
The scat 7/16" capscrew I beam rods I used will clear any camshaft without having to use a reduced base circle cam.
The reduction in reciprocating weight is HUGE. Those lil SRP's only weigh 404 grams! That's 130 less than a forged TRW slug in the standard 350 deck HT!
Bobweight was only 1830 grams, and they had to take 2 pounds of metal OUT of the crank when they internal balanced it.
Any time you can take moving weight out of a car without losing strength, you are winning, in power and in longevity
For a street car, it doesn't make much difference (in power) at all.
The 400 used short rods to keep the piston compression height where Chevy wanted it to be.
A 6" rod and a 3.75" stroke in a 9" deck ht SBC puts the wrist pin right through the oil ring, not something an OEM would ever do.
When I built the 383 for my camaro, I used 6" rods and SRP forged pistons. I did it because:
It didn't cost any more.
The scat 7/16" capscrew I beam rods I used will clear any camshaft without having to use a reduced base circle cam.
The reduction in reciprocating weight is HUGE. Those lil SRP's only weigh 404 grams! That's 130 less than a forged TRW slug in the standard 350 deck HT!
Bobweight was only 1830 grams, and they had to take 2 pounds of metal OUT of the crank when they internal balanced it.
Any time you can take moving weight out of a car without losing strength, you are winning, in power and in longevity