What are the pros and cons of the 5.7"/6.0" rods in a 383?
Thread Starter
Supreme Member
Joined: Feb 2000
Posts: 1,196
Likes: 0
From: Fort Collins, Colorado
What are the pros and cons of the 5.7"/6.0" rods in a 383?
?????
------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End
Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.
Best ET: 14.3 @ 97mph
------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End
Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.
Best ET: 14.3 @ 97mph
Senior Member
Joined: Feb 2000
Posts: 592
Likes: 1
1. Longer rods reduce sideloading on the piston skirt. This reduces the resistance felt by the piston as it accelerates away from top-dead center and bottom-dead center. It also reduces the wear on the cylinder walls.
2. More importantly, a longer rod will allow the piston to dwell near top-dead center for a longer period of time between the exhaust/intake(increased cylinder filling) and compression/ignition strokes(increased combustion pressure and reduced likelihood of detonation). All of this aids power production throughout the powerband and helps to move the horsepower peak higher in rpm(assuming there is sufficient airflow at the higher rpm).
3. There are two main disadvantages to longer rods: added weight and reduced clearance. The added weight means it requires more power to move the reciprocating assembly, however that is more than offset by the increased power and reduced frictional losses. The clearance issue has largely been addressed by the aftermarket. Many rod manufacturer's offer narrower I-beam rods specifically designed to clear the cylinder walls in stroker applications. The I-beam rods tend to be a little more expensive than the conventional H-beam rods. This however is offset by eliminating the need to clearance the block and because: most I-beam designs are stronger than their H-beam counterparts.
------------------
He who hesitates,... is lost!
[This message has been edited by 88IROCs (edited September 11, 2000).]
2. More importantly, a longer rod will allow the piston to dwell near top-dead center for a longer period of time between the exhaust/intake(increased cylinder filling) and compression/ignition strokes(increased combustion pressure and reduced likelihood of detonation). All of this aids power production throughout the powerband and helps to move the horsepower peak higher in rpm(assuming there is sufficient airflow at the higher rpm).
3. There are two main disadvantages to longer rods: added weight and reduced clearance. The added weight means it requires more power to move the reciprocating assembly, however that is more than offset by the increased power and reduced frictional losses. The clearance issue has largely been addressed by the aftermarket. Many rod manufacturer's offer narrower I-beam rods specifically designed to clear the cylinder walls in stroker applications. The I-beam rods tend to be a little more expensive than the conventional H-beam rods. This however is offset by eliminating the need to clearance the block and because: most I-beam designs are stronger than their H-beam counterparts.
------------------
He who hesitates,... is lost!
[This message has been edited by 88IROCs (edited September 11, 2000).]
Senior Member
Joined: Jul 1999
Posts: 700
Likes: 0
From: Pineville, NC US
Car: An '87 Italian Retard Out Cruisin'
Engine: LS1 install in progress
Transmission: 4L60e
Axle/Gears: 9 bolt
Would 5.85" rods be worth getting for a 383?
------------------
1987 Iroc 350
GTS headlight/tail light covers
Camaro SS Wheels w/Sumitomo HTR ZII 275 rear, 255's in front
K&N filters
Adjustable Borla cat back
Large tube runners
ported plenum
Holley afpr
Hopefully Coming Soon: Emissions legal daily diven 383,afr heads, cam??, Slp 1 3/4 headers, super ram, high flow base, strengthened 700r4. any suggestions please tell!!
Some pics of it at
http://photos.yahoo.com/john5911
------------------
1987 Iroc 350
GTS headlight/tail light covers
Camaro SS Wheels w/Sumitomo HTR ZII 275 rear, 255's in front
K&N filters
Adjustable Borla cat back
Large tube runners
ported plenum
Holley afpr
Hopefully Coming Soon: Emissions legal daily diven 383,afr heads, cam??, Slp 1 3/4 headers, super ram, high flow base, strengthened 700r4. any suggestions please tell!!
Some pics of it at
http://photos.yahoo.com/john5911
Guest
Posts: n/a
5.85 rods? Depends on how much you want to spend. Try finding pistons for a 5.85 rod sometime. It would be much cheaper to just pick a 5.7 or 6.0 rod, and run with that. The difference in the performance characteristics of a 5.85 isnt really worth what I can imagine the pistons would cost.
Junior Member
Joined: May 2000
Posts: 91
Likes: 0
From: AK
Junior Member
Joined: Jul 1999
Posts: 29
Likes: 0
From: Langhorne, Pa. 19047
Whoa there, the only REAL disadvantage is the piston pins location being made higher and it's bore being where the oil rings are. Also the clearance problem is not from the rod, but the larger throw of the crank. This is a concern with the camshaft also. It doesn't matter what length rod it is. Also H beam rods are much stronger than I beams (stock type) and more expensive. Anyway, many companies now sell rods that use cap bolts, instead of normal rod bolts, which makes it unnecessary to use a small base circle cam. They are not that expensive either.
Thread Starter
Supreme Member
Joined: Feb 2000
Posts: 1,196
Likes: 0
From: Fort Collins, Colorado
Thanks guys, that was a tremendous help!!
------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End
Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.
Best ET: 14.3 @ 97mph
------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End
Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.
Best ET: 14.3 @ 97mph
Trending Topics
Junior Member
Joined: May 2000
Posts: 91
Likes: 0
From: AK
Originally posted by dan:
Whoa there, the only REAL disadvantage is the piston pins location being made higher and it's bore being where the oil rings are. Also the clearance problem is not from the rod, but the larger throw of the crank. This is a concern with the camshaft also. It doesn't matter what length rod it is. Also H beam rods are much stronger than I beams (stock type) and more expensive. Anyway, many companies now sell rods that use cap bolts, instead of normal rod bolts, which makes it unnecessary to use a small base circle cam. They are not that expensive either.
Whoa there, the only REAL disadvantage is the piston pins location being made higher and it's bore being where the oil rings are. Also the clearance problem is not from the rod, but the larger throw of the crank. This is a concern with the camshaft also. It doesn't matter what length rod it is. Also H beam rods are much stronger than I beams (stock type) and more expensive. Anyway, many companies now sell rods that use cap bolts, instead of normal rod bolts, which makes it unnecessary to use a small base circle cam. They are not that expensive either.
Hate to disagree with you Dan but rod length does affect clearance. When the longer rod is used, the angle between the crank rod journal and the piston pin is reduced (with a longer rod). The reduced angle brings the rod beam and rod end closer to the cam and the bottem of the cylinder. When long rodding a 400 sbc, you will almost always have to grind windows at the cylinder base.
Aftermarket rods that use the cap screws will also require clearancing. The head of the cap screw will either hit the pan rail area or come too close for adaquate clearance (.050" clearance is the minimum you want to shoot for when clearancing).
When using a stroker rod, a small base circle cam is not "always" needed, but usually regardless if you use H-Beam or not. It will also depend upon the lift of the cam.
For example, the 406 with 6" H-beam rods I'm building required a small base circle cam, pan rail and cylinder clearancing. The cam has a .602 lift with 1.6 rockers for your reference.
Moderator
Joined: Jan 2000
Posts: 20,981
Likes: 11
From: Mercedes Norte, Heredia, Costa Rica
Car: 1984 Z28 Hardtop
Engine: 383 Carb
Transmission: 4L60
Axle/Gears: 3.54 Dana 44
I think Dan's trying to say that the longer stroke may introduce a VALVE clearance problem, since the piston is moving slower at TDC.
Member
Joined: Mar 2000
Posts: 217
Likes: 0
From: Louisville, KY USA
Originally posted by md:
For example, the 406 with 6" H-beam rods I'm building required a small base circle cam, pan rail and cylinder clearancing. The cam has a .602 lift with 1.6 rockers for your reference.
For example, the 406 with 6" H-beam rods I'm building required a small base circle cam, pan rail and cylinder clearancing. The cam has a .602 lift with 1.6 rockers for your reference.
The 406 I'm building will have 5.7" rods and will make a faster, less costly 406 than one with 6" rods.
Why? No pumping losses from slowed piston acceleration away from TDC. Max piston acceleration is at 15* ATDC, exactly where the long rod motor is trying to build back up the speed it lost on that increased dwell time.
5.7 rod is harder on cylinder walls, but saves a lot of grace when balancing and clearancing for a "street/strip" build.
Also, 6" rods call for a piston with a rail support for the oil ring, since its' space was encroached upon by the need to relocate the pin upward. They force the builder to compromise the bottom of the cylinders (which, IMHO, the 400 sbc needs no more of),
and also to pop the extra cash for custom pistons, small base-circle cam, additional machine work, and many times Mallory metal for balancing.
All of this to make less power.
Dan, stick with the 5.7 rod 383 - and the rest of you guys can squeal all night about how wrong I am. Or, maybe you won't, because I'm not. (yeah, I know, the 6" rodded 406 will have a little more torque at the very bottom).
Well, that oughta stir the pot sufficiently.
BOR
"It's in "The Essence" man, trust me".
Junior Member
Joined: May 2000
Posts: 91
Likes: 0
From: AK
Originally posted by Box of Rocks:
ROCKY,
Where did I state that the 6" rods would be a better choice than 5.7" rods? No where in any of my replies did I take that stand. I merely provide some information so that the readers of this post could make there own determination of which would be better for their particular application.
I also made a clarification that the longer rods (or any aftermaket rod for that matter) may require clearancing. I felt the clarification was necessary to prevent a reader of this string from buying a rod with the assumption they would not have to work the block over, or would not need a custom ground cam (small base circle).
Seeing how you decided to quote me, I'll reply to each of the points you brought up.
Doc,
The 406 I'm building will have 5.7" rods and will make a faster, less costly 406 than one with 6" rods.
Faster? Maybe, maybe not, I'll address that later.
Less costly? Come on now. You know that cost is indicative to the build. 6" rods are common in the aftermarket world now. The 6" rotating assemblies are no more expensive than the 5.7" rotating assemblies. The only way a 5.7" rotating assembly is "less costly" is if you are using "stock" donor parts (crank, rods, pistons). Even if a person decides to use doner parts, they should be re-conditioned for a performance build. Re-conditioning is costly, and only slightly less than new parts.
---------------------------------------------
Why? No pumping losses from slowed piston acceleration away from TDC. Max piston acceleration is at 15* ATDC, exactly where the long rod motor is trying to build back up the speed it lost on that increased dwell time.
The longer rod will cause the piston to dwell at TDC and BDC longer than the short rod. We're in agreement there, but this will maintaing a longer state of compression and maintain peak cylinder pressure for longer periods. The benefits this provides are more efficient combustion, higher cylinder pressure after the first few degrees of rotation passed TDC, reduced unburnt hydrocarbons due to higher temperatures within the combustion chamber (more efficient combustion) and the less likelyhood of the piston out-running the flame front. If a piston does out-run the flame front (which it will with short rods), the forces from expanding gasses generated by the combustion proccess exerted on the piston will be reduced.
When the crank pin is at 90* of its rotation in relation to the piston pin (half way between TDC and BDC), the downward forces of the combustion proccess are most effective in turning the crank. When using a "longer rod", there will be more crank rotation at this point than the shorter rod. This benefit the loger rod provides is more effective durring mid to high rpm after the engine has already began to spin up and the drive train is already in motion. Therefor "long rod" moters will produce more mid to upper rpm torque than the shorter rod. Not low rpm torque.
If building an engine for low rpm torque, the short rod will be beneficial. Mid to upper rpm, the longer rod will help. 383/400 engines have an inherent low rpm torque potential because of a longer 3.75" stroke than a 350 with its 3.48" stroke. To sacrifice a small amount of that low rpm torque and move it to the mid-high end of the rpm range with longer rods is, in my opinion, desirable.
---------------------------------------------
5.7 rod is harder on cylinder walls, but saves a lot of grace when balancing and clearancing for a "street/strip" build.
Balancing? This is also dependant upon the rotating assembly used. A stock, cast iron crank that was originally externally balanced is expensive to internally balance regardless of the rod/pistons used. If 6" rods are used in lue of 5.7" rods, more heavy metal will be needed depending on the rod/pistons used. The bulk of cost to add mallory (heavy metal), is the machine work and labor involed. The added .3" of the rod beam and extra mallory needed for that .3" will be negligable.
Now if an aftermarket forged crank is used, there will be no added cost to balance the rotating assembly. Metal is typically removed from the counterweights depending on the crank.
If an external balance is performed, the cost between the two diferent rods will be the same.
---------------------------------------------
Also, 6" rods call for a piston with a rail support for the oil ring, since its' space was encroached upon by the need to relocate the pin upward. They force the builder to compromise the bottom of the cylinders (which, IMHO, the 400 sbc needs no more of),
and also to pop the extra cash for custom pistons, small base-circle cam, additional machine work, and many times Mallory metal for balancing.
All of this to make less power.
---------------------------------------------
The 6" rods WILL required a piston with oil support rails. Custom, no. They are readily available. Longer rods require a smaller piston with a tighter ring package, no disagreement there. This is where a person must use common sense when selecting rods. The max length of rod I'm comfortable with is 6" for a 3.75" stroke. The ring package with this combination is no tighter than any performance piston. It still uses 1/16 X 1/16 X 3/16 rings. As far as the oil ring in the pin area, this has an advantage. Better pin lubrication. Will oil control be affected? I don't think so. The oil control ring still affectively scrapes oil and so does the second ring (unless Total Seal rings are used). There is also another advantage with the pin moved toward the piston top. There will be less piston rock when transitioning between piston stroke at TDC/BDC. This will keep the rings seated against the cylinder more effectively.
Compromise the bottom of the cylinders? I had to grind windows/releifs approximately 1/2" wide and .050" into the bottom of the cylinders. I would hardly concider this amount detrimental to the structural integrity of the cylinders.
The "custom" small base circle cam cost me an extra 20$.
Less power? Depends upon what kind of power your talking about. If your referring to low end torque, yes. Longer rods will sacrifice low end torque but they will increase the mid to upper end of the torque curve.
---------------------------------------------
Dan, stick with the 5.7 rod 383 - and the rest of you guys can squeal all night about how wrong I am. Or, maybe you won't, because I'm not. (yeah, I know, the 6" rodded 406 will have a little more torque at the very bottom).
Well, that oughta stir the pot sufficiently.
BOR
"It's in "The Essence" man, trust me".
ROCKY,
Where did I state that the 6" rods would be a better choice than 5.7" rods? No where in any of my replies did I take that stand. I merely provide some information so that the readers of this post could make there own determination of which would be better for their particular application.
I also made a clarification that the longer rods (or any aftermaket rod for that matter) may require clearancing. I felt the clarification was necessary to prevent a reader of this string from buying a rod with the assumption they would not have to work the block over, or would not need a custom ground cam (small base circle).
Seeing how you decided to quote me, I'll reply to each of the points you brought up.
Doc,
The 406 I'm building will have 5.7" rods and will make a faster, less costly 406 than one with 6" rods.
Faster? Maybe, maybe not, I'll address that later.
Less costly? Come on now. You know that cost is indicative to the build. 6" rods are common in the aftermarket world now. The 6" rotating assemblies are no more expensive than the 5.7" rotating assemblies. The only way a 5.7" rotating assembly is "less costly" is if you are using "stock" donor parts (crank, rods, pistons). Even if a person decides to use doner parts, they should be re-conditioned for a performance build. Re-conditioning is costly, and only slightly less than new parts.
---------------------------------------------
Why? No pumping losses from slowed piston acceleration away from TDC. Max piston acceleration is at 15* ATDC, exactly where the long rod motor is trying to build back up the speed it lost on that increased dwell time.
The longer rod will cause the piston to dwell at TDC and BDC longer than the short rod. We're in agreement there, but this will maintaing a longer state of compression and maintain peak cylinder pressure for longer periods. The benefits this provides are more efficient combustion, higher cylinder pressure after the first few degrees of rotation passed TDC, reduced unburnt hydrocarbons due to higher temperatures within the combustion chamber (more efficient combustion) and the less likelyhood of the piston out-running the flame front. If a piston does out-run the flame front (which it will with short rods), the forces from expanding gasses generated by the combustion proccess exerted on the piston will be reduced.
When the crank pin is at 90* of its rotation in relation to the piston pin (half way between TDC and BDC), the downward forces of the combustion proccess are most effective in turning the crank. When using a "longer rod", there will be more crank rotation at this point than the shorter rod. This benefit the loger rod provides is more effective durring mid to high rpm after the engine has already began to spin up and the drive train is already in motion. Therefor "long rod" moters will produce more mid to upper rpm torque than the shorter rod. Not low rpm torque.
If building an engine for low rpm torque, the short rod will be beneficial. Mid to upper rpm, the longer rod will help. 383/400 engines have an inherent low rpm torque potential because of a longer 3.75" stroke than a 350 with its 3.48" stroke. To sacrifice a small amount of that low rpm torque and move it to the mid-high end of the rpm range with longer rods is, in my opinion, desirable.
---------------------------------------------
5.7 rod is harder on cylinder walls, but saves a lot of grace when balancing and clearancing for a "street/strip" build.
Balancing? This is also dependant upon the rotating assembly used. A stock, cast iron crank that was originally externally balanced is expensive to internally balance regardless of the rod/pistons used. If 6" rods are used in lue of 5.7" rods, more heavy metal will be needed depending on the rod/pistons used. The bulk of cost to add mallory (heavy metal), is the machine work and labor involed. The added .3" of the rod beam and extra mallory needed for that .3" will be negligable.
Now if an aftermarket forged crank is used, there will be no added cost to balance the rotating assembly. Metal is typically removed from the counterweights depending on the crank.
If an external balance is performed, the cost between the two diferent rods will be the same.
---------------------------------------------
Also, 6" rods call for a piston with a rail support for the oil ring, since its' space was encroached upon by the need to relocate the pin upward. They force the builder to compromise the bottom of the cylinders (which, IMHO, the 400 sbc needs no more of),
and also to pop the extra cash for custom pistons, small base-circle cam, additional machine work, and many times Mallory metal for balancing.
All of this to make less power.
---------------------------------------------
The 6" rods WILL required a piston with oil support rails. Custom, no. They are readily available. Longer rods require a smaller piston with a tighter ring package, no disagreement there. This is where a person must use common sense when selecting rods. The max length of rod I'm comfortable with is 6" for a 3.75" stroke. The ring package with this combination is no tighter than any performance piston. It still uses 1/16 X 1/16 X 3/16 rings. As far as the oil ring in the pin area, this has an advantage. Better pin lubrication. Will oil control be affected? I don't think so. The oil control ring still affectively scrapes oil and so does the second ring (unless Total Seal rings are used). There is also another advantage with the pin moved toward the piston top. There will be less piston rock when transitioning between piston stroke at TDC/BDC. This will keep the rings seated against the cylinder more effectively.
Compromise the bottom of the cylinders? I had to grind windows/releifs approximately 1/2" wide and .050" into the bottom of the cylinders. I would hardly concider this amount detrimental to the structural integrity of the cylinders.
The "custom" small base circle cam cost me an extra 20$.
Less power? Depends upon what kind of power your talking about. If your referring to low end torque, yes. Longer rods will sacrifice low end torque but they will increase the mid to upper end of the torque curve.
---------------------------------------------
Dan, stick with the 5.7 rod 383 - and the rest of you guys can squeal all night about how wrong I am. Or, maybe you won't, because I'm not. (yeah, I know, the 6" rodded 406 will have a little more torque at the very bottom).
Well, that oughta stir the pot sufficiently.
BOR
"It's in "The Essence" man, trust me".
I went 6" based on my research and the recomendations of others that have successfully used them. One in particular was an engine builder in my area. He built a 406 for his ski boat and used 6" rods. He runs the engine at 5000 rpm for extended periods of time. The engine has 5000 hours on it without a hint of excess oil consumption.
Did I make the right decision? Only time will tell. I hope so. I warentee my work.
The engine should be flogged on the dyno in about two weeks and I'll post the results if your interested. I guess we'll see then if your engine will "be faster".
Thanks for the new handle "DOC", I like it. I think I'll keep it.
I'm looking foward to continuing this discussion with you.
DOC
[This message has been edited by md (edited September 14, 2000).]
Junior Member
Joined: Jul 1999
Posts: 49
Likes: 0
From: Coventry, CT
Unless you are building a race only motor I would stick with the 5.7. With the extra money you will spend on longer rods could be spend on head work which will show far more gains that rods that are 3/10" longer.
------------------
86 Iroc, 383 Ported Sportsman II, Ported RPM Airgap, 750 Edelbrock, Slp 1 3/4, Comp Cams roller 218 224, 10" 2600 stall, Fairbanks 700r-4 W/superflow pro pump, 2.73 posi (for now) Harwood bolt on 2 1/2 glass hood.
87 K30 Chevy P/U 355 TPI TH400, headers and 2 1/2 duals, flowmasters, 8" lift, 36" super swampers, 4.10 detriot lockers all the way around
------------------
86 Iroc, 383 Ported Sportsman II, Ported RPM Airgap, 750 Edelbrock, Slp 1 3/4, Comp Cams roller 218 224, 10" 2600 stall, Fairbanks 700r-4 W/superflow pro pump, 2.73 posi (for now) Harwood bolt on 2 1/2 glass hood.
87 K30 Chevy P/U 355 TPI TH400, headers and 2 1/2 duals, flowmasters, 8" lift, 36" super swampers, 4.10 detriot lockers all the way around
Thread Starter
Supreme Member
Joined: Feb 2000
Posts: 1,196
Likes: 0
From: Fort Collins, Colorado
I think that since I will be running a cam with a lot of lift, I will go with the 5.7" rod to be 100% sure there is no valve clearence problems, even though that isn't a huge possibility. There are also a lot of cost issues concerning the use of the 6.0" rod. I don't want to have to have an engine re-balanced or whatever else may need to be done with the 6.0" rod. But thanks for all the help and things you have taught me.
------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End
Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.
Best ET: 14.3 @ 97mph
------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End
Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.
Best ET: 14.3 @ 97mph
Junior Member
Joined: May 2000
Posts: 91
Likes: 0
From: AK
You've made a marked improvement over the stock 5.565" rods. I'm sure you'll be pleased with the package when it's complete. Just be patiant and take your time.
The 5.7" will also need a little block work. Don't sweat it. It's not all that dificult or time consuming. Just make sure you have a minimum of .050" clearance between swinging and stationary parts.
Valve clearance will not be an issue regardless of the rod length. Your going to check valve to piston clearance anyway arn't you?
Good luck Dan, and have fun.
Mike
The 5.7" will also need a little block work. Don't sweat it. It's not all that dificult or time consuming. Just make sure you have a minimum of .050" clearance between swinging and stationary parts.
Valve clearance will not be an issue regardless of the rod length. Your going to check valve to piston clearance anyway arn't you?
Good luck Dan, and have fun.
Mike
Thread
Thread Starter
Forum
Replies
Last Post
