For my 385, The Machine Shop Says...
04-22-2005, 08:58 PM
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For my 385, The Machine Shop Says... He is firmly reccomending a 5.7" rod for my 383 because he says i need to worry about detonation(which i would anyway) cuz the 5.7 rod doesn't dwell (ATDC) as longer rod would. But from what i know you want a longer rod for the first 3 important reasons i can think of.
1) rod ratio,you need to go longer especially w/ longer stroke
2)cylinder side loading,a longer rod reduces thrust side cylinder wear
3)you want more dwell,for less piston speed and better combustion efficiency
I would prefer a 5.8x or a 6.0 with the proper dish piston and pin height to keep my comp.ratio in check. i know he will build to my wants but this is what he reccomended.
if any of you who have done this have any reccomondations or comments, please post
Thanks,James
1) rod ratio,you need to go longer especially w/ longer stroke
2)cylinder side loading,a longer rod reduces thrust side cylinder wear
3)you want more dwell,for less piston speed and better combustion efficiency
I would prefer a 5.8x or a 6.0 with the proper dish piston and pin height to keep my comp.ratio in check. i know he will build to my wants but this is what he reccomended.
if any of you who have done this have any reccomondations or comments, please post
Thanks,James
04-22-2005, 11:32 PM
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IMO the 5.7 vs 6.0 rod is really a moot point....people dwell on it FAR too much.
Here's a short read from Isky Cams that really hits on everything that needs to be hit.
"Rod Lengths/Ratios: Much ado about almost nothing.
Why do people change connecting rod lengths or alter their rod length to stroke ratios? I know why, they think they are changing them. They expect to gain (usually based upon the hype of some magazine article or the sales pitch of someone in the parts business) Torque or Horsepower here or there in rather significant "chunks". Well, they will experience some gains and losses here or there in torque and or H.P., but unfortunately these "chunks" everyone talks about are more like "chips".
To hear the hype about running a longer Rod and making more Torque @ low to mid RPM or mid to high RPM (yes, it is, believe it or not actually pitched both ways) you'd think that there must be a tremendous potential for gain, otherwise, why would anyone even bother? Good question. Let's begin with the basics. The manufacture's (Chevy, Ford, Chrysler etc.) employ automotive engineers and designers to do their best (especially today) in creating engine packages that are both powerful and efficient. They of course, must also consider longevity, for what good would come form designing an engine with say 5% more power at a price of one half the life factor? Obviously none. You usually don't get something for nothing - everything usually has its price. For example: I can design a cam with tremendous high RPM/H.P. potential, but it would be silly of me (not to mention the height of arrogance) to criticize the engineer who designed the stock camshaft. For this engine when I know how poorly this cam would perform at the lower operating RPM range in which this engineer was concerned with as his design objective!
Yet, I read of and hear about people who do this all the time with Rod lengths. They actually speak of the automotive engine designer responsible for running "such a short Rod" as a "stupid SOB." Well, folks I am here to tell you that those who spew such garbage should be ashamed of themselves - and not just because the original designer had different design criteria and objectives. I may shock some of you, but in your wildest dreams you are never going to achieve the level of power increase by changing your connecting rod lengths that you would, say in increasing compression ratio, cam duration or cylinder head flow capacity. To illustrate my point, take a look at the chart below. I have illustrated the crank angles and relative piston positions of today's most popular racing engine, the 3.48" stroke small block 350 V8 Chevy in standard 5.7", 6.00", 6.125" and 6.250" long rod lengths in 5 degree increments. Notice the infinitesimal (look it up in the dictionary) change in piston position for a given crank angle with the 4 different length rods. Not much here folks, but "oh, there must be a big difference in piston velocity, right?" Wrong! Again it's a marginal difference (check the source yourself - its performance calculator).
To hear all this hype about rod lengths I'm sure you were prepared for a nice 30, 40, or 50 HP increase, weren't you? Well its more like a 5-7 HP increase at best, and guess what? It comes at a price. The longer the rod, the closer your wrist pin boss will be to your ring lands. In extreme situations, 6.125" & 6.250" lengths for example, both ring and piston life are affected. The rings get a double whammy affect. First, with the pin boss crowding the rings, the normally designed space between the lands must be reduced to accommodate the higher wrist pin boss. Second, the rings wobble more and lose the seal of their fine edge as the piston rocks. A longer Rod influences the piston to dwell a bit longer at TDC than a shorter rod would and conversely, to dwell somewhat less at BDC. This is another area where people often get the information backwards.
In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power!
Now to the subject of rod to stroke ratios. People are always looking for the "magic number" here - as if like Pythagoras they could possibly discover a mathematical relationship which would secure them a place in history. Rod to stroke ratios are for the most part the naturally occurring result of other engine design criteria. In other-words, much like with ignition timing (spark advance) they are what they are. In regards to the later, the actual number is not as important as finding the right point for a given engine. Why worry for example that a Chrysler "hemi" needs less spark advance that a Chevrolet "wedge" combustion chamber? The number in and of itself is not important and it is much the same with rod to stroke ratios. Unless you want to completely redesign the engine (including your block deck height etc.) leave your rod lengths alone. Let's not forget after all, most of us are not racing at the Indy 500 but rather are hot rodding stock blocks.
Only professional engine builders who have exhausted every other possible avenue of performance should ever consider a rod length change and even they should exercise care so as not to get caught up in the hype. "
http://www.iskycams.com/ART/techinfo/ncrank1.pdf
http://www.iskycams.com/ART/techinfo/ncrank1.pdf
Here's a short read from Isky Cams that really hits on everything that needs to be hit.
"Rod Lengths/Ratios: Much ado about almost nothing.
Why do people change connecting rod lengths or alter their rod length to stroke ratios? I know why, they think they are changing them. They expect to gain (usually based upon the hype of some magazine article or the sales pitch of someone in the parts business) Torque or Horsepower here or there in rather significant "chunks". Well, they will experience some gains and losses here or there in torque and or H.P., but unfortunately these "chunks" everyone talks about are more like "chips".
To hear the hype about running a longer Rod and making more Torque @ low to mid RPM or mid to high RPM (yes, it is, believe it or not actually pitched both ways) you'd think that there must be a tremendous potential for gain, otherwise, why would anyone even bother? Good question. Let's begin with the basics. The manufacture's (Chevy, Ford, Chrysler etc.) employ automotive engineers and designers to do their best (especially today) in creating engine packages that are both powerful and efficient. They of course, must also consider longevity, for what good would come form designing an engine with say 5% more power at a price of one half the life factor? Obviously none. You usually don't get something for nothing - everything usually has its price. For example: I can design a cam with tremendous high RPM/H.P. potential, but it would be silly of me (not to mention the height of arrogance) to criticize the engineer who designed the stock camshaft. For this engine when I know how poorly this cam would perform at the lower operating RPM range in which this engineer was concerned with as his design objective!
Yet, I read of and hear about people who do this all the time with Rod lengths. They actually speak of the automotive engine designer responsible for running "such a short Rod" as a "stupid SOB." Well, folks I am here to tell you that those who spew such garbage should be ashamed of themselves - and not just because the original designer had different design criteria and objectives. I may shock some of you, but in your wildest dreams you are never going to achieve the level of power increase by changing your connecting rod lengths that you would, say in increasing compression ratio, cam duration or cylinder head flow capacity. To illustrate my point, take a look at the chart below. I have illustrated the crank angles and relative piston positions of today's most popular racing engine, the 3.48" stroke small block 350 V8 Chevy in standard 5.7", 6.00", 6.125" and 6.250" long rod lengths in 5 degree increments. Notice the infinitesimal (look it up in the dictionary) change in piston position for a given crank angle with the 4 different length rods. Not much here folks, but "oh, there must be a big difference in piston velocity, right?" Wrong! Again it's a marginal difference (check the source yourself - its performance calculator).
To hear all this hype about rod lengths I'm sure you were prepared for a nice 30, 40, or 50 HP increase, weren't you? Well its more like a 5-7 HP increase at best, and guess what? It comes at a price. The longer the rod, the closer your wrist pin boss will be to your ring lands. In extreme situations, 6.125" & 6.250" lengths for example, both ring and piston life are affected. The rings get a double whammy affect. First, with the pin boss crowding the rings, the normally designed space between the lands must be reduced to accommodate the higher wrist pin boss. Second, the rings wobble more and lose the seal of their fine edge as the piston rocks. A longer Rod influences the piston to dwell a bit longer at TDC than a shorter rod would and conversely, to dwell somewhat less at BDC. This is another area where people often get the information backwards.
In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power!
Now to the subject of rod to stroke ratios. People are always looking for the "magic number" here - as if like Pythagoras they could possibly discover a mathematical relationship which would secure them a place in history. Rod to stroke ratios are for the most part the naturally occurring result of other engine design criteria. In other-words, much like with ignition timing (spark advance) they are what they are. In regards to the later, the actual number is not as important as finding the right point for a given engine. Why worry for example that a Chrysler "hemi" needs less spark advance that a Chevrolet "wedge" combustion chamber? The number in and of itself is not important and it is much the same with rod to stroke ratios. Unless you want to completely redesign the engine (including your block deck height etc.) leave your rod lengths alone. Let's not forget after all, most of us are not racing at the Indy 500 but rather are hot rodding stock blocks.
Only professional engine builders who have exhausted every other possible avenue of performance should ever consider a rod length change and even they should exercise care so as not to get caught up in the hype. "
http://www.iskycams.com/ART/techinfo/ncrank1.pdf
http://www.iskycams.com/ART/techinfo/ncrank1.pdf
04-22-2005, 11:33 PM
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To sum that up.....it really doesn't matter. The pro's and con's between the two aren't anything to make a big deal of at the normal person's setup, expectations and goals. Wider ring pack vs. sidewall loading, blah blah blah....it's become a bigger topic than it really should be.
04-23-2005, 04:45 AM
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That's based on quench height which can vary with gasket thickness, decking the block, etc.
I can pull countless articles supporting and reinforcing everything that was pasted above. Rich Krause said it best "I think this whole thing started with Smokey Yunick. He was trying to get the last few hp out a combo optimized in every other way in the context of some fairly strict rules. Has very little to do with anything other than an all out race motor." Which I believe is absolutely true. Many builders, enthusiasts and folks who want more knowledge use Yunick as a biblical source which is where quite a few good ideas and some other things like this debate come from.
Sure a shorter rod will help detonation but as well as not seeing FI anywhere in the sig, many things can and should be taken into account with any build more to the point, cam and DCR along with quench will influence detonation far more profoundly than a 5.7 vs. 6.0 rod ever will.
While I don't think this has been gone over ad nauseum on LS1tech, it sure has on CZ28....you may want to do a search for 5.7 vs. 6.0 or rod length or something along those lines....some of the folks I feel retarded around like Bret and his dad, Rich, Fred
In the end I think you'll find that rod length isn't anywhere near the top of the list when finalizing a build.
I can pull countless articles supporting and reinforcing everything that was pasted above. Rich Krause said it best "I think this whole thing started with Smokey Yunick. He was trying to get the last few hp out a combo optimized in every other way in the context of some fairly strict rules. Has very little to do with anything other than an all out race motor." Which I believe is absolutely true. Many builders, enthusiasts and folks who want more knowledge use Yunick as a biblical source which is where quite a few good ideas and some other things like this debate come from.
Sure a shorter rod will help detonation but as well as not seeing FI anywhere in the sig, many things can and should be taken into account with any build more to the point, cam and DCR along with quench will influence detonation far more profoundly than a 5.7 vs. 6.0 rod ever will.
While I don't think this has been gone over ad nauseum on LS1tech, it sure has on CZ28....you may want to do a search for 5.7 vs. 6.0 or rod length or something along those lines....some of the folks I feel retarded around like Bret and his dad, Rich, Fred
In the end I think you'll find that rod length isn't anywhere near the top of the list when finalizing a build.
04-23-2005, 11:13 AM
#7
Ghost Not tryng to argue just pointing out what is coming to light. You see alot of it in the Engine master challenge as well. He ask a Question on a specific point. I was just adding informaion on THAT point.
Those very people you are mentionining are suguesting this at times. Yes Rod length is not at the very top but depending on the build the rod lenghth can dicate performance and reliability issues
The only reason I am using my 6in rods is that is what I had It is a budget build up only shooting for 600-700hp. Bret has been a large help in this build up along with many others. Lets hope it hold up long enough for me to finish my 7.0L reverse cooled , OptiSpark fired monster!
BTW I am OneFlying95z28 over there
Those very people you are mentionining are suguesting this at times. Yes Rod length is not at the very top but depending on the build the rod lenghth can dicate performance and reliability issues
The only reason I am using my 6in rods is that is what I had
It is a budget build up only shooting for 600-700hp. Bret has been a large help in this build up along with many others. Lets hope it hold up long enough for me to finish my 7.0L reverse cooled , OptiSpark fired monster!BTW I am OneFlying95z28 over there
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04-23-2005, 12:12 PM
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GhostZ, Thank you for the detaild info,i appreciate the time you took to reply.
Since this is one of the few chances i get to do a stroker(unfortunately) i just wanted the best/most durable rotating combo. I wasn't looking to make ALOT more power by thinking if i got a longer stoke that it would. I was merely tryin to reduce internal stress if i could by SLIGHTLY increasing the length. I'm gonna step on this motor HARD! so i want it to stay together and be as numerically efficient as poss. i'm not tryin to change a well educated engineers orig design or intentions,but merely add to it since i'm chaging his well thought out original design. Well, based on what my machinist says and what iv'e read here and this GREAT article i found.(connecting rod vs. stroke analysis:panic paper no.1)(type this in ur search engine,i don't know how to bring it here) and the rest of my head cam combo, i'll go w/the 5.7's (4340 H-beams) Thanks for everyones replies,if there are any more please post.
Since this is one of the few chances i get to do a stroker(unfortunately) i just wanted the best/most durable rotating combo. I wasn't looking to make ALOT more power by thinking if i got a longer stoke that it would. I was merely tryin to reduce internal stress if i could by SLIGHTLY increasing the length. I'm gonna step on this motor HARD! so i want it to stay together and be as numerically efficient as poss. i'm not tryin to change a well educated engineers orig design or intentions,but merely add to it since i'm chaging his well thought out original design. Well, based on what my machinist says and what iv'e read here and this GREAT article i found.(connecting rod vs. stroke analysis:panic paper no.1)(type this in ur search engine,i don't know how to bring it here) and the rest of my head cam combo, i'll go w/the 5.7's (4340 H-beams) Thanks for everyones replies,if there are any more please post.
04-23-2005, 05:48 PM
#9
the way i approach this is fairly simple. are you in need of new rods and pistons? if so get six in rods. the cost is minimal and the gains are there. i personally desire to have an engine that is not over built and has minimized parasitic loss as much as possible. with in reason of course. which is why i ask are you replacing the rods and pistons? if you are going to be building that hardcore of a motor then yes looking at it more than what ive just done is a very good idea, but if your just building a good street/strip motor thats honestly nothing spectacular or exotic then i bet youll be fine with a 6in rod. everything is a compromise unless funds are unlimited. heck im looking at running two bolt steel main caps on a 396 when i get around to it. most people say four bolt it. i know people that are running 7500 in there road course 383 motors using only a steel two bolt cap. right now its looking like an option for me. it may turn out that i should four bolt it, but maybe not. either way will be fine for me im betting. 6 vs 5.7 rods are the same way in the vast majority of cases. you wont go wrong staying with the 5.7 and the 6 in may not be right for you, but most likely either will be a perfectly fine choice.
04-23-2005, 11:38 PM
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Originally Posted by TwoFast4Lv
Ghost Not tryng to argue just pointing out what is coming to light. You see alot of it in the Engine master challenge as well. He ask a Question on a specific point. I was just adding informaion on THAT point.
In the end it's really personal choice and doing what you want...IMO, I think people make more out of rod length issues than they need to especially when the build doesn't justify squeezing every little bit out you can.
On the other hand I'm not an engine builder and there are too many folks out there who know a hell of a lot more than me
If you trust your engine builder, which I assume he does, go with what he says.I plan on seeing if Bret will do my next build....and if he told me that it would be best to use these new compressed butter pistons, well....that's what I'll be going with since he's the builder and he's the man.
