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still beating a dead horese i think

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#21 ·
onovakind67 said:
Where does it make a difference and how much difference does it make?
Click to expand...
I second that. can one of the board experts take the time to explain this to us in the dark..

LOL at the camle hump comment...too true too true...theya re junk, but people try to sell them for an arm and a leg..
 
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#22 ·
onovakind67 said:
Where does it make a difference and how much difference does it make?
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By my brief drawings, it reduced the rod angle from 19.313 degrees to 18.887 degrees, a 2.5% change. That's alot.

I know 2.5% doesn't sound like much, but think of this:
1. Think about how much 2.5% changes the hundreds of pounds of thrust load the cylinder wall sees at high RPM...and how that effects frictional losses, oil temperature, bore wear, etc.
2. Consider how many people would be happy with a 2.5% increase in HP, why not have the same enthusiasm over the benefits of decreased rod angular velocity?

There's benefits to be had. How much is it really going to cost you to run a stock 5.7" rod? They're practially free. Size 'em, polish 'em, they'll work great.
 
#23 ·
Sorry guys just came back on and saw all the responce. It has to do with piston dwell time at the top and bottom of the cylinder (rod ratio) a longer rod keeps the dwell longer on each end giving the rod a chance to move to the other side of the piston when it's in the bottom of the hole. While the top is not affected much the bottom is is. Look at the angle of a rod when the piston is BDC in the hole. A longer rod keeps the piston dwelled longer. With the rod being short @ 5.565 it starts to push the piston up the cylinder faster and at an angle or rocking the piston trust side into the cylinder wall creating ring wear and vibration and also cylinder out of round and taper on the trust side of the hole. This is why the 5.565 rod strokers start to smoke and viberate. The 5.7 rod on the top dwells longer at BDC (dwell is the gap between the time it reached full motion to the bottom of the cylinder and the time it starts back up the cylinder) thus increasing efficancy of the engine (it's not working against it's self) and increasing power and reliability along with RPM which means you can cam for top end with out loosing the benifit of the strokers bottom end torque that is a freebie witha stoker.

Look at it like this, the angle the rod is pushing the piston at is greater with a 5.565 rod than what it is with a 5.7 rod and a six inch brings it down even farther. You will need pistons specific to a 5.7 or 6.0 inch rod stroker though and cam profiles can get tricky because you have to clearance for the rod and watch the base circle of the cam.

Like I said you go 5.565 and be happy but you run the risk of vibration and wear. I would put one of these (and I have built many of them) in a truck. I would put one in a car also but not one I plan to run hard or street/strip use.

I personally like a 5.7 rod stroker in a street car more than anything else but I don't run one now. I never will because I am stuck on 327's I love the little engines and they do for me what I need out of life now.

Hope that helps, I am not real good at putting some of this type of stuff to printed word. This to me is one of those lookat at it and break it down in the shop kinda things.

Joe
 
#24 · (Edited)
Just posted above then Silver69 chimed in also. "What he said"...:thumbsup: Also by todays standards 6,000 RPM is not much. There is way more to be had from a small block than that.The differance is what do you want, then what can you afford. 5.7 and 6.0 inch rod 400's run into the 6,500 to 7,000 RPM range at circle tracks and run many races.
 
#26 ·
Lt.Longarm
My motor has been together for over 10 years minus the ocasional tare down foe checks and gaskets. I ran stock ported heads for a long time and 5.7" rods since first built. Seen 2 cam swaps,1 head change, and a few intake swaps. (results below)
Now buddy with a 383,huge heads,6" rods, and way big cam is low 10's on motor but has a lot of issues due to the RPM's he runs.

I feel both motors would do what you want with the right combo and great machine work just at different RPM's. I also think you should go with atleast 5.7" rods. Both motors would cost darn near the same minus block.
Just something to think about.
 
#30 ·
It's interesting that one or two questions create a bunch more...

a longer rod keeps the dwell longer on each end

1. How can a longer rod increase the 'dwell' time at both ends of the stroke?

2. What is "decreased rod angular velocity'?
3. How does a 2.5% reduction of the maximum rod-bore angle equate to an across-the-board 2.5% increase in power? Aren't there some sines and cosines involved here in the resolution of the forces?
4. Does Newtons third law apply here? If I push harder on the cylinder wall with an increased rod-bore angle, what do I have to brace the rod on to accomplish this?
5. If I push harder on the crank, will this make more torque?
6. What's the coefficient of friction of oiled aluminum on cast iron?
 
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Discussion starter · #31 ·
summits stroker kit look mighty tempting. if u can sell my **** localy for $500 ish, it will be cheaper for me to build a 5.7" rodded motor with this kit then to rebuild mine with stock 350 pistons
 
#32 ·
In even the most high end street strip motors, rod length is splitting hairs. In my reading, even on the dyno I have never seen mention of any real gain of even 1% in horsepower recognized through an increase in rod length (but of course we don't race dynos ;) ), so in a street strip car in real world conditions, you will never know the difference.
No doubt there is a possible gain, but just like the 4/7 swap cam, unless your in an all out racing situation, it really will never be realized.
 
#33 ·
Has it been proven that a short 5.565 rod will wear a bore quicker than a 5.7 rod with a 3.750 stroke? I am still in contact with the first stroker I built years ago with short rods w/ARP bolts and a turned down crank with TRW forged flattop pistons. I ran that motor hard for a few years, then sold it and with a freshen it ran a few more years. Now it's been sold and refreshed again. 8yrs old with the same pistons, rods, crank, and block, it's running high tens.

That engine has over 35K miles along with no telling how many passes and has been on nitrous and run hard. The bores are somewhat egg shaped, the rings were file fit and the pistons have a slight rattle. With a pretty lumpy solid roller, you can't really tell and it does run high 10s on pump gas alone. Would the bores be in better shape with longer rods?
 
#34 ·
onovakind67 said:
It's interesting that one or two questions create a bunch more...

a longer rod keeps the dwell longer on each end

1. How can a longer rod increase the 'dwell' time at both ends of the stroke?

2. What is "decreased rod angular velocity'?
3. How does a 2.5% reduction of the maximum rod-bore angle equate to an across-the-board 2.5% increase in power? Aren't there some sines and cosines involved here in the resolution of the forces?
4. Does Newtons third law apply here? If I push harder on the cylinder wall with an increased rod-bore angle, what do I have to brace the rod on to accomplish this?
5. If I push harder on the crank, will this make more torque?
6. What's the coefficient of friction of oiled aluminum on cast iron?
Click to expand...
I'm going to provide short answers, but...
1. It's a geometric relationship. Draw pictures , imagine models, etc. to understand it. Imagine a 2" rod, then imagine a 10" rod. See the relationship?
2. A decreased rate of rod angle change, meaning when the piston is moving through it's stroke, the angle of the rod is changing at a lesser rate.
3. It doesn't. Rod-to-stroke relationships are not a power issue. Only a mechanical efficiency problem.
4. Nothing, the rod isn't to worry about. It's the piston skirt and bore.
5. Always.
6. Don't know why this matters, but 0.2-0.25 for a "lubricated" situation.

Again, this whole thing will not show itself true on the dyno. There is basically no power to be made with a longer rod, its basically an efficiency issue that can lead to less vibrational problems and bore wear.
 
#35 ·
Silver69Camaro said:
I'm going to provide short answers, but...
1. It's a geometric relationship. Draw pictures , imagine models, etc. to understand it. Imagine a 2" rod, then imagine a 10" rod. See the relationship?
2. A decreased rate of rod angle change, meaning when the piston is moving through it's stroke, the angle of the rod is changing at a lesser rate.
3. It doesn't. Rod-to-stroke relationships are not a power issue. Only a mechanical efficiency problem.
4. Nothing, the rod isn't to worry about. It's the piston skirt and bore.
5. Always.
6. Don't know why this matters, but 0.2-0.25 for a "lubricated" situation.

Again, this whole thing will not show itself true on the dyno. There is basically no power to be made with a longer rod, its basically an efficiency issue that can lead to less vibrational problems and bore wear.
Click to expand...
1. Your model shows an increase in 'dwell time' at both ends of the stroke? Mine doesn't. You only get one end or the other, not both. Which is which?
2. The rod angle changes all the time at different rates based on rpm, stroke and rod length. What is the significance of this parameter?
3. What's the mechanical efficiency problem?
4. How can I increase the loading on the cylinder wall without pushing on something else? My model shows that Newton's third law isn't abated just because you're inside a cylinder.
5. Then you'd agree that a shorter rod will make more torque. Hopefully your model will show that having the rod-crank angle closer to 90° while the cylinder pressure is high results in more force transmitted to the crank.
6. It matters a lot. If your theory is based on increased friction and power loss it's good to know how much friction you have. You're off by a factor or 50 or so here. Brake systems have CF's in the 0.4 range, 0.2 when they're wet. The piston/wall surface operates with hydrodynamic film lubrication and the CF is typically less than 0.007, depending on the speed.

Here's a calculation to try:
4.03" bore, 3.75" stroke, cylinder pressure is 300 psi, no leaks.
Crank angle is 30° ATDC. Negate any flywheel effects, etc
What is the side load on the piston at this point for a 5.7" rod? 5.565" rod?
What is the pressure on the crank at this point for each rod?
How much force is lost to friction assuming a 0.007 CF?
 
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#37 ·
I am not an engineer so I will not get into some of this and only answer what I can. Bore wear is reduced and an engine with 35,000 miles should almost be on just the break in side of things sort of speak. If it's been freshen that many times, why? I know it's been raced. bores that are egg shaped and have taper are signs of wear.

This is also one of those issues that what works for some may not work for others. Short rods vs long rod can be in the same debate as using a 400 block. They work for alot of people and some have no luck at all. The same goes for rods. My personal experiance with short rods is vibration. Sometimes it not bad not bad at all other have been horrid. I have never experianced this problem with long rod strokers.

Also power gains might not be noticeable and when I posted power gains i should not have because as someone posted above you don't race dyno's. What I didmean by that is any loss in friction by deceasing the rod angle would make more power. Meaning that like a roller cam and lifters any decrease in friction is a power gain. Friction is a power robber and every little bit helps. It also helps with reliabiltiy because you have less wear (in most cases).

As for pressure on bore sides ect I can't give you that, but look at the rings and what is stopping the piston from hitting the bore side. The skirt mainly but also the rings too. It's all little stuff but it adds up. It's my opinion that if givin the choice of short or long rod. I would spend the money on long rod because there are no negatives and the price is not much more if anymore these days. So why not go with the better choice.........that's just me though.

Joe
 
Discussion starter · #38 ·
Lieutenant Longarm said:
summits stroker kit look mighty tempting. if u can sell my **** localy for $500 ish, it will be cheaper for me to build a 5.7" rodded motor with this kit then to rebuild mine with stock 350 pistons
Click to expand...
yeah im down for the long rod 383
 
#39 ·
What I didmean by that is any loss in friction by deceasing the rod angle would make more power.

A loss in friction will make more power available, provided you don't give up any mechanical advantage. There is a serious trade-off between rod length and leverage on the crank. If you had an infinitely long rod, where the rod-bore angle was always 0°, you would lose all the leverage you have on the crank due to the push off the cylinder wall. The effective stroke would be quite a bit shorter, resulting in much less torque. If by some miracle of engineering you could maintain a constant 90° rod-crank angle you could produce some enormous torque.

You will never lose more to friction than you gain in leverage by being able to push on the cylinder wall, unless you exceed some very high rpm.

When you ride a bicycle, you don't want to start off with your pedal at the top of the stroke, you want it down in the stroke so you can get leverage on the crank. If you happen to be at the top of the stroke, what do you do? You lean back, developing a better angle on the pedal (less than the 180° you started with) and you make more torque to accelerate the bike. Leaning your leg back is the same as having a higher rod-bore angle.
 
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