Do power levels really determine the grade rod bolt required?

Sitting in class today bored out of my mind, doing some math applying to crank angles and piston speed/acceleration and got to thinking about this.

I always hear people say if you are making that much power you need this grade rod bolt or it will break apart. Well logically in my mind power levels have absolutely nothing to do with the rod bolts. The rod bolts are only needed on the change of direction that happens at the top of the cylinder (very basically speaking). And power has nothing to do with the lateral acceleration the piston sees changing direction there, that is based solely on RPM and piston/rod weight (as well as a few other stroke/rod length numbers, but not as drastically).

I am thinking more or less that the sole determining factor in choosing rod bolts should be max RPM and piston/rod weight?

Forces and RPM..... That's why you need good bolts.

Forces are due to stroke and mass.... More stroke means more Piston G's with the same RPM.

F=MA man.

Bret

Yes, but is my thinking correct. Power levels have NOTHING to do with why you would need a good rod bolt right?

Theoretically if you had a 2000hp engine, say a 4" stroke and 4.155 bore, and 6" rods, but the rods were supersuper lightweight billet pieces, say 300grams. And your pistons were up to what sounds like F1 spec at 150grams, I know this isnt really possible, or not with normal metals, but if the engine only spun to 8000rpm, would a super exotic rod bolt really be necessary?

Im too tired to actually go through the math of finding out how many psi of force this setup would exert changing directions, but it seems like it would have to be less than an engine only making 500hp but with normal weight forged pieces at 500+grams on the rods and 400+ pistons?

Yes, but is my thinking correct. Power levels have NOTHING to do with why you would need a good rod bolt right?

Theoretically if you had a 2000hp engine, say a 4" stroke and 4.155 bore, and 6" rods, but the rods were supersuper lightweight billet pieces, say 300grams. And your pistons were up to what sounds like F1 spec at 150grams, I know this isnt really possible, or not with normal metals, but if the engine only spun to 8000rpm, would a super exotic rod bolt really be necessary?

Im too tired to actually go through the math of finding out how many psi of force this setup would exert changing directions, but it seems like it would have to be less than an engine only making 500hp but with normal weight forged pieces at 500+grams on the rods and 400+ pistons?

You are pretty much on the right track. Inertia loads trying to pull the rod apart at TDC reversal are the worst loads the rod bolts see. So mass and rpm are the primary culprits, along with stroke. Of course, super strong rod bolts can be smaller so there is less rotating mass. "How fast do you want to go?"

I could be argued that very heavy combustion loads trying to shorten the rod may cause the big end to oval, and try to bend the bolts. Maybe stronger bolts here could help keep it round. That's secondary to the clamping the bolt must do, however. If your rods are strong enough (LS1 PM for example), but the bolts are stretching and leading to wiped out bearings, upgrading the bolts might be all that is needed for more rpm, which will probably result in more power if you've improved the airflow .

FWIW be careful about saying things like "psi of force". Either, but not both. The "pounds" in psi are pounds force rather than pounds mass, right? :)

Yes, I guess I realized now that is kind of a redundant statement. PSI would be the amount of pounds applyd to each in^2 of the piston and in turn the rod bolts correct? Im trying to find some info on calculating this but getting nowhere.
What is a unit of force?
Force would be something measured in Lbft or newtons correct?
And work would be how much of this force is done over time?

But how do we relate something like force to a pressure acting on the bolts.

The more I think of it force might not be involved in this at all, seems like the only things needed to know would be the piston speed, and calculate out of that its acceleration to a stop. Acceleration is just change in velocity over a given time. So if a piston slows from 60mph in .001s, then its acceleration is 60,000mph^2, is that even close?

But then what. Once its acceleration is known, the mass must come into play here in figuring out the tensile force that is applied on the rod bolts??? :confused:

FWIW Im not trying to calculate this for any given application or anything Im making as of now, just seems like it would be useful information. Mightve saved me $150 on those L19 bolts I bought for probably no reason.

little jon :)

Think about this...

There's an Oldsmobile guy by the name of Andy Miller, who is on the same level as Joe Mondello and Dick Miller (no relation) in terms of expertise.

Years back, before he got into dragsters, he used to run a 2-door oldsmobile with a gas-converted 350 diesel engine.

This car ran consistant 9.01's @ 149mph, which annoyed him no end, being that he couldn't get it into the 8's or crack the 150mph mark.

That's not the point though...

He ran aluminum rods with 5/16" rod bolts. I mean, feckin' header bolts are 3/8", and his rod bolts were smaller than that.


The moral of the story?

It's not so much about the size of your bolts, it's the lightness of your reciprocating assy and your engine prep that really determines if it'll survive.

Race and street or street/strip use are quite different. In the latter case, while there is less peak stress on parts, they go through many more cycles. This makes fatigue strength rather than tensile strength paramount. This is why aluminum rods are no good for street motors. It's light and strong but does not have as much resistance to fatigue as steel (at least when we compare the alloys used for this purpose in commercial examples). In some ways, you need better parts in a hi-po street motor than in a less than max effort race motor. The race motor is going to be torn down and freshened up more often. I have better parts in the Camaro than in my race car.

Rich

Sounds like you guys are all saying the same thing which supports his initial thought. It's my opinion that this logic carries through the remainder of the engine. That RPM pretty much is the killer of most all components (block, crank, rods, rings). Add some detonation and presto you need stronger pistons, also.

It's the destructive tensile force of switching direction at TDC that's requiring the beefy rod bolts not the compressive loads from combustion.

In theory then one can limit rpm and use stock or small rod bolts. Especially if the piston/ring/rod assembly has been lightened.

Now, if the rod is cowering (ovaling) over the journal at high compression loads, that's another story.

Any more information on cowering rods? I'd bet the worry about tensile forces will far outweigh the worry of ovaling....with no detonation.

If I figure right, and I dont happen to have the exact #s I got (on lunch now), but it as somethin like 7500lbs of force acting on the piston/rod assembly switching direction at TDC. Assuming a piston acceleration of something like 115000 from rest. Which translates to only about 15000psi on the rod bolts, which makes no sense to me at all, I mustve messed up somewhere, so correct me if Im wrong, but if Im right, why would any bolt need 190000psi tensile strength.

Even further, that bolt based on the youngs modulus for a strong steel, 30x10^6 only stretched like .000007" under that load, and the same steel breaks at like .06" stretch.

My numbers are probably off slightly since Im just going off of memory right now, so ill post up later tonight on what i got for sure, then Ill let Jon correct me where i went wrong.

litttle jon

If I figure right, and I dont happen to have the exact #s I got (on lunch now), but it as somethin like 7500lbs of force acting on the piston/rod assembly switching direction at TDC. Assuming a piston acceleration of something like 115000 from rest. Which translates to only about 15000psi on the rod bolts, which makes no sense to me at all, I mustve messed up somewhere, so correct me if Im wrong, but if Im right, why would any bolt need 190000psi tensile strength.

Even further, that bolt based on the youngs modulus for a strong steel, 30x10^6 only stretched like .000007" under that load, and the same steel breaks at like .06" stretch.

My numbers are probably off slightly since Im just going off of memory right now, so ill post up later tonight on what i got for sure, then Ill let Jon correct me where i went wrong.

litttle jon
I don't see how you are able to calculate that. wouldn't timing and such with the valves opening and closing effect that greatly? say if at TDC your exhaust valve is open *.8 inches*
this is on the stroke when the exhaust is being pushing out.
approaching TDC there will be resistance, exhaust, pushing down on the piston as it goes up.
compare that to a valve that is open .4 inches at TDC, the .4 inch one would have a harder time getting out that exhaust and there would be more force pushing down on the piston as it appoaches TDC as opposed to the .8 inches one. the extra force translates into more compression type stress on the rod/piston/crank/etc when it goes up, and thus less of a stretching type of stress on them right before/at TDC.
conclusion:i just went over one part of the engine cycle, there are tons more variables also, like compression, head design, fuel type and such
i hope i'm correct, but i may not be. :)

Race and street or street/strip use are quite different.
Rich


You'll get no argument from me on that, the difference between Street and Race Ring & Pinion sets being an excellent example.
However, the basic point; that's it's about a SYSTEM as opposed to an individual part, is still valid.
Or at least... that's what my observations over the years seem to indicate.

You'll get no argument from me on that, the difference between Street and Race Ring & Pinion sets being an excellent example.
However, the basic point; that's it's about a SYSTEM as opposed to an individual part, is still valid.
Or at least... that's what my observations over the years seem to indicate.

Agree! And just to illustrate your point as it relates to what I trying to say, consider street pistons and rods. They are often (much) heavier than race parts. So, even at lower rpm may put more stress on rod bolts. My street car has a set of ARP 3.5 material rod bolts while my race car has generic 7/16" chrome moly bolts from GM.That's a $50 set of rod bolts in a race motor and a ~$300 set in a street car. And that makes sense to me!

Rich

I don't see how you are able to calculate that. wouldn't timing and such with the valves opening and closing effect that greatly? say if at TDC your exhaust valve is open *.8 inches*
this is on the stroke when the exhaust is being pushing out.
approaching TDC there will be resistance, exhaust, pushing down on the piston as it goes up.
compare that to a valve that is open .4 inches at TDC, the .4 inch one would have a harder time getting out that exhaust and there would be more force pushing down on the piston as it appoaches TDC as opposed to the .8 inches one. the extra force translates into more compression type stress on the rod/piston/crank/etc when it goes up, and thus less of a stretching type of stress on them right before/at TDC.
conclusion:i just went over one part of the engine cycle, there are tons more variables also, like compression, head design, fuel type and such
i hope i'm correct, but i may not be. :)

This is a generalization, but very close to actual running environment Im sure. Just think of a single cylinder with a piston/rod and a crankshaft, but no combustion. Then picture an electric drill/motor spinning it at 7000 RPMs, this is "sorta" whats happening in a running engine.

The force created by the combustion process is miniscule compared to the force of a 1200gram assembly slowing down from say 3000FPM to 0 and back to 3000FPM in about .0000714seconds. At 7000rpm I calculated the crank to be spinning at 42000degrees/s, or 1 degree every .0000238s. Reading out of this handbook, piston acceleration can be seen over 120,000ft/sec^2, or 3750g's.

I still havent perfected my calculations yet so I dont think that the force I calculated earlier is correct, although no matter how I figure it with a piston acceleration of 119000 I only get 15,500lbs of force being applied to the assembly, but this only takes into acct its acceleration from 0-1* of crank travel, I dont know how to acct for the stop/start from 359-0-1 yet....calling engineers!

jon

Agree! And just to illustrate your point as it relates to what I trying to say, consider street pistons and rods. They are often (much) heavier than race parts. So, even at lower rpm may put more stress on rod bolts. My street car has a set of ARP 3.5 material rod bolts while my race car has generic 7/16" chrome moly bolts from GM.That's a $50 set of rod bolts in a race motor and a ~$300 set in a street car. And that makes sense to me!

Rich


Not bashing you Rich, but how do you know you NEEDED those $300 rod bolts. Im simply trying to decide mathematically what grade bolts are needed, I know fatigue stress plays into this, but if a bolt is only stretching .00005", I dont know if that would be enough to even affect the metals fatigue stress level. I know Jon will know this as soon as he chimes in on this discussion....I am yet to start reading up on fatigue life of metals, I just got started on the veryveryvery basic stress/strengths/stiffnesses of basic materials.

jon

Jon: I don't know enough to decide this on a calculator. Calculating the forces is less than the 1/2 of it. Once you have, you need to still decide how "strong" is strong enough for that level of force. "Strength" is complicated in this context. It includes a lot more than tensile strength alone. Fatigue and corrosion resistance, modulus of elasticity, etc., etc. And then there is the matter of your own "failure tolerance" and your pocketbook.

In the case of my race motor, I did not built it but rebuilt it. Since I knew it had been running sucessfully with OEM 7/16" bolts, I replaced them with a new set of the same, since they were cheap and available. The street motor involves heavy pistons and pins with a short rod at 7,000rpm, so I went as strong as I could justify spending. Just guesswork. I admire your attempt to be more precise but urge you to keeep in mind that a very large margin of safety is often cheap in the long run.

You might call up ARP and ask them for how they make recommendations.

Rich

All I gotta say is...

Rod bolts do break!!!

http://www.socalmuscle.com/~mleaf/engine/kaboom/1024x768%20pics/Bottom%20End/DSCN4840.JPG

This was a 383 that was spinning at about 6100 when it let go...

At 7000rpm I calculated the crank to be spinning at 42000degrees/s, or 1 degree every .0000238s. Reading out of this handbook, piston acceleration can be seen over 120,000ft/sec^2, or 3750g's.

I still havent perfected my calculations yet so I dont think that the force I calculated earlier is correct, although no matter how I figure it with a piston acceleration of 119000 I only get 15,500lbs of force being applied to the assembly, but this only takes into acct its acceleration from 0-1* of crank travel, I dont know how to acct for the stop/start from 359-0-1 yet....calling engineers!

jon


A 9500+ Cup engine has about 5000 gs on the piston at TDC reversal, while BMW quoted their 19,200 rpm 2003 F1 engine at 10,000 gs. Since the F1 rpm is about twice the Cup engine, and the strokes are about a 2:1 ratio, piston speeds, both average and max are similar, but the gs are double for the F1. Witha bore about the same as an LS1, the pistons have to be VERY light to keep the rod tension loads within reason. There was a "lively" discussion of this here a while ago. :)

I cheat and use an engine simulator to calculate piston gs. .

The worst condition for rod bolts is lifting completely with the engine at max rpm, like at the end of a straightaway in circle track. Under power the combustion reduces the tension load for 1/2 of the revs, but with closed throttle and high manifold vacuum and practically no combustion, every rev is a max tension load on the rod/bolts. If you visit short tracks enough you'll see an engine let go at the end of a straight. It's not fun running over your crank while trying to turn in.

Hmm, spend a few hours with Roark calculating stress/strain to come up with a rod bolt that just does the job or go to something that might be considered overkill? :think:

I'll take 8 of those marginally adequate rod bolts please!

That's craziness....

although no matter how I figure it with a piston acceleration of 119000 I only get 15,500lbs of force being applied to the assembly

Then you are doing something wrong. Please show work.

7000rpm, ~1.7 r/s ratio, max piston velocity should be in the neighborhood of 6600 fpm... tensile loads ~8200 lbs, compressive ~4500 with a 1200 gm bobweight.

I have a spreadsheet you can have if you're interested Jon. From there you can track through the formulas.

-Mindgame

Hmm, spend a few hours with Roark calculating stress/strain to come up with a rod bolt that just does the job or go to something that might be considered overkill? :think:

I'll take 8 of those marginally adequate rod bolts please!

-Mindgame

Eight? Are you building some sort of killer four-banger, MG? :)

Alright heres what I got:

first off.
7/16" rod bolt=.6013in^2 cross sectional area
using a 1150g rod/piston/pin/ring combo = ~2.53lbs

assuming a max piston acceleration at 7000rpms of 119385ft/sec^2
that becomes 3699g's for the force equation

F=MA> 2.56x3699 = 9472lbs of force

9472lbs/.6013sq/in = 15,786psi ?????

But like I said earlier, it doesnt sound like this accounts for the pressure involved in the rod first stopping from the say 2500fpm to 0, then back to 2500fpm in a matter of 3* crankshaft revolution.

I also am not saying I would not be one to overkill, I love overkill, my 381 was all forged with L19 bolts, splayed billet caps, everything, all for a sub 7k redline N/A LT1 casting engine, totally pointless, but I knew it wasnt going to break.

But if say you could get this down close to a science, I mean you have to be able to figure it out, how did GM decide what kind of rod bolts they needed in the LSx engines and so on? I doubt they just bought the best most expensive bolts they could so they wouldnt break, they probably designed them to work right up to and a little after the levels the engine would run at....then if you were say an engine builder, you could offer better engine combinations to customers for reduced prices, and this doesnt go just for rod bolts either, anything metal in the engine could be calculated to how much it will handle I would assume.

"Every engineering material is rubber" , "all solid materials behave like springs"-sir henry royce.

And it seems that the properties of all metals are known, and if the stresses applied to those pieces is roughly known, then you could more accurately pick a part. Obviously if you have unlimited budget then the strongest metal is best since you can make it so much lighter in return for the strength it gives. Like the crankshaft that baffled my mind in the BMR project SB2 engine, an LA Billet Kryptonite crank....28lbs!!!!! I dont even know if thats the best, but thats insane...assuming a good lightweight forged unit is ~43lbsish.

Anyway, rambling now....am I way off base here, have I gotten too excited about something for nothing or am i on to anything here? I also tried to apply this to a rod, but im sure the design/shape of the piece affects things in this situation.

jon

Jon: I am sure that there are very sophisticated ways to model this. In the end, they still do testing though! Sims only go so far.

Rich

Alright heres what I got:

first off.
7/16" rod bolt=.6013in^2 cross sectional area
using a 1150g rod/piston/pin/ring combo = ~2.53lbs

7/16 = .4375. I get .1503 in^2 CSA. Forget to divide by 4? :)

assuming a max piston acceleration at 7000rpms of 119385ft/sec^2
that becomes 3699g's for the force equation

F=MA> 2.56x3699 = 9472lbs of force

9472lbs/.6013sq/in = 15,786psi ?????

Check your units. Somewhere in there you need to convert lbs. of force (wt) to lbs. (mass). Slugs come to mind.

But like I said earlier, it doesnt sound like this accounts for the pressure involved in the rod first stopping from the say 2500fpm to 0, then back to 2500fpm in a matter of 3* crankshaft revolution.

I also am not saying I would not be one to overkill, I love overkill, my 381 was all forged with L19 bolts, splayed billet caps, everything, all for a sub 7k redline N/A LT1 casting engine, totally pointless, but I knew it wasnt going to break.

But if say you could get this down close to a science, I mean you have to be able to figure it out, how did GM decide what kind of rod bolts they needed in the LSx engines and so on? I doubt they just bought the best most expensive bolts they could so they wouldnt break, they probably designed them to work right up to and a little after the levels the engine would run at....then if you were say an engine builder, you could offer better engine combinations to customers for reduced prices, and this doesnt go just for rod bolts either, anything metal in the engine could be calculated to how much it will handle I would assume.

"Every engineering material is rubber" , "all solid materials behave like springs"-sir henry royce.

So how much do you want your rod bolt to stretch under 4000 gs? If it stretches x amount, does that let the cap fret and eventually (after a few millions of cycles) screw the bearing? Sometimes failure analysis is less than exact science. What was the root cause (hate that PC term) of running over your crank?

And it seems that the properties of all metals are known, and if the stresses applied to those pieces is roughly known, then you could more accurately pick a part. Obviously if you have unlimited budget then the strongest metal is best since you can make it so much lighter in return for the strength it gives. Like the crankshaft that baffled my mind in the BMR project SB2 engine, an LA Billet Kryptonite crank....28lbs!!!!! I dont even know if thats the best, but thats insane...assuming a good lightweight forged unit is ~43lbsish.

Anyway, rambling now....am I way off base here, have I gotten too excited about something for nothing or am i on to anything here? I also tried to apply this to a rod, but im sure the design/shape of the piece affects things in this situation.

jon

Just to keep you thinking, jon...

Jon

From ARP's web site.

Examining the “Over-Kill” Fallacy
If there’s one thing I’ve heard over and over from visitors to trade shows and races it’s,“Your fasteners are great. I’m not having any problems but I’m being told, by your competitors, that ARP® is over-kill and therefore I’m wasting some money when I buy ARP® pan bolts, manifold bolts or just about everything except for certain critical engine, drive train or suspension fasteners.” My first instinct is to say they are full of _ _ _ _.

But the subject is worth talking about. Cost is an important consideration when you choose a particular vendor’s offering. Still, if you use lesser quality fasteners and they were not subject to many assembly and disassembly cycles, by people with varying skills from professional to rank amateur. Maybe, just maybe, you could make a case for minimum grade fasteners that are over designed, size-wise, to allow a reasonably safe application for conservative usage.

Now, lets get back in our world. The real world. We can expect the engines and vehicles to be leaned on, from a little to beyond any sensible extreme. We can expect 10 or more assembly/disassembly cycles. We can expect over-torquing, which will leave the fastener looking 100%—but actually in a condition RED, semi-failed mode. We can expect some fasteners that are minimal in quality to end up in a critical, high stress area. We can’t expect everyone to be able to look at a fastener and determine its quality—by looks, or even by markings.

So we leave ourselves wide open for expensive and possibly dangerous results. For the amount of money saved by “type rating” every fastener’s capability, and consideration of a long range view of the best mix of customers—I recommend all fasteners be of a quality that does exceed the minimum standards.

Jon..Why would I have divided it by 4? The CSA of a cylinder (IE rod bolt) is nothing more than the area of the cirlce created by chopping the bolt in half correct? If so then A=pi.4375^2 = .6013, I looked but cant understand why that wouldnt be correct?

And I didnt even realize I had to do the conversion between mass and weight. To do that I would simply multiply it by the acceleration of gravity (~32fps^2)correct?

And is there a more detailed chart of values of "E" for selected materials than the one given in the Auto Math Handbook online somewhere? Like for specific grade materials? Also it would probably include, but would want the typical strengths for different grade materials as well.

Thanks for putting up with my crazy head guys, I think Im doing all this more to keep me busy than anything, talking about brake systems in class this week.... :o :o :o Now I just wish I could get my TI83 that I painted back in highschool with permanent marker working again so I dont have to use these sin/cos/tan tables to do trig on paper :mad:

jon

From ARP's web site.

Examining the “Over-Kill” Fallacy
If there’s one thing I’ve heard over and over from visitors to trade shows and races it’s,“Your fasteners are great. I’m not having any problems but I’m being told, by your competitors, that ARP® is over-kill and therefore I’m wasting some money when I buy ARP® pan bolts, manifold bolts or just about everything except for certain critical engine, drive train or suspension fasteners.” My first instinct is to say they are full of _ _ _ _.

But the subject is worth talking about. Cost is an important consideration when you choose a particular vendor’s offering. Still, if you use lesser quality fasteners and they were not subject to many assembly and disassembly cycles, by people with varying skills from professional to rank amateur. Maybe, just maybe, you could make a case for minimum grade fasteners that are over designed, size-wise, to allow a reasonably safe application for conservative usage.

Now, lets get back in our world. The real world. We can expect the engines and vehicles to be leaned on, from a little to beyond any sensible extreme. We can expect 10 or more assembly/disassembly cycles. We can expect over-torquing, which will leave the fastener looking 100%—but actually in a condition RED, semi-failed mode. We can expect some fasteners that are minimal in quality to end up in a critical, high stress area. We can’t expect everyone to be able to look at a fastener and determine its quality—by looks, or even by markings.

So we leave ourselves wide open for expensive and possibly dangerous results. For the amount of money saved by “type rating” every fastener’s capability, and consideration of a long range view of the best mix of customers—I recommend all fasteners be of a quality that does exceed the minimum standards.

This I know is true Rich, but I think more or less it applies more to the typical at home garage wrencher that doesnt have either the resources or (dont like to say this) but knowledge to pick the CORRECT part, instead of what will DEFINITELY work. I am really starting to backfire on myself and realize that this discussion should apply more towards things like rods and wrist pins, since things like that you can actually reduce the strength therefore reducing weight and actually gaining something if you can do it safely. A rod bolt will always be the same size for the most part, no matter the strength, and weights do not change all that much, so choosing the LEAST strength needed bolt will not really gain you anything in the end, except more $.

Again Rich, I dont want you to take this like Im bashing you, or anyone else for that matter, since like I said I am a victim of overkill as well, just thinking out loud, and my thinking needs help from you guys which is why i posted.
jon

This I know is true Rich, but I think more or less it applies more to the typical at home garage wrencher that doesnt have either the resources or (dont like to say this) but knowledge to pick the CORRECT part, instead of what will DEFINITELY work. I am really starting to backfire on myself and realize that this discussion should apply more towards things like rods and wrist pins, since things like that you can actually reduce the strength therefore reducing weight and actually gaining something if you can do it safely. A rod bolt will always be the same size for the most part, no matter the strength, and weights do not change all that much, so choosing the LEAST strength needed bolt will not really gain you anything in the end, except more $.

jon
i don't know if i'm reading your post right, but you seem to be blurring racing applications with street apps.
the quote rich posted was talking about the bolts being used by average joes of different skill. if you are talking a custom application just for you specific engine, then i'm sure all sort of oddities come into play like depth and spacing of the threads. the correct part is what works, now if you wanna push it to its limits, you can do as they said earlier in the post and rebuild it ever few thousand miles. i kinda of like the way rich put it about his car with one type of rods, and his race car with another type of rods. kinda like fork in the road, you can only go one way. :)

Where the hell do you guys learn all this stuff :confused:

Where the hell do you guys learn all this stuff :confused:
magazines, articles, talking to folks, etc.
its funny cause the more things i learn, the more things i find i don't know. :)

Jon..Why would I have divided it by 4? The CSA of a cylinder (IE rod bolt) is nothing more than the area of the cirlce created by chopping the bolt in half correct? If so then A=pi.4375^2 = .6013, I looked but cant understand why that wouldnt be correct?

Area of a circle is PI times radius squared, not PI times diameter squared. Radius is diameter/2, so (diameter/2)^2 = diameter/4.

If you divide PI by 4 you get a constant almostly exactly .7854, which are the numbers in the upper left corner of a calculator keyboard, when taken clockwise. So an easy way to calculate area of a circle is diameter^2 x .7854. Therefore .4375 x .4375 x .7854 = .1503.



And I didnt even realize I had to do the conversion between mass and weight. To do that I would simply multiply it by the acceleration of gravity (~32fps^2)correct?

Review the difference between Mass and Weight. Using F=Ma, you need to get the ft/sec^2 units to cancel each other out to end up with pounds (force). You figure out whether you need to multiply or divide. If you don't get the units to work, the numbers will be wrong.

And is there a more detailed chart of values of "E" for selected materials than the one given in the Auto Math Handbook online somewhere? Like for specific grade materials? Also it would probably include, but would want the typical strengths for different grade materials as well.

Thanks for putting up with my crazy head guys, I think Im doing all this more to keep me busy than anything, talking about brake systems in class this week.... :o :o :o Now I just wish I could get my TI83 that I painted back in highschool with permanent marker working again so I dont have to use these sin/cos/tan tables to do trig on paper :mad:

jon

If you don't get the basics correct, everything you derive from a bad start is bad. I'm not bashing you, but don't get ahead of yourself. Go back to the basics.

When some typical 8740 rod bolt is stretched to spec,
what is the preload {aka clamping force} ?

When some typical 8740 rod bolt is stretched to spec,
what is the preload {aka clamping force} ?

Correctly installed rod bolts will be at ~75% of their yield strength. My math is terrible, but for a 3/8" bolt with 180,000psi yield strength I get the following.

area = .1104sq.in.
tensile strength 180,000psi
clamping force = 180,000*0.1104*75 = 14,900lbs*2 = 29,800lbs total for two bolts

If you switch to a really strong alloy, with say 250,000psi tensile strength you get ~20,700lbs/bolt or a total of 41,000lbs. That's a LOT more force. A 7/16" 180,000psi bolt gives 40,600 total clamping force (for both). So, you can see why I only "need" regular CM bolts for the big block and use the $$$ bolts in the small block. BTW, I checked the receipts and those ARP 3.5 bolts cost me approximately $25/bolt (~$400) while the OEM big block bolts were ~$3 a piece (~$50/set)!!!

Rich

a couple things
1. are rods made with a bow in themlike this ()
maybe they could straighten out as it hit tdc. i don't know much about these things and to me it would make sense to want to take some load off of the the open circle (i'm sure there's a name for that) that goes around the crank. it seems like it would go elliptical after a while.
2. do engine builders put alot of thought into the size of the radius of that rod hole *technical term*? from the basic physics course i took 4 years ago it seems that the farther apart those bolts are from eachother, the more force they will have to deal with. but if your bolts are up to that, you can make the rods hole radius (techincal term) larger and put less stress on the circumference of the crank that goes in there. if this is true, i wonder if anyones ever graphed it out as the just before failing crank radius vs. the pistons rod radius (or force on the bolts)
3. i'll give this a shot, if i haven't confused you all with my incoherent questions so far.
http://img116.exs.cx/my.php?loc=img116&image=scissors3ef.jpg
if you made a rod do something like what is pictured, would it work. the red dot is a bolt, sort of like an axle point. when the rod is pulled the crossing design would absorbe more force. the drawing is that good, but the red dot, axle part where the metal would cross would be lower than what is pictured. so then when the rod is pushed down on, a scissor actino would sort of happen. so not only would the bottom open circle be pushed down, wanting to go oval, but the scissor type action would pull out on the sides, reducing the force on that open circle.
:)

Wow, cant believe I messed that one up, I knew that too, just for some reason never devided 7/16 in half to finish it up.

Ill work on the rest, my linear algebra is a little sketchy so Ill have to be giving my engineer brother or sister a shout when I get stuck on stuff. Really need to take another basic algebra class again, I really screwed up when I tried college the first time, didnt take it seriously whatsoever, barely passed, but I understood everything in highschool very well.

Does anyone know:
Young's Modulus for 8740 steel?
the typical 'free grip lenght' of a bolt
in a rod for SBC?

tia

Does anyone know:
Young's Modulus for 8740 steel?
the typical 'free grip lenght' of a bolt
in a rod for SBC?

tia

I doubt you will find a young's modulus specific to a grade of steel. It vary's so little by different alloys, heat treatements, ect that the value of 30 Mpsi (30*10^6 psi) is used for all steels. The only time you use a different value is for brittle metals in tension like cast iron.

annealed
Tensile yield strength 60 kpsi
Ultimate tensile strength 95 ksi
2" elongation 25%
Rockwell Hardness 190HB

Tempered
Tensile yield strength 133 kpsi
Ultimate tensile strength 144 ksi
2" elongation 18%
Rockwell Hardness 288HB

I can't help you with with the rod question.

-brent

Eight? Are you building some sort of killer four-banger, MG? :)

:lol:

Only 4-bangers I touch have two wheels. ;)

-Mindgame

:lol:

Only 4-bangers I touch have two "wheels". ;)

-Mindgame


Banger Sisters?

Or isn't legs what you meant by "wheels"? :)

http://www2.foxsearchlight.com/thebangersisters/index_flash.html

Jon: I am sure that there are very sophisticated ways to model this. In the end, they still do testing though! Sims only go so far.

Rich


They go very very very very far

Banger Sisters?

Or isn't legs what you meant by "wheels"? :)

http://www2.foxsearchlight.com/thebangersisters/index_flash.html

I'd work on those two-Bangers too....








at the same time! :lol:

-Mindgame

You two crack me up.... lol