Date: 06-Oct-99 11:49 PM
Author: forcedsol
Subject: rod ratio revisited.....

i was wondering, with all this talk of ratios etc, what kinda ratio does my D16A6 have? is it pretty good? close to this 1.75 ratio ive been reading about...

if its not that good, what are somethings i can do to better it? i am running a turbo on this engine and would like to keep the piston as happy as possible. tia

Date: 07-Oct-99 06:56 PM
Author: NITRO
Subject: RE: rod ratio revisited.....It Stinks

That long 90 mm stroke may be good for torque production in street applications, but combined with a rod length of 137 mm, it works out to a 1.52-1 LR and it's getting on down the list for excessive side thrust. The only thing we've done is to weld a deck plate on to raise the deck enough to get a longer rod inside.

Unfortunately the ring pack and the compression height are already in areas where we can't gain much by moving the pin up. Larry's best fix is a 1.5 stroke of 84.5 mm. The displacement goes down, but when turbocharged or blown, who cares. It does allow you to go to a rod length of 139.5 mm and that works out to a LR of 1.65 and no welding the block. Since the Honda 1.5 cranks are shit, you may assume that there will be a plentiful supply of new forged 85 mm cranks coming shortly along with rods and pistons designed to maximize effeciency on boosted engines by mechanically enhancing the combustion process. They're shape will be worth several points of octane and it's safe to say that they aren't your same old forged pistons (even the price!)

All our new pistons are priced under the the going rate for "generic" forged pistons and even the stock compression units feature the latest in combustion technologies. Soft Head, anyone???

Date: 09-Oct-99 07:51 PM
Author: Owen
Subject: OK, let's talk for awhile here...

Tell me if I'm wrong here...

l/d is a ratio that correlates with side load, and is not the only factor that goes into side loading right?

I've gone throught the dynamics of the sit. and here is where I'm at:

a l/d ration only means something if all else is held equal. There are two primary variable components of power lost to skirt friction, piston speed and side load. Let's assume that we are trying to force an engineering resolution to a certain stroke in an available area. While many might say that a l/d ratio 1.5 is getting excessive the reality is that the side loading is directly related to the wieght of the connecting rod and rpm. The weight of the connecting rod (in NA apps anyway) based on the tensile stress (and bending stress) cuased by rpm. This means that piston weight directly effects the rod weight and the rod weight directly effects the sidewall loading. SO....

If we get some good light pistons and good light rods than a l/d of 1.5 doesn't look so bad... right?

Along the same lines..Ti rods. I've heard people say that they are only really needed at high rpm. What gives with that? I would think that you would want them when you have high side loading, in other words, when high piston speed is present. Put another way, why not Ti rods for long strokes or high rpms rather than the explanation that I always get of just for high rpm use.

And lastly, that could very well make the whole paragraph above mute, is do you know of any companys that make Ti rods right? When I say right, I mean like how cariilo does steel rods. Where the whole proces has been adapted to the requirements rather than just sounds cool or high tech. Unfotunately that is the feeling I get when I starting asking manufacturers about Ti rods. DO you know anyone who does good Ti rods or do you think I would be better off just sticking to the tried and true well developed steel rod?

Just curious..

and tired of trying to seperate the bull,


Date: 09-Oct-99 09:05 PM
Author: NITRO
Subject: RE: Is Your Real Name Don Bell?? Or, Do You Have A Degree In Astro Physics?

The old fucker came here to learn Honda tricks many years ago.

Apparently he spent too much time answering and not enough listening and learning. We're way behind the curve on this technology.

If you lay the engine down where the cylinders are parallel to the ground, the rod weight would actually increase the load on the lower axis of the cylinder. The heavier the rod, the greater the load (weight), so if you used titanium instead of steel, there would indeed be less load on the cylinder.

Never quite thought about it that way, but the load would even be present when the engine's not running. What a bummer.

No Bull

Date: 10-Oct-99 12:32 AM
Author: eg2
Subject: hmm, are we talking "logically" or are there data to prove it?

I guess obviously lighter internal components is always better if cost is no object. I have a little hard to picturing why a heavier rod would increase side loading.

I imagine if the majority of the weight is on the big end... it won't affect the side loading at the piston much. Unless there is a lot of rod stretch. Ohh wait, I think I'll be quiet before I really make a fool out of myself here... :-)

Date: 10-Oct-99 08:50 PM
Author: XT6Wagon
Subject: Um 1 Question, Nitro?

Did you calculate the forces required to rotate the rod? This may reduce the sideloading you calculated signifigantly. Even at high RPMs I cant see a rod pushing through the side of a cylinder in a engine that is free spinning. I would think that the rod breaking would be the main falure in a engine spinning at high rpm with no combustion load.

Date: 10-Oct-99 11:03 AM
Author: Owen
Subject: Would you believe my real name is Owen?

In Reply To: RE: Is Your Real Name Don Bell?? Or, Do You Have A Degree In Astro Physics?

My degree is in Mechanical Engineering

You guys all have engineering degrees right? I had to calc out the simple (no harmonics, everything rigid)dynamics of a piston-cylinder assy for a class when I was back in college. If it makes you feel any better, I actually spend a lot more time on the neon board.

I never thought of the static portion of the load either (suppose that's why my prof hated my solution?). Actually I thought of any of it other than for an upright, inline engine. That would also mean that the side loading of a V configuratation is not the same from one V to another.


I believe (it's been a few years) the lions share of the load would be from the rotation of the rod. The moment that cuases the rotation comes from the moment between the rods side load at the crank and the rods side load at the piston wall (through the piston).

As I recall the power lost goes up at the square of engine speed.

You never did answer my question about Ti rods.


Date: 10-Oct-99 03:01 PM
Author: alloy_625
Subject: side loading and Ti

(note to frank: if I get this all wrong, please don't archive my stupidity for eternity =)

Owen, with the disclaimer that I hate dynamics (and statics and mechanics) with a passion, while the mass of the rod/piston play a big part on the exhaust stroke, what about the power stroke? Assuming forced induction, the cylinder pressure can be very high, and the resulting force is transferred into the cylinder wall with a component based on the l/d ratio (and the pin location in the piston yada yada yada). When do turboed Hondas blow the sleeves to bits?

The other reason that TOO/NITRO gave for 1.75 was the performance benefits based on piston velocity, dwell near TDC, etc. At 1.5 l/d, you're still going to have very high piston speeds and assuming that everyone is going to buy the same lightweight pistons and use the same $50/ea rod bolts, that Ti rod is going to end up having to be stronger than the steel one.

On Ti rods, I looked into it at one point because I figured reducing the weight could only be good. Unfortunately, I don't have $1600 to spend on 4 rods. I'm not sure what Carillo does that makes them right (they are $$$, heavy, but very strong, and slow to get), but if I was to buy a set, I would call HR Machine @ 517/543-5000. They didn't have a lot of forgings, but the one they use for a Rennsport Mercedes engine would have been perfect. The only thing that might cause a metallurgist concern is they hone the journals to size rather than roller burnish. I think it has something to do with Ti's propensity to be notch sensitive, but don't remember. I never talked to Pankl or Impo-Milano as I was prewarned that they are VERY expensive. Cunningham also makes them from forgings and the finished rod is very light.

Date: 10-Oct-99 06:59 PM
Author: Owen
Subject: RE: side loading and Ti

Truthfully, the highest loads are during combustion from combustion presure. In additin the FBD's show that a component of the combustion pressure induces additional side loading of the piston. At high rpm the side loading of the dynamics is large copmpared to the combustion pressure portion. Side loading is normally used for the force from the piston on the cylinder wall, rather than just the force on the wall itself. It is the major compenent of internal friction and cylinder wear.

As for everyone wants to use the same lightweght.... is true but there is a problem even there. The value for l/d are not a theoretical ideal, but rather based on experience. This means that the values stated are only good if you use the same "types" of material used in each experience. If the previous attempts that worked well at l/d of 1.7 were already ultralight internals then someone who uses heavier (and cheaper) compents might need to use an l/d of 1.8 or more to achieve similar results. NO BASELINE.

As for what carillo does, well, they are very tight lipped but what I have figured out is:

1. They use the right steel. I was amazed how many rod manufacturers a few years ago used 4310. Wrong. 4340. 2. Highly polished. 3. Multi stage forging process. 4. small highly tested lots of base material. In other words they don't just pull billet off the shelf and go to work. 5. Good heat treat process. I've alays been surrised how often heat treat is misapplied. 6. H beam. Not sure if good or not. I can't help but think that I have always been missing something here. 7. minimal machining.

Yes they are fairly expensive, very strong, and slow to get. For what they are, they aren't very heavy. You have to be pretty specific with them though regarding application, or they will give you a monster rod.

Thanks for the additional info on the Ti rods. Now I cn look other places. So far I have only talked to Pauter and Crower. Both CNC machined from "billet" Ti.

What engine were they perfect for?


Date: 10-Oct-99 08:40 PM
Author: RacerX
Subject: And now for all the mentally retarded out there...

In Reply To: RE: side loading and Ti

I figured i'd ask a question or two for all of us morons out there. Whats l/d?? Is is length (rod i suppose) over diameter (of the bore). Also, how does this relate to r/s ratio, which we've all started to get a grasp on here? And finally, a quickie question, where do you take the measurements for rod length? From centerline to centerline? Meaning center of wrist pin to center of crank journal? Also, (ya i know, i said only a couple questions) how does titanium act compared to steel? Does it stretch the same, expand the same, what are some good things about it besides its lighter weight.

Thanks RX

Date: 11-Oct-99 01:39 PM
Author: alloy_625
Subject: Damn board ate my message!

In Reply To: And now for all the mentally retarded out there...

It used to be when you forgot a field, the board would give you a chance to fix it without losing your whole damn message!

Ti for dummies from a dummy

The most important thing about Ti is it feels funny when you hold it. I collect surplus Ti bolts because they are cheap and hi-tech and the first thing you notice aside from the weight is the warmth. This comes about because of the lower thermal conductivity of Ti (and to answer one of your questions, Ti has a low thermal coefficient of expansion).

Anyhow, back to rods. Ti has a density about 55% that of and a tensile modulus (measure of stiffness) about 65% that of steel. What this means is if you take two identically sized bars of material, the Ti one will be about half the weight of the steel one, but if you hang a big weight at the end of each bar, the steel bar won't deflect as far. To make the Ti bar as stiff, you would have to increase the cross section slightly (but not necessarily by 50% depending on how clever you are).

So back to rods. 6Al-4V (which is one of the common alloys of Ti) has a tensile strength of 170kpsi vs. 220kpsi for 4340 steel as used in good rods when both are heat treated. That means that to make a Ti rod as strong as a steel rod (in stretching strength as in keeping the piston attached), we would have to increase the cross section of the beam by 30%. It gets better though, to prevent buckling of the beam under high combusion pressure (say that monster T04 turbo), you have to ensure that the stiffness of the beam is equivalent (to first order disregarding a whole bunch of ME stuff I'm not interested or versed in). Since Ti has a modulus 65% that of steel, we need to increase the cross section in a way that will stiffen the structure without adding too much weight. Look on for a nice explanation of rod beam strength and H vs. I and consider the tradeoffs between packaging and weight by making things thicker or farther apart etc. If you got lucky, both things (strengh and stiffness) could be done at the same time and so the Ti rod is now 60 to 65% the weight of the steel rod. Pretty cool.

Ah, but it gets better. Ti likes to, on a small scale, swap spit with steel when they're rubbing against each other. That's galling. Chunks of material will transfer from one side to another or they'll just get stuck. That means you have to be real careful with your steel bolts in Ti, either by getting coatings or silver plating, or by using lots of antiseize. Also, your Ti rod is going to want to stick to the sides of your rod journal so the whole rod has to be coated with something from moly disulfide to titanium nitride to something really hi-tech whatever that might be.

Ok, but you can deal with all of that. Oh, forgot to mention, Ti is notch sensitive. That means that if you have little scratches on the surface, they are more likely to form cracks. Better hope that they treat your rods carefully when they assemble the engine and don't decide to go stamping them with a punch. (This is sort of like the time I took an ARP stud to the machine shop to see if they thought I could shorten them on the lathe with a steel tool (because they are hardened) and they whipped out a file and started filing to see!) That earlier comment about roller burnishing vs. honing, that was (I believe) due to this notch sensitivity issue. Honing is like sanding on a small scale so it leaves lot of little tears and scratches which can act like micro cracks. Roller burnishing rubs the material smooth and probably leaves a compressive stress on the surface. (squeeze a crack and it does nothing, stretch it and it grows and grows)

On top of all of that, the rods are major bucks. Very few people have forgings for import size rods [Owen, I was looking for a 146mm rod, 51mm and 20mm] and all the rest would be made from billet (back to for an explanation of the advantages of forging). On top of all of that, they are DAMN expensive. $350 to $450 a rod! And on a more direct note, I asked TOO if he thought it was worth it (for what most of us want to do) and he said no. But it was an interesting little journey and I learned something along the way.

Date: 11-Oct-99 10:42 AM
Author: NITRO
Subject: RE: Stupid One To Stupid 1

In Reply To: And now for all the mentally retarded out there...

Everybody has a different acronym to represent the simple "rod length divided by stroke ratio" formula. Larry has used LR, as it was the term back in the 50's, 60's, 70's etc when working with renowned engine designers around the world. I guess that old age has created an non-willingness to adopt new terms.

As for the "readable" engineering jargon, this is the primary reason that all engineers spend about 6 years in the "real world" here before they are actually allowed to do what they were hired for. It's amazing how many more communication skills they can develop, when they aren't trying to impress people who don't speak the same language.

Doctors are also good at this "art", when they're in mixed company, reassuring us normal folks that they're actually dwelling on a much higher intellectual level.

I might also suggest that when you see people spending this much research, time, and verbage on a singularly small subject that it's a hobby for them. These folks can spend a lifetime and a fortune determining how to rebuild an engine, and if it's ever completed, it'll be ready for vintage racing, because the rest of the world has passed them by.

We've chosen to paint simpler pictures that enthusiasts can understand, so making mortal decisions (in their lifetimes) regarding their engines and drivelines may be a bit easier. If the head/piston configuration provides a more efficient burn, do enthusiasts really want to know flame speed in feet per second at every rpm under specific loads? Will they read the numbers? Would they be smarter if they did?

Truth be known, the only thing that's remotely worth looking at when going for a big picture on the LR numbers, might be the cylinder diameter and wrist pin off-set.

As for titanium rods, we certainly use a lot of titanium for connecting rods. We also make rods from many more exotic materials, all to insure that we've achieved the maximum strength from the least weight, with satisfactory durability. The programs using these components are typically those with few budget constraints and that places the components well out of the range of affordability for most enthusiasts.

When properly done, a titanium rod can be as strong as it's steel counterpart (assuming one's using the correct steel alloy) and do to the nature of titanium, they tend to be a little easier on bearings than steel rods.

I believe that an honest engine builder should be the one to determine if the use of these expensive rods is necessary or not.

The young in this country will buy anything if it's hi tech (carbon, titanium, computer generated, etc.), so don't fall victom to excessive engineering and sales hype. In most instances, running titanium rods is a total waste of money, and once they're installed, you can't even show then to your friends!

Date: 11-Oct-99 09:12 AM
Author: Owen
Subject: RE: And now for all the non mentally retarded out there...

In Reply To: And now for all the mentally retarded out there...

l/d is the rod length to stroke ratio. r/s is probably the same thing using letters that are easier to understand. The l/d is how the rod length to stroke ratio is portrayed in text books and papers. l is for the length between centers of the rods, and d is the diamter of the circle that the big end travels through (which happens to equal stroke).

l is supposed to be measured center to center as you said. Typiclly it is easier to measure from the close edges of the holes and the far edges of the holes and then average them to get the center to center distance.

Compared to good steel, good Ti is 90%-95% as strong in normal stress with a fatigure limit that is 100%-110%, while being 40% lighter. It stretches twice as much. At higher temperatures it is far stronger than any regular steel and below ~2000 degrees is is one of the most corrosion resistant materials known to man. It is also has really poor notch sensitivity - so no scrathes.

For most applications, the half as stiff part makes Ti really unsuitable. What it is really good for (in theory) is rods and valves. It also makes some pretty good springs (if you can fit them), and I have heard of some people who make ultra light weight headers out of it.

The most outsounding property of Ti is it's specific toughness. In english that means that pound for pound it is the most impact resistant steel. By a long way. If the price comes down, excpect to see bumper frames and seat frames made out of Ti, cuase they are excellent applications.

Just about everything else, there are better materials.


Date: 12-Oct-99 11:01 AM
Author: alloy_625
Subject: Oops, I goofed

In Reply To: Damn board ate my message!

I was using 220kpsi for 4340 which is a bit too high, must have been thinking about rod bolts or something. Somewhere around 180kpsi is much more realistic so 6-4 looks real good strength wise.