But aluminum rods have a "shelf life" in the engine. Or are there some mead these days that will live like steel? .....and WHAT is the possible advantage to aluminum main caps? I'm wantin to be ejeekated here.
You can run aluminum rods on the street. Oil temp and bearing clearance is critical. Bill Miller has some discussion about this on his home page.
Aluminum rods do have a shorter life, but most every big power Drag & Drive type engine is using aluminum rods.
Aluminum rods take up a huge amount of shock in the system.
Aluminum caps do the same thing. Like I have said before, everything has a resonance frequency. If you change the frequency of something you change how it behaves.
An example of that is a flimsy pushrod. They too can start vibrating like a tuning fork. And they bend and unbend under load. When that pushrod unbends all the stored energy in it is like a jack hammer. It will loosen nuts and bolts and crazy things like that. Rocker adjuster nuts, bell housing bolts…starter bolts.
I had a customer with a MFI 377 Chevy. The F’ing starter kept coming loose. We used red locktite and all that did was make it take longer to get loose.
Tearing it down after some dyno pulls (killed a set of springs on the dyno after about 10 pulls) we noticed witness marks where the pushrods were rubbing the head and it had .100 clearance.
We ordered up a new set of pushrods with a bigger diameter (cheap assed 5/16 .060 wall to 3/8 .120 wall) and the starter bolts never came loose again.
You can never underestimate what something vibrating in the wrong frequency will do.
Main studs moves the screw load out of the bolt hole and up to the nut. Now the threads see only a straight pull against them. It’s changes how the block sees the clamping load.
The damper has to deal with all this **** flexing and vibrating. Elastomer dampers (doesnt make a pinch of **** difference who’s name is on it) have an incredibly narrow tuning range. Pro Stock and ASScar teams and some very well funded sportsman classes all have engineers on hand a dyno’s fully outfitted with measuring tools that can plot the amount, duration and intensity of the crank bending.
When they have that data they can change the durometer (and maybe the diameter but I’m not 100% sure of that) on the O rings in the damper to change the frequency to calm the crank down.
Guys that are hell bent on pinching every single penny they can fail to understand the consequences of what happens when you change ANY one component that relates to the crank.
When Chrysler developed an engine package they spent millions of dollars testing stuff like this. And they considered the most expected operating range their passenger car engines would likely use.
With that operating range established, they developed the damper that would be most effective in THAT a RPM range with that crank weight and materiel, that connecting rod and weight and that piston and weight.
Change any ONE of those components, just ONE and you have effectively made the damper less effective.
Now let’s just jack everything up. Let’s think it through.
Chrysler figured the engine would spend the majority of time at cruise RPM. That’s easy to figure. Say a 25 inch tire with a 3.23 rear axle ratio and you are right about 3000 RPM. Roughly.
So they built a damper that would be the most functional at that RPM because that’s where the engine would spend the most time. And don’t forget that even if you have a harmonic issue as long as you get through it you can live with it.
Now we come along and the first thing we do is go to a lighter piston. And we have now made the damper less effective in two ways. It’s probably lighter and it’s a different materiel with a different resonance frequency. Oh ****. But we keep going.
We throw some cam it, slam some barn door capable valve springs in there and we start RPM’ing the engine way higher than what the damper was designed for. But we still have that OE damper.
That big cam sounds cool and all but it’s a bit piggy down low so we run down and grab some 4.56’s off the shelf (this is back when men weren‘t afraid of gearing the **** out of something and you could buy the stuff local) and you slam those mothers in there.
Now you can rotate the earth but your cruise RPM is now significantly higher than what Chrysler planned for. And the OE damper is still hanging on the crank. But we have changed the piston weight, piston materiel and RPM range the engine typically operates in.
Now we are bored. So we say **** it, I’m going to light up the sky and we stick the hose to it. We decide a 150 shot of nitrous will do the trick (add in any power adder here…I used nitrous because it’s my favorite power adder) and impress not only our buddies but all the hot chicks (hot chicks used to dig fast cars…now they want a guy with a Honda and a fart can and a cool phone…thank GOD I’ll be dead soon) and off we go.
Now the cylinder pressure is much higher than what Chrysler ever intended. And…we still have the OE a damper on there.
After a few hits on the street, smoking the tires like only Joe Camel could, a couple of rods **** the bed and uncouple from the crank. Nitrous is like a hooker, you KNOW you want to hit it but the consequences are usually never good.
Now we decide we need more. So we get a nice long stroker crank (thats one big change) and instead of being 1018 materiel (thats what Chrysler used) it’s 4340 and it’s a non twist forging instead of a twisted forging like Chrysler used) so that’s THREE big changes. Stroke length, crank materiel and forging process and which affect its resonance frequency.
Of course, two rods are now hanging on the wall of shame so we say FTW! And buy some really nice H beam 4340 forged rods. Now we have changed two more critical components and their frequencies but we still use an OE damper that was never designed for any of this.
We have all this new **** together and off we go. All the girls want jump in the car and all your buddies are jealous. After a year or so the power is down (if you’re lucky it makes it a year) so out the engine comes and we take it apart.
The main bearing look like fresh baked garbage and we hit the interweb where all the experts hang out (and of course none of the experts agree with each other!!!) and the general consensus is we NEED a main girdle.
Is a picture forming in your mind of how absurd this is?? It should be.
We have done everything we can to make the crank damper as ineffective as we can and **** is getting trashed. So the answer is to use some rinky dink piece of 3/8 plate (maybe half inch of the manufacturer really wants to impress the customer) with 10 holes in it to make the try and make the block stronger and more ridged when most of the time the block isn’t the issue.
The last thing we do is consider what changes we have made and how that affects the damping ability of the OE damper.
As I have pointed out many times, the elastomer damper has a very limited damping range. It’s big selling point is it’s cheap to build and relatively effective in it’s tuned range. Other than that, it’s not worth a **** really.
I‘ve told this story before but I’ll repeat it here because it fits the discussion.
In 1988 I switched to aluminum rods. I was also going from shifting at 8k to 8500 or if I could get it 8800. And I could see the main bearings were pissed off.
It was time upgrade from the OE damper and all the big hitters were using the much vaunted ATI “Super Damper” (its always a clue for me when the marketing department puts “super” in the name so I’m skeptical) so I had all my info at hand like Bob weight, crank weight (the 8 bolt cranks weighed more than a production 6 bolt and had a different heat treat which affected the frequency) and called ATI.
I figured that they would have to build me a custom damper to deal with what I was doing. Fat chance.
I tell the clown on the phone that I need a damper for a small block Chrysler. He interrupts me and gives me a part number. I have the catalog right there and it’s their off the shelf piece.
So I say dude, my bob weight is about 200 grams LESS than what most guys use and I don’t know anyone near me shifting at 8500 or a bit higher. Don’t you think I need a custom damper?
He says nope, our dampers are so sophisticated it controls damping at most frequencies. And I promptly told him he was full of ****. Even in 1988 you could find research into this stuff and the elastomer damper has the most narrow effective range of any style of damper.
I said can you make me a custom damper. He said why? Rather than continuing on a conversaction with a guy who was crapping in my mouth and telling me it was chocolate cake I said buy-bye and hung up.
As far as I know 01/25/2023 there are only TWO dampers that have a wide frequency range. Fluidamper and Innovators West. If you look at some Steve Morris builds he uses mostly Innovators West.
During the 2023 Engine Performance Expo (I posted a notice in the racers forum…hopefully people took advantage of it) John Callies gave a lecture on cranks and in it he advocated for the new aluminum Fluidamper. I know he didn’t like the steel Fluidamper because when they first came out guys were not fitting the damper to the crank snout. If the damper was too tight it would split the damper at the keyway and off came then damper. Or they were too loose (the beginning of the china crank era was filled with cranks with undersized snouts) and the damper didn’t work and off came the damper with the snout in it.
So I said all of that to sum it up.
The damper is far more critical than people think. If someone is running an elastomer damper they may want to spend some time looking at the available research out there and question why they are doing it.
And before 67 dudes chime in and say they have been running an elastomer damper for 30 years and never touched it I‘ll say it’s better to be lucky than good.
It’s a testament to how shitty a build can be made and have it live.
And ATI has recommended service intervals for their dampers.
From the day an elastomer damper, any elastomer damper is made it is degrading.
Bet your *** on that. And no stud girdle will fix that.