Alum Rods and Road Racing

[Lucas English]

So over the last few years we have found the Alum rods to amazing on bearings for our high hp EVO's and I have tested them to about 20k so far with no problems on the street with no oil cooler.

Many have said that they well not work on the street and so far that have.

I think I am going to start using my Evo for the road and not just the strip. I am wondering if I really may be asking to much of my alum rods. I plan on putting a large oil cooler on to help.

I feel for some lap days it should be fine but I plan on doing the Silver State Classic. Which I will be at 100-120mi for 90mi on 100+ deg day.

So far I have been a find out for my self guy but I like to here different ideas and opinions.

[precisionpsi]

Ive build a 2.3 stroker alum rod motor it has about 20,000 miles on it. Ive had no problem with them yet. I would like to look at the bearings just to see, how bad ass these rods are.

[evodan2004]

i am about to have a 2.0l motor built. i would love to have an aluminum rod setup but i DD my car hard all the time and i dont know if i feel conferable with it lasting. 20 to 30k miles IMO is not near enough. 60 70k is more like it to me.

what aluminum rods is everyone using? and how are they holding up?

[Lucas English]

We have used R&R and Groden. I have yet to personally see a falure of any alum rods.

[Lucas English]

I have done about 150mi at 90mph on a 50deg day last year on the alum rods but not sure if the 90mi at 110-120 will be much different. Will be around 5k-5.5k the whole time in 5th.

[Uncle]

I ran aluminum rods in my daily for a year before I got rid of it. And we are talking -13F in the winter to 100F in the summer.
Im not going to be the one to say whats right and wrong, ill just say it worked for me.

[Frosty]

I've been wanting to run aluminum rods in my evo for quite some time. I think I'm hesitant because I have had problems with them lasting very long in my old V-8's. But that was many years ago too.:)

[Kiggly]

Fatigue strength of 7xxx series aluminum completely goes to shit starting by about 200F. It is easy to see 250-300F oil temps and hotter rod temps in road racing situations. I've never seen alum rods used in a road race application.

Lucas, if you want I can get you some more detailed info and predict rod life in your application. I'll need some rod beam measurements and piston and rod masses.

Kevin

[Lucas English]

So if I keep the temps under 200deg I should be ok? I guess a oil temp gauge is in order. Hope a large cooler will keep the temps down.

I will try and get Aaron to get the full spcs up tomorrow.

[JC evo1]

can you post pics of some used bearings from both a steel rod and an alum?

[Aaron@English]

302g per piston, 500g rod weight, rod thickness is 26.25 at the wrist pin and big end is 26.50mm. Beam width at the big end is 81.25mm and is 16.55mm thick around the bearings. The little end is 36.55mm wide and 7.5mm thick around the wrist pin.

They are standard length, and measuring at the beginning of the taper past the big end (up 40mm from the rod split which is offset some it appears) the rod is 47.75mm wide.

[The Wookie]

He needs the cross sectional area at the smallest point. Easiest way to do this would be draw it on graph paper with x mm or .100" squares and add up the squares.

[The Wookie]

People do use aluminum rods in circle track stuff, but they have a finite life, not an endurance oriented part. The fatigue cycle life near yield is much much lower than steels, and when you get over 100c as Kevin mentioned it really goes to shit in a hurry.

There were some trick 7xxx series rods with a surface treatment that made them about as good or better fatigue properties as steel but NHRA outlawed them so the mfg said 'fuckit' and quit.

[Aaron@English]

okay so at the smallest part of the "I" right under the wrist pin I come up with 548-550 mm2. Its not quite a true eye and I cant get the exact angle of the wall of the I. It is no less than 548 though.

[Lucas English]

Do you think oil temp will give me a good idea of rod temp? What is the highest oil temp you would want to see on a alum rod motor that I am trying to make last?

[Kiggly]

okay so at the smallest part of the "I" right under the wrist pin I come up with 548-550 mm2. Its not quite a true eye and I cant get the exact angle of the wall of the I. It is no less than 548 though.

That doesn't sound right. A 23mm x 24mm solid block is 552mm2. Can you verify these measurements, or maybe just post up the beam measurements at the smallest part?

550mm2 is 0.85in2. One steel rod I know of is 0.20in2, so over 4x that big sounds too big.

Kevin

[Kiggly]

Temperature:
7075 is a pretty linear fall-off in tensile strength up to about 300F for brief exposure. At 300F it is about 75% room temp strength with no heat exposure history.
The problem is time exposure to anything above about 200F continuously weakens the material. After 10,000hrs at 300F, strength at 300F is down to about 30% room temp strength. This behavior totally goes to shit starting about 230F, but keeping it under 200F is the best idea. That will not be easy to do, and will probably cost 5-10hp compared to 250F oil.

Completely wild and unfounded guess - rods are probably 20F hotter than oil at the big end. I would guess small end at 30F hotter or more.

Kevin

[The Wookie]

At the very least you'd want to keep the oil squirters, and use a ring package with good heat transfer characteristics. Consider forced pin oiling to keep heat down in the upper rod area.

[Da Fuhrer]

What about coatings in this case? Like coating the rods with a coating designed as a heat dispersant? Would there be any benefit? I've been researching different coatings for different applications lately, and it's got me to wondering about using them in areas that they haven't been traditionally used

[Aaron@English]

Box dimensions- 33.85mm x 22mm. Instep of the I is 7.1mm and the long edges of the I are 10mm thick (with taper that I didnt account for).

I calculated 3 rectangles from this, 2 at 10x22 and one that was 7.8x13.85.

22-14.2=7.8 and 33.85-20=13.85 with the remaining being 10x22

[The Wookie]

I came up with 475-480 mm2 min. CSA.

[Lucas English]

Good info.

Well this motor is all ready in my car and running well. Has no oil squirters in it. The Silver State with my car was a new idea so my motor was never built with this kinda of use in mind.

I will have a oil temp gauge on next week to see with what kinda temps I am dealing with now so I can see how extreme of a cooler I need to keep the temps down if it can even be done.

[Aaron@English]

I admit I dont fully follow exactly what I was supposed to be measuring but here is my diagram that I based my calc off of. There is a very slight taper in on the I, and this is under the wristpin at the smallest point. Directly and I mean directly under the wrist pin is smaller but a solid measurement.

http://img.photobucket.com/albums/v505/Hurrikain/rodCSA.jpg

[Aaron@English]

A quick check directly under the wristpin and a hairs breadth above where the eye ends the measurements are 22x33.4 solid box.

[The Wookie]

22*33.5 - (2*(19*7))= 471

[Lucas English]

So talking with the guys they think trying to fit the oil squirts with the 1400hp Marco spec R&R rods might be hard. TJ who builds my motors think the rods might run quite a bit hotter then the oil.

The other thing I was thinking if i try and run the oil to cool it might not get hot enough to evaporate the moisture out of the oil.

What do you guys think the min temp I would ever try to run the oil?

This car also runs on E98 with EGTS around 1300deg. If I run the the thing little extra rich I might be able to get cruse EGTS in the 1200deg range. How do you think this will affect my rod temp?

Hope I am not annoying you guys to bad.

Kevin can you build me a cust rod temp gauge :) Blue tooth would be preferred. ;)

[Paul Nelson]

So the answer is if you can keep the oil cool enough the rods would be badass???

[Kiggly]

Well, the numbers on this aren't as straight forward as I was hoping they might be. I really expected the rod to have less cross-sectional area.

Assuming a ~125g wristpin and average ring pack weight you've got almost 8500lbs of tug in that rod slinging those masses at 10k. That 8500lb force over 0.85in2 makes 10,000psi stress (8500/0.85), plus stress risers for any transitions that we won't truly know without some FEA work. Wild guess lets give that a 50% increase factor and say 15ksi tensile stress.

Wild guess at cylinder pressure (since I don't have data - yet) would say about 3000psi. 3000psi is about 27,000lbs compression force on the rod, maybe plus a little bit. With the same +50% factor, call it about 45ksi compressive stress.

Stress ratio is the -15/45 = -0.333 with max stress at 45ksi. Pick that off the DOD fatigue chart (MILHBK5H) and we've got somewhere around 1-million cycles, or almost 2hrs run time. Take out my +50% wild guess on stress concentrations and it will go 100-million cycles, or about 200hrs. Add in material degradation to heat and you've got a way different answer on the low-life side.

Sorry, I now realize that exercise wasn't much help if any at all. I guess it says its not a lost cause to try running them, but don't be too surprised if they spit themselves out.

For rod temp, how about some of that welding temperature marker stuff? Don't they have different temp marking sticks that melt away when it exceeds that temp?

Kevin

[JakeLehmkuhl]

Is the whole purpose for light weight or light and inexpensive?

[Aaron@English]

Light and inexpensive is the word I think. If we had the budget some Ti like yours would be good. The other thing is that they dont hurt bearings at high horsepower and extended mileage at said power levels.

[JakeLehmkuhl]

I can't really speak to extended mileage with the Ti rods because I really don't have an excessive amount of time on them, but I can say after beating on them at the track (and on the street a little) the bearings looked good. This year we switched our pistons from Ross to Mahle, and dropped over 100g's worth of weight. We'll continue to wrap it up to 9k until it spits another main stud out. The hardest thing with Ti is knowing that your tuning has to be absolutely perfect. They don't take stress well.