Best Conrod Materials? 11

[jp83]

Hello, I'm new to this site. I hope someone may be able to help me.

I'm designing conrods for an 320hp, 4 cylinder, 2.0 litre engine. I'm basically looking for a material to use. Money is no real object, I just dont really have a direction to go with in the investigation. I have been told that EN24V steel alloy could be good, but I really want the lightest possible material that can get. I thought about titanium alloys?

If anyone has any suggestions for me, they would be much appreciated.

Thanks

 

[Tmoose]

I'd buy Carillo rods, and spend my money on cylinder head work, etc

 

[patprimmer]

Titanium rods will give the best strength to weight if cost is no problem.

I believe that Crower offer titanium rods.

Carillo are excellent rods for normally aspirated and moderate boost engines, but are not recommended for high boost, as "H" beams buckle more easily in compression than do "I" beams.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[TVP]

Two things to keep in mind when designing Ti con rods are stiffness and surface engineering. Ti only has ~ 1/2 the elastic modulus of steel, so deflection of the crank end has to be considered. One estimate is that the reduction in mass from a well-optimized steel design to one in Ti is only 12-20%. The most popular alloy is Ti-6Al-4V. Go to Matweb or alloy producers like Timet or RMI for more information on properties. Search this site as well.

Regarding surface engineering, Ti has a tendency for fretting and galling, due to its low inherent wear resistance. High end con rods that use titanium are coated, some times with flame-sprayed Mo in order to improve its surface characteristics. Other coatings are possible.

 

[MNRaptor]

I am having Titanium connecting rods machined as well. The above post from TVP has me wondering what coatings would be optimum.

The machinist is top notch so I know the quality will be perfect. The engine in question is a destroked, over square DOCH V6 with a rod ratio of 2.14 I wan't it to handle a lot of RPM and power. It will be running twin turbo's with boost levels above 35 psi. The car is being built specifically for quarter mile use. I am looking for over 1000HP in this setup.

Any info on the coatings or other considerations for the connecting rods would be appreciated.

 

[NickE]

"I am having Titanium connecting rods machined as well."

be sure to have the surface cleaned and bead or shot blasting might not be a very bad idea. Machining tends to cause large amounts of surface defects that can lead to failure.

 

[MNRaptor]

Is polishing ti a benefit at all for a rod?

 

[NickE]

Polishing will always help fatigue life. Although you have to be sure that you are not rolling material over small cracks or notches.

 

[MNRaptor]

Thanks, that is a good thing to watch for I may not have considered. Any thoughts on a coating combined with the polishing, or is that a bad idea. I am still also curious if anyone can say what coating would be optimum.

 

[TVP]

Polishing after shot blasting/peening can be helpful in reducing surface roughness, which minimizes local stress concentration during use, while maintaining the beneficial residual compressive stress. Regarding coatings for titanium, this is definitely a specialized area, and there are only a few vendors that can properly apply them. I would start with Bodycote Thermal Processing in Santa Ana, CA or a company that specializes in thermal spray like Sulzer Metco.

 

[MNRaptor]

Thanks TVP, that is very helpful. Probably the last question I have on this is the use of a floating Titanium pin, they are coated as well, I am guessing the correct way to do this would be with a bronze bushing or maybe some better material. I have read on here about using silicon bronze and Trojan as well as Beryllium bronze for valve guides and seats, would one of thos e materials also be better for a pin bushing?

 

[carnage1]

as far as coating goes what about having them anodised? It helps a lot with surface wear. I don't know how much friction polished anodised Ti would have but it should wear much beter than plain Ti. (and it's such a nifty looking purple)

 

[ZoRG]

The forged ones are 4340 chrome moly, Titanium can be good, a tip if you are having your machined could be to use a titanium top with a steel bottom, then make the bottom .25mm wider on each side.

As for Carillo, they make I-beams. Cunningham also makes some of the best rods around, and also do titanium, you should give them a try. The russian company I bought my valves from might offer some Ti rods in a month or two, ill keep you guys updated if you are interrested, so far they are talking of around $200-$250 per rod, but they use their own titanium, which have improved properties over the commonly used 6Al-4V, also do excellent coatings.

 

[ZoRG]

http://www.cunninghamrods.com

Had a quick look, the Russian Ti has a elastic modulus of around 139-142 vs +-114 for all other grades available, this could mean a considerably lighter rod than previously possible.

 

[WilliamH]

ZoRG,

You stated that you bought valves (titanium) from a Russian supplier. Did you take delivery before the Bush administration imposed the tariff on Russian titanium products? I believe this tariff went into effect in early November 2004.

If you could elaborate on this I would be thankful. We are looking for a new supplier of titanium parts. The US companies are overpricing the material without justification as compared to the world wide abundance of titanium currently.

Will

 

[GaryFB]

Does anyone have "facts" on titanium's ability to cycle? I think everyone knows that aluminum connecting rods are used for short term applications and then the aluminum con rod is discarded. How many different titanium alloys are available? How many different heat treatment processes must be done to the titanium to bring the material to its highest strength? I believe the best titanium alloy only has a tensile strength of 170,000 psi, while 4340 300-M alloy steel has a tensile strength is excess of 240,000 psi. That means to me, that if I use titanium, to get the strength of steel,dimensionally my rod has to be bigger and possibly heavy.
Also, even tightening the connecting rod bolts can be difficult because they will want to gall to the titanium. I have seen the plasma moly spray come off and I have seen microwelding on titanium rods. I believe the F1 engines use DLC coatings to prevent galling.
Carrillo has a Gen IV steel that is light as titanium, yet has the charateristics of steel, according to "Race Engine Technology" magazine editor Ian Bamsey, issue 008 dated June 2005.
Porsche used thrust type bearings on their titanium connecting rods, this way there was never a chance of microwelding or galling. I believe Pankl made the connecting rods for Porsche.
Then there is another issue of grain structure. Are the titanium rods going to be forged, or cut from billet? Obviously, forging titanium is going to be even more expensive, but that is how to get the maximum strength.
I think too many people think titanium is just one alloy, and they are not familiar with the many different alloys and heat treatment processes involved to obtain the strength. Having a rod made of titanium is no guarantee you have a strong and reliable connecting rod.
How do you test titanium for cracks and fatigue, you can not use MagnaFlux testing.
Aerospace landing gear is all made of 300M steel, and they could use titanium if they wanted. Why is titanium not used in this most demanding application?
I know Porsche has had suspension springs made of titanium and even drive axles made of titanium, but I know of no one making a crankshaft of titanium. I suspect titanium has some unique but limited qualitiies.
How about some knowledgable engineers commenting on this very important subject?

 

[Metalguy]

So many questions!

Aircraft are built with a very keen eye on cost/weight ratios. It's cheaper to use 300M than a Ti alloy for such large parts as landing gear. But a good Ti alloy gear would be lighter for the same strength, but somewhat larger.

You need to keep in mind that the strong Ti alloys are ~75% of the strength as high strength steel, but only half the weight.

 

[GaryFB]

Hi Metalguy; thanks for your response.
I would love to have answers, that is why I am in this forum.
I believe that 300M is used because it is much less notch sensitive. I think titanium is very sensitive to scratches, which would result in cracks and then failure. Also, 300M can be easily inspected for cracks using MagnaFlux process.
If titanium is 75% the strength and 50% the weight, then for equal strength the titanium part is only 33% lighter. Are all other properties of titanium equal to high strength steel?

 

[mloew]

Stiffness (elastic modulus) is less with Ti.

Best regards,

Matthew Ian Loew


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[GaryFB]

Hi mloew; would you mind explaining more on the subject? I get the impression you know more about titanium. If the tensile strength is less then high strength steel and the stiffness is less then high strength steel, then a connecting rod in titanium would have to be dimensionally more robust to be equal with high strength steel. If the titanium connecting rod was dimensionally the same as the steel counter part it would not have the tensile strength or the compressive strength, is that correct? Thanks.