Titanium Rods/ aftermarket pistons
01-19-2003, 04:03 AM
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Titanium Rods/ aftermarket pistons
What do you guys think of Titanium Rods in a turbo motor, and where could I possably get some? Any idea on cost? And while were at it, lets talk about pistons too. They would obviosly have to be custom, but what are my options other than JE? Pauter for rods maby?
01-19-2003, 11:57 AM
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Why titanium? Are you busting rods regularly?
I was looking at getting some upgraded rods/pistons on my 931 a while back. I opted instead of titanium ($), for lightening, static balancing (which you can do yourself) and shotpeening the rods. And I replaced the pistons with an upgraded MAHLE piston, and then thermal coated the crowns and coated the skirts with a teflon. Then, of course, had a shop dynamically balance the system again.
I'm probably echoing stuff you already know here, but I'll regurgitate it anyway. Basically, I can't immediately see the benefits of titanium or Carillo rods on these cars, especially when there are other useful, expensive, high priority things to do. Lots of 944 Turbos run some incredible speeds without titanium and when they blow, they don't seem to be necessarily busting rods (although I guess it happens). I'd ask "Are rods and pistons really the weak spot on your cars?"
On turbocharged cars, or even ones equipped with nitrous, I think it's prudent to go with a plan that covers off more than just these two parts (pistons and rods), or something like this:
</font>
I was looking at getting some upgraded rods/pistons on my 931 a while back. I opted instead of titanium ($), for lightening, static balancing (which you can do yourself) and shotpeening the rods. And I replaced the pistons with an upgraded MAHLE piston, and then thermal coated the crowns and coated the skirts with a teflon. Then, of course, had a shop dynamically balance the system again.
I'm probably echoing stuff you already know here, but I'll regurgitate it anyway. Basically, I can't immediately see the benefits of titanium or Carillo rods on these cars, especially when there are other useful, expensive, high priority things to do. Lots of 944 Turbos run some incredible speeds without titanium and when they blow, they don't seem to be necessarily busting rods (although I guess it happens). I'd ask "Are rods and pistons really the weak spot on your cars?"
On turbocharged cars, or even ones equipped with nitrous, I think it's prudent to go with a plan that covers off more than just these two parts (pistons and rods), or something like this:
</font>
- <font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Resize the rods, reduce weight and flashings, static balanced and shotpeened.</font></li>
- <font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Select the highest quality bearings you can find - I read a lot about spun bearings here (the dreaded #2). Consider methods to forestall spinning bearings.</font></li>
- <font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">New rod bolts and nuts, and go one size up if it's possible - check the Rockwell "C" rating of your stock bolts and nuts, and then select the hardness that suits you - just don't go too brittle.</font></li>
- <font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The bolt-nut seating areas on your rods can be made parallel to each other, and squared to the bolt holes, then polished slightly to reduce the chances of a crack forming on a sharp edge.</font></li>
01-19-2003, 03:26 PM
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Stock rods in a really strong 944 become the weak point- it is very cheap insurance to buy pauter or Carillo Rods at about 1000.00 a set, as if it breaks it generally takes out the rest of your motor along with it. Not worth it. Shotpeening and polishing stock rods is a worthwhile idea on say- a steet car that is nearly stock, but if you modify pistons, cams, boost, etc, work the crank and buy the rods.
The 924 bottom end is pretty strong, not needing major attention(other than lightening the truck crank it comes with) until you hit the 200hp mark, at which point it is a 50/50 chance everything will hold together. Part of the issue is that a 4cyl engine isnt an optimum design, and is pretty much trying to tear itself apart all the time. we get away with alot because they are after all Porsches, but you cant get around physics, and the simple fact is stock rods will break, and very dramatically.
The 924 bottom end is pretty strong, not needing major attention(other than lightening the truck crank it comes with) until you hit the 200hp mark, at which point it is a 50/50 chance everything will hold together. Part of the issue is that a 4cyl engine isnt an optimum design, and is pretty much trying to tear itself apart all the time. we get away with alot because they are after all Porsches, but you cant get around physics, and the simple fact is stock rods will break, and very dramatically.
01-19-2003, 04:44 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by fusionsport:
<strong>we get away with alot because they are after all Porsches, but you cant get around physics, and the simple fact is stock rods will break, and very dramatically.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">I have a slightly different take on the physics at work...inertial loads on a connecting rod far exceed the load it experiences when hit by the combustion front when the engine fires. The vast majority of 951 engine failures have two causes: oiling problems [evident from scoring/wear on the rod bearings] and from a lean condition. When the engine begins detonating the heat and pressure are so great that the connecting rods, head, head gasket, pistons, etc are all subject to failure. Stronger connecting rods aren't the weak point of these cars...half-assed tuning and oiling problems are.
You could benefit from titanium connecting rods if you plan to rev the engine significantly higher than stock. I'm sure you're aware of the changes that will be required in the cylinder head if you go this route [as it's been covered extensively in other threads].
Using titanium connecting rods and lighter pistons will reduce inertial loads on the rods themselves but huge displacement cylinders aren't ideal for high revving, especially the 3 liters...afterall, mass and inertia are one in the same. Massive piston and rod assemblies will cause catastrophic failure at high revs because connecting rods simply don't have the strength to withstand the forces. An interesting fact from Maximum Boost by Corky Bell: inertial loads on a connecting rod assembly at 6000 RPM are HALF of those experienced at 7200 RPM. <img border="0" title="" alt="[Eek!]" src="eek.gif" />
<strong>we get away with alot because they are after all Porsches, but you cant get around physics, and the simple fact is stock rods will break, and very dramatically.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">I have a slightly different take on the physics at work...inertial loads on a connecting rod far exceed the load it experiences when hit by the combustion front when the engine fires. The vast majority of 951 engine failures have two causes: oiling problems [evident from scoring/wear on the rod bearings] and from a lean condition. When the engine begins detonating the heat and pressure are so great that the connecting rods, head, head gasket, pistons, etc are all subject to failure. Stronger connecting rods aren't the weak point of these cars...half-assed tuning and oiling problems are.
You could benefit from titanium connecting rods if you plan to rev the engine significantly higher than stock. I'm sure you're aware of the changes that will be required in the cylinder head if you go this route [as it's been covered extensively in other threads].
Using titanium connecting rods and lighter pistons will reduce inertial loads on the rods themselves but huge displacement cylinders aren't ideal for high revving, especially the 3 liters...afterall, mass and inertia are one in the same. Massive piston and rod assemblies will cause catastrophic failure at high revs because connecting rods simply don't have the strength to withstand the forces. An interesting fact from Maximum Boost by Corky Bell: inertial loads on a connecting rod assembly at 6000 RPM are HALF of those experienced at 7200 RPM. <img border="0" title="" alt="[Eek!]" src="eek.gif" />
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01-19-2003, 10:23 PM
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Yes, the troll hunter is right on. The inertia of the massive pistons & rods spinning around is what ultimately breaks them. Even the force of a 400rwhp 4-cylinder is small compared to the inertial forces of those pistons & rods spinning around at 8000rpm.
On the geometric design of the rods, I-beam rods have a more optimized shape to combat compression forces while H-bean have an advantage in tension.
There are a lot of Ti rods available and you have to be careful of their construction and composition. Commercially pure Ti is cheap and worthless. It has less strength-to-weight ratio than a chromoly rod. A 3al/2.5va alloy is about twice as strong as chromoly for the same weight. And 6al/4va is about 4x stronger than chromoly for the same weight. Good compromize would be a 6/4-Ti rod that's 1/2 the weight of the stock ones for double the strength.
These typically don't come set up to use bushings on the small end, although you can specify that if you want. Match that with a tapered Ti wrist-pin and you just saved 400-800grams.
I can get you a set of 6/4 Ti rods for a 951 for about $595/each.
On the geometric design of the rods, I-beam rods have a more optimized shape to combat compression forces while H-bean have an advantage in tension.
There are a lot of Ti rods available and you have to be careful of their construction and composition. Commercially pure Ti is cheap and worthless. It has less strength-to-weight ratio than a chromoly rod. A 3al/2.5va alloy is about twice as strong as chromoly for the same weight. And 6al/4va is about 4x stronger than chromoly for the same weight. Good compromize would be a 6/4-Ti rod that's 1/2 the weight of the stock ones for double the strength.
These typically don't come set up to use bushings on the small end, although you can specify that if you want. Match that with a tapered Ti wrist-pin and you just saved 400-800grams.
I can get you a set of 6/4 Ti rods for a 951 for about $595/each.
01-19-2003, 10:49 PM
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"The 924 bottom end is pretty strong, not needing major attention(other than lightening the truck crank it comes with) until you hit the 200hp mark, at which point it is a 50/50 chance everything will hold together."
Hmmm. I can see how you might believe that is so, but I don't think that's true. The same bottom end held up for the 924 GT at 210 HP (GT) regularly and its variants up to GTS 245 HP! Only at 375 HP with the Porsche GTR was it necessary to replace the rods. I've taken a 924 up beyond redline to 7000 RPM after a little head work and the motor was fine.
I think it's a more rare happening to see a rod break on upstroke from structural weakness, unless, as has been said, you're exceeding redline by some whopping margin. It's more likely that you have seen broken rods that broke for other reasons.
I don't mean to be fussy, but I think titanium rods might be over the top for your needs. Are you doing a rebuild for certain?
PS: That's a really nice looking car by the way...
Hmmm. I can see how you might believe that is so, but I don't think that's true. The same bottom end held up for the 924 GT at 210 HP (GT) regularly and its variants up to GTS 245 HP! Only at 375 HP with the Porsche GTR was it necessary to replace the rods. I've taken a 924 up beyond redline to 7000 RPM after a little head work and the motor was fine.
I think it's a more rare happening to see a rod break on upstroke from structural weakness, unless, as has been said, you're exceeding redline by some whopping margin. It's more likely that you have seen broken rods that broke for other reasons.
I don't mean to be fussy, but I think titanium rods might be over the top for your needs. Are you doing a rebuild for certain?
PS: That's a really nice looking car by the way...
01-19-2003, 11:35 PM
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I PLAN on having 550HP to the wheels, and revving to 7100RPM. Yes this is a 3L too. Will Carillo make ti rods? I just want to eliminate all possable weak points in the next engine, not that I think I will break a rod. Plus Reving faster is Allways good too! I would also like pistons that will be significantly lighter too. I already have a cylinder head that I think is up to the task too.
01-20-2003, 02:09 AM
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Danno, when you talk in terms of I beam vs H beam is this in reference to the pauter vs the carillo? Is there really a difference because I have never heard of either one ever going bad so is it safe to say its a matter of preference between the pauter and carillo?
01-20-2003, 02:25 AM
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Yes the Carillos use an H-beam design and Pauter uses an I-beam design. I believe they are both Chromoly, and they're both forged, but the Pauter rods are significantly lighter than the Carillos. I've heard great things about both.
01-20-2003, 02:36 AM
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The main failure I have seen in Porsche rods are from the rod bolts, not the rod itself. However when I have seen a Porsche rod fail it has been dramatic, and I have seen them fail due mainly due to the above mentioned lean/overrev conditions. I do not believe in taking the chance though with the OE rod, as it is a very small expense to put in good quality aftermarket rods.
The stock 924 has a good solid bottom end, and you are correct that they used the rods in the 210 hp GTS, but those were "stock rods" in the same way a RSR had stock rods- they are specially selected and machined. Also when they tried to turn the engine at high(over 7k) rpm the bottom end went. I raced a 924 in GT-3 and managed to produce 225hp in a 20-hour race motor with the stock crank, Pauter rods, JE pistons, and a lot of raceware/aerospace fasteners. Those motors turned about 8500, and I never lost a rod, but they were rebuilt after only 20 hours, any longer and bad things happened. I did get really good at 924 head gaskets for awhile.
For 550 atw in a 944 turbo I strongly suggest Pauter or Carillo rods- Do try and keep in mind though that even the 935s rarely revved above 7k, whereas the RSRs would rev to 8 or 9k. The turbo motors do not have to rev as high to make power, which eases the strain on a lot of components like valve springs, rods, etc
The stock 924 has a good solid bottom end, and you are correct that they used the rods in the 210 hp GTS, but those were "stock rods" in the same way a RSR had stock rods- they are specially selected and machined. Also when they tried to turn the engine at high(over 7k) rpm the bottom end went. I raced a 924 in GT-3 and managed to produce 225hp in a 20-hour race motor with the stock crank, Pauter rods, JE pistons, and a lot of raceware/aerospace fasteners. Those motors turned about 8500, and I never lost a rod, but they were rebuilt after only 20 hours, any longer and bad things happened. I did get really good at 924 head gaskets for awhile.
For 550 atw in a 944 turbo I strongly suggest Pauter or Carillo rods- Do try and keep in mind though that even the 935s rarely revved above 7k, whereas the RSRs would rev to 8 or 9k. The turbo motors do not have to rev as high to make power, which eases the strain on a lot of components like valve springs, rods, etc
01-20-2003, 04:39 AM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by fusionsport:
<strong>Do try and keep in mind though that even the 935s rarely revved above 7k, whereas the RSRs would rev to 8 or 9k. The turbo motors do not have to rev as high to make power, which eases the strain on a lot of components like valve springs, rods, etc</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Good point, also I will be using racewear studs all around. So what about pistons? There has to be other places than JE.
Oh, BigPorscheGuy39 I missed the nice comment the 1st time around, THANKS! That is actually my old car in my avatar, the new one is a 968.
Danno, "Good compromize would be a 6/4-Ti rod that's 1/2 the weight of the stock ones for double the strength.
These typically don't come set up to use bushings on the small end, although you can specify that if you want. Match that with a tapered Ti wrist-pin and you just saved 400-800grams.
I can get you a set of 6/4 Ti rods for a 951 for about $595/each."
Tell me more!!!!
<strong>Do try and keep in mind though that even the 935s rarely revved above 7k, whereas the RSRs would rev to 8 or 9k. The turbo motors do not have to rev as high to make power, which eases the strain on a lot of components like valve springs, rods, etc</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Good point, also I will be using racewear studs all around. So what about pistons? There has to be other places than JE.
Oh, BigPorscheGuy39 I missed the nice comment the 1st time around, THANKS! That is actually my old car in my avatar, the new one is a 968.
Danno, "Good compromize would be a 6/4-Ti rod that's 1/2 the weight of the stock ones for double the strength.
These typically don't come set up to use bushings on the small end, although you can specify that if you want. Match that with a tapered Ti wrist-pin and you just saved 400-800grams.
I can get you a set of 6/4 Ti rods for a 951 for about $595/each."
Tell me more!!!!