86 951 forged bottom end
 

I was wondering if some materials engineers could shed some light on this issue for me. What are the differences between the forged bottom end of the 86s and the cast (I think) bottom end of the later cars? Why did they switch, and which is better?

Justin

forgeing is a process to strengthen a metal. the 86 is a stronger crankshaft, but it was more expensive to produce for an engine that didnt even come close to stressing what a cast crank can hold.

Cranks are the same, the only diffrence in the bottom end is the connecting rods. '86 cars got forged rods, others were cast.

The forging process is pressing a block of metal with high pressure and heat to produce the desired shape. This is very hard on tools, and takes a good amount of energy to accomplish.

Casting is where the molten metal is poured into a mold and the part is cast. The metal structure is not as tight, and the possibility of defects are much higher.

my bad, thought it was the crank too.

Nope.. they are the same. Learn something new every day on here. Love it!

<img src="graemlins/wave.gif" border="0" alt="[byebye]" />

How hot is the metal in the forging process?

VERY HOT! ~2600 degrees according to a couple of sources I checked out.

I thought the rods on the later cars were sintered not cast.

[quote]Originally posted by guardsred951S:
<strong>VERY HOT! ~2600 degrees according to a couple of sources I checked out.</strong><hr></blockquote>

Maybe 2600 for aluminum, but iron/steel is probably more like 3200-3500 (this is for casting, I'm sure the pressure involved in forging ups the HEAT significantly) And more like 4500 if they are using a Mg alloy

Forge Temps in F:

Mg alloys 750-400
Al alloys 900-750
Monel alloys 2100-1850
Inconel alloys 2300-1580
Stainless alloys 2200-1900
Carbon Steels 2400 for 0.10% C
1900 for 1.5% C

In a forging process the the density is greater and the structure is more uniform. Impact and fatigue strength are much higher in the longitudinal direction, the long dimension of a rod.

And none of it means squat if it's put together wrong <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

Alan

[quote]Originally posted by Alan C.:
<strong>Forge Temps in F:

Mg alloys 750-400
Al alloys 900-750
Monel alloys 2100-1850
Inconel alloys 2300-1580
Stainless alloys 2200-1900
Carbon Steels 2400 for 0.10% C
1900 for 1.5% C

In a forging process the the density is greater and the structure is more uniform. Impact and fatigue strength are much higher in the longitudinal direction, the long dimension of a rod.

And none of it means squat if it's put together wrong <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

Alan</strong><hr></blockquote>


are you sure? stainless steel doesn't even melt until 2900 F. how could the temperature be less after you apply a HUGE amount of force. And Mg burns (melts and vaporizes) at 4500 F.

<img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" /> ( just thinking about the heat,..I would kill for a glass of Guiness right now )

I have physically taken the Pyrometer readings myself out of the laddles......

You don't melt the metal when it is forged. That would defeat the purpose of compressing the metal. You want the grain structure to be as tight as possible, when melted, it expands and allows air to fill in the gaps.

By the by, Alan works for a steel company.. pretty sure he has the numbers down pat since that is what he does.

So are any of the rods sintered? Is there any weakness of sintered rods compared to forged rods?

[quote]Originally posted by Perry 951:
<strong>You don't melt the metal when it is forged. </strong><hr></blockquote>
that makes sense. Thank you

For a sintered rod you's start with a powdered metal. Less dense and apply force in a hydrogen atmosphere. The temperature is near the molten state. At temperatue the atoms begin to diffuse. Thus you end up with a very dense product but not as dense as forging but better than cast.

You can bump it up a level by taking the powder metal preform and heating it to intiate sintering. The hot preform could then be put in a metal die and pressed to the final shape. This makes a very strong part and uses nearly 100% of the metal. Pretty close to a forged part. I think this is what they are using in the 996/986 rods.

Alan