[QUOTE=vader1,Dec 1 2009, 11:34 AM] Just a random thought, if they can make plastics that are strong, impact resistant, can stand temp extremes, and can save lots of weight, the most logical use it seems to me would be one piece pickup truck beds.

 

right, but the gentlemen has spent the past 40 years trying to design a plastic engine that doesnt melt instead of designing a more efficient engine that doesnt lose all of its power to the laws of thermodynamics.

 

My point is that an engine can only be so efficient. It WILL produce heat, and will never be 100% efficient. You said it, they're laws.

 

Laws are meant to be broken, dammit!

 

I wouldn't even care about the average engine not lasting more than 100K miles, if it cost $599 to replace 90% of the motor...plastic should make it MUCH cheaper to produce.

 

That brings up a good point.

If a steel engine can last 200k miles but costs 4k brand new and a plastic motor lasts 100k but only costs 1.5k, I'll take the plastic any day.

 

That's a simplistic approach to the cost of the engine. The majority of the cost in an engine is not material, it's machining, assembly, and setup time. You have high-precision parts that require very exact machining. You can't do it quickly. The plastic might save $300 or $400 in material but it wouldn't save you much (if anything) in machining because nothing critical is going to be plastic. You'll still have a high-precision crankshaft, valvetrain, pistons, cylinder bores/sleeves, valve cover, etc, etc...

 

Install cost/labor cost? You'll spend $1.5K on the motor but another $1K or more to install it (more, at a dealership). Now you're at half the mileage for half the price, which isn't exactly a deal any more.

 

I don't think plastic will save much of anything in material costs. Plastic prices are all over the map depending on the type of resin. Basic polycarbonate (PC) is ~$1.30/lb. That puts the price around the same as aluminum per lb. The aluminum alloys actually used in the engines are almost certainly more expensive than the commodity cost of aluminum by a fair margin. However, a fancy engineered resin can easily be $4-5/lb. So per lb we aren't really saving vs alloy. PC is about half the density of aluminum so that does save some cost via weight savings. That would assume that the plastic block is the same volume as the alloy block and that the engineered plastic is about as dense as PC.

The big savings in plastic could come from post processing. Cast surfaces are rough and often require post processing. Plastic parts can often be used as is. A cast alloy intake manifold will have a rough surface finish unless you take the time to polish the whole thing. An ugly plastic part will have near perfect interior surfaces. Snaps and other attachment features can be molded in rather than machined, drilled and tapped after the fact.

There is some potential for cost savings but initially I wouldn't count on it. The weight savings alone seems very compelling. However, I can also see the car companies being very cautious about this sort of thing. Sometimes people accuse them of dragging their feet with respect to promising technology. Well GM was one of the first on the block with aluminum cylinder walls (vs iron liners in an alloy block). That alloy engine did not help the Vega's reputation. A decade later BMW made the same mistake with their V8s.

Given the high cost of recalls and what not I can understand a company not wanting to jump too far. If the idea works your brilliant and forward thinking. If the idea has some sort of failure that only shows up after 5 years you get slammed by the media and any more some class action lawyer is going to try to force you to replace engines that are clearly outside of warranty. The potential to lose is really big.

 

after doing a quick google search, I came up with a combustion engine being only 26% efficient by the time the power gets to the wheels. an electric motor for reference is 90% efficient. call me crazy, but rather than wasting my time trying to put a band-aid on something that doesnt work too well, I would rather invest my time trying to make it more efficient withOUT braking any thermodynamic laws. as in, creating something totally new, instead of replacing parts with the same fundamental formula. a great example of this would be direct injection. you now see cars with 300hp that get 30mpg naturally aspirated, which ten years ago was very hard and/or expensive to do.