Carbon Fiber Hood/Trunk

[Levi]

Ok. Thanks. I wish to know how much lighter the CF hood of the BRZ STI is, compared to the aluminuim hood of the BRZ.


PS: Isn't CF an abrev. for CFRP?

[bambbrose]

Originally Posted by Levi

Ok. Thanks. I wish to know how much lighter the CF hood of the BRZ STI is, compared to the aluminuim hood of the BRZ.

I'm sure we all want to know that, but at the end of the day, the aluminum hood will probably weigh 8 to 12 lbs, and the carbon hood maybe a few lbs lighter. Its just bragging rights, not really function IMO.

The carbon roof has more merit, if the steel roof structure can be reduced from the use of carbon. It also has chassis rigidity merits, as carbon has very high compression strength.

[JDLM]

Originally Posted by Levi

Ok. Thanks. I wish to know how much lighter the CF hood of the BRZ STI is, compared to the aluminuim hood of the BRZ.


PS: Isn't CF an abrev. for CFRP?

Carbon Fiber vs Carbon Fiber reinforced polymer/plastic (I have seen both) (http://en.wikipedia.org/wiki/Carbon_%28fiber%29) Wiki link

Carbon fibers are usually combined with other materials to form a composite. When combined with a plastic resin and wound or molded it forms carbon fiber reinforced plastic (often referred to also as carbon fiber) which is a very high strength-to-weight, extremely rigid, although somewhat brittle material. However, carbon fibers are also composed with other materials, such as with graphite to form carbon-carbon composites, which have a very high heat tolerance.

[Itgb]

Here is an example of weight savings through CFRP. The BMW M3 CRT used CFRP for it's hood and stated a 75% reduction in weight vs. steel. Aluminum is about 50% lighter than steel, so CFRP is a further 50% reduction from aluminum.

Rough Example:
Steel Hood: 40lb
Aluminum Hood: 20lb
CFRP Hood: 10lb

Here's a cross section of the CFRP hood

[Dave-ROR]

Originally Posted by Itgb

Here is an example of weight savings through CFRP. The BMW M3 CRT used CFRP for it's hood and stated a 75% reduction in weight vs. steel. Aluminum is about 50% lighter than steel, so CFRP is a further 50% reduction from aluminum.

Rough Example:
Steel Hood: 40lb
Aluminum Hood: 20lb
CFRP Hood: 10lb

Here's a cross section of the CFRP hood

Aluminum is about 1/3rd the weight of steel btw. If you use a structure under the CF (of whatever variant) the CF will be heavier.

[Itgb]

Originally Posted by Dave-ROR

Aluminum is about 1/3rd the weight of steel btw. If you use a structure under the CF (of whatever variant) the CF will be heavier.

Such a general statement about weight difference is not valid for this purpose. A hood(and any part for that matter) is designed specifically for the material. Metal thickness, load points, structure, etc. are all taken into account when the part is designed. If you were to switch a hood from steel to aluminum, you don't just switch the material and call it a day. The whole part is redesigned.

Here is an example of a cost analysis between steel and aluminum. They say there is about a 40% difference in weight(sorry I was off a little) after all the inner structure is trimmed away.

The purpose of CFRP is that the structure is built-in. There is no externally added structure as many times happens with CF.

[stott]

it's a bit disingenuous to say that 'aluminum is 50% the weight of steel' or 'aluminum is 1/3 the weight of steel' when referring to car parts, since this does not imply that an aluminum hood will actually weigh half as much as a steel hood.

as an example of what i mean, look at a copper radiator vs. an aluminum radiator. copper is significantly heavier, and also more expensive than aluminum. but you can make an efficient copper radiator using less copper than you'd have to use of aluminum for similar heat dissipation results. copper is more than 3 times heavier than aluminum, and about that much more expensive too, yet an aluminum radiator doesn't really weigh 1/3 of what a copper radiator weighs. at best, it might weigh half, but typically closer to 60%

[Levi]

Saying CF is heavier than ALU is like saying an 18" rim is lighter than a 17" rim.

It depends on construction not material, and when you make a part of CF instead of METAL, it is in the aim of being lighter, not to look good. If this thread is about CF look, then I am off-topic, and this is a ricers thread.

[old greg]

Originally Posted by Levi

It depends on construction not material.

Exactly. What previous posters have been saying is that the vast majority of "carbon fiber" hoods/trunks etc. are made cheaply with a layer of carbon over fiberglass and are usually laid up wet (excessive resin = a heavy part). These parts are much heavier than they could be if done properly but are still lighter than their steel counterparts. It's this cut-price "carbon" that is heavier than an aluminum panel. Properly made cfrp parts are indeed lighter than the aluminum equivalents, but they come with such a high price tag that they are the exception rather than the rule.

[Dimman]

^ Fiberglass hoods with CF appearance layer...

[DommerEOD]

If you really want to save weight, do it the red neck way.... take the effing hood and decklid off!

[Dave-ROR]

Originally Posted by Itgb

Such a general statement about weight difference is not valid for this purpose. A hood(and any part for that matter) is designed specifically for the material. Metal thickness, load points, structure, etc. are all taken into account when the part is designed. If you were to switch a hood from steel to aluminum, you don't just switch the material and call it a day. The whole part is redesigned.

Here is an example of a cost analysis between steel and aluminum. They say there is about a 40% difference in weight(sorry I was off a little) after all the inner structure is trimmed away.

The purpose of CFRP is that the structure is built-in. There is no externally added structure as many times happens with CF.

My statement was actual fact. It really is about 1/3rd the weight difference of steel. Your statement is just as variable when it comes to part contruction as mine, both are useless statements there.

I have yet to see any reasonable priced CF hood be 50% lighter than an OEM aluminum piece.

[Dave-ROR]

Originally Posted by old greg

Exactly. What previous posters have been saying is that the vast majority of "carbon fiber" hoods/trunks etc. are made cheaply with a layer of carbon over fiberglass and are usually laid up wet (excessive resin = a heavy part). These parts are much heavier than they could be if done properly but are still lighter than their steel counterparts. It's this cut-price "carbon" that is heavier than an aluminum panel. Properly made cfrp parts are indeed lighter than the aluminum equivalents, but they come with such a high price tag that they are the exception rather than the rule.

[bambbrose]

Originally Posted by Dave-ROR

My statement was actual fact. It really is about 1/3rd the weight difference of steel. Your statement is just as variable when it comes to part contruction as mine, both are useless statements there.

I have yet to see any reasonable priced CF hood be 50% lighter than an OEM aluminum piece.

Correct. Hypothetically the carbon fiber can never be more than 37% lighter than aluminum, let alone 50%.

All construction methods aside, just looking at density.

A 20 lb steel hood, if made entirely of aluminum, would weigh 6.8 lbs.

The equivalent hood in CFRP would weigh 4.32 pounds.


Which leads me back to my very first argument. Why spend $1000 + to save a couple pounds?