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Discussion Starter · #1 ·
Giving up on finding an affordable lighweight hood (bonnet).
The next best thing looks to be taking (some of) the internal reïnforcing structure out.
Has anyone done that and weighed the gain?

Thanks.

p.s. yes I know, crumple zones and all... I already have an all original second one for periodic inspection.
 

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Please do weigh before and after (before because we wont know the accuracy of your scale). I am very curious since the hood is steel and quite heavy compared to other cars. My Volvo for example had aluminum for the hood. I still put speed holes in it but it was larger than the MR2 hood and MUCH lighter.

FWIW, there is a good bit of pressure that builds up under the hood and a lot of surface area. The OE latch is pretty strong but AFAIK the latch hoop on the hood is hooked to the reinforcement. The skin is not welded to the web everywhere. In some places it is just glue. If you cut keep that in mind.
 

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I am really curious. I replaced my deer impacted hood a couple years back and I recall being amazed how light it was and found it a bit of a curiosity how much lighter a carbon hood could actually be and still retain the structural integrity necessary for our topless box. The continual question with removing structural components is if the risk of not having that protection underweighs the desire to get lighter. I am not that obsessed and would elect to increase power over increased risk.

And BTW that glue is some pretty strong stuff and I figure that the use of it does not impact the thin metal sheeting from heat like welding might.
 

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Discussion Starter · #5 · (Edited)
and would elect to increase power over increased risk.
Interesting ´reasoning´.


structural integrity necessary for our topless box
The hood does not add ány structural rigidity.
Our car body is not even a túb.
Please have a look at the threads about the TRD and DEV door spacers/stabilizers. Thóse add structural rigidity. I have both.

Fiy less weight is more áctive safety.

Also I already wrote being aware of crumple zones but thank you for sharing your opinions.



@Node, the glue connection is the reason why I will only cut the inner web out. also note that at the front there are two mechanical fittings connecting the skin to the webbing.
Remember I already vented the hood to reduce lift. As such the before will be lighter already :sneaky:



Ispy: I recall being amazed how light it was

Node: the hood is steel and quite heavy compared to other cars

Hilarious no?! All is relative to one´s personal perspective and perception.
 

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"Quite heavy", I have no personal perspective outside of having carried many hoods on many cars. American muscle car hoods are close to 100lbs. But that is not a fair comparison. Pounds per square inch surface area would be the most accurate means of judging a comparison. Regardless, since Node said that and you remarked, I was curious. So simply for reference:
2005 MR2 OEM Front: 22lbs; OEM Rear: 19lbs; Seibon Front: 16.2lbs
1965 Porsche 912 hood: 13.2lbs
1965 Porsche 914 hood: 14lbs
2007 Gen 8 Honda Civic hood:20lbs
2005 Porsche Boxter hood: 33bls
2005 Mini hood: 45lbs
2005 Mazda Miata hood: 19.5lbs

Area to weight ratios seem pretty close to me. Perspective, I guess.
The internal structure of the hood provides resistance to torsion I would think.
Force = Mass x Acceleration is a circular argument when talking structure and safety. One might say removing the hood components results in lesser mass and therefore less force. But then that same argument could be applied to bumpers. There are reasons that you may understand, that I do not about how a car handles different forces or impacts and how the hood structure is not related. But I simply dunno. I wish nothing but perfection.
 

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The hood isn't rigidly connected enough to the vehicle frame to provide much of an increase in chassis torsional strength. It can be a good place to lose some weight - the CF hood on my Supra dropped about 30lbs! The MR2 hood isn't super heavy but you can drop a bit of weight from cutting some bracing. Just be sure it won't weaken the latch or hinge attachment points, or make the hood so floppy that it will move around. Perhaps if you remove a lot of structure it would be good to add some concealed hood pins/latches like aero latch or similar. I have some on my Supra because the CF hood is more floppy even with the bracing and moves around a LOT at higher speeds at the track without the latches.
 

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Discussion Starter · #12 ·
Again thanks for the feedback.

Imo the bonnet is neither heavy nor light. The car was designed to be affordable so at the time the use of steel instead of aluminum, even partly, was a given. It coúld have been designed to weigh roughly 7 (skin alu) or 5 kg (all alu) but... at a price.
For what it is, I think it weighs what is to be expected.

It sits quite flexible in flexi hinges in flexi rubber and lay in the latch. It offers NO rigidity. Shedding even 1,5 kgs for free.... I´ll take it.

@Funkycheeze already have no less than FOUR push button hood latches in case I need those, That is unlikely though as I intend to leave the whole outer rim untouched.
Shedding 30 lbs on the hood/bonnet sure is (y)
 

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Discussion Starter · #13 · (Edited)
Force = Mass x Acceleration is a circular argument when talking structure and safety. One might say removing the hood components results in lesser mass and therefore less force. But then that same argument could be applied to bumpers. There are reasons that you may understand, that I do not about how a car handles different forces or impacts and how the hood structure is not related. But I simply dunno. I wish nothing but perfection.
For 1, the MR2 is named like that for a reason (an imo übercool pun) and the hood is rather at a large R so the effect of M reduction is relatively ´significant´.

Secondly M is linear in kinetic energy ánd the avilable friction from the tyres slightly increases as M is reduced. Hence shorter stopping.

So, there we have a car easier to change direction and stopping shorter. Ok, from 1,5 kg on a 900 kg car it is little more than negligible but however slightly, it is an increase in áctive safety.

I removed the front crash bar and lightened the rear one. Neither offers ány structural stiffnes because of how they are mounted which follows from what they are designed to do; absorb energy by deforming.

It is all about risk assessment. Risk being likelyhood times consequence. Living where I live, driving where I drive, the factor likehood is a fraction of what most here. Nóóó commuting, no need to drive in the rain, véryVERY low traffic density. I´ll take the extra consequences. It is a convertible anyway.
 

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The hood isn't rigidly connected enough to the vehicle frame to provide much of an increase in chassis torsional strength. It can be a good place to lose some weight - the CF hood on my Supra dropped about 30lbs! The MR2 hood isn't super heavy but you can drop a bit of weight from cutting some bracing. Just be sure it won't weaken the latch or hinge attachment points, or make the hood so floppy that it will move around. Perhaps if you remove a lot of structure it would be good to add some concealed hood pins/latches like aero latch or similar. I have some on my Supra because the CF hood is more floppy even with the bracing and moves around a LOT at higher speeds at the track without the latches.
Interesting that you notice it moving around. I have my hood under tension with the latch and stoppers. I have not noticed any movement even in the triple digits. I am curious, is your Supra hood vented?
 

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Living where I live, driving where I drive, the factor likehood is a fraction of what most here. Nóóó commuting, no need to drive in the rain, véryVERY low traffic density. I´ll take the extra consequences. It is a convertible anyway.
The OE hood is designed to fold at least once in a front impact providing some contribution to crumple force. The hinge hooks also stop the hood from traveling backward and cutting through the windshield. Carbon just tends to shatter during an impact. A hood with bracing removed will not "fold" in the right place and may turn into a ginsu. Look at the bracing. There is an indention that causes the hood to buckle upward rather than travel backward through the drivers head.

Food for thought. (Says the guy with as many body panels as possible on his car lightened)
 

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Discussion Starter · #16 ·
Food for thought. (Says the guy with as many body panels as possible on his car lightened)
As I wrote in the opening post I understandt it :cool:

It is also why over here any mod to the ribs or a fiber after market hood is grounds for automatic fail at periodic inspection. But then so are adjustable coil overs, improvements of the lighting or of the braking system. Heck fitting of FL lamp units to a PFL or even replacing the rear bulbs by LEDs is.
 

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It flutters at the corners over 150kph or so on track. Gave me major worries it might flip up, a catch at each front corner eliminated this. Car has belly pans and hood can vent at back edge but 1980s aero is not in my favour. Already trying to get as much flow as possible thru the radiators to keep temps reasonable.

it's not a super good comparison to the MR2 as the hood is much flatter and larger.


Interesting that you notice it moving around. I have my hood under tension with the latch and stoppers. I have not noticed any movement even in the triple digits. I am curious, is your Supra hood vented?
 
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