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Ugly Duckling Bonnet Scoop


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I looked at the price of GU bonnet scoops and just cant justify spending that much on a model specific jobbie . A mate of mine has a sheet metal bender so I grabbed a bit of thin zincalume (.8 or .9) and started bending. The project should be finished in the next week or so when I shape the bottom a little and find some pinch mold rubber to go around the bottom. I got a colour matched pressure pack made up for $25 or so. The end product will be body colour with black pinch molding.





Edited by Bogmeister
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I think you may be wise to put some rubber edging around the inlet.

I think the cops will be right onto those sharp corners and fine edges. If a pedestan went up on the bonnet ( they would be rs already, but...) they could be cut and further injusred by the scoop. that's how the cops will look at it I believe and you may have rego trouble with it as well. Ot

Other than that, nothing like the satisfaction of making your own stuff especially when the commercial items are completely over priced.

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I just found out the hard way that you cant buy spray putty or bog in Oakey on a Saturday morning :-(. I have some pinch mold left over that I might put across the inlet. I also plan to put some stainless fly screen underneath to stop rocks etc. Hitting my IC.

How ever, I painted it with blemishes and all but will putty and repaint at a later date. So far it has cost me $48.

I did a few measurements and the new one is nearly 3 times the size at the inlet than the standard one.

Once the silastic dries I cant wait to do a few Ks and measure the difference.





Edited by Bogmeister
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OK, I did about 30km and found that my egts are down about 20c across the board and drop a bit quicker than they used to. I will put a deflector at the front of the I/c and brace the inside lip to stop it vibrating. I will also experiment with the rubber shroud that the factory fitted underneath and keep you updated.

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How High is it at the front?

You will get the real benifit over an inch because the first inch sees poor airflow due to the boundry layer of air clinging to the bonnet and would probably be heated anyway when the sun was shining on it.

I'd like to do a Pro stock stye scoop where the inlet sits up above the bonnet. I know there is a law regarding the opening size of the scoop but not sure if there is a total height restriction. I'd like ot have the thing up about 1.5 inches then have the actual inlet above that. This would make the scoop most efficent from an airflow and air temp POV.

Whether it would be legal enough to get away with however would be a different thing.

For my little turbo Jobbie I'd like to do a frontmount cooler but there is no way to rout the pipes without some major re-engineering.

Think I'll have to settle for a good water spray instead.

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Those rules are national rules:









Here is a relevant section if lazy to look for VSB14:




The following modifications may be carried out without certification under an LH Code, provided

that the vehicle continues to comply with relevant ADRs and AVSR and provided that the

vehicle meets the following general safety requirements.



Modifications to the bonnet of a vehicle must take into account the possibility that a pedestrian

or cyclist might strike the scoop or bonnet projection in a collision. The top surface of a scoop

must not be more rigid than the original bonnet.

For vehicles manufactured prior to 1 July 1988, there are no specific design rule requirements

relating to bonnet scoops. However any such fixture that is a dangerous protrusion or obstructs

the driver’s forward view of the road, is prohibited by both the ADRs and AVSR. For vehicles

manufactured on or after 1 July 1988, ADR 42/... prohibits external or internal protrusions that

are not technically essential and are likely to increase the risk of bodily injury to any person.

Rigid engine-mounted components that are likely to increase injuries to a pedestrian in a

collision must not project through and above the vehicle’s original bonnet profile, unless

protected with a cover mounted to the bonnet.

Bonnet-mounted scoops must meet the following requirements:

When a 165mm diameter sphere is placed on the bonnet in front of the scoop (or

bonnet projection) and rolled rearwards until it touches the scoop, no point of contact

between the sphere and the scoop must lie above a horizontal plane passing through

the centre of the sphere (refer Figure in previous post);


Last time I checked Queensland is still part of Commonwealth of Australia no matter how hard you are trying to be different ;)


Edited by Rumcajs
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Thanks for the tips on law.

I still have very little interest in being a part of any society.............Let alone the rest of the states. I am actually thinking of moving back to Katherine so I can call myself a "Territoooooorian" again. :P

I will put the little bit of rubber around the edge of the scoop, just so it looks like I care about people that take the trip to the top of my bonnet. My first question would be WTF are they doing there in the first place??????? :ph34r:

I will also do the sphere thing. The best part about my scoop is that It doesn't look that high. the 60mm height looks a little low to what I would have done if I didn't have to escort loads with Police on a regular basis. ;)

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. My first question would be WTF are they doing there in the first place??????? :ph34r:

And if it's a woman on you're bonnet, WTF is she doing out of the kitchen Right?? :D

I seem to be missing something in the laws or I have found fault.

The scoop I would do is much like the one Fail one in the diagram example. Reading the code, If I lower the bottom edge so it contacts under the halfway plane of the sphere and then recess the top edge so it can't contact ablve the sphere, I can virtualy make the scoop 2 ft tall.

The talk about rolling the sphere back and the point of contact. By " artificially inducing that point of contact, seems to me I can make anything behind that as tall as I like. This was kind of the question I had originaly with these things. I understand about the sphere and all that but if you look at the way the OEM scoop is cut back so the point of contact would be within the lower half of the sphere, what is the reg of the max height I can have behind and above that.

Same as in the fail example diagram. If the contact point of the lower edge is below the halfway plane of the sphere, how wide/ high can the actual inlet be?

That fail scoop esign is actually the effective one and what I would want. The inch between the bonnet and the lower lip is just hot, disturbed air with a lower velocity. you want to get above that which is what that scoop design does. It's not the point of contact that matters, its the height of the top edge and the overall inlet area that is going to decide upon how efficent the thing is.

I'm also confused with the 2nd pass Diagram. That to me appears to be a reverse flow scoop which I have read was illegal. anyone got the actual up to date stipulations on those?

One other thing I wonder about is the material the scoops are made from. Years ago I made up some spoilers and air ducts from Cinveyor belt.

The stuff was great for that application. At lower speeds the stuff was stiff enough to lie direct in the airpath taking the maximum " Bite" into the airstream. when the speed and therefor airpressure increased, the belt would flex and have a lesser angle of attack to the airstream therefore reducing the drag but still allowing for a high pressure zone of air to be forced where you wanted it.

In the case of airdams to force air through radiators, this stuff was great because you could run over anything without smashing the chit out of it on the first gutter or stop you nosed too far into.

You could make a good scoop out of this stuff because when it was laid with the edge leading into the airflow it would be more than strong enough to duct the air but as far as wonmen whom had strayed from the kitchen and onto you're bonnet, the belt would deform and be soft as anything and obviously far softer than the material the bonnet was made from as specified in the regs.

Also if the belting was laid right, it would be possible to have the stuff easily meet the height regs of the law but then when moving through the air, it could catch it and pop up to a far greater height and remain there untill the speed dropped back near stationary again.

Would also seem pretty easy to control the height of a ridgid scoop with the aid of a small actuator like found all over cars these days running off boost pressure or vacuum.

With boost the scoop would pop up to it's greater height once boost was achieved and with vac it could be automatic with engine start or manualy controlled.

I'm pretty sure the cops don't measure the height of these things when the vehicle is in motion so this would be an easy way to comply with the regs as they stand.

I'm motivated to find a bonnet and build one for the hell of it now! :D

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  • 2 weeks later...

when i had my commodore i spent hours on the phone with Qld transport department talking about bonnet scoops and filters exceding the bonnet ect

Anyways to cut a long story short finally one of the head honshos told me i can have a filter out of the bonnet as long as there is no moving parts that can crush fingers ect and no sharp edges and height requirments where measured based on the princaple of if the cop stood infront of the left fender infront of the car (can not remember the distance away) you had to be able to see his feet while in the seated postion behind the wheel.

My filter was 8" high and 14" round, got pulled every time i drove it one cop gave me a ticket that i scrunched up and threw back at him told him all this above and said ill see you in court and never went to court he threw out the ticket and left me alone after that. My secret tho was i had height adjustable seats, the lip around the filter top had small chrome condu crap around it and when i cut my bonnet i placed a full rolled brace around the hole.

Edited by Evil!
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  • 3 months later...

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