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Hi guys,
I am going to get some louvres pressed into a stock NA bonnet. I know the location I'd like them on the topside of the bonnet, but how do I accurately mark the location on the underside (which is where they'll be pressed from)?
The bonnet is curved and has bracing, so it is not a flat surface. In a perfect situation I'd like to cut two rectangles from the bracing and mark where the pressing should happen. I'm thinking I may have to cut out a large section of bracing and mark it from the edge of the bonnet (taking account the bonnet is not square). Even then there will still be the edge bracing of the bonnet in the way. Afterwards, I could glue bracing back in. No, I'm not going to drill pilot holes in my bonnet. I was thinking maybe a strong magnet to somehow trasfer the location to the underside (think about it...)
Thinking......
Ta
Bruce

Look at Singular Motorsports site.

Don't they supply a stick on template? No use to me as it is only suits their vents.
Hmmmm, maybe I can do something in vinyl on the top and stick it on the underside? But I will still have the edge bracing in the way if I remove the rest of the bracing...

Easiest I can. Think is just very careful measuring from a known point.

Run a stringline down the centre and then measure from that.

And the other axis measure from the front edge or something.

Then flip he bonnet and measure from the same points and Mark out on he underside.

Locating the centre line of the bonnet on the top is not easy but doable (as there is a curve to account for).
Underside will still have some bracing which interferes with laying down a line on a concave surface.
A measurement from the outside does not translate to the underside just due to the curve.
I thik I may need a laser!?

Try reading these excellent articles [below] about airflow and heat exchange. Simply opening up the bonnet does not necessary mean heat will escape and/or cold air enters. Choosing the wrong spot could create air pockets with positive pressure which will stop any airflow from entering the engine bay.

These were already shared in this forum before but I couldn't find them using the search, so here are the links again.

Undertrays, Spoilers & Bonnet Vents, Part 1

Undertrays, Spoilers & Bonnet Vents, Part 2

Undertrays, Spoilers & Bonnet Vents, Part 3

Considered all that already.
Conventional MX5 thinking does not necessarily apply to my car due to an engine bay full of uniqueness.

Depending on exactly how you want to go about the final result, tidying up work required, level of precision necessary, this may be an option.....

- Mark out exactly where on the top of the bonnet you want the vents.
- Define the four corners of each rectangular section and mark them.
- Drill a small ~1mm hole at each corner of these sections.
- Flip the bonnet over, find the holes, remove bracing as required.
- Patch holes after the vents have been pressed.

Sorry, but pilot holes you don't want to drill, to me anyway, is the best option for a reliable result.

Drilling is a real caveman way to do things. Then the holes will need welding and grinding.
There must be an easier way as I'd like it to be accurate.

bruce wrote:Considered all that already.
Conventional MX5 thinking does not necessarily apply to my car due to an engine bay full of uniqueness.

This is absolutely incorrect.

Be careful.

bruce wrote:Drilling is a real caveman way to do things. Then the holes will need welding and grinding.

You're worried about holes in your bonnet?

I've got some bad news for you about bonnet vents.......

Far too many negative comments.
You'd think by putting in vents my car will blow up.
I'm searching for that genius suggestion. I think a laser is the answer.

There are no negative comments, just advice?

I'm also going to do this when I pick up my spare bonnet but was just going to mark them on the topside and drill similar to what Nevyn72 suggested.
You're going to cut it anyways so I don't understand the issue.
Re the airflow, it's still a mx5 but I think your exhaust manifold is on the other side.

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Location of under bonnet components won't change anything unless the radiator has been moved by a foot or more.