View Full Version : make your own custom vented/ scooped hood

01-01-2010, 02:01 PM
lots of people on other forums have asked about my bonnet so i wrote a how to. hope it helps anyone wanting to attempt something like this.

Before you decide to go hacking away at your bonnet make absolutely certain that its what you want, if you or a friend has the ability try and get a photchop done then do it.

these are simply the steps in wich i made MY bonnet. By following this "how to" the ownes is entirely on you. I am not responsible if you ruin your bonnet or if it falls apart while driving. Depending on where you live there may be legal implications aswell. Be sure to check that the bonnet will comply with local regulations.

ok here we go.
things you will require:
-1 bonnet (a spare would be preferable)
-Fibre glass matting \
-Fibre glass resin }-amounts
required will vary
-Catalyst for resin /
-Angle Grinder
-Cheapo paint brushes
-1 scoop/vent of your liking
-Permanent marker
-Body filler
-Lots of sand paper varying grades
-Dremel or similar ( not essential but helps)
-Orbital sander (again not essential but wil make life alot easier)
-Rubbing blocks
-STRONG adhesive such as sickflex or preferably panel bond
-Measuring Tape
-Masking tape
- Series of G-Clamps and or similar

You must really think about this process and plan where evrything will go, how it will sit relevant to the engine bay to increase effectiveness. What will happen to the support bracing underneath, will it be to flismy afterwards etc etc.


Decide where your vent will sit. Start by measuring out the middle and marking both the horizontal and verticle halfs with either tape or a marker and ruler. Then once you know where it will sit, draw an outline onto the bonnet.
You then need to decide how big the hole you will cut is relative to the scoop itself. This will vary and youl need to make your own judgement on this the factors you must allow for are that you have enough area for the scoop and hood faces to meet and create a good seal, How much you will be cutting into bonnet supports and obviously over all appearance.
i cannot stress how important the measuring is, measure 10 times if need be because once you cut, you cant go back.

One thing alot of people over look is how the shape of the bottom of the vent is relative to the bonnet. If the bonnet and the vent surfaces do not allign you will be putting more strain on the adhesive making it more likely to pull away and also cause ugly warping in the vent and bonnet.
If the surfaces do not sit flush either sand the vent to shape or build up with fibreglass or glass filler (also known as Kahglass or kitty hair essentially it is body filler with fibre glass mixed in). Mine had to be modified, i chose to use the glass filler as its less fidly. I also used it as a chance to create a wider surface on the vent for contact with the bonnet to create a greater sealing area.

now comes the scary part. With the hole marked out use your angle grinder to make your cuts. Start your cuts on the inside of the outline and work your way out. More work is a much better option then making the hole wider then it needs to be.
Once you have the hole essentially cut to shape (with in 5mm of the outline) take either a dremel or similar ( i used a air powered small belt sander) and gradually grind the hole out to the outline.
remember TAKE YOUR TIME.


first test fit the vent a few times to make sure that the previous 3 steps all went to plan. Assuming they did your now ready to mount the vent. Scuff up both surfaces with sand paper, 80g paper should do it. blow/ wipe off the area.
When it comes to wich adhesion product to use i STRONGLY recomend Panel Bond. once it sets its ridiculously strong. It is pricey and may be hard to find but IMO its worth it. Sickaflex/ Eurathane will do the job i have very little doubt of that fact, some would say i was simply overly cautious.

Apply the adhesive to the mating surface of the vent. alligning it correctly on the bonnet and press it down evenly and firmly. Clamp the bonnet and vent together using G-Clamps or similar, make sure its tight enough that surfaces are held flush. DO NOT over tighten though or you WILL cause damage. Wipe away excess sealant and then let it set. I recommend giving it a full 24 hours. at this stage your bonnet should look similar to this


Now its time to take the paint srounding the vent back to metal. Sand it back to metal using 80-40g paper (this is where the orbi comes in handy) and sand the vent back to 80g finish. The glass will not bond very effectively to surfaces much smoother then these. Blow/wipe away the dust.

At this point i advise rubber gloves, its about to get messy. Begin cutting up your glass matting in thin strips. The key to getting this right is a gradual build up of glass. it needs to be solid. The matting needs to be able to fit in all the nooks and crannys not just the resin.
After cuting to shape the matting its time to start with the resin.

Add the catalyst to the resin as per instructions and mix it up. Apply the resin to the bonnet liberally then lay down your sections of matting. Apply another healthy dose of resin on top. Push the matting down flat. The secret to a good fibreglass job is to ensure there isnt any air in there. Air bubble will cause cracks further down the road and can cause the layers to seperate.

Build up the shape slowly, layer by layer. As soon as your resin begins to set STOP. the moment it start going tacky all you will do is ruin what you have done so far.
at this stage mine looked like this

Let it set over night, if it needs more it can wait till tomorow.
If more is required ( mine needed more) sand the new glass back to 80g, wipe away dust and repeat the process.

my bonnet then looked like this

So youve now built up the over all shape with glass. Time to finish the job with my best friend body filler. Same as the glass sand back to minimum 80g, mix up the bog and whack it in. If your new to body filler application it can be messy and you need to find the right level between firm and soft application. To soft, lots of air bubbles and poor bond. to hard and your essentially scraping the filler away.

dont be affraid to put to much in, all it means is you have more to rub out.

So your filler is now set, here comes the fun part. SANDING lol.
What grits you should do so with depends on how much needs to come out. Generally with a job with as much filler applied as this i start with 40 to knock the top off, then do the bulk of my rubbing with 80 then when its getting close will finish with 180.
This will be the most time consuming part of this process especially if you went with something like the CS vent as its a deceptively complicated shape. without being there with you its hard to give advice other then let the paper to the work not you and continually blow off the surface and run your hand over it in EVERY direction feeling for hi's and low's. Also sand at different agles, simply going left to right and up and down will give you ripples and ridges.

if you rub to much out (happens to the best of us) simply rough up the surface with 80g and re apply.

this is a picture taken inbetween coats of filler after i felt a few lows

another coat

stupidly didnt get any more shots of the filler work then that.

when done inspect for pin holes (where bubbles formed in filler) and scrape in some fine filler if you have some or just use a lil bog. and when i say scrape in i mean it, your aim is to try and fill nothing but the tiny hole. and shallow low spots you can use fine filler in aswell.

this is your last chance to adress an problems any small dings etc that need filling or attention

once done give everything a light rub with 240g ready for High Fill.

after a coat of paint its time to fit to the car but before you do so. now is your chace to fit your mesh (if you so desire).
Now bolt that sucker up, allign it and be proud of the hard work you put in.


PLEASE NOTE. you may notice i didnt cover anything about the underside. i didnt get a chance to finish the underside as i would have liked. My boss cracked the shits and said he wanted the bonnet out of his shop and as a consequence i never finished the underside, when i do i will update.
also yes the colors wrong, was just left over paint at work and i was broke lol

thanks for reading any queastions just ask .
this is my 1st HOW TO i hope it was very helpful sorry if i left anything out

01-01-2010, 06:46 PM
wow that is so nice

The Captain
01-01-2010, 07:19 PM
nicely done.

joe's gt
01-01-2010, 07:28 PM
Awesome job man. Looks like it was there from the start. Can't wait to try my hand at fiberglass.

01-01-2010, 07:44 PM
Wow, that is really nice work Rob. We'll be sure to get this added into the Tech Write Up section.:bigthumbu

01-02-2010, 04:56 AM
thanks guys glad it helps

02-10-2010, 07:30 PM
Yeah, that's the exact scoop I'm planning on installing on my gen4. God I wanna violate your car right now :whackit:

03-06-2010, 05:41 PM
i think im going to use a wrx scoop on mean

07-31-2010, 08:57 PM
Your pictures are dead. =(

07-31-2010, 09:54 PM
Please host them in the gallery.
If nobody has caught on, Photobucket has changed their hosting, and it deletes images that haven't been accessed by the owner over time.

08-01-2010, 12:30 PM
sorry i re-organised all my photobucket a while and forgot about this.

all fixed :)

08-02-2010, 05:23 AM
Where did you get the scoop?

08-03-2010, 09:18 AM
egay, was 2nd hand

08-03-2010, 06:03 PM
I cannot find a alltrac or cs replica scoop anywhere!!!

08-04-2010, 02:37 AM
Chaser has them for $29.


08-04-2010, 05:09 AM
Ebay is like $150. lol Here's another one


Be sure to check out the shipping. Some of them are overpriced. Like $60 to ship the scoop. Actually I just looked and Maikeru's site's shipping is around $35. Go with his.

08-04-2010, 07:05 AM
What's funny is the one says it's made by CFH and the other Chaser, but they have the same pics.

08-06-2010, 03:56 PM
wow, final pics are awesome

11-18-2011, 06:40 AM
Wow it came out really good! (thumps up!) Sure makes your 4th generation stand out