Fish Gill Bonnet Mazda FD RX7

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Fish Gill Bonnet

Standard finish is White gel coat, Black is available upon request.


We set out to design and create a bonnet which fulfilled the following parameters -

It would have to provide good venting of hot air from the engine/turbo as well as cold air from the intercoolers requirements.

What we ended up with we feel fulfils the criteria in its entirety. The four gills are all purposeful vents and they proved a challenge as to what degree of radius both laterally and vertically we should make them. Not only that but the underside of the gills cannot protrude beyond the dimensions of the stock bonnets support frame (this would cause fowling on engine components). This then meant we could not construct a framework underneath the gills to give it strength, it would have to be created another way. We made a number of models and finally have used a combination of different weight fibreglass mats and finally a top layer of a kevlar type cloth. This has been road tested and found to be sufficiently strong enough, so we are now happy to produce from this configuration. The gills themselves all sit above the top line of the stock bonnet which gives an aggressive look when viewed from the side but a very subtle look when viewed from the front. The width/length of the fins has been determined by the natural bulge which occurs in the centre of the stock bonnet and gradually tapers out as it travels towards the rear. We have kept to these lines to then raise up the gills in a gradual arch. You will also notice that the outward curve that starts in the front of the stock bonnet in the area between the lights has been exaggerated as it leads up to the first gill in our design. This creates a more curvaceous line across the top of the bonnet when viewed from the front. The plus side to using a vertical vent this way is that exiting air doesn’t have to loose momentum making any radical changes in direction and can flow out the vents as it travels, both at the front from the intercooler and towards the rear across the engine. The negative to this of course is you have to stop water flowing into the engine bay through the vent opening. So we’ve put a 10mm upright at the base of each vent where water runs along down to an escape hole in the middle of the vent (the lowest point) where it can exit. Here it falls into a catchment channel and away through an outlet pipe. The water catchment channel we wanted to make in one single piece joining all four vent outlets and giving the bonnet linear support/strength. Unfortunately we didn’t have space to do this courtesy of the strut brace. So we now make the channel in two parts collecting from the rear two vents and a separate one for the front two vents with the strut brace sitting between them.

NB/ We have made clearance for a number of different strut braces, to be sure there will be no clearance issues, contact us for more information.

After carrying out a simulated rain test we found the vent lip could cope easily with heavy rain without any overflow into the engine bay and the drain system working perfectly. Obviously rain can fall at many angles of course for this purpose we simulated it falling vertically. For this test the bonnet was positioned at a downward angle measured to be the same as that on a STD car. We have made a small video to show the system working where a pipe is fitted to the front and rear outlets and you can see them at full flow depositing water away while the surface underneath remains dry. The video can be seen here: Product Videos (scroll to the bottom). With the car in motion this would offer much less of a challenge to the drain system while rain from the rear when stationary could cause issues unfortunately. We found after measuring several aftermarket bonnets a big difference in sizes and most being a poor fit. To overcome this we first had to take a mould from an OEM bonnet and use this as our starting point before modifying and then re-moulding. This means our Fish Gill bonnet is of OEM SIZEING !!

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