Silvia Club of NSW

I have just change my manifold to a Tune Agent SS one. Everyone says how much hotter under bonnet temps get with SS manifolds so years back everyone was raising their bonnets near the hinges with a few washers. Does that even work? I spoke to my mechanic about it but he reckons that it doesn't really let that much heat out.

Anyone with experience please feel free to share what you know.

you have to take the rubber seal off of the firewall also to get the full effect.

it can help with reducing underbonnet temps by a few degrees. it also makes your cabin hotter as the air leaving the engine bay will be sucked in through the cabin vents. in cold weather the bottom edge of the windscreen can fog up when stationary also.

it's also illegal,as you're modifying the hinge mechanism and the security of the bonnet on the hinges. jack it up enough and the bonnet can come back through the screen in an accident - taking your head off...

a safer and more leagl option would be some vents cut into the bonnet. as long as you don't cut the support frame,you can go for broke.


Justin...

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STI - Made in Texas,not Japan.

It was done to my S13 at one stage; More trouble than its worth (turbulence galore), with no noticeable change in engine bay temps.

air naturally flows through the front, along the engine, then down the firewall/trans tunnel, so adding an escape path up top just makes it all quite gay.
Justin is quite right about it allowing the bonnet to decapitate you in a crash, too; the safety pins that catch the bonnet if the hinge breaks will not work at all if the bonnet is raised.

Oh yeah, and it looks shit.

raising the rear of the bonnet does not work

The angle change between the bonnet and the windscreen is a high pressure zone (this is why the air con intake vents are there).

Raising the rear of the bonnet not only looks stupid, but reduces safety, can actually make engine bay ventilation worse, lets the rain in when the car's parked, and can let your a/c suck engine bay fumes into the cabin.

Do a little experiment - while driving along, turn off the a/c fan.
If the vents are set to outside air it will keep blowing, thanks to the high pressure area at the base of the windscreen.

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The Engine Whisperer - fixer of things