Why? Rear Edge Of R32 Bonnet Looks "raised"

[sl33py]

I'm not sure if this is more cosmetic related or engine related, you'd have to read the Q to see why:

I often see R32's with a bonnet and the trailing (rear) edge of the bonnet looks like it actually not sitting flush with the guards, but sitting slightly higher up. An example is the R32 from Dubai in the Skyline only edition of HPI. My guess would be that the bonnet isn't even attached to hinges like normal, but only bolted down by those 'peg' things (proper name?) on the leading edge, and simply left sitting without being secured on the windscreen end. But I don't think that's right cos it sounds dumb.

So Wtf is this? How is it attached? I would hazard a guess it's done simply to accommodate something to do with the ENGINE, rather than a COSMETIC change done just for the looks... ? If not, someone explain and just move this thread

Thanks in advance.

[FATAZZ]

It's raised to let the hot air out of the engine bay.the hinges in most cases are left but have added washers to help raise the bonnet,it also helps to rip that rubber seal that runs along just infront of

the windscreen.

P.S those 'pegs' are known as 'bonnet pins'

Edited March 20, 2008 by FATAZZ

[SEX-DR.]

if i am understanding the question correctly (which i might not be) but ur talking about the bonnet sitting up 20 or so millimetres above the front guards, this is done to increase the quantity of hot air which can be released from within the engine bay.

it is done with a couple of spacers placed between the bonnet and the bolts on the hinges....

costs about $3 for a pack of spacers, and done in a matter of a few minutes.

I had it for a little while, till i bought a vented bonnet.

hope that helps,

Peter

[SEX-DR.]

FATAZZ, you beat me too it!!

Edited March 20, 2008 by SEX-DR.

[sl33py]

I see. God it looks annoying to me hahaha. I KNEW it had to be done for a purpose, not just looks. You'd think that Dubai dude would just buy a vented bonnet then, he didn't even have an air filter or anything anyway (... or a seat belt, crazy buggers). Thanks guys.

[GeeTR]

Cant complain for $3 and 10min's haha!

[Simon-S14]

any proof that it works tho?

drifters do it just for the look... doesnt seem to lower the underbonnet temps

[Duncan]

now there is the real question.

raising the rear of the bonnet will not let extra air in. Air at the base of the windscren is high pressure (due to the angle of the windscreen starting) and in the engine bay is lower pressure. if anything raising the rear will let more air in.

look at v8 super cars....they run air intakes at the base of the windscreen because of the higher pressure.

[Dan_J]

now there is the real question.

raising the rear of the bonnet will not let extra air in. Air at the base of the windscren is high pressure (due to the angle of the windscreen starting) and in the engine bay is lower pressure. if anything raising the rear will let more air in.

look at v8 super cars....they run air intakes at the base of the windscreen because of the higher pressure.

its not done to let air in, its done to let air out, = somewhat less warmer engine bay which would effect the engine slightly (cooling) i guess

Edited March 24, 2008 by Dan_J

[subie]

Duncan:

so, u mean raising the rear bonnet will suck the air into the engine bay.. how about the air enter from the front and push the hot air out at the rear when it raising?

by the way, can anyone show me some pics of where to put those washers to raising the bonnet

cheers

Edited March 24, 2008 by subie

[Dan_J]

u dont put washers, thats just plain unsafe. just get longer new 8mm bolt and nut that have the japanese type of thread

Edited March 24, 2008 by Dan_J

[Duncan]

it doesn't work like that. air moves from high pressure to low pressure, it doesn't just head to the back of the car because that would be convenient.

if you raise the rear of the bonnet you are letting air in not out. have a good look there, almost all cars use bottom of the windscreen for the inlet for cabin air.

[cpt_impossible]

I couple of guys here in the states did a huge writeup testing the effectiveness of the raised hood modification. I don't feel like searching for the thread right now but using several temp loggers and pieces of yarn attached to the back of the hood, here is what they found.

-After hot runs, the under-hood temps drop much more rapidly while at a stop or staging between runs.

-While at speeds under about 25mph, the cooling fans are able to push hot air out of the back of the hood which should provide some cooling effect.

-When traveling over 25mph, the air pressure at the base of the windshield overcomes the pressure created by the fans and the hot air's need to rise and forces air into the back of the engine bay.

-At speeds over 25mph, there is no noticeable difference in under-hood temps

I have the RB20 shoved into the S13 which cooks like an oven so I settled on just removing the weather stripping at the back of the hood. Immediately I noticed that when I park after driving and pop the hood, that huge gust of heat has already dissipated and the car cools down much more quickly when you slow down enough for the hot air to escape.

So to recap, the mod is useful for those who do a lot of stop and go driving or idling after hot runs at the drag strip and such, but has no benefit for those keeping a constant high speed.

Edited March 24, 2008 by cpt_impossible

[abu]

Looks tuff

[Alf]

any proof that it works tho?

drifters do it just for the look... doesnt seem to lower the underbonnet temps

People were doing it before drift was around, back then it was called rallying on tarmac.

People were doing it to their toranas and Falcons when they were newish.

[GeeTR]

I couple of guys here in the states did a huge writeup testing the effectiveness of the raised hood modification.

Great post even greater if you could find that link!

[dano4127]

lots of people do it because it looks "FULLEY SHICK BRAH!"

[Dan_J]

it doesn't work like that. air moves from high pressure to low pressure, it doesn't just head to the back of the car because that would be convenient.

if you raise the rear of the bonnet you are letting air in not out. have a good look there, almost all cars use bottom of the windscreen for the inlet for cabin air.

yea that sounds around right i guess, i thought u were just stating what everyone was doin it for.

[charlie25T]

Hey boys...................

I have R33 and yeah i have raised the rear of my bonnet but 2omm

its better for the cooling down of the turbo and all

im still running a standard manifold and with my set up

it get pretty hot in there

Raising the bonnet help the circulation of hot air and cold air

sum shit likt that

[cpt_impossible]

Here are some posts from NICO, the second one is one of the experiments I was refering to but after reading it, I realize I did some "rough" rounding on some of the statistics:

"Thoughts:

I did this right after I installed my water temp gauge in the upper radiator hose. Temps on the gauge dropped 6-8 degrees after propping the hood. The only real downfall is cruising in the summer, the heat from the hood cooks the cabin, but I removed my AC when I did my swap, so I have to crusie with my windows down. Oh well. It works."

________________________________________________________________________________

_______________________________________________________

"There are some pics of my RH with a cowled hood. Mine is alittle more extreme than just putting washers under the hindges. My hood has been tweaked and bent into that shape. I have a high point of 2.5" with the weather stripping removed on the rear edge as well.What I did was use an .5" wide piece of delicate cotton linen that was about 5 inches long. I duct taped it to the very edge of my hood at its highest point leaving about 4" of cloth to test. With as high as my hood is there, it is extremely easy to see.

The wind was also not blowing much.

79*F

14% humidity

Engine at normal operating temp and I use a clutch fan with a new clutch.

What I found.

Up to about 25 I had the linen standing against the windshield with occaisional flips up. That tells me that there is a negative pressure there allowing the heat out of the engine bay.

After 25 up to about 60 there was a positive pressure as the linen was pushed under the hood. The highest pressure being about 45-50. This pressure is strong as the linen was laid flat up against the bottom edge of the hood.

After 70 it was in and out left and right... very chaotic. Buffeted (sp) pretty much.

What do I think?

I think my mod isnt a waste of time as it helps in town driving with stop and go traffic. Above town driving, your moving enough that adequate air is hitting the radiator and the negative pressure under the car is sucking it out.

Because my hood is humped in the middle and not flat like most of y'alls, maybe it will be different, but I doubt it.

I am going to channel the air from the "snorkels" in my hood over the radiator to see if that adds enough pressure to overcome the positive pressure at the base of the windshield.

I hope this answers some quetions.

Then the real test

I taped off my hood today to ensure my cowling worked... I provided pics. I drove the same roads, in the same gear, same speed, about 10 minutes apart to ensure consistantancy.

It was hot today... 90's here. sux to be in PHX when I tested. By the time I smoked two joints before I smoked two joints it was cooler before I wrote this so I cant vouch for actual outside temp.

This is what I found:

On my rag-tag thermometer that I use to check internal case temps on my Overclocked PC's...

HI = 158.0*F Plus

Hood Cowled with a 2.75" ( I raised it with a gradual from the body line in the hood) inch opening to the world. It is different now with better distinction.

25-35mph in 3rd = HI

40-55 mph in 3rd = 145-149*

65 in 4th gear = 147*

65 in OD = 133 - 137*

______________________________________________________

Hood Cowled but covered with plastic and good duct tape... not that [censored] stuff Alfred, no doubt, has in his tool box... but almost as good as Frankie has...

:lol:

anyways with the hood sealed up as shown....

up to 60mph it was over 158* plus in my engine bay as indicated by the "HI" so I have no indication of actual temp.

at 65-68 in 4th gear it dropped to 155* and held fast for like 5 minutes.

HERE IS THE KICKER !!!!!!!!!!!!!!!!!

At 65 in OD for several minutes... I saw 120* to 137*

The odd thing I found. I found that the plastic on my Hood was always inflated but seemed to suck in at 50-60 at 2.75" on center ( highest ) hood... the corners were pushed way away from the body.

My conclusion...

Cowling works. period. Temps in general are lower at typical city driving. Above that it is still acceptable by showing no more than 60* higher than ambient.

Cowl that rascal. Let the heat out.

Are you scared about teaking that hood? Show some damn commitment and get something done.... let the heat out.

Nothing says slow car like a heat induced [censored] performance... especially to 90% of us N/A drivers.

I took the time to cowl my hood. I bent it and ruined it for "stock" looking applications. I spent time shaping it so it raises only in the middle... dont get excited Alfred... I'm still talking about my car...

There is your proof boys...."

Edited March 25, 2008 by cpt_impossible