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Aug 22, 2012 17:01:12 GMT
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hi all, just got my 48dcoe powered mercedes 16v on the road! been working on a few niggles, and posted a thread a couple days ago about heat resistent carb/inlet spacers to reduce inlet temps: retrorides.proboards.com/index.cgi?board=techni&action=display&thread=135256anyway, after a day of hooning about, it seems that under bonnet temps in general (not just inlet) are certainly on the high side. i've always liked the look of bonnet vents, and thought that one near the front of the bonnet near the carbs to get cold air in would help. then one at the rear of the bonnet near the back to release the hot air near the exhaust manifold. my questions are: do you get bonnet vents that are 'vented' in different directions to let air in or out or are they all the same and it doesnt matter? i always thought that series 2 rs turbo vents woud look nice as they are pretty quare/boxy like the 190e is - are you able to install these easily? ideally i don't want to have to paint the bonnet so if you could cut the hole and drop the vent in with fixings/etc, that would be helpful! can anyone suggest any vents that can be installed by cutting a hole and dropping them in as opposed to something that would need chopping/welding/etc resulting in paint? pics of car in question as thanks!
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luckyseven
Posted a lot
Owning sneering dismissive pedantry since 1970
Posts: 3,839
Club RR Member Number: 45
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Bonnet Ventsluckyseven
@luckyseven
Club Retro Rides Member 45
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Aug 22, 2012 17:09:24 GMT
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It's a very hard question to answer succinctly, and the simple answer is it depends mostly on the aerodynamics (or lack of) on your car. The idea is to exploit the venturi effect of low pressure air leaving the top of the bonnet and thus sucking air out through the vent from the engine bay, but where the point at which this effect is most pronounced varies wildly from car to car. Bear in mind if you get it wrong it'll be sucking air in the wrong way (mostly irrespective of how fast you're going) which isn't really what you want. Remember the Yank Cowl induction hoods on like Chevvies and Pontiacs especially that used the high pressure standing wave of air building up at the base of the windscreen to force air down into the intakes for the carburettors? This is the same effect utilised by every manufacturer since like 1920 who've put the cabin air intake in the scuttle for maximum effectiveness. This is why your proposal of a vent at the trailing edge of the bonnet is probably a big wahhh-wahhh as it not only won't work, if it does you'll be sucking engine bay fumes right into your cabin Rule of thumb is the air will leave the bonnet and create a low-pressure suction somewhere fairly close to the top leading edge but it's hard to say where precisely without a wind tunnel. Worth considering that most engine heat is evacuated out the rear of the bay down the trans tunnel so the relief of heat through even an accurately-sited bonnet vent may be marginal... with that said, you can actually see the waves of heat burning the air through the vents on my RX-7 bonnet but it's a rotary with a head-sized turbo so it runs slightly hotter than the heart of the sun EDITED FOR SPELNILG
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Last Edit: Aug 22, 2012 17:10:50 GMT by luckyseven
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gn3dr
Part of things
Posts: 391
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Aug 22, 2012 17:51:56 GMT
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Ni;ce loloking Merc. Any build thread on it? The link in your sig doesn't seem to work
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Aug 22, 2012 19:22:39 GMT
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Aug 22, 2012 20:19:43 GMT
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Have a look at some DTM 190e or other "race-modified" 190e for inspiration on where to put the hood vents. It's not entirely fool proof, but the bigger companies probably put considerable effort and money in where to put them.
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Ryannn
Posted a lot
Posts: 2,421
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My mini has a vent on the rear of the bonnet to let heat out, however it's covered aswell to stop rain going in!
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LAndy
Posted a lot
Posts: 1,061
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As joostvdw said, look at racing cars of a similar shape/style. The first one that I saw on my laptop was The Audi 90 GTO race car. Similar shape to your 190 and my 80. Here's a pic Andy
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Previous retros: 92 AX GTi 92 Scirocco Scala 94 80 sport 87 Golf Cab GTi Current retro: 1965 Clark Cortez YouTube Website Instagram
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Aug 23, 2012 12:41:58 GMT
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curse word photo I know but the only one I one I can find at the moment available from any decent marine chandlers and work very well in the right place marinestore.co.uk/Stainless_Engine_Vent_208x111mm.htmlbonnet now has a ERA style vent at the back as there is high pressure spot at the base of the screen, so the high pressure forces cold air into the engine bay just where my throttle bodies are. the chrome vents are in bonnet low pressure areas so hot engine air (under high pressure) escapes, thus keeping engine temps down. engine is c20XE so gets pretty hot in that engine bay matt
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bigsyd
Part of things
Posts: 179
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Aug 23, 2012 12:46:52 GMT
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could you not modify your bonnet by adding wedges of metal in to raise the center slightly allowing hot air out. sort of bonnet lifter style. also use the grills to driect cold air to push heat out and up to carbs too
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2001 astra sri {soon to get a retro inspired make over)
1990 golf(put away for now)
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Aug 23, 2012 12:49:10 GMT
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could you not modify your bonnet by adding wedges of metal in to raise the center slightly allowing hot air out. sort of bonnet lifter style. also use the grills to driect cold air to push heat out and up to carbs too lifting the bonnet at the base of the screen lets cool air in as its a high pressure zone at the base of the screen.
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Aug 23, 2012 12:53:43 GMT
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Aug 23, 2012 12:58:55 GMT
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good reads /\
the basic principle is cold air in = put scoop in a high pressure spot, hot air out = put vent in low pressure spot
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smellyferret
Posted a lot
Back in a retro after 7 years!
Posts: 1,121
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Aug 23, 2012 13:39:48 GMT
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I'd be off to a scrappy for a 2nd hand bonnet to test things out on! Interesting thread too, never thought to much about thermodynamics.
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luckyseven
Posted a lot
Owning sneering dismissive pedantry since 1970
Posts: 3,839
Club RR Member Number: 45
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Bonnet Ventsluckyseven
@luckyseven
Club Retro Rides Member 45
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Aug 23, 2012 13:56:53 GMT
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Dug out some pics to illustrate my earlier (slightly random) post lol... This is the Cowl Induction Hood style utilised by Yank draggers back when... uses the high-pressure wave at the base of the screen (sorry, windshield) to force air back into the trailing edge of the hoodscoop. Looks counter-intuitive but at any speed it works. As modelled by the RC Autos Nova; This is roughly where the lowest pressure is liable to be (sorry it's a totally "wrong" car for the context, this is my FD). It's the approximate point where the laminar airflow leaves the top edge of the bonnet and thus creates a veturi that literally sucks the air out of the engine bay. The little flip-up lip in front of the vents exagerrates the effect A (very) rough guide is: Front airdam = high pressure = air in Top of bonnet front = low pressure = air out Rear of bonnet = high pressure = air in Of course, at a standstill or very low speed any of them will allow air out but it really doesn't need much speed for aerodynamic principles to wake up to the scheme and start wreaking havoc ;D
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Aug 23, 2012 14:38:29 GMT
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I would run a temp probe under the bonnet with the display inside the car and go for a drive up the motorway, and then one in town, if it stays cool on the motorway but gets hot in town you can put the vent pretty much wherever you want as it only needs to let air out while the car isn't moving.
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Volvo back as my main squeeze, more boost and some interior goodies on the way.
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Aug 23, 2012 15:19:37 GMT
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Aug 23, 2012 15:26:41 GMT
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also don't forget about a places that can louver your bonnet, can look quite cool, don't know if its been mentioned, but heat wrapping the exhaust manifold and down pipe cuts temps done a tonne!
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cars: orion 1600 i ghia mk2 orion 2.2 vtec ghia mk1
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LAndy
Posted a lot
Posts: 1,061
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Aug 23, 2012 15:39:32 GMT
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also don't forget about a places that can louver your bonnet, can look quite cool, don't know if its been mentioned, but heat wrapping the exhaust manifold and down pipe cuts temps done a tonne! Also improves gas flow by keeping the temps as high as possible. Watch for smoke when the wrap cures tho! lol
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Previous retros: 92 AX GTi 92 Scirocco Scala 94 80 sport 87 Golf Cab GTi Current retro: 1965 Clark Cortez YouTube Website Instagram
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Aug 23, 2012 22:47:53 GMT
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that too!but he seems more interested in the under bonnet temps, lol it does seem its about to catch fire...like wrapping a tea towel around ya manifold! but it doesn't, unless U spill a litre of oil on it like I did...not recommended..
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cars: orion 1600 i ghia mk2 orion 2.2 vtec ghia mk1
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LAndy
Posted a lot
Posts: 1,061
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. . . . . oops.
I know it was kinda off topic but its just another bonus.
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Previous retros: 92 AX GTi 92 Scirocco Scala 94 80 sport 87 Golf Cab GTi Current retro: 1965 Clark Cortez YouTube Website Instagram
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