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  1. #31
    Join Date
    Dec 2011
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    Rugby,West Midlands.
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    60
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    596
    Quote Originally Posted by aaronjb View Post
    I agree re heat, too (and Camcoat, as noted) - after coating I could still get the headers (and turbo exhaust housing!) on my old MR2 to glow orange under sustained full throttle pulls.. if it's glowing orange, I'd say it's safe to say it's still radiating rather a lot of heat!

    After wrapping, no such issues, and the engine bay was much cooler with something like a 10ºC reduction in intake air temperature as there was just much less heat soak going on - that said, the manifold cracked, which could have been a manufacturing defect or a result of extreme temperatures..
    If your manifold was glowing orange on your Mr2 , for what ever reason, and you insulated it with wrapping, ie trapping the heat from escaping ,causing a monstrous build up of heat under the wrap,this probably caused huge metal fatigue ,leading to cracked manifold .
    Paul.

    AK Huddart Chevy 383 Stroker, BMW Royal Grey Metal Metallic , 5 speed Jaguar Getrag , Holley 670cfm 4 barrel street Avenger Carb, 450 BHP at flywheel , 460 Ibs/ft torque, and luvin it !

    " We dont stop playing because we grow old, we grow old because we stop playing" - George Bernard Shaw.

  2. #32
    Join Date
    Sep 2010
    Location
    Cambridge
    Age
    35
    Posts
    1,188
    I remember doing some work at uni on bonnet scoop size and orientation, mainly research on existing published work with a bit of our own verification in cfd and it was really interesting. The bonnet scoops on cobras would probably be more effective if they were facing backwards. If a forward facing scoop is too small or narrow, the faster you go the air sort of queues up to get in and you get a big high pressure blob of air just standing around doing nothing, the opening effectively becomes blocked off at high speeds. The rad opening in the front of the nose is probably where most of the air gets in. If the scoop faces backwards then once you've achieved some minimum speed depending on the shape of the bonnet and scoop you get a low pressure area which draws the air in far more effectively than a front facing scoop (unless the front facing scoop is absolutely enormous).

    With a narrow top scoop it wouldn't surprise me if hardly any of that nice cool air is going anywhere useful. With a narrow letterbox bonnet scoop opening unless you've got a turkey pan setup I would expect that most of the air feeding the carb has probably already been through the radiator and washed its way over the top of the engine, especially if your just cruising along high speed but low load. Perhaps when the engine is trying to gulp some air in the high pressure air at the front of the scoop has somewhere to go and starts flowing...

    If I stand next to my car with the fan on and have a feel around for where the air is coming out, there's hardly anything coming out the side vents when its stationary, its all coming from underneath the car. As with probably most cobras my rad is angled backwards slightly so the air is already on a slightly downward trajectory so it makes sense it would naturally wash over the lower part of the engine and out underneath.

    Dave A

  3. #33
    Join Date
    May 2011
    Location
    Flimwell
    Posts
    777
    When I bought my pre-owned Dax body 8 or 9 years ago it came with a rear facing bonnet scoop. It was quite big too. When I queried it with Dax they told me it was a customer one-off but they had made a couple over the years.
    Might well help cool things down but looked really weird so I never fitted it.
    Colin
    Dax Standard Chassis. Ford 302, AOD auto, DB s/s sidepipes, 2017 T reg.

  4. #34
    Join Date
    Dec 2011
    Location
    Rugby,West Midlands.
    Age
    60
    Posts
    596
    Quote Originally Posted by hifihedgehog View Post
    I remember doing some work at uni on bonnet scoop size and orientation, mainly research on existing published work with a bit of our own verification in cfd and it was really interesting. The bonnet scoops on cobras would probably be more effective if they were facing backwards. If a forward facing scoop is too small or narrow, the faster you go the air sort of queues up to get in and you get a big high pressure blob of air just standing around doing nothing, the opening effectively becomes blocked off at high speeds. The rad opening in the front of the nose is probably where most of the air gets in. If the scoop faces backwards then once you've achieved some minimum speed depending on the shape of the bonnet and scoop you get a low pressure area which draws the air in far more effectively than a front facing scoop (unless the front facing scoop is absolutely enormous).

    With a narrow top scoop it wouldn't surprise me if hardly any of that nice cool air is going anywhere useful. With a narrow letterbox bonnet scoop opening unless you've got a turkey pan setup I would expect that most of the air feeding the carb has probably already been through the radiator and washed its way over the top of the engine, especially if your just cruising along high speed but low load. Perhaps when the engine is trying to gulp some air in the high pressure air at the front of the scoop has somewhere to go and starts flowing...

    If I stand next to my car with the fan on and have a feel around for where the air is coming out, there's hardly anything coming out the side vents when its stationary, its all coming from underneath the car. As with probably most cobras my rad is angled backwards slightly so the air is already on a slightly downward trajectory so it makes sense it would naturally wash over the lower part of the engine and out underneath.

    Dave A
    While I was conducting air flow tests using an air velocity meter borrowed from work, to see how various aperture sizes on different grills restricted the amount of air passing through, before I designed and fitted my radiator stone guard /grill, I set up a huge fan blowing air at the bonnet scoop and a reasonable amount of air entered the scoop, which was probably helped by my AK having a fairly large scoop opening. However, when I tried different sized grills in the scoop, there was practically no air entering the scoop, which is why I decided not to fit a grill to the scoop.

    The side vents on most cars work better while the vehicle is moving forwards .As the air enters the engine bay via the open front and the bonnet scoop ,and the air on the outside of the car rushes past the side vents, it creates a difference in air pressure over the vent, which sucks the air out the engine bay.
    Paul.

    AK Huddart Chevy 383 Stroker, BMW Royal Grey Metal Metallic , 5 speed Jaguar Getrag , Holley 670cfm 4 barrel street Avenger Carb, 450 BHP at flywheel , 460 Ibs/ft torque, and luvin it !

    " We dont stop playing because we grow old, we grow old because we stop playing" - George Bernard Shaw.

  5. #35
    Join Date
    Aug 2002
    Location
    Through the Darien Gap
    Posts
    1,027
    The 2nd Generation Pontiac Firebird Trans Am 'shaker' scoop had the air inlet at the rear based on the very same logic.


    Attached Images Attached Images
    Steve Brown

    CRC Regional Rep - East Anglia

  6. #36
    Join Date
    Dec 2011
    Location
    Rugby,West Midlands.
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    596
    Quote Originally Posted by aaronjb View Post
    Downside being, in my experience (on a previous car) that the coating stayed on about, ooh.. two weeks? After which the exhaust looked worse than before. Coating was done by Camcoat, so a professional outfit.. Performance 1 or Zircotek have good reputations these days, though I would guess at £500-1000 to coat a set of V8 headers.
    Cost for Zircotec to ceramic coat my two SBC Stainless Steel tubular manifolds would be a whopping £ 571 in total, which is way more than I expected, and I am not prepared to pay that much, so as some of you guys have wrapped your manifolds without problems to good effect and Jon’s comments have mirrored pretty much what the guy at Zircotec told me, which was that decent wrapping done properly pretty much matches the ceramic coating for heat retention. The advantages to ceramic coating, was aesthetics and permanency, as the coating should not deteriorate if done properly, whereas he said wrapping over time discolours and its integrity/efficiency deteriorates. Also wrapping trap moisture, but with a stainless steel manifold, this should not be a problem. So I will be looking for a decent wrap, and at least I won’t have to remove my side pipes and manifold now.

    Ths list just gets bigger and bigger, i need to retire
    Paul.

    AK Huddart Chevy 383 Stroker, BMW Royal Grey Metal Metallic , 5 speed Jaguar Getrag , Holley 670cfm 4 barrel street Avenger Carb, 450 BHP at flywheel , 460 Ibs/ft torque, and luvin it !

    " We dont stop playing because we grow old, we grow old because we stop playing" - George Bernard Shaw.

  7. #37
    Join Date
    Feb 2011
    Location
    Northampton
    Age
    41
    Posts
    3,895
    You can get paint designed to go over the top of the wrap and make it more waterproof .. I would imagine it's far from 100% effective, but it's an option I didn't paint mine and it did discolour, but then so did the stainless manifold
    My DeDion build diary..
    Hon Sec of the Digidash branch of the Unpopular Kit Car Design club

  8. #38
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    8,560
    Had my tubular headers coated with Zircotec premium white for similar price quote above. Looked nice when first done, now they look a bit grubby and show a few signs of odd bits of superficial rust.

    Ofcourse I dont know how hot everything would get without the coating, but i can say the headers are still bloody hot, as is the engine bay.

    If doing it again, I would be temped to just spray the headers in high temp barbeque paint using a rattle can.
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  9. #39
    Join Date
    Feb 2011
    Location
    Northampton
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    41
    Posts
    3,895
    On the road yet, Kev? Or are the headers just keeping the garage warm
    My DeDion build diary..
    Hon Sec of the Digidash branch of the Unpopular Kit Car Design club

  10. #40
    Join Date
    Jan 2002
    Location
    Reading, Berks, UK.
    Posts
    1,573
    Quote Originally Posted by aaronjb View Post
    On the road yet, Kev? Or are the headers just keeping the garage warm

    Ohhhhhhhhhhhhhh Biatch

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