Hamish Posted February 15, 2020 Report Share Posted February 15, 2020 (edited) Took my bonnet to this guy in rural Coventry area young bloke who has an old unit full of old engineering wizardry I’ll share the results my dremel and hammer method would have taken ages Louvres punched into your bonnet Modified Car Hot Rat Rod Custom Historic Racing https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F283742763771 Edited February 16, 2020 by Hamish Correct link Quote Link to post Share on other sites
BlueTR3A-5EKT Posted February 16, 2020 Report Share Posted February 16, 2020 Thank you Hamish Peter W Quote Link to post Share on other sites
Hamish Posted February 19, 2020 Author Report Share Posted February 19, 2020 Just got this picture by text to say louvres ready. will collect Saturday and post more. looks great. And done in a timely manner as promised. Quote Link to post Share on other sites
John Morrison Posted February 19, 2020 Report Share Posted February 19, 2020 Looks really good Hamish, you should be chuffed. John. Quote Link to post Share on other sites
john.r.davies Posted February 19, 2020 Report Share Posted February 19, 2020 Louvres look good, but are dreadful air extractors. The first one works, but thickens the boundary layer behind it so that the next is about a third as effective. The one after that is a third of a third, and so on. Just saying - they look really nice! Quote Link to post Share on other sites
Hamish Posted February 19, 2020 Author Report Share Posted February 19, 2020 32 minutes ago, john.r.davies said: Louvres look good, but are dreadful air extractors. The first one works, but thickens the boundary layer behind it so that the next is about a third as effective. The one after that is a third of a third, and so on. Just saying - they look really nice! John most of it is performance related as everyone knows that louvres make you go faster. Just like stripes do. then it’s looks then it’s to let a bit of heat out, but typically when stationary waiting for your run in the sprints or up the hills. As the longest run has 7 louvres what is the performance of the last one ? Quote Link to post Share on other sites
Bfg Posted February 19, 2020 Report Share Posted February 19, 2020 (edited) ^ surely it is less about airflow over them as pressure differential under-bonnet and over bonnet ? ..or as Hamish says ; thermal convection (and perhaps a little air movement courtesy of the cooling fan). . Edited February 20, 2020 by Bfg Quote Link to post Share on other sites
john.r.davies Posted February 20, 2020 Report Share Posted February 20, 2020 (edited) 11 hours ago, Hamish said: John most of it is performance related as everyone knows that louvres make you go faster. Just like stripes do. As the longest run has 7 louvres what is the performance of the last one ? LOL! And for 7 louvres the last one will be 3^7 = 2187 times less effective. More or less. And BFG, a large hole with the same area would deal with any pressure diference, but FLOW is a different matter! Edited February 20, 2020 by john.r.davies Quote Link to post Share on other sites
Bfg Posted February 20, 2020 Report Share Posted February 20, 2020 11 minutes ago, john.r.davies said: a large hole with the same area would deal with any pressure difference, but FLOW is a different matter! Absolutely agree with you John ..and large holes are indeed often done, particularly along the sides of the car (albeit then fitted with mesh or a grille to dissuade inquisitive little fingers from exploring the shiny bits inside). However on the top face of a panel ; louvres do help deter driving rain &/or beads of water which ride up the length of the bonnet from going in. This is an issue with some layouts because HT leads, the starter motor, or a battery are directly under the hole. Unfortunately some louvred bonnets have this issue when the car is parked because then water can run forward from the back edge of the bonnet and into the louvre. This is not uncommon on the Jaguars E-type ..and I recall the same on my Mk.2 Spitfire which was fitted with a GT6 bonnet. Perhaps the central bonnet bulge worsens the situation because it seems a less common issue with other marques such as the big Healeys. Pete Quote Link to post Share on other sites
TR NIALL Posted February 20, 2020 Report Share Posted February 20, 2020 That’ll look excellent Great Job. Quote Link to post Share on other sites
Hamish Posted February 20, 2020 Author Report Share Posted February 20, 2020 2 hours ago, john.r.davies said: LOL! And for 7 louvres the last one will be 3^7 = 2187 times less effective. More or less. And BFG, a large hole with the same area would deal with any pressure diference, but FLOW is a different matter! Thanks John. I knew someone out there could do the maths for me. but the 2187 is a good omen number as it’s my cc. 87mm bore. so I’ll take that. water ingress is a concern but I hope there isn’t too much bonnet up stream of the louvres for very much water to flow into them. as the bonnet will be black I don’t expect the louvres to be too “in your face bling” BFG quote..or as Hamish says ; thermal convection (and perhaps a little air movement courtesy of the cooling fan) Now there is an idea fit a flat flush elec fan on the underside of the bonnet to blow the hot air out hhhmmmmm. Quote Link to post Share on other sites
Bfg Posted February 20, 2020 Report Share Posted February 20, 2020 5 minutes ago, Hamish said: water ingress is a concern but I hope there isn’t too much bonnet up stream of the louvres for very much water to flow into them. I don't suppose you have an issue with this because of your bonnet's shape. I'm guessing water would run off to the sides (..which isn't possible on the e-type or GT6's bulbous wing + centre bulge shape of their bonnet). Personally speaking I think they'll both look good on your car and serve the purpose you ask of them. Pete Quote Link to post Share on other sites
iain Posted February 20, 2020 Report Share Posted February 20, 2020 (edited) Hamish, just for fun you could apply an array of thick cotton tell tales on the bonnet and film with your action cam! We’ll soon know who is the aerodynamicist ........I know where my money will go! Iain Edited February 20, 2020 by iain Quote Link to post Share on other sites
john.r.davies Posted February 20, 2020 Report Share Posted February 20, 2020 Taking BFG's point, a large extractor hole does need a small frontal lip, rather like a single louvre. This reaches through the boundary layer and trips the ambient flow into a vortex in the mouth of the hole. Fast vortex = low pressure, so it sucks out the air beneath! It does need a sloped back to the hole (not more than 15 degrees to avoid stalling). You can see here an effective one I installed on a previous Vitesse: OK, that's on the side, so not much water can get in, and any that does, falls down onto the road. But in a horizontal surface, that sloped back will prevent direct rainfall, and could be shaped to collect any water and direct it away from vulnerable parts, if necessary by a pipe. John Quote Link to post Share on other sites
Hamish Posted February 20, 2020 Author Report Share Posted February 20, 2020 6 hours ago, iain said: Hamish, just for fun you could apply an array of thick cotton tell tales on the bonnet and film with your action cam! We’ll soon know who is the aerodynamicist ........I know where my money will go! Iain Iain you will have to remind me when it’s fitted and I’m back on the road. Quote Link to post Share on other sites
Hamish Posted February 24, 2020 Author Report Share Posted February 24, 2020 Well it’s ready for primer and paint. took me ages to cut with a dremel then hammer the louvres. Quote Link to post Share on other sites
brenda Posted February 24, 2020 Report Share Posted February 24, 2020 H they look fantastic, are you keeping the bonnet black as before, I think you made the right decision to have them done professionally as it’s such a focal point. Mike Redrose Group Quote Link to post Share on other sites
Hamish Posted February 25, 2020 Author Report Share Posted February 25, 2020 Well it’s in primer after rubbing down the metal edges. Quote Link to post Share on other sites
4Mal Posted February 25, 2020 Report Share Posted February 25, 2020 They look lovely Hamish. Definitely driver motivation! Don't worry about the airflow calcs......the only thing to worry about would be if they were the wrong way round Quote Link to post Share on other sites
john.r.davies Posted February 25, 2020 Report Share Posted February 25, 2020 Beautiful work, Hamish! I see your forming tool. Do you have a dolly or an 'anvil' for the other side? JOhn Quote Link to post Share on other sites
Hamish Posted February 25, 2020 Author Report Share Posted February 25, 2020 1 hour ago, john.r.davies said: Beautiful work, Hamish! I see your forming tool. Do you have a dolly or an 'anvil' for the other side? JOhn Sorry John I couldn’t resist suggesting they were hand done I’m afraid I could only ruin a panel if I set about it with a hammer and dolly etc if you check out the link on my first post you will see that Graham an engineer in rural Coventry did my louvres for me as he could cope with a full size panel. Very please with his work and dealings. where I now work the fly press can only cope with 12” from an edge. But can make Louvre panels to weld in, but I wanted the bonnet pressed. one of the painters is doing a quick blow over paint job for me using my original black paint. In between jobs. H Quote Link to post Share on other sites
John Morrison Posted February 25, 2020 Report Share Posted February 25, 2020 Spot on Hamish, well sorted. John. Quote Link to post Share on other sites
john.r.davies Posted February 25, 2020 Report Share Posted February 25, 2020 Hamish - you tease! This is a louvre tool made and shown by Geoff Purnell, in his book The Car Restorer's Workshop Companion Quote Link to post Share on other sites
Hamish Posted February 26, 2020 Author Report Share Posted February 26, 2020 Sorry John. that looks like a complicated bit of kit. Look like to make that is harder than doing the louvres. Quote Link to post Share on other sites
Hamish Posted March 7, 2020 Author Report Share Posted March 7, 2020 All finished and fitted. Quote Link to post Share on other sites
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