#71
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Hi Richard, you have done a lovely job on your transition cone and have thought the process through logically. Is this for your family road car ,or your racing car?? If it is for your racing car,could I offer some unsolicited advice?
Im not trying to teach my grandmother to suck eggs ,but there may be some things that you, or others are not aware of.The idea of extractors is to have a "slug" of exhaust gas from a previously fired cylinder just passing the pipe intersect as the exhaust valve opens so that the gas in the cylinder sees a negative pressure and rushes out to fill the void faster than it would if just pushed out by the piston.Pretty basic and well known .Not so easy to achieve.Once the mathematics have been done ,and this is the same maths as open ended organ pipe theory in church organs,the pipe size calculated and the lengths of the primaries , secondaries etc the trick is to get it all to fit in the physical space available and get the lengths correct and equal.Nearly impossible especially in a RH drive BMW (the 2002 being nearly the worse)Now , the exhaust tuners and racers ace in the hole.if things are not perfect the cylinder can see a slug reversion coming back at the valve when it opens having the exact opposite effect and negating all the good fabrication work.The time honoured way to fix or allieviate this is to have a reversion "ring" for want of a better word. This requires the pipe inside diameter to be 1/8" bigger than the port diameter so that any returning slug sees a 1/16" ring,or reversion "stopper" and reverses in the correct direction to do its intended job.So ,if your port area is the same as ,say a 1 1/2" round port then you need to have a pipe with 1 5/8" ID or 1 3/4" OD if you are using 16 guage tube.Always do your maths and strive for equal lengths, but this trick will see you not gain horsepower, but not loose it to reversion,a very hard thing to pick on a dyno ,but easy to see in back to back tests with pipes made exactly to port diameter and those with the reversion ring.If its just for your road car ,disregard this ,but put it in the memory bank for the racing car set.Qualifications for these thoughts?? 46 years to date making sand bent extractors(headers) for everything from Manx Nortons to F1 engines and all the stuff in between.Good luck and Cheers Greg
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Greg Smith |
#72
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A supercharged Hillman ,dear to the hearts of Kiwis and Aussies,and a F5000 set to give you some space, length and suspension constraint ideas.The BMW will be a real test as that steering box is right in the way and tacking in place through the inner guard is a nightmare!! All the best with it,looking forward to seeing your results.
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Greg Smith Last edited by Steve Hamilton; 08-01-2017 at 07:34 AM. |
#73
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Hi Greg. Thanks for the sage words - this is in fact the old 633 road car, so is just for looks and a bit more noise. I'm quite an old fart really and many many years ago followed Dave Vizard who I remember posted huge gains with anti reversion stubs on a 2.0ltr Pinto engine, allowing him to run say a race cam in a rally application and have it still produce torque from relatively low rpm. The issue here is that the space is really really cramped and even running 1 5/8 primaries would probably increase the CLR of the bends and hence clout the steering box, or require that to remove the headers, you first dropped the diff and sent a trained ferret in through the headlights etc... Also not a hope of making the headers equal length in this application. The race car was different as it is a turbo application, but wish I'd had the mockup kit to help with the development of that. If it's not quite right we will just have to turn the boost up a few PSI Mate, lovely work on the sand bent headers! Oohh Manx Norton...
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Richard "I know nothing. I from Barcelona" (Manuel - Fawlty Towers) Link to our racecar project https://www.facebook.com/pages/Elan-...ab=public&view |
#74
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Ok - I'm nearly back... Wireframes
Few distractions of late, but I'm nearly back onto the Group 5 bodywork.
My buddy, a local metalshaping god, is a huge fan of MDF bucks, but I bloody hate the dust and can't get my head around building a dirty great heavy eggcrate buck, which for example will fit around the rear mounted radiators. So for better or worse, I'm going to try to make a wireform. I have a bunch of bright drawn rod and figure that I'll probably hit the joins with the mig. However I've been trying to research how people have gone about bending and curving said bright drawn rod. There seems to be precious little on any of the forums or on the web. I quite like the look of the little bench mount thingy from Eastwood - http://www.eastwood.com/eastwood-rod-forming-tool.html? which if mildly abused will create fixed radius bends with the various rollers and also if used to nudge the rod at intervals, also sweeping larder radii. Have enough scrap and new stock here to knock something like this up. So a question please for all of the sages who have been down this road many times - are there other time honoured methods of rod wrangling? Bend over knee Bend over gas bottle Bend over corner of bench etc... Any pearls of wisdom on wireframe bucks gratefully received. Thanks.
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Richard "I know nothing. I from Barcelona" (Manuel - Fawlty Towers) Link to our racecar project https://www.facebook.com/pages/Elan-...ab=public&view |
#75
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I’m not an expert, but I have built a wire frame buck once. If you don’t have the radius that you need lying around, cut a radius out of plywood and bend the rod around that. 1/4” (6mm) is not too hard to form with your bare hands. When you’re done with the first side, cut the tacks and reassemble into the mirror image.
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Bob Innes |
#76
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Cheers Bob - yes I've used a ply/mdf/chipboard former before when I bent the square tube for the rear wheelhouses. Works well but you need to calculate or guess the springback. My MDF buddy said that the side radiuses should all be the same when building diaphragms, but just to vary the rear dimension to account for the change in plan profile. You could use a fixed former to generate the wire forms and then shorten the horizontal dimension I guess.
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Richard "I know nothing. I from Barcelona" (Manuel - Fawlty Towers) Link to our racecar project https://www.facebook.com/pages/Elan-...ab=public&view |
#77
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nice to see you getting back on to it richard
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Neil |
#78
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Good source of info, the Art of bending from Di-Acro.......
https://www.diacro.com/wp-content/up...nding_2013.pdf If you have access to a lathe and a mill, you could make your own copy? I made a copy of the Di-Acro bender years ago using a large bearing, worked great!
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Kevin. |
#79
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Cheers Neil - been a bit going on. Kids got me into bikes again, joined a gang (finally a fully patched member at 62) done 10,000 kms in the last 6 months, big mechanical refurb on the old 6 Series, t'boss just gone through a pancreatic cancer op, we are in the middle of a refurb of the family home and have been let down by a number of the trades, plus we have to be out of the rental at the end of January. What did the Queen say about 'horrible anus' or something?
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Richard "I know nothing. I from Barcelona" (Manuel - Fawlty Towers) Link to our racecar project https://www.facebook.com/pages/Elan-...ab=public&view |
#80
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Quote:
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Richard "I know nothing. I from Barcelona" (Manuel - Fawlty Towers) Link to our racecar project https://www.facebook.com/pages/Elan-...ab=public&view |
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