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Old 05-29-2020, 11:08 PM   #21 (permalink)
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Originally Posted by California98Civic View Post
It's really quite clear to me what aerohead is arguing: re-examine the previous page. There, the VW flow body longtail, the closest to the template, has the lowest drag of these four shapes (0.14). So if we argue that these are four ways to the LOWEST drag, we'd been incorrect since their Cd figures were not the same (VW flow body longtail, the template roughly, was lowest). Lowest is lowest, just like fastest is fastest.

That's not my argument. I don't have the second edition. I have the 4th.
The VW flow body longtail is only closest to the template?! Surely then we should all be using the VW flowbody long tail as the template, and not something that is only close? Then, once we are using an even more correct template, we'd all get even better results with our car modifications, no?

I just believe that, for people modifying their cars to achieve lower drag, all these templates (pick whichever one you want) are almost completely irrelevant.

That would certainly not be the case if we were developing solar race cars, or even human powered vehicles, but for people modifying their road cars, I just can't see it. But I can see people wasting a lot of time following a special curve that they're been assured will give them best results.

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Old 05-29-2020, 11:25 PM   #22 (permalink)
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Originally Posted by JulianEdgar View Post
... I just believe that, for people modifying their cars to achieve lower drag, all these templates (pick whichever one you want) are almost completely irrelevant. ...
That's your belief? I think you mean you don't PREFER them. But they are effective. The tests of the various boat tail projects modeled on the angles and compound curves of the template that I posted and that you admitted you were not surprised would show a benefit demonstrate that one can use the template to effecctively modify road vehicles for greatly reduced drag. The Gen1 Insight projects of Botsapper and MetroMPG on this site reported 9 to 15% improvements in FE in testing. They proved its an effective approach.
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Old 05-29-2020, 11:41 PM   #23 (permalink)
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Originally Posted by California98Civic View Post
That's your belief? I think you mean you don't PREFER them. But they are effective. The tests of the various boat tail projects modeled on the angles and compound curves of the template that I posted and that you admitted you were not surprised would show a benefit demonstrate that one can use the template to effecctively modify road vehicles for greatly reduced drag. The Gen1 Insight projects of Botsapper and MetroMPG on this site reported 9 to 15% improvements in FE in testing. They proved its an effective approach.
Well I did ask you for links to threads where there had been proper testing of various different template style shapes for real car modification, but you didn't reply.

Yes, I think following a template in the mistaken belief that will get you a stellar outcome is wasting people's time. Far better that they do some testing and find out what is optimal on their cars.

As for your examples, as I've already said - if the extension has attached flow down to a smaller wake, I'd expect pretty good results... template or no template.

To make it categorically clear, I think posting a template for car shape on a discussion group and very strongly implying that it is the best shape for people to follow (no matter their car) is misleading and wasteful of people's time.

It might have been helpful in a past era when testing panel pressures, drag and lift were difficult, but that is not the case now.
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Old 05-29-2020, 11:56 PM   #24 (permalink)
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Well I did ask you for links to threads where there had been proper testing of various different template style shapes for real car modification, but you didn't reply. ...
I had already given you testing results. Exellent examples that show ways in which it works. I am not your research assistant. If you want more, you know how. Your beliefs are your own. The evidence is all there.
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Old 05-29-2020, 11:58 PM   #25 (permalink)
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The template is just like any other rule of thumb in car modification.

Like, run 12.5:1 air/fuel ratio for best power.
(In fact, you'll often find that best power comes from AFRs that are not 12.5:1. It depends on the engine.)

Or, suspension natural frequency should be 1:1.3 front/rear.
(Yes, if you want to reduce pitch. But sometimes you'll find that pitch accelerations are the least of your worries.)

Or, size your turbo so that you get peak torque by 1/3rd redline rpm.
(That's one I like but for many people, it will limit top-end power too much.)

Rules of thumb are useful for people who have no idea at all, but in nearly every case, where you can do some testing on your own vehicle, you'll achieve better results than by using rules of thumb.

And the beauty of aero modification is that it's so easy to test different approaches on your car.

(And I am sorry, but citing a modification and then saying 'it worked' is not evidence that the approach is the best. I could say that about 12.5:1 AFR, 1:1.3 natural frequency, or turbo sizing. "It works!")
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Old 05-30-2020, 12:22 AM   #26 (permalink)
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I already know all that Julian, as do lots of people. It takes no special training. And it's beside the point. I showed you tests of applications and not mere vivid assertion of success and what's best for all vehicles in all circumstances. You have a crappy method of of dialogue, dude. Didactic condescension like this is a real turn off. Good luck with that book you're selling.
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Old 05-30-2020, 12:56 AM   #27 (permalink)
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Originally Posted by California98Civic View Post
I already know all that Julian, as do lots of people. It takes no special training. And it's beside the point. I showed you tests of applications and not mere vivid assertion of success and what's best for all vehicles in all circumstances. You have a crappy method of of dialogue, dude. Didactic condescension like this is a real turn off. Good luck with that book you're selling.
I am sorry that you cannot see the parallels. The template is a good example of a rule of thumb being applied to car modification. People love rules of thumb in car modification because they are easy, but in every area of car modification that I know of, testing beats rules of thumb every time.

(And so far, you haven't shown me even one test where different 'template approaches' were compared. You've shown me some successful outcomes that followed one template, and said: there you are. I could equally show you an engine successfully running 12.5:1 AFR and say: there you go.)

I think that rules of thumb in all areas of car modification should be avoided, as they often deceive as much as they enhance knowledge. In my car modification books I avoid using rules of thumb as much as possible.

In fact I'd go further: as soon as you see a rule of thumb stated in any area of car modification, be very skeptical.
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Old 05-30-2020, 01:24 AM   #28 (permalink)
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Sure Julian. Rules of thumb. Be skeptical. I remember my mom teaching me that when I was a teen. Thanks for the reminder. Your style of marketing here reminded me of someone:

I am sorry if you cannot appreciate the parallel.
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Old 05-30-2020, 01:39 AM   #29 (permalink)
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Marketing? If I were here to market my book, I'd agree with every silly thing that people said. And, unfortunately, there would be a lot to agree with!

Rules of thumb abound on this group, and very few people ever challenge them. So yes, I think a warning against using rules of thumb in car modification is very apt here.

In fact I did a video on it a while ago:



I am sure you'll enjoy the comments and my responses - more of my marketing!
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Old 05-30-2020, 02:12 AM   #30 (permalink)
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Professor Wagstaff! Such epistemology, such methodology! Oh, benighted internet, your rule of thumb, he's against it!

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