1.5" DIY ISC rear top hat interference - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 01-02-2015, 01:58 PM   #21
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gotcha.
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Old 01-02-2015, 04:49 PM   #22
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Here are the measurements I took last night with the three hats in the rear. I measured from the fender to center of axle like I do to measure ride heights.

NB hat:
Droop = 16.5" Compressed = 10.5" (lots of room around tire)

1" top hat:
Droop = 16" Compression= 9.5" (room around tire, doesn't hit a-arm)

1.5" top hat:
Droop = 15.5" Compression = 9.75" (a-arm hits)

I am shooting for close to 13" ride height.

I started looking at adding a spacer under the bump stop or using taller bump stop to keep from metal on metal contact, but I feel safer on the 1" top hat where I know I won't be hitting anything. I will eithen make another set of 3/4" for the fronts or more than likely throw the NB hats back in.

What is the ideal split in travel between droop and compression, 50/50 ? Or do you want more compression travel than droop?
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Old 01-09-2015, 03:41 PM   #23
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I've read anywhere from 50/50 to 60 comp/40 droop. I'm sure it depends on the car, driver, road surface, etc. I'd planned on just being somewhere between the two ranges and calling it a day.

FWIW, I'll be playing this game shortly, once I finish with all the other junk laying around waiting to be fixed.. grumble grumble grumble.
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Old 01-09-2015, 03:45 PM   #24
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Quote:
Originally Posted by sbcrx007 View Post
I've read anywhere from 50/50 to 60 comp/40 droop. I'm sure it depends on the car, driver, road surface, etc. I'd planned on just being somewhere between the two ranges and calling it a day.

FWIW, I'll be playing this game shortly, once I finish with all the other junk laying around waiting to be fixed.. grumble grumble grumble.
Unless you're getting non-standard length shocks, realistically your compression is limited by the tire or control arm hitting the chassis and your droop should just be whatever is left of the stroke.
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Old 01-09-2015, 04:31 PM   #25
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Well yeah of course, but where you're at in the stroke with the car on the ground and settled is otherwise ride height dependent. So assuming a set ride height, you can still target a certain range of comp/droop by adding extension to the top hats, right?
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Old 01-09-2015, 04:35 PM   #26
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Assuming a set ride height and a set shock length there is only one correct comp/drop ratio.
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Old 01-09-2015, 04:44 PM   #27
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Right, isn't that what Relte is asking? And to get to that ratio, he is using extended top hats.
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Old 01-09-2015, 04:50 PM   #28
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Right. But I cant tell you what the correct ratio is. Its whatever happens when you use an appropriate length bump stop that hits infinite rate just before the control arm or tire hits the chassis, and then whatever droop results.
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Old 01-09-2015, 04:55 PM   #29
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Hmmm... I think I see what you mean, thank you. You could keep moving the top of the shock higher and higher, but the A-arms still hit the frame at the same point regardless. Cool beans. I'm assuming this is all patently obvious once you're under the car with a tape measure...
Quote:
1.5" top hat:
Droop = 15.5" Compression = 9.75" (a-arm hits)
So, he just needs a bump stop long enough for the a-arm not to hit, and that's basically as good as it gets, whatever that ratio works out to, as it won't get any better short of custom arms. Agree?
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Old 01-09-2015, 04:58 PM   #30
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Theres some magic here in how long and what rate bump stop because you want the stop to be unnoticeable when it engages. But you still need to end up with the stop hitting infinite spring rate just before contact happens.
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Old 01-09-2015, 05:03 PM   #31
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Right, so probably a progressive rate bumpstop would be preferred. You could jack up the car on that corner sans spring to try compressing the bumpstop to see where it ends up, but thats only 1g on the bumpstop, not the 3-5gs it might see on the road.. although hopefully it's not seeing that high of loading on the track. My home track maybe, haha.
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Old 01-09-2015, 05:06 PM   #32
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Thats basically what I do. You're hitting essentially infinite rate when the chassis lifts off the jack stands, at most you're talking a 32nd of an inch more travel.
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Old 01-11-2015, 12:50 PM   #33
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I ended up adding one 1/8" rubber washer from Lowes on each corner. In the rear I used the BFH to massage the low point arout the upper shock mount where the upper rear a-arm was hitting. With the shim, I can lift the whole back end of the car off the lift and still maintain > 1/8" clearance between the arm and chassis.

I test drove it yesterday and it feels sooooooooo freaking much better on rough roads. No metal to metal contact even on real rough roads with big bumps. It also feels a lot more confidance inspiring when pushing it to the limit. I can't wait to take it on my daily route to work so I can really tell how much the ride quality has improved.

Last edited by Rallas; 01-11-2015 at 07:07 PM.
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Old 01-11-2015, 07:12 PM   #34
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Here are some pictures of the 1/8 spacing washer I added and the massaging I did with the BFH.









Attached Thumbnails
1.5" DIY ISC rear top hat interference-20150110_104519_resized.jpg   1.5" DIY ISC rear top hat interference-20150110_104626_resized.jpg   1.5" DIY ISC rear top hat interference-20150110_114955_resized.jpg   1.5" DIY ISC rear top hat interference-20150110_115153_resized.jpg   1.5" DIY ISC rear top hat interference-20150110_120031_resized.jpg  

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Old 01-12-2015, 10:11 AM   #35
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Looking good, your top hats look like mine - I had the same thought with some nubs on the spring OD as retainers.. Nice work.
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Old 01-13-2015, 11:19 PM   #36
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I found that 1 inch tophats front and rear worked best for me.
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Old 01-14-2015, 08:43 AM   #37
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I had a real world test last night when I hit a monster pothole. I though I bottomed out for sure, but checked everything front and rear with no evidence of bottoming out.
The car is handling the rough roads to work much better now, but I'm still getting a lot of chassis movement. It just feels like the shocks are not dampening the springs.
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Old 01-19-2015, 10:03 AM   #38
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Who revalved them?
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Old 01-20-2015, 09:46 AM   #39
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Our nearest and dearest Bernie!
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Old 01-28-2015, 02:34 PM   #40
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I'm a bit confused as to your compressed height measurements. How can the 1" top hats allow travel to 9.5" at full compression, but 1.5" hats only go to 9.75" before the A-arm hits? Shouldn't the A-arm hit at the same ride height regardless of the top hat used?
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