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Old 12-08-17, 09:43
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Cameron Cameron is offline
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Shifting A Sequential Gearbox!

Hello chaps,

I've been rather quiet on here recently as I've been building another 205.. this one has a Formula Renault 2000 engine with Sadev sequential gearbox. As we get nearer to its track debut I have a question about gearshifts - particularly downshifts and how best to do them. Searching the interweb yields a whole load of contradicting info as you'd expect, so I figured ask where the majority of drivers will be using these boxes regularly.

The car uses a DTA with flatshift (switch to initiate and closed loop via barrel position to complete) so I'm not worried about upshifts.

However, I've set the car up with a linkage on the throttle connected via cable to the shift lever, so when pushed to downshift it opens the throttle for an auto-blip. My understanding of sequentials comes from reading an excellent article by Mr Hewland (which unfortunately I can't find anymore) who states you want to shift as quickly as possible for smooth changes (and therefore good life on the dogs) and never under any circumstances try to change like a syncro - i.e. with the clutch and throttle. However, there are loads of people out there, and loads of footwork videos, saying for downshift you MUST both dip the clutch and stab the throttle.

This seems to be totally contrary to Hewland's advice, which is to EITHER dip the clutch (if you can't / don't want to heel-toe) or stab the throttle to unload the dogs, but never do both.

My actual experience with sequential boxes is limited to test-driving this car, so probably barely 100 gear changes. But when testing the auto-blip yesterday I downshifted with zero pedal input (other than the brake) and seemed to get smooth, quick, consistent shifts. This seems to square with the method of paddle-shift systems, which do not use the clutch and only blip the throttle but still manage perfect shifts.

So which is it? What do you do to downshift and how has it worked out for you?
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Old 12-08-17, 09:47
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A pic of the car..

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Old 12-08-17, 10:28
RobertT RobertT is offline
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Radical SR8 has an excellent gearshift system with uses various inputs from Life ECU (that tbh I dont fully understand) and has a Geartronics Box. No clutch is used up or down once the car is moving but it does use a throttle blipper. Its recommended that you change gear at high revs, and if your going at low revs, use the clutch before pulling the shift paddle. Very little dog wear ever seen on this box. Shift is very quick with a air pressured cylinder. Very cool feature is that if you order a downshift and it would buzz the engine, it doesnt action.

ps. love your cars dude.
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Old 12-08-17, 20:47
Dj_mini Dj_mini is offline
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Have you spoken to Steve at swr? (sadev) may be worth a shout we fitted one in a mates rally car that Steve supplied great people to deal with.

Any more pics of the 205?
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Old 12-08-17, 23:19
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Having used the set up that Cameron has (with DTA) and spoken to SWR about it, clutch use on the up and down changes are what Steve recommended to prevent dog wear (the gears and dog rings are v expensive), to have an amount of delay where up shifts are easy with flat shift if you really want to use it and only Geartronics for up and down shifts. His opinion may have changed in the past few years however.
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Old 13-08-17, 10:32
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Thanks for the responses. I did speak with SWR quite a lot while building the car as they inspected our gearbox.. his advice for upshift was just let the flatshift system do the work. I don't remember him giving any specific advice for downshift though.

I think I'll play it by ear tbh.. I'll try downshifts both with and without clutch input and see how it responds. Certainly my testing at ~3-4krpm seemed to work very nicely without the clutch but I'm sure it could be different under track / race load.

A full build for this car can be found here!
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Old 13-08-17, 22:11
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Hi Cam

My EcoBoost (Life ECU) has a throttle blipper (it uses drive by wire) and the clutch is not used for downchanges. So long as you have some means to remove the load on the dogs, it should shift down without the clutch. Blipper is essential I'd have thought to achieve this.
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Old 14-08-17, 16:55
darkone darkone is offline
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Hi Cam

The moment you take your foot off the throttle you have unloaded the gearbox, the throttle blip is to match the revs required by the lower gear. Most sequentials will go down the box without a blip but doing so puts a lot of strain on the box.

Regards Len
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Old 14-08-17, 20:41
Dj_mini Dj_mini is offline
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Wow what a build thread cameron a credit to you!
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Old 14-08-17, 22:02
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Quote:
Originally Posted by darkone View Post
Hi Cam

The moment you take your foot off the throttle you have unloaded the gearbox, the throttle blip is to match the revs required by the lower gear. Most sequentials will go down the box without a blip but doing so puts a lot of strain on the box.

Regards Len
That's not correct, lifting off loads the dogs in reverse. The blip while decelerating has the same effect as lifting while accelerating, it momentarily unloads the dogs allowing for a smooth change with the clutch.
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