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Sprite Rear end ratios

Posted by lrderry

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Sprite Rear end ratios #1
lrderry Mark Derry Chicago, USA 1968 Austin-Healey Sprite	Posted: July 04, 2012 10:07AM Registered: 6 years ago Posts: 40

Need some help
Recently went from a stock gearbox to a SCCR box in my 1275 vintage Sprite and while now going through the twisty bits extemely well, I have actualy increased my laptimes significantly overal. I feel like I am going realy fast but in actual fact I am going slower!!!!
Out of interest what rear end ratios are recomended for a SCCR box. Most of my racing is done at Blackhawk (short track) with a once a year pilgrimage to Road America (long fast track)
Thanks in advance
Mark

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Re: Sprite Rear end ratios #2
dickmoritz Dick Moritz Philly 'burbs, PA, USA	Posted: July 04, 2012 10:30AM Registered: 3 years ago Posts: 7,412

Mark,

Your choice is not directly related to your new gearbox since, in any event, fourth gear will be direct 1:1 as it was with your stock gearbox. Rather, your choice of rear gear is really determined for each track you'll be running, and you should choose a gear that allows you to max out rpm's and speed at the end of the longest straight.

Too tall a gear (numerically lower...) and you'll have unused rpm's left at the end of the longest straightaway, and too short a gear (numerically higher...) and you'll run out of rpm's before you reach the end of the straight.

If you have multiple diff's to choose from, and if you're using welded rears as many do, you may choose to change rears for specific tracks. On the other hand, if you have a limited slip unit and a limited budget (like so many of us...) you may choose to install the limited slip in the diff with the best compromise ratio.

Dick

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Re: Sprite Rear end ratios #3
saysprite Darryl Saylor TN, USA 1953 Austin-Healey 100 "Ole Blue" 1960 Austin-Healey Sprite Bugeye "Smokey" 1965 Austin-Healey Sprite "Porky" 1965 Austin-Healey Sprite "Speedracer" 1970 MG Midget "Jack" → more	Posted: July 04, 2012 11:38AM Registered: 7 years ago Posts: 1,490

For Nashville and Barber which are really tight, I used a 4.22. For VIR and Road Atlanta, I'd use a 3.9. Over on the Prod Forum, it looks like most of the guys are trying to run a 3.7, if they can find them at Road America. I switched from a stock to a SCCR box and it didn't change my rear end gear. It just let me use 2nd in some tight corners where with the stock box, I just used 3rd and 4th.

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Re: Sprite Rear end ratios #4
Speedracer Hap Waldrop Greenville, SC, USA 1967 MG MGB "The Biscuit"	Posted: July 05, 2012 07:55AM Registered: 7 years ago Posts: 20,606

Mark, As already mentioned, you would use different ratios for different tracks, ask the local hot shoe what gear ratio he is running , you tune the diff ratio for 4th gear on the longest straight, mostly all 4th gears are 1 to 1 ratio, so it doesn't matter if you have a SC/CR or Taylor dog box, you use the same final drive ratio on given track, if you are both running the same size engine, I would ask Colin Comer, since his Bugeye beat everything is that group in the Blackhawk Vintage Classic XX , including all the MGBs, TR4s, Elvas, and all the cars with much larger engines, that guy freaking honks around Blackhawk, he would be the guy to ask.

Hap Waldrop
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Re: Sprite Rear end ratios #5
bluemij Neil Janota Addison, IL, USA	Posted: August 04, 2012 07:38AM Registered: 3 years ago Posts: 161

Mark, for Blackhawk, I run a 4.55:1 gear. I know most of the vintage guys run this gear.

Neil

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