![\"J-Rho's](\"http:\/\/www.rhoadescamaro.com\/build\/wp-content\/uploads\/2015\/10\/IMG_0632.jpg\")
<\/a><\/p>\nNot looking to track the car any time soon, I only had two requirements of the gearing situation:<\/p>\n
- \n
- Produce the right top speed in second gear for autocross use<\/li>\n
- Produce a reasonable cruising RPM for any trips on the freeway<\/li>\n<\/ol>\n
Below is a cut from one tab of my super-duper everything-I-know-about-cars spreadsheet.\u00a0 Getting gearing right is important and key to understanding thrust.\u00a0 By messing with the stuff in green I can see the resulting outputs.\u00a0 Column K, 2nd Gear Max, is important to ensure your car has “long enough legs” for autocross.\u00a0 Column M, RPM @30mph, tells you about where the engine will be coming off the slowest of corners – especially important for peaky or boosted engines.\u00a0 Plugging the highest transmission ratio into the second gear column and them multiplying column M by 2-2.5, gives me a quick idea of cruise RPM.<\/p>\n
![\"gearing_xls\"](\"http:\/\/www.rhoadescamaro.com\/build\/wp-content\/uploads\/2015\/10\/gearing_xls.png\")
<\/a><\/p>\nThe problem with the old school Muncies is second gear (1.64 typical) tends to be too close to top gear (always 1:1).\u00a0 So while 10mph per 1000rpm is perfectly reasonable for second gear (column N), with a Muncie that means you’re only getting 16.4mph per 1000rpm in top – which puts you in a situation like the above.<\/p>\n
This is where the world kinda explodes for me.\u00a0 Every car I’ve monkeyed with in the last 15 years, has been done within the tight constraints of an autocross ruleset.\u00a0 The only exception maybe was building the 240sx for Street Mod in 2007, where sizing and building a turbo system was a ton of fun – but where I also learned that there was such a thing as too hardcore of a race car for me.\u00a0 Every time before and since, the rules had kept me from going too far – and in my current frame of “just don’t do anything that’s illegal in CP or CAM” – the sky is the limit.<\/p>\n
One option would be to stick with the Muncie.\u00a0 To produce a good autocross gear and a decent highway gear, would mean having to autocross in first gear.\u00a0 For regular Solo that might kinda work but for anything with a launch it would not.\u00a0 The little 302 just doesn’t have the beans to get off the line with a 70+mph first gear.\u00a0 An 8 liter Viper with a 60mph first barely does.<\/p>\n
Another is the Gear Vendors overdrive<\/a> unit, which adapt to the Muncie and give a quick overdrive at the touch of a button.\u00a0 Thought about this for a while, and it might be neat in an autocross setting, to basically be able to paddle-shift up or down on course between second gear and “second-over”.\u00a0 The biggest concern I had with this, is the “upshift” into overdrive wasn’t instantaneous (“down”shifts out of OD are) – the engagement of overdrive is actuated by a pump on the transmission output shaft, and the faster it’s turning, the quicker the engagement.\u00a0 In videos where they show it engaging in first gear, there’s a delay of maybe three quarters of a second before it kicks in.\u00a0 That maybe doesn’t sound like a long time, but when you’re trying to time that on an autocross course, it’s an eternity.\u00a0 Seemed likely that it wouldn’t be totally consistent either.<\/p>\n
The other issues were the unit is pricey (more than a good new 5 speed trans) and the overdrive is “only” .78.\u00a0 Better than nothing, but not as much of an overdrive as offered elsewhere.\u00a0 Lastly, my M21 leaked like oil was going out of style.\u00a0 Not an easy fix either, a worn countershaft hole in the case, the only way to repair is to drill out the hole and put in a new bushing, or buy a whole new case.\u00a0 So to fix the M21 and do the GV Overdrive was quickly becoming a $4k proposition<\/p>\n
Elsewhere, there are some really beefy 4 speeds, like the Jerico transmissions commonly used in circle track racing.\u00a0 Common now in Street Modified and Prepared classes autocross, they are strong and light, and for this common RWD Chevy application, not that much more than some of these other options.\u00a0 Their non-synchronized straight cut gears sound great too.\u00a0 Problems there, they’re quite noisy, a bit of a pain to use on the street, and I’ve heard stories of them actually having a hard time with extended durations at light load, like cruising on the highway.<\/p>\n
The most common swaps for these cars are Tremec 5 or 6 speeds.\u00a0 The 5-speed come in the TKO500 and 600 flavor (the number representative of their steady-state torque limits) and the six speed is the T56 Magnum, good for ~700.<\/p>\n
![\"Tremec](\"http:\/\/www.rhoadescamaro.com\/build\/wp-content\/uploads\/2015\/10\/tremec_tko600-1024x768.jpg\")
<\/a><\/p>\nAn advantage of the T56 is you get 5 well spaced gears and a good cruising overdrive.\u00a0 If you want your car to stay in a narrow rpm range from 50 to 150mph, you want a 6 speed.\u00a0\u00a0 With the 5 speed you get 1-4 similar to the 6-speed, but you have to choose whether you want your fifth gear to be like a T56’s fifth – maintaining good acceleration on a racetrack, but a bit buzzier on the highway (.82) – or more the like the T56’s 6th, where acceleration on track would be feeble, but you get a more relaxed cruise (.64).<\/p>\n
For its superior strength and flexibility across speeds the 6-speed can’t be beat.\u00a0 The cost isn’t that much more either, only a few hundred bucks more than a TKO600.<\/p>\n
There are some downsides though.\u00a0 First, is it’s a physically much larger transmission than the 5-speeds, which themselves are already a fair bit bigger than the 4-speed Muncies.\u00a0 While the TKOs can fit these old Camaros without tunnel mods, the same isn’t really the case for the T56.\u00a0 The other, is they’re heavy – over 130 pounds.<\/p>\n
<\/p>\n
![\"Tremec](\"http:\/\/www.rhoadescamaro.com\/build\/wp-content\/uploads\/2015\/10\/tko600_in_box-1024x768.jpg\")
<\/a><\/p>\nLong story coming to an end, I went with a TKO600.\u00a0 I don’t plan on acceleration above 4th gear speeds to be something I need to worry about (just don’t want to go that fast in this old thing) – and the fitment and weight benefits sealed the deal.<\/p>\n
My motor is nowhere near 500 ft-lbs. of torque even after its planned upgrades so the TKO500 would have been fine, but the 600 was only a little bit more and should provide some future-proofing if things escalate in the future.<\/p>\n