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A few question

Old 03-09-13, 03:28 PM
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A few question

Hi everyone, I'm Randy and live in Franktown, CO. I have been road racing for many years in the big bore class. 2 years ago I bought a 1984 RX7 built for the Spec7 class so I had something fun and realtively inexpensive to race in. I can say I have just as much fun racing this little car as I do any of my big bore cars.

I am looking to get some tips from you experienced RX7 guys though. I have moved the Mazda out of the SCCA racing and in to a vintage racing group. Its a little less competitive and more about just having fun racing each other. So the rules are a little looser than Spec7 as far as upgrades. I've done some searching and read the FAQ's but would like some direct feedback:

1-I only get 2-3 race weekends out of a set of front brake rotors. By then they have either cracked or are close to cracking. Will a good set of aftermarket rotors be less prone to cracking like this? I see where KC raceware sells a front replacement rotor. It looks like you can unbolt the rotor from the hub and just replace the rotor if it breaks. Any other recommendations?

2-I usually only get 1 season out of a stock 5 spd tranny, then the 3rd gear synchros start to disintegrate. I begin the slow shift process to make it survive and eventually replace the tranny. I've just about exhausted my stock of spare trannys. I've seen reference to rebuilding one of these trannys using Miata components. What does that involve or are there other recommendations for solving the tranny issue?

3-I need to replace the oem fuel tank with a fuel cell. I can part together something that will work from Summit Racing. But I would like to retain the stock filler location and functionality so I dont have to build a bulkhead in the car to separate the fuel cell from the driver. Does anyone have a recommendation for a mfg and part number of a fuel cell that meets the requirement with minimum modification?

TIA-Randy
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Old 03-09-13, 05:13 PM
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i don't have direct experience with 1 and 3, but #2 is fairly simple.

the Miata uses the same basic transmission design, but with a different bellhousing for the uppy downy engine and a different mount to put it in the car.

but the gearing is better on the miata, and its really straight forward to take the gears and shafts from the miata box and put it in the Rx7 case.

the only modification you need to make is to shorten the input shaft a little like this Miata Input Shaft Modification
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Old 03-10-13, 12:01 PM
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Thanks for the link, exactly the type of info I'm looking for. I get that the Miata gear ratios are better, but does this modification also strengthen the gearbox to avoid the issues you have with the stock RX7 box?
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Old 03-11-13, 12:36 AM
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Well, the Miata box is pretty robust if you shift it properly and keep it properly lubed. Using some Redline MT90 (80w/90) and change it at least once a season. Maybe take a sample mid-season and send it out to Blackstone labs for analysis to judge when the properly oil change interval is and how much the oil degrades.

Regarding fuel cells, ATL is the best known name in the market. Not sure about some no-name Summit cell.... Be safe.


Since you are in vintage, try getting bigger and thicker (or at least thicker) rotors and a better caliper like Wilwood or something if the rules allow. Thicker rotors do better at managing heat. Bigger diameter rotors provide more mechanical leverage.

Last edited by gracer7-rx7; 03-11-13 at 12:38 AM.
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Old 03-11-13, 12:49 PM
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Originally Posted by Spec7ner View Post
Thanks for the link, exactly the type of info I'm looking for. I get that the Miata gear ratios are better, but does this modification also strengthen the gearbox to avoid the issues you have with the stock RX7 box?
there are a bunch of little updates, i think the real reason that the miata is more durable is mostly because the ratios are closer so the synchro's aren't working as hard.

best thing you can do is put a longer shifter on it, it'll slow down your shifts.

pretty much no matter what trans you have 3rd gear is the one you're shifting in and out of the most so it'll wear out the fastest
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