RX-Snake: Axle and Drive Shaft
How much would a built 8.8" cost vs. a built 9"
How much torque/power can a built 8.8" hold vs. a 9"? What is the approximate weight differential between the 8.8" 9"? My practical side says go with a built 8.8". It will probably hold forever, be a bit smaller and lighter, and maybe be a bit cheaper. My red neck side says 9 is bigger than 8.8 so do that. |
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http://www.chevyhiperformance.com/te...son/index.html |
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Cool. What's your recommended source for an 8.8? |
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What type of rear axle does the RX7 have under it now? Is it a solid axle or is it independent? |
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After looking at it more closely last night, with sticky tires, I'd expect total destruction in less than ten runs with the stock unit, if not the first one. :huh: I can post some pics later tonight. |
If you want to measure it tonight and post it I'll measure the Explorer and Cobra. Measure from the wheel mounting surface. Otherwise I can do it when I have the car.
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I'm doing some research with the V8RX7 boys. From what I've found so far, the stock NA unit is "designed for failure behind a V8". However, it seems the Turbo unit is pretty stout, and has a 4.1 ratio as we'd want. More to come. It'd be kind cool to keep the IRS because then we could use it for straight line and single lap AutoX type stuff just for shits and giggles. We'll see. I'd just like to avoid too many complex re-engineering efforts more than anything.
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I would be willing to bet, with the first popped clutch at 3,500RPM, that stock unit will grenade.
For straight line work, a 9" with a spool............. Street car needs compromising on racing. Autocross needs compromising on street and straight line. Straight line needs....................well, you get it.:D |
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One specific question about the spool. I was under the impression the spools were really only necessary on very high HP cars; like way beyond 500hp to thw wheels. |
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Also, if this is going to be an autocross car we are going to want to keep that independent rear and stay away from the solid axle if at all possible. Then again, if it is going to see a lot of autocrosses and road racing we may want to modify the firewall so the we can set the engine back some to improve the weight balance. |
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Think of it this way: Swapping out the whole rearend with a narrowed 8.8 is not a trivial matter. Swapping in a Turbo II diff and upgraded half shafts would be considerably easier overall, and possibly plenty stout. Remember we're not talking 1,000hp here, almost certainly well below 500 to the wheels. Anyways, this will be dictated by what the TII rearend can take, which I'm researching now. |
This is from a site that does nothing but sell conversion parts for RX-7s.
"...The RX-7's layout and structure is well suited to engine conversions. The rotary engine's eccentric shaft centerline is way up in the center of the rotary engine, dictating a much higher transmission location than that of a piston engine. The net result is that Mazda designed the RX-7 with a HUGE transmission tunnel, big enough to fit even the monster T-56 6 spd manual transmission which was used in the Viper and Corvette. The rotary engine's low torque output required Mazda to use a very heavy flywheel and a high rear gear ratio, a combination of factors that combined induce large amounts of stress on the RX-7's rear axles and hubs. Mazda planned accordingly, and designed plenty of strength into the RX-7's rear differential/axles/and hubs. Experience has shown that the stock NA RX-7 components are strong enough to withstand low 10sec 1/4mi passes, a feat that requires around 500hp. " Well, that's interesting. . . |
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1 - Stay with the stock unit til it go boom 2 - Replace with T II unit (if I can determine that it's up to the task) 3 - Replace with narrowed 8.8 For now we'll go with 1, research 2, and do basic planning for 3. |
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I say we test that statement and when/if it blows up we can say for certain it can't handle it.
I will say over, but not by much. |
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Of course, without D/S and Axle Safety Hoops, I won't.:smack: |
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That is with slicks. I USED to do 6,000 rpm blast starts with my Vette in the Seventies -on street tires "L60s" and NEVER twisted the 2.5 inch shafts I had then.:judge: Hey, I talked to Doug last night. He is thinking of going on the Motorgen run Sat. How about you? |
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Ok, I'll test it. :gatlin: |
There will certainly be DS and HS hoops. And I'm strongly leaning towards a fuel cell as well. I want this thing to get driven hard but be safe. I was joking with one of the guys last Sunday, probably Leedom; we could take it to the track, blow up the rear end in the first pass or two. The announcer will go, "well, that's it for them today." Of course, they don't know we'll have a rear end ready to swap, and we come back around two hours later. :drive:
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Measuring Rear End
Ron, while you have it, can you measure the rear end so we can have a tentative idea of what might be required for an 8.8? I'm still thinking to the stock unit for now, but it really is, even in a rosey scenario, just a matter of time before it go boom.
I've been reading a lot more anecdotal cases, and it really seems all over the place. |
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Will do. It's been too windy here to work on it but the wind seems to be dying down some today so hopefully I can back back to work on the cage tonight.
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