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Old 01-07-2009, 02:53 PM   #11
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Originally Posted by big2bird View Post
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.
Gots'd it. The unit that's in there now will almost certainly go boom on the first launch or shortly thereafter, so it'll get swapped. The Turbo II unit *may* be up to the task. There certainly are RX-7s with more power than we'll have, but they don't "hit" like we will.

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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Old 01-07-2009, 03:13 PM   #12
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Originally Posted by Vettezuki View Post
Gots'd it. The unit that's in there now will almost certainly go boom on the first launch or shortly thereafter, so it'll get swapped. The Turbo II unit *may* be up to the task. There certainly are RX-7s with more power than we'll have, but they don't "hit" like we will.

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.
Don't use a spool. They are horrible on the street and not designed for autocrossing. All we need is a good limited slip which will work well in all three. If the car is going to be used a lot for both drag racing and autocrossing then just get two sets of front struts with different spring rates, two sets of rims and tires and adjustable shocks for the rear.

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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Old 01-07-2009, 03:25 PM   #13
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Originally Posted by 94cobra69ss396 View Post
Don't use a spool. They are horrible on the street and not designed for autocrossing. Yes. They only have one use.All we need is a good limited slip which will work well in all three. If the car is going to be used a lot for both drag racing and autocrossing then just get two sets of front struts with different spring rates, two sets of rims and tires and adjustable shocks for the rear.

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 inprove the weight balance.
I think as an autocross car, with that weight in front, and that narrow little wheelbase, it will suck.
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Old 01-07-2009, 03:30 PM   #14
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Originally Posted by big2bird View Post
I think as an autocross car, with that weight in front, and that narrow little wheelbase, it will suck.
I read on an V8 RX7 forum that they actually do well with the SBF because the engine sits low in the car but they don't do as well with a SBC. SBF's have thin walls so they are not that heavy. Then again it is going to have the added weight of the blower but like I said we could set it back some by modifying the firewall it's that the direction Ben has in mind.
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Old 01-07-2009, 04:02 PM   #15
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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 inprove the weight balance.
This will be a must for good ( or fair ) balance.
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Old 01-07-2009, 04:05 PM   #16
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This will be a must for good ( or fair ) balance.
For the first project car lets just concentrate on going in 1 direction as opposed to many. I vote for straight line.
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Old 01-07-2009, 04:06 PM   #17
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Originally Posted by Leedom View Post
For the first project car lets just concentrate on going in 1 direction as opposed to many. I vote for straight line.
I vote for forward!
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Old 01-07-2009, 04:24 PM   #18
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Originally Posted by Leedom View Post
For the first project car lets just concentrate on going in 1 direction as opposed to many. I vote for straight line.
It's not a matter of going extreme in one direction, or of having an exquisitely balanced all around performer, but a matter of balancing time, money, and effort requirements for the vehicle's different subsystems and enjoying the result.

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.
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Old 01-07-2009, 07:25 PM   #19
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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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Old 01-07-2009, 08:18 PM   #20
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Quote:
Originally Posted by Vettezuki View Post
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. . .
That's good news.
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