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.

The 8.8 can be just as strong as the 9" plus they are easier to get. Here is a great article that Chevy High Performance did comparring the 9" to a Chevy 12bolt (8.75") which is equal to the 8.8.

http://www.chevyhiperformance.com/te...son/index.html

Cool. What's your recommended source for an 8.8?

I thought we were going to run the Mazda rearend at first to see how it held up? If not, wait until I pick up the car and I'll measre the rear axle to see how wide it is. Then I can compare it to the Explorer and the Cobra to see if either would work without narrowing. If one of those is the right width we can just pull one from a wrecked car or truck. If they're both too wide I say we pull one from an Explorer and then narrow it.

What type of rear axle does the RX7 have under it now? Is it a solid axle or is it independent?

It's an IRS witha wee pumpkin and ity bity half shafts. I've heard the diffs from the Turbo II cars are pretty stout, but obviously the way a turbo rotary delivers power is completely different than a blown V8, but *maybe* that'd work. We'd at least have to beef up the half shafts in that scenario.

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.

Will do. I'm also going to do a little more research on Turbo II diffs and aftermarket half shafts to see what they can hold. There certainly have been JDM RX-7s that put out way more power than we will be, but it's super high revving turbo power, not blown displacement.

There is an all Ford junkyard in Placentia. Maybe we could get it out of a wrecked Explorer there?

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.

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

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.

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.

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.

I vote for forward!:drink:

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.

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.

They should know, but I'm not sure I totally believe it. I guess we could proceed with the stock unit, knowing that it'll probably go boom sooner or later. I want us to use and enjoy this thing. :thumbs_up:

Kinda surprising. Well, should we test that statement?:confused:

Obviously we have no idea what the internal condition of the diff is right now. We have three options.
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.

That is a GOOD plan.:bigthumbsup:

Second or third pass.:pot_stir:

LOL, I love your cynasism. I say we set the over/under at 3 passes. I'll take the over :D

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.

Under. (If I drive it first, 1 pass);)

Of course, without D/S and Axle Safety Hoops, I won't.:smack:

Ever seen what 350 HP does to a 3 1/2" Vette Halfshaft? I have. Looks like a donut/twist.:judge:

Pussy!!!:rolling::rolling::rolling::rolling:

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?

I might. Teri has a yearly migraine. It depends on how she feels.

Street tires, yes. Stickey Mickeys?

Ya ever see Ben's driveshaft on the Vette?

Maybe then. Hell, "we won't know till we know" Yogie Beara

Yes, but the diff is in the rear. :huh:


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:

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.

Pieces of the rear end or the information?:sm_laughing:

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.