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Project RX924 begins!
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Andrew NZ  



Joined: 22 Jun 2004
Posts: 744
Location: New Zealand

PostPosted: Sat Dec 01, 2007 4:22 pm    Post subject: Reply with quote

Thanks everyone for your help and advice

Converting to hydraulic clutch sounds quite straight forward, thanks.

Using the engine as a crossmember is not really an option with a rotary due to thier modular construction.

Please keep the ideas coming!
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Andrew
1977 RX924 rally car
12a bridgeport
www.race4-dcup.co.nz
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RC  



Joined: 25 Mar 2007
Posts: 2625
Location: Australia

PostPosted: Sun Dec 16, 2007 3:35 pm    Post subject: Reply with quote

Sure you have/are putting lots of time into planning this mod and have considered various options re fitting the rotary behind, above, or through the front crossmember. But if you havent thought of modding the bellhousing or torque tube I`ll mention it anyway.

Theres room to move the stock bellhousing rearward a few inches, but would involve shortening the torque tube and driveshaft. Then you have adapt to the 12A? and work around the clutch that will more than likely slip at the revs needed for much torque. Had a few rotaries myself and know theyre fun. Fitted one behind a VW kombi transaxle in a fibreglass body Eureka. Used the 13B auto counterweight (that bolts to the crank and driveplate) and mated it to the VW flywheel. Big mistake! Even with only 700Kg and custom built double diaphragm pressureplate couldnt stop it slipping.

So how about using the mazda clutch and bellhousing and adapting that to the torque tube and driveshaft. Recall there are quite a few boxes and bellhousings that will fit the rotary pattern. The rotary flywheels have a large counterweight on them. The clutches are hydraulic. A shop specializing in tailshafts and cutting down diffs would have little trouble cutting the tube and welding on a plate. Possibly you may even get away with the drive shaft length and then find a bigger clutch plate with similar splines like Endwrench did. But at worse may have to get splines remachined to suit.

Then the 12A may fit behind the crossmember. A bigger PITA is also the steering rack mounted there that that if dropped would affect your geometry. Obviously a lot to measure and work out there. Would like to see you do it though. Where theres a will theres a way.

Also I take it you are not worried about the overall reliability of the rotary? Expect they have better hi-tech seals available these days.

Roger
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Andrew NZ  



Joined: 22 Jun 2004
Posts: 744
Location: New Zealand

PostPosted: Sun Dec 16, 2007 8:50 pm    Post subject: Reply with quote

RC wrote:
Sure you have/are putting lots of time into planning this mod and have considered various options re fitting the rotary behind, above, or through the front crossmember. But if you havent thought of modding the bellhousing or torque tube I`ll mention it anyway.

Theres room to move the stock bellhousing rearward a few inches, but would involve shortening the torque tube and driveshaft. Then you have adapt to the 12A? and work around the clutch that will more than likely slip at the revs needed for much torque. Had a few rotaries myself and know theyre fun. Fitted one behind a VW kombi transaxle in a fibreglass body Eureka. Used the 13B auto counterweight (that bolts to the crank and driveplate) and mated it to the VW flywheel. Big mistake! Even with only 700Kg and custom built double diaphragm pressureplate couldnt stop it slipping.

So how about using the mazda clutch and bellhousing and adapting that to the torque tube and driveshaft. Recall there are quite a few boxes and bellhousings that will fit the rotary pattern. The rotary flywheels have a large counterweight on them. The clutches are hydraulic. A shop specializing in tailshafts and cutting down diffs would have little trouble cutting the tube and welding on a plate. Possibly you may even get away with the drive shaft length and then find a bigger clutch plate with similar splines like Endwrench did. But at worse may have to get splines remachined to suit.

Then the 12A may fit behind the crossmember. A bigger PITA is also the steering rack mounted there that that if dropped would affect your geometry. Obviously a lot to measure and work out there. Would like to see you do it though. Where theres a will theres a way.

Also I take it you are not worried about the overall reliability of the rotary? Expect they have better hi-tech seals available these days.

Roger


Yes, there has been a lot of thought and trial fitting of parts and hours of measuring. I had originally thought of shortening the torque tube, but that would then cause clearance issues for the clutch lever and starter motor and require cutting the fire wall. If I have to I'll modify the body, but at the moment I'm trying to have it so that I can put it back to standard down the track if I need to.

I've got the bell housing just about finished now and will put up some photos next weekend if I get a chance. I'm using the Mazda flywheel and clutch pressure plate and fork/release bearing with the 924 clutch disk. The bell housing is a modified RX7 S1 item.

I'm probably going to move the steering forward, as the angle to the ball joints will be similar, just the other way around (they go forward about 25mm at the moment). Ill just have to lengthen the steering shaft about 50mm too. By moving it forward I might even be able to lift the steering rack a bit to compensate for the problems associated with a low ride height. Hopefully I'll get some time after Christmas to start playing with the crossmember, steering and engine mounts.

Thanks for your thoughts,

Andrew.

I've seen a couple of Eurekas over here with rotaries in them - they look like a lot of fun!
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1977 RX924 rally car
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www.race4-dcup.co.nz
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Khal  



Joined: 26 Sep 2003
Posts: 4863
Location: Warm and sunny interior BC, Canada

PostPosted: Mon Dec 17, 2007 9:58 pm    Post subject: Reply with quote

Of course, you could always buy an RX-7... I've been told you don't have to modify anything to put a rotary into them..?


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Andrew NZ  



Joined: 22 Jun 2004
Posts: 744
Location: New Zealand

PostPosted: Mon Dec 17, 2007 10:03 pm    Post subject: Reply with quote

Khal wrote:
Of course, you could always buy an RX-7... I've been told you don't have to modify anything to put a rotary into them..?

True, but then I'd be trying to stop it swapping ends all the time on the track. I like the sure footed 924 too much now to go back to a 7!
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1977 RX924 rally car
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www.race4-dcup.co.nz
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Andrew NZ  



Joined: 22 Jun 2004
Posts: 744
Location: New Zealand

PostPosted: Wed Jan 02, 2008 6:57 am    Post subject: Reply with quote

Slowly making progress, but this is not really an easy conversion. I've had to change the crossmember a lot more than I thought I would, and I'm also going to have to do some rethinking over the engine mounts. The oil filter hits the firewall by the brake booster (remote filter should fix this) and the waterpump housing will have to be modified to clear the steering (would be fine on LHD model though). The biggest problem is going to be the ground clearance on the sump, as it has to sit lower than expected.

The good news is that the bellhousing worked out well, and everything aligns up nicely at that end. I seem to be working 24/7 at the moment, so I'll post again once I've had time to work on it again.
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1977 RX924 rally car
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Khal  



Joined: 26 Sep 2003
Posts: 4863
Location: Warm and sunny interior BC, Canada

PostPosted: Thu Jan 03, 2008 2:11 am    Post subject: Reply with quote

Andrew NZ wrote:
True, but then I'd be trying to stop it swapping ends all the time on the track. I like the sure footed 924 too much now to go back to a 7!


Funny... they pants'd the 993's five years running at the Bathurst 12 Hour. And some would argue that a 993 would outrun a 924...
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Andrew NZ  



Joined: 22 Jun 2004
Posts: 744
Location: New Zealand

PostPosted: Thu Jan 03, 2008 4:47 pm    Post subject: Reply with quote

Khal wrote:
Andrew NZ wrote:
True, but then I'd be trying to stop it swapping ends all the time on the track. I like the sure footed 924 too much now to go back to a 7!


Funny... they pants'd the 993's five years running at the Bathurst 12 Hour. And some would argue that a 993 would outrun a 924...


Aahhh.....here we go, Khal is here to knock my next project You may recall that the last one you mocked ended up with more power than your beloved 931

I'm referring to the first generation RX7 - the one the same era as (and designed off) the 924, and the only one available with the 12a engine I'm installing in the 924, hence the comparrison. The series 6 and 7 models that you're referring to are quite a different chassis, but also use the 13B twin turbo engine. They cost a wee bit more than a 924 too
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Andrew
1977 RX924 rally car
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www.race4-dcup.co.nz
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Khal  



Joined: 26 Sep 2003
Posts: 4863
Location: Warm and sunny interior BC, Canada

PostPosted: Thu Jan 03, 2008 7:13 pm    Post subject: Reply with quote

Andrew NZ wrote:
Aahhh.....here we go, Khal is here to knock my next project You may recall that the last one you mocked ended up with more power than your beloved 931


Aw, y'know I'm just kiddin' around! Can't honestly say I understand why anyone would wanna put a rotary in a 924 -other than "because I can" -but they're certainly lighter and more compact than the standard engine so if you can get the balance right, I reckon she might be a pretty tight-handling little beast... and you might even get a magazine feature out of it

Step back in reliability, though, isn't it? And power-wise it's gonna be a disappointment, I'd suspect. And what the deal with the gear ratios? Won't they be way off if you're using the standard gearbox? (as I understand it the rotaries have comparatively low torque and like to spin much faster than the standard four?)

(Hey, and I thought you Kiwi's got all those super-cheap Jap imports over there?! How much would a Series 7 cost there?)
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Peter_in_AU  



Joined: 29 Jul 2001
Posts: 2740
Location: Sydney, Australia

PostPosted: Thu Jan 03, 2008 9:47 pm    Post subject: Reply with quote

must be something wrong with my Internet connection, the photos aren't showing up
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11356
Location: PacNW

PostPosted: Fri Jan 04, 2008 3:35 am    Post subject: Reply with quote

Khal wrote:
Step back in reliability, though, isn't it?


Not even close. I drove a 79 RX7 for years, and with 120k on it, the 12A pushed that little car at to 130+. Never broke down or failed to start either. . .started one morning at 20 below (just to see if it could - I didn't drive anywhere as the tires were frozen to the street). Outstanding, high-revving motor and a pretty nice little car.
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moone924  



Joined: 05 Feb 2003
Posts: 865
Location: Southwest Littleton Colorado

PostPosted: Fri Jan 04, 2008 6:15 am    Post subject: Reply with quote

Rasta Monsta wrote:
Khal wrote:
Step back in reliability, though, isn't it?


Not even close. I drove a 79 RX7 for years, and with 120k on it, the 12A pushed that little car at to 130+. Never broke down or failed to start either. . .started one morning at 20 below (just to see if it could - I didn't drive anywhere as the tires were frozen to the street). Outstanding, high-revving motor and a pretty nice little car.


In high school tons of my fellow classmates bought first generation rx-7s... Most were in perfecto condition with as low as 40k miles. Not a one of them passed emissions no matter what work was done to them short of cracking open the engine. Sure this isn't emissions testing, but that tells me the rotaries are not as durable and were worn out already at 40k miles.
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW

PostPosted: Fri Jan 04, 2008 6:34 am    Post subject: Reply with quote

Mine passed in Colorado in 1990 with 130k miles.
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Andrew NZ  



Joined: 22 Jun 2004
Posts: 744
Location: New Zealand

PostPosted: Fri Jan 04, 2008 6:46 am    Post subject: Reply with quote

Quote:
Aw, y'know I'm just kiddin' around!


I know Khal, me too! We can't let people think that Aussies and Kiwis could ever get on though, can we??

Quote:
...and you might even get a magazine feature out of it


It was featured in a 4 page spread with GT3s, 944s and 911s a couple of years ago, so you never know your luck (although it'll never be allowed around that company again now ).

Quote:
Step back in reliability, though, isn't it? And power-wise it's gonna be a disappointment, I'd suspect.

I've had more than 10 rotary engines, and only 2 of them have ever blown up. I've had 2 924 engines, and both of them have blown up!! Power wise it should be similar to the turbo initially with a lot more to come later on (this is a bridge port don't forget, not a standard 12a).

Quote:
And what the deal with the gear ratios? Won't they be way off if you're using the standard gearbox? (as I understand it the rotaries have comparatively low torque and like to spin much faster than the standard four?)


It'll lose abit down low possibly, but should work well on the track.

Quote:
(Hey, and I thought you Kiwi's got all those super-cheap Jap imports over there?! How much would a Series 7 cost there?)


Still at least $15k for a cheapie
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Andrew
1977 RX924 rally car
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www.race4-dcup.co.nz
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Andrew NZ  



Joined: 22 Jun 2004
Posts: 744
Location: New Zealand

PostPosted: Fri Jan 04, 2008 6:47 am    Post subject: Reply with quote

Peter_in_AU wrote:
must be something wrong with my Internet connection, the photos aren't showing up


Sorry, I took a few, but now i've lost the camera! Will keep looking today.
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1977 RX924 rally car
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