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View Full Version : N/A 13B into a Capella.. how hard?



Beavis
21-07-02, 10:10 PM
Umm, as the subject suggests, really.

How hard's the conversion? What gearbox would I use - S5 RX-7, Supra, etc? Any major body mods required? Coupe or four-door better/easier/cooler?

Thanks lads,


Chris

Beavis
22-07-02, 04:33 PM
Geez you guys are helpful.. not.. :rolleyes: :)

Apparently the easiest way is to get an automatic Capella to start with, and then an RX-2 series 3 crossmember. Best gearbox is apparently the RX-7 series 4/5 turbo, which hopefully will not mean transmission tunnel remodelling.

I'm looking at a 13B-PP with either a 51IDA Weber or MoTeC M4.. comments?


Chris

Spac
22-07-02, 05:30 PM
S4/5 boxes are the best Mazda boxes, but are also hardest to fit. AFAIK, the whole auto tunnel thing is all a load of crap - it might help you with an auto conversion, but the problem with most manual boxes is that they are too tall, but the auto tunnels are WIDER, not higher than the manual tunnels. I can tell you without doubt that a Supra box will fit (just) into an unmodified manual 808 tunnel, so there shouldn't be any dramas with a manual Capella tunnel (though this might depend on year model - early manual ones have 808 sized tunnels, later ones have almost RX-4 sized tunnels).

If you can't find S3/4 RX-2 bits (they're damn rare) the other method of fitting a 13B into a RX-2 / Capella is to get a Capella X-member, and cut the piston engine mounts off, and then get a (genuine or reproduction) RX-3 engine X-mem and fit it, and then use the front mounts and sump that you'd use in an RX-3 or RX-4.

Sedans are stiffer/ stronger than coupes, as well as being much more plentiful. But the Capella coupe shape is still (IMO) the sweetest shape to ever come out of Japan.

13B PP with either induction would be very sweet. And a lot faster than the current turbo craze would lead you to believe. Go for it.:):):):):)

Beavis
22-07-02, 05:39 PM
Originally posted by Spac
S4/5 boxes are the best Mazda boxes, but are also hardest to fit. AFAIK, the whole auto tunnel thing is all a load of crap - it might help you with an auto conversion, but the problem with most manual boxes is that they are too tall, but the auto tunnels are WIDER, not higher than the manual tunnels. I can tell you without doubt that a Supra box will fit (just) into an unmodified manual 808 tunnel, so there shouldn't be any dramas with a manual Capella tunnel (though this might depend on year model - early manual ones have 808 sized tunnels, later ones have almost RX-4 sized tunnels).

Hrm.. is the auto-to-manual conversion difficult? To me it'd probably be the hardest thing to do! If the auto tunnels are a little wider, I take it that a Supra manual will still fit into one? Unless they've got something dumb that would get in the way (like a curved top of the tunnel)


If you can't find S3/4 RX-2 bits (they're damn rare) the other method of fitting a 13B into a RX-2 / Capella is to get a Capella X-member, and cut the piston engine mounts off, and then get a (genuine or reproduction) RX-3 engine X-mem and fit it, and then use the front mounts and sump that you'd use in an RX-3 or RX-4.

Whatever is easiest, is easiest. If there's an okay-priced bolt-in option, then I'd go for that. IMHO, the less fabricating the better, even if it means you have to pay a few bucks for buying pre-fab'd bits.


Sedans are stiffer/ stronger than coupes, as well as being much more plentiful. But the Capella coupe shape is still (IMO) the sweetest shape to ever come out of Japan.

I like the original GT-Rs as well.. probably around the same vintage? And yeah, both great shapes. Autos are plentiful and look okay-bordering-on-crap.. I'd even put a bowls hat on the rear parcel shelf! Sleeperville central.. only giveaway would be super sticky tyres on the 13" rims ;)


13B PP with either induction would be very sweet. And a lot faster than the current turbo craze would lead you to believe. Go for it.:):):):):)

What would a 51IDA setup cost me.. about $1k? What would be the best clutch and flywheel combo? What extractors - Racing Beat for PPs (non-factory PPs, that is)? What diameter for the rest of the exhaust?

Beavis
22-07-02, 05:46 PM
Couple more questions - but pardon me, I'm dumb when it comes to these things. If I go for a Supra box, would I need to shorten & balance the tailshaft? Is there any chance of fitting the RX-7 S5 box, or is it just not worth it?

What diff setup should I use?

ORX400
22-07-02, 06:52 PM
Chirs - good on u for thinking this through. I dont know all that much, but I'd say you are looking at just over $1k for a good 51IDA, mani, fitment, and tune(and id say thats a good price). You never know where you're gona find the stuff either...this has been my experience :)

Beavis
22-07-02, 06:56 PM
ORX: Cheers for that. Us two-strokers have to band together! :)

So do I take it that Webber don't make carbs new anymore?

Spac
22-07-02, 08:08 PM
S4 box WILL fit, but there are some hassles you won't have with an earlier Mazda box - mostly the gearbox mount is on a stupid angle and will require custom (there's that word!) gearbox x-member, and the shifter is a stupid "remote" type like a S2, which can be cut down, but make the box much taller just in front of the shifter. These are what stopped me putting a S4 box into my RX-5 rally car, but it may be possible with a more generous time-frame than I had...
Supra and S4 boxes will both need their respective yoke put on the front of the tailshaft.

Auto to manual is dead easy. You need to do the clutch pedal and hydraulics and pretty much everything else is just part of the rotary conversion. Bits from a Capella will work perfectly. Only other potential catch is the shifter hole - auto 808s have a tiny hole (about 50mm x 60mm), unlike manual ones that have a ~120mm diamter hole. Sorry for vagueness, I've never owned an auto Capella!

Engine mountings are 6 of one, half a dozen of other in terms of difficulty. See what you can find, and how much it's gonna cost you and go from there. Using RX-2 bits will require a re-drilled (ie reversed) RX-4 sump, whereas the RX-3 / Capella option will just use a straight RX-4 sump. And is stronger if you're going to race it.

IDA? With some shopping around, and some haggling, you should be able to get one for about $600. BigJ had one for sale on here a while ago, and it didn't look like moving for $750. If YBI-12V doesn't get it, I'll have one for sale soonish. Tuning shouldn't cost too much - there's LOTS written about what jets to use, so if you can start with them, it will only be fine-tuning, and therefore minimal dyno time. Weber jets are cheap.

Diff? Depends on what you're going to do with it... Hard street use won't need anything more than a stock diff - you WILL eventually break it, but it will give you a fair bit of warning and will probably take about a year. Burn-outs and launches will drastically shorten its life though... Locking it will help a huge amount (normal weak point is the pin the pinion gears run on - welding it up side-steps that problem), but then axles can become an issue. If you're into abuse, a Hilux diff seems to be the best option. My RX-5 rally car (healthy 13B BP, has a Mazda LSD with 121 axles - which are the same size as the Capella / RX-2 items, only longer to suit the 121 diff) has done about 1500kms competitive, and in that time it just started to twist one axle.
Oh, and RX-2 and Capella diffs are the same (except that early RX-2s have crappy 3.7:1 ratios, and all the others have marginally better 3.9S).

Beavis
22-07-02, 08:21 PM
Cheers for all the info, Spac.. :)


Originally posted by Spac
S4 box WILL fit, but there are some hassles you won't have with an earlier Mazda box - mostly the gearbox mount is on a stupid angle and will require custom (there's that word!) gearbox x-member, and the shifter is a stupid "remote" type like a S2, which can be cut down, but make the box much taller just in front of the shifter. These are what stopped me putting a S4 box into my RX-5 rally car, but it may be possible with a more generous time-frame than I had... Supra and S4 boxes will both need their respective yoke put on the front of the tailshaft.

Okay, so it can be done.. but, I take it from what you were saying the Supra conversion is much easier? I'm not totally against custom stuff.. I'd just rather avoid it where possible ;) if you were going to do this conversion yourself (or even have it done for yourself), would you go the Supra route? What kind of a bell-housing would I need, I imagine they'd be common?


Auto to manual is dead easy. You need to do the clutch pedal and hydraulics and pretty much everything else is just part of the rotary conversion. Bits from a Capella will work perfectly. Only other potential catch is the shifter hole - auto 808s have a tiny hole (about 50mm x 60mm), unlike manual ones that have a ~120mm diamter hole. Sorry for vagueness, I've never owned an auto Capella!

Okay, cool. Are the bits I need - master cylinder, booster if they used one, etc. still easily available? Or is it a matter or sorting out aftermarket bits to do the job? How does the Supra box line up in terms of mounting the shifter?


Engine mountings are 6 of one, half a dozen of other in terms of difficulty. See what you can find, and how much it's gonna cost you and go from there. Using RX-2 bits will require a re-drilled (ie reversed) RX-4 sump, whereas the RX-3 / Capella option will just use a straight RX-4 sump. And is stronger if you're going to race it.

I doubt it will see much race use to be honest.. I just want something fun. How easy would an RX-3 crossmember etc. be to find, or am I looking for rocking-horse dung?


IDA? With some shopping around, and some haggling, you should be able to get one for about $600. BigJ had one for sale on here a while ago, and it didn't look like moving for $750. If YBI-12V doesn't get it, I'll have one for sale soonish. Tuning shouldn't cost too much - there's LOTS written about what jets to
use, so if you can start with them, it will only be fine-tuning,
and therefore minimal dyno time. Weber jets are cheap.

There was a 51IDA Weber in the Quokka (sorta like the Trading Post) for $850.. hm. What throttle setup is best to use? Twin throttle bodies, or what? Simple is good, though (in terms of paying big bucks for an EFI install)


Diff? Depends on what you're going to do with it... Hard street use won't need anything more than a stock diff - you WILL eventually break it, but it will give you a fair bit of warning and will probably take about a year. Burn-outs and launches will drastically shorten its life though... Locking it will help a huge amount (normal weak point is the pin the pinion gears run on - welding it up side-steps that problem), but then axles can become an issue. If you're into abuse, a Hilux diff seems to be the best option. My RX-5 rally car (healthy 13B BP, has a Mazda LSD with 121 axles - which are the same size as the Capella / RX-2 items, only longer to suit the 121 diff) has done about 1500kms competitive, and in that time it just started to twist one axle.
Oh, and RX-2 and Capella diffs are the same (except that early RX-2s have crappy 3.7:1 ratios, and all the others have marginally better 3.9S).

Yeah, moderate to hard street use is fine for now. So long as it doesn't explode into a thousand tiny pieces if I breath on the accelerator, it ought to be fine. Burn-outs aren't for me, ditto launches at >2000rpm. I might take it down the quarter once just to see what it'd run, but certainly nothing regular.

Any other comments? Clutch/flywheel? Tailshaft need shortening & balancing?

thanks again,


Chris

Rota_Motor
22-07-02, 09:08 PM
hey, good idea, I dont know heaps about capellas or the S4 RX-7 gearbox thing, but using an RX-3 type x-member would be easier, as I think there are more around :) either gearbox the gearbox x-member would need to be modified to suit, as well as the tailshaft.

the auto to manual conversion is dead easy as people have said before, I converted my auto piston engined mazda 1300 over to rotary manual, all it needed was the pedals from the manual version, and the clutch master cylinder and lines, and it all bolts straight in. Im not sure about the capellas, but my 1300 had the hole and studs in the firewall, just a blanking plate over the master cylinder hole, dead easy to change :) you will also need to cut a new hole in the tunnel for the shifter to emerge from, as someone else said, the manuals have very small shifter holes.

and my auto 1300, the trans tunnel does appear to be taller, not just wider than the manual, but capellas could be different.

Beavis
22-07-02, 09:40 PM
Rota: Thanks for that.. good to hear that the auto-manual conversion is easy! Makes me feel a little better. What gearbox and tailshaft did you end up using? Did it all bolt straight up?


Chris

Spac
23-07-02, 06:26 PM
The Supra conversion is possibly a little bit easier, but its really insignificant. I haven't done a Supra into Capella conversion, but 13B + Supra into manual 808 had the shifter in the right spot. There's probably different lengths though - I KNOW the old Celica box had a couple (3?) options, and I know the Supra type boxes came in all different sorts of cars, so anything is possible. AFAIK, Supras are a better box, but the whole lot costs a fair bit more:
Box - $400
Adaptor plate - $200
Clutch plate - $200
RX-4 bell-housing $200
Tail-shaft shortening - $200

The S4 conversion doesn't need an adaptor to bolt to the RX-4 BH, and the clutch plate is cheaper $150ish. Although the "proper" Dellow BH was more like $280, which saves buying both the RX-4 BH and an adaptor. I'd do the sums and see what you can actually get a hold of at the time. (prices are from when I looked into it a few years ago, so could be very wrong...)

Clutch and flywheel - use as light flywheel as you can. Just make sure it is an aftermarket steel one (or alloy if you're cashed up), not a lightened cast iron one... Potential to go bang and remove feet is huge if you chop into a iron one... Clutch - HD pressure plate (preferably a billet steel one for same reasons as flywheel), with an un-sprung button. NOTHING else will cope at all well. Centreforce pressure plates will have an effective weight of 2tons at 10,000rpm, and are therefore almost impossible to use...

Clutch bits are all NO problem to get - you can buy 'em all new, or get bits from wreckers and have 'em re-co'ed. Booster - just use the Capella one.

Original RX-3 x-members are hens teeth, and as dear as sin. You can get reproduction ones fairly cheaply, but the price varies like crazy. Cheapest I know of is Reliance Automotive here in Canberra - a mate recently paid $140. I'm 99% sure they are made by Rod Kilby out at Lochleigh Enterprises (in Hall) - he may sell you one direct, even more cheaply. www.whitepages.com.au :)

TBs and stuff? I've been thinking about this, and if you're going to MoTeC it, I wouldn't bother with PPing it. You can get more, more reliable power out of a well built side port (ie bridge port) motor than you can from a PP if you're using decent EFI. The club-car boys are almost universally going for BPs, even when the don't have to... and those that DO go for PPs are still usually using Webers.
A Weber fed PP will be a dog on the street. Noise will be an issue as they are even more sensitive to exhaust back pressure than usual. My BP is perfectly, wonderfully drivable at anything above (roughly) 15% throttle, but below that it is pretty awful. Revs aren't really an issue, so long as you're above that magical 15% mark... A PP will only be worse...

But you're not building this to take your grandmother to bowls are you? If you're unsure, I'd go and do a spot of tyre kicking - find something (anything) out of the paper that has a PP in it, and go for a ride. See what you think. I know its a bit of a prick of an act, but if you don't lead the guy on at the end (you know, the whole "I'll give you a call" or "I'll just go and get the money" routines) you shouldn't make any enemies...

Beavis
23-07-02, 07:19 PM
Originally posted by Spac
The Supra conversion is possibly a little bit easier, but its really insignificant. I haven't done a Supra into Capella conversion, but 13B + Supra into manual 808 had the shifter in the right spot. There's probably different lengths though - I KNOW the old Celica box had a couple (3?) options, and I know the Supra type boxes came in all different sorts of cars, so anything is possible. AFAIK, Supras are a better box, but the whole lot costs a fair bit more:

Okay, that all makes sense. I'm sure a basic Supra gearbox would do, I don't see why I'd need either the all-alloy box (W154?) or the Getrag six-speed (V161?)


The S4 conversion doesn't need an adaptor to bolt to the RX-4 BH, and the clutch plate is cheaper $150ish. Although the "proper" Dellow BH was more like $280, which saves buying both the RX-4 BH and an adaptor. I'd do the sums and see what you can actually get a hold of at the time. (prices are from when I looked into it a few years ago, so could be very wrong...)

So what, the only problem with the S4 conversion is potentially fitting the thing in?


Clutch and flywheel - use as light flywheel as you can. Just make sure it is an aftermarket steel one (or alloy if you're cashed up), not a lightened cast iron one... Potential to go bang and remove feet is huge if you chop into a iron one... Clutch - HD pressure plate (preferably a billet steel one for same reasons as flywheel), with an un-sprung button. NOTHING else will cope at all well. Centreforce pressure plates will have an effective weight of 2tons at 10,000rpm, and are therefore almost impossible to use...

Yeah, I like my feet & toes (though they're a bit big), so I'm gonna stay away from anything lightened and iron and factory. Okay, clutch sounds fine, I'm not adverse to driving something heavy/agressive (cue "your mother" jokes.. here ->)


Clutch bits are all NO problem to get - you can buy 'em all new, or get bits from wreckers and have 'em re-co'ed. Booster - just use the Capella one.

Original RX-3 x-members are hens teeth, and as dear as sin. You can get reproduction ones fairly cheaply, but the price varies like crazy. Cheapest I know of is Reliance Automotive here in Canberra - a mate recently paid $140. I'm 99% sure they are made by Rod Kilby out at Lochleigh Enterprises (in Hall) - he may sell you one direct, even more cheaply. www.whitepages.com.au :)

Okay cool, that all sounds fine.


TBs and stuff? I've been thinking about this, and if you're going to MoTeC it, I wouldn't bother with PPing it. You can get more, more reliable power out of a well built side port (ie bridge port) motor than you can from a PP if you're using decent EFI. The club-car boys are almost universally going for BPs, even when the don't have to... and those that DO go for PPs are still usually using Webers.
A Weber fed PP will be a dog on the street. Noise will be an issue as they are even more sensitive to exhaust back pressure than usual. My BP is perfectly, wonderfully drivable at anything above (roughly) 15% throttle, but below that it is pretty awful. Revs aren't really an issue, so long as you're above that magical 15% mark... A PP will only be worse...

Well, obviously Webering is cheaper, and I was thinking that I'd prefer to keep it carbied. I'd only inject if it was just nigh-on impossible to have on the street (i.e. idles at 6000rpm style). How much horsepower can you reasonably (price, drivability, reliability, noise) extract from a BP without getting too extreme?


But you're not building this to take your grandmother to bowls are you? If you're unsure, I'd go and do a spot of tyre kicking - find something (anything) out of the paper that has a PP in it, and go for a ride. See what you think. I know its a bit of a prick of an act, but if you don't lead the guy on at the end (you know, the whole "I'll give you a call" or "I'll just go and get the money" routines) you shouldn't make any enemies...

I've never been in a PP rotor.. but finding one in Perth to take a trip in might be a little difficult! :( But yeah, if I find one, I'll go and check it out, and then offer them some beer afterwards to placate them or something..


Chris

Spac
23-07-02, 07:43 PM
The only real hassle with the S4 box is fitting it in - the input and putput shafts are different to the early cars so you'll need a custom tailshaft and a "custom" clutch plate (but they are available off the shelf). This much is the same as the Supra, although Supra clutch plates seem dearer(?!).

I've been talking about this using early type 8.5" clutch, rather than the S4's 9.5'(? - bigger) clutch - if you go the later bits you need to do it ALL - flywheel, bell-housing, starter etc - these cost a lot more, and are harder to fit (clutch fork is further rearward in BH). And the decent bits you'll need (light FW, HD pressure plate etc) are also much dearer...

Power from a BP. The club car guys are talking 320hp... but that's with BIG money spent on injection.
Back in the real world, an honest 250hp is available from a sensible BP, that is drivable, and will last. A good mate of mine had a J-port in his RX-5 rally car, and it put out 148-RWHP, so had about 220hp at the flywheel.
My car was apparently a LOT healthier, with a much smaller port, so I'm guessing it has some-where around the 250 mark (well, until I over-revved it and blew it up...:(). And that's with no dyno time, a tiny port, a 48mm Weber and an exhaust that passes the rally noise test ( <96dB @ 5,000rpm). And the basic build was just a cheapy one too... :) - in hindsight, I was probably running it on a razor's edge, but that's nothing a decent build wouldn't fix. Ask Ballast or Daveee what they thought of it, if you want to hear an opinion from some-one other than the owner... :)

Realistically, a PP in the same state would put out about the same, but with less drivability... Open up the exhausts and the PP asserts itself, but...

Beavis
23-07-02, 07:58 PM
Originally posted by Spac
The only real hassle with the S4 box is fitting it in - the input and putput shafts are different to the early cars so you'll need a custom tailshaft and a "custom" clutch plate (but they are available off the shelf). This much is the same as the Supra, although Supra clutch plates seem dearer(?!).

Is the jury still out on getting it to fit in the trans tunnel? Hooray for buying bits off the shelf.. chequebook racing at it's finest ;)


I've been talking about this using early type 8.5" clutch, rather than the S4's 9.5'(? - bigger) clutch - if you go the later bits you need to do it ALL - flywheel, bell-housing, starter etc - these cost a lot more, and are harder to fit (clutch fork is further rearward in BH). And the decent bits you'll need (light FW, HD pressure plate etc) are also much dearer...

Eek, staying with the old-style then sounds a lot better.. "old-skool"


Power from a BP. The club car guys are talking 320hp... but that's with BIG money spent on injection.
Back in the real world, an honest 250hp is available from a sensible BP, that is drivable, and will last. A good mate of mine had a J-port in his RX-5 rally car, and it put out 148-RWHP, so had about 220hp at the flywheel.
My car was apparently a LOT healthier, with a much smaller port, so I'm guessing it has some-where around the 250 mark (well, until I over-revved it and blew it up...:(). And that's with no dyno time, a tiny port, a 48mm Weber and an exhaust that passes the rally noise test ( <96dB @ 5,000rpm). And the basic build was just a cheapy one too... :) - in hindsight, I was probably running it on a razor's edge, but that's nothing a decent build wouldn't fix. Ask Ballast or Daveee what they thought of it, if you want to hear an opinion from some-one other than the owner... :)

Yikes.. 320hp is some serious aspirated power! Would probably sound good, too. ;) I was thinking that, with carbies, a 51IDA would be fine? Exhaust noise and fuel consumption don't really bother me, unless I need a support vehicle for fuel when going down to the shops :)


Realistically, a PP in the same state would put out about the same, but with less drivability... Open up the exhausts and the PP asserts itself, but... [/B]

Asserts itself well enough to bother with, do you think? Excluding noise/economy from your thoughts for a second..

Spac
24-07-02, 10:21 AM
The rally car gets about 3kms per litre, OVERALL - that's transport and competitive included - I have no idea at all what the splits are. And that's with a 5.1 diff.

If you go for a carby, a 51 IDA is pretty much THE only choice. a 48 will work, but will stifle the top end a fair bit. And some people have played with side-drafts succesfully (inc myself), but the IDA is so well known, so easy to get bits for that you'd be crazy to do anything else.

Personally, I'd go for a small J-port - IE a wide bridge port, that isn't very tall. This keeps the overlap to a sensible amount, while still providing a good sized hole to flow lots of gas... :). Extened BPs and Monster ports WILL make marginally more power, but IMHO they lose way too much bottom end for it to be worthwhile.

The other thing to mention is the longevity of the different types of motors - all PPs WILL end up leaking water after time (unless you use horrifically expensive factory PP housings...), and Monster ports will do it very quickly (talking 5,000kms, max!), whereas a BP will last until the apex seals wear out (around 15,000kms if you treat it right), and then you just pull it down and freshen it up - shouldn't need any of the "big" bits, like housings...

And getting back to my rally car once again, it NEVER, EVER felt underpowered even on the road, and often down-right scary on the dirt... :D

Dazz
24-07-02, 12:41 PM
I've only just seen this thread, but Spac has pretty much summed it all up really, so not much to add here.

From experience, the only advantage with an auto tunnel is that you have more clearance for the starter motor. In some instances with a manual tunnel you need to masage the tunnel with a nice big copper hammer to clear the starter motor.

Depending on what 'box you use, sometimes you will need to slightly massage the top of the tunnel for clutch fork clearance as well, but only with some box's.

To be perfectly honest though, and I have looked into it a few times, I have never found that it is much cheaper, if at all, to begin with a Capella rather than an RX-2.

By the time you do all of the re-wiring, buy x-members, radiator, oil cooler etc, and are then still stuck with Capella instruments, small fuel tank with no return line, less room for exhaust at the rear etc etc, you'll probably wish you simply began with an RX-2.

If you use an RX-4/5 engine, with the tall port centre housing, and get a nice sized bridge port which is just recessed into the rotor housings but without going near the o-ring, and use a 48ida Weber with about 43mm chokes (no bigger otherwise it will become a bit doughy in the mid range), and something like 1-7/8" or 2" extractors into a twin 1-7/8" exhaust with a single 2-3/4" or 3" over the diff, you should see about 240-250hp (flywheel) at about 8500rpm, which is about the safe limit if you use steel apex seals.

If you want a 5-speed, a Celica or Supra will not really be any more expensive than going for a SIV/V Mazda box anyway. On the cheap an RX-5 box with a 121 gearset is a pretty good box if treated ok. RX-4 4-speed's are pretty much indestructable though if you think you can do without that 5th gear.

mr808
24-07-02, 09:39 PM
what about an rx4 crossmember? i got one along with mounts and engine bracket for $150. It had to be shortened and redrilled to suit my 808 though it was previously fitted to a capella.

Rota_Motor
27-07-02, 05:15 PM
hey its been a while since I read thru the thread, and I got asked what gearbox I am using? and did it all bolt straight up?

I am running the twin dizzy 12A, with a T/D RX-4 bellhousinmg thru to a 121 5 speed into a S3 RX-7 tailshaft and an R100 diff.

it all bolted straight together, except for the drama's actually finding the T/D RX-4 bellhousing and starter, single dizzy parts are much easier to find :) and I also had to do a little tunnel massage to get clearance for the starter, and the clutch fork, but it was all pretty easy.

oh and I had to modify the gearbox crossmember, would possibly be easier on an RX-2 as the 1300 has the dash-mounted handbrake with the cable bracket on the crossmember.

oh and just reading thru, I noticed spac said around $200 for an RX-4 bellhousing, I feel mighty lucky that I found one at a wreckers, he didbnt know what he had, I got the engine mounts, crossmember and bellhousing for about $80, how lucky was I?

mr808
27-07-02, 11:07 PM
[i]Originally posted by Rota_Motor
I am running the twin dizzy 12A, with a T/D RX-4 bellhousinmg thru to a 121 5 speed into a S3 RX-7 tailshaft and an R100 diff.


I have the same setup, a a 12A twin dizz and the T/D rx4 4 speed, so does the 121 5 speed bolt up to my bellhousing?
Cheers;)

Spac
29-07-02, 10:33 AM
You need the ultra rare twin dizzy bell-housing with the bottom mount starter motor. I've seen a total of about half a dozen of these ever. Mazwreck in Revesby (Sydney) had a couple a while ago, for $60 (this is a very good price!).
You also need the matching starter motor, which is even harder to find (starter motors die, bell-housings don't!).

But if you do find these bits, they are generally much cheaper than the single dizzy equivilants.

A 121 5-speed WILL bolt up to the top mount bell-housing, but the box is then twisted on an awful angle, so you'd have to do some VERY ugly things to your transmission tunnel and gear-box x-member.

mr808
29-07-02, 05:03 PM
Originally posted by Spac
You need the ultra rare twin dizzy bell-housing with the [b]bottom mount starter motor. I've seen a total of about half a dozen of these ever. Mazwreck in Revesby (Sydney) had a couple a while ago, for $60 (this is a very good price!).


Ahha, looks like i am the owner of a very rare bellhousing then!:) Cool, i might have to get myself a five speed now, you got one Spac?
Cheers.

Spac
29-07-02, 06:09 PM
Nah... not quite hen's teeth, maybe more like Queanbeyan street worker's teeth...

Honestly, the old 121 boxes are getting hard to find. They're out there, but they take some looking now-days. And as the cars are getting older, there are more of them with 626 5-speeds and other such dross... The "proper" 121 box looks like a RX-2, 3, 4 box, with the external webbing, not smooth like the later RX-7 / 626 gearboxes. I am also pretty sure that the later 121s came with the 626 type box from the fgactory - change-over seems to be mid 1977.

But I could be wrong there - just what I've seen in cars, which is hardly conclusive 20+ years after they were made, and from a fairly small sample.

Rota_Motor
29-07-02, 08:29 PM
as far as I know, ALL twin dizzy RX-4s have the bottom mount starter motor, just an RX-4 thing.

the 121 gearbox bolts straight up, but as said it must be the type with removeable bellhousing, look like S4 gearboxes with external webbing as also mentioned.

and, yeah these parts are pretty hard to find, unless you are lucky and have contacts. my bellhousing was picked up at an all you can carry sale down at AFR, $20 with 2 rotor housings, a 1300 tach dash, and a full RX-3 guage setup. the gearbox I stumbled upon in a wreckers down here when me and my bro were looking for other parts, picked it up for $150, and then I got one given to me by a friend out of his 121 :), and the starter motor was very easy to find, if you look in the right places ;) mine cost me under $100 for a fully rebuilt item, but that was trade price.

MR808, do you want to pay for freight on a gearbox, Im not selling mine, but I can keep an eye out if you want, just after I got mine, I keep seeing them in wreckers, it seems people have given up looking for the box, and there are getting to be a few in wreckers.

as for bolting the 5 speed up to the top starter bellhousing, the oil level would need to be checked with the nox as it would sit on a bottom starter housing, as the filler plug is in a different spot.

mr808, if you need any other questions answered about this shit, feel free to PM me :)

mr808
29-07-02, 08:34 PM
Thanks rota motor i'll PM you when i have my next of many T/D related questions! :) I think i will see how i go with the 4 speed first and go from there. I just want to get my car going but i'm a bit stuck this being my first engine conversion i've done and all!
Cheers guys:)

BigJ
30-07-02, 10:29 AM
Its still for sale guys, $700 and its yours, i had one fella going to get it but i havent heard from him for a month or so.

If you do decide to go injection Motec is the way to go :) I run an M4 with twin 55mm throttles on a very large J port and we made 303hp @ 10200rpm on the engine dyno. I wouldnt risk building a ported screamer without carbons either. Not worth the risk, i once had a extend with steels and it dropped a seal and gouged out the whole motor. In the bin she went.

Good luck with the buildup!

Cheers
BigJ

Rota_Motor
04-08-02, 09:21 PM
hey guys, especially mr808, seeing as this thread bought up the popularity and hard to get nature of 'proper' 121 5 speeds, as stated I have 2 good ones here,
and today I found another 3 at the local upullit wreckers,
they want around $200 for the gearbox,
I think that is exchange so another $10-20 with no changeover.


I know you guys are mostly interstate, but if anyone wants one maybe I can arrange something with the yard to freight it over. PM me if you are interested.

the wrecker is in Adelaide. U-PULL-IT lonsdale. you may be able to ring them direct, but they might also send the wrong box by mistake.