www.RX7fb.com

TOOL wrote:Ditch the oil interheater

Fixed that for you I'll definitely be interested to see what sort of powerz you can get out of the humble 12A, since I'm going that route myself as soon as I can get all the bits together.

Lucky wrote:

TOOL wrote:Ditch the oil interheater

Fixed that for you I'll definitely be interested to see what sort of powerz you can get out of the humble 12A, since I'm going that route myself as soon as I can get all the bits together.

What bits do you need?

TOOL wrote:

Lucky wrote:

TOOL wrote:Ditch the oil interheater

Fixed that for you I'll definitely be interested to see what sort of powerz you can get out of the humble 12A, since I'm going that route myself as soon as I can get all the bits together.

What bits do you need?

Mostly waiting on a quote for Holley stuff atm Can't face the idea of trying to re-tune a Weber every other Tuesday A built engine would help too...

TOOL wrote:Ditch the oil cooler.

Ditch the thermal reactor.

Of course lol

TOOL wrote:That's a nice S3 motor and I hope the housings are good.

Yeah me too! *crosses fingers*

So my planning for this engine swap should include a transmission upgrade. RX7 transmissions have awfully tall ratio's in low-gears, along with a big spread between 2nd and 3rd.

Non-turbo transmissions are known to be weak in terms of power handling and durability but the turbo's are quite a bit heavier so I'm gonna keep running a non turbo transmission for now. Every RX7 transmission I've felt has had issues with its synchronizers. The only way to make them function half-way decent is to run Redline synthetic fluid in them.

Using ATF is a no-no. I've seen people get their transmission completely froze up doing that. There may be some merit to adding a small amount of ATF in with the gear oil to try and 'clean' it while you use it. But I think it's wiser just to rebuild it.

My least favorite aspect of RX7 transmissions is their shifter feel. It's just garbage... but the FB shifter and knob feels better, even when installed in an FC transmission.

What I'm running right now...

Mazda Rx-7 87-88 13B 6PI (Type M) Gearbox
1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th: 0.697

Vs. my original GSL-SE transmission...

Mazda Rx-7 84-85 13B (Type M) Gearbox
1st: 3.622
2nd: 2.186
3rd: 1.419
4th: 1.00
5th: 0.807

Vs. Mazda Miata

Mazda Miata Gearbox
1st: 3.136
2nd: 1.888
3rd: 1.330
4th: 1.00
5th: 0.814

The Miata gearbox seems like a good bet. Lower 1st and 2nd gears should be better in the mountains and the shorter split between 2nd and 3rd should improve overall driveability. The .814 overdrive should even allow for some acceleration in 5th... hard to say if it could improve overall top speed though. In the past when I've tested top speeds on various cars, the rev-limit in 4th gear is the maximum gear-limited top speed unless you have enough power to overcome all that wind resistance in an overdrive gear. (Or just happen to be driving down a really long steep hill)

In order to adapt a Miata transmission unto an RX7 you must use an RX7 bellhousing and modify the miata input shaft. Reading up about modifying the miata input shaft got me thinking though... I saw this pic on Mazdatrix and I was wondering if it was possible to use an RX7 input shaft on a miata gearset? That would simplify things a lot.



However, after searching about it, it seems that it has been tried with no success.

RX7 Club wrote:All right. I made some measurements and tried to assemble a hybrid box today using an RX-7 input shaft and a Miata gearset.

The initial problem is that the diameter of the input gear of the RX-7 shaft is about .100" larger than that of the Miata shaft. I did not measure the diameter of the gear on the counter shaft because I do not have a mic that large. I figured I'd try to put everything together, see what fit and how it all mated. I measured 3 RX-7 shafts and 2 Miata shafts and all the numbers were spot on among the lot.

The tooth count is different between the two input shafts and counter shafts but the pitch appears to be the same because once they are together they mesh very well and the assembly initially rotated very freely.

I assembled the whole front side of the box (1st-4th gears) and everything looked great. The problem occurred after reverse gear was in place and I began to add the OD gear. The OD gears would not go on. There is enough of a side load on the shafts from the diameter difference of the input gears that the clearance is ruined on the backside of the tranny.

So that settles that. A custom hybrid Miata/RX7 transmission will be in the works for my FB to go along with its motor swap. I'll try and include a flywheel/clutch upgrade to go along with it. I may also need a custom driveshaft depending on how I end up mounting the 12A itself.

I've got a S4 NA box behind an early style 13B BP and it's more than capable of the power. This isn't an issue but I intend to upgrade it to a S5 turbo box when I put the S5 NA motor in.

The ratios are definitely better than FB boxes. I couldn't justify modifying boxes any more than that.

I reckon you would get much more benefit from changing the diff ratio to say a 4.3:1 out of a Miata. It will make it much more lively.

TOOL wrote:I've got a S4 NA box behind an early style 13B BP and it's more than capable of the power. This isn't an issue but I intend to upgrade it to a S5 turbo box when I put the S5 NA motor in.

The ratios are definitely better than FB boxes. I couldn't justify modifying boxes any more than that.

I reckon you would get much more benefit from changing the diff ratio to say a 4.3:1 out of a Miata. It will make it much more lively.

True, an increased final drive ratio is already planned for my FB. I mentioned it earlier in my build thread. It says on your sig that you supply LSD's for FB's? I read somewhere that my GSL-SE LSD is less aggressive then those from an FC is that true?

I've started dabbling in LSD diffs, yes.

It's not quite as simple as comparing FB vs FC.

There were 2 FB LSDs. Both clutch type. The FB LSDs came in either race type or street type, which meant the ramp rate was a bit different between the two.

The FC had 3 different LSDs. The NA cars had a 7 inch clutch type LSD, exactly the same as a S3 LSD (GSL-SE big axle LSD to you). The turbo FC cars had a bigger diff (8 inch I think, same as the FD anyway) and this was a viscous LSD. We only had S4 NA and S5 turbo in UK, so this could be a S4/S5 variation.
I believe there was also a Torsen centre for the US FC cars but unsure which ones got them.

You can set the breakaway on the clutch type LSDs to be more aggressive by shimming them, so to answer your question, I don't think that statement is true, or even accurate unless you specify which LSD diff you're even referring to.

I'm very happy with my clutch type LSD fwiw

TOOL wrote:I've started dabbling in LSD diffs, yes.

It's not quite as simple as comparing FB vs FC.

There were 2 FB LSDs. Both clutch type. The FB LSDs came in either race type or street type, which meant the ramp rate was a bit different between the two.

The FC had 3 different LSDs. The NA cars had a 7 inch clutch type LSD, exactly the same as a S3 LSD (GSL-SE big axle LSD to you). The turbo FC cars had a bigger diff (8 inch I think, same as the FD anyway) and this was a viscous LSD. We only had S4 NA and S5 turbo in UK, so this could be a S4/S5 variation.
I believe there was also a Torsen centre for the US FC cars but unsure which ones got them.

You can set the breakaway on the clutch type LSDs to be more aggressive by shimming them, so to answer your question, I don't think that statement is true, or even accurate unless you specify which LSD diff you're even referring to.

I'm very happy with my clutch type LSD fwiw

Ah ok. I'll need to look into shimming mine then when I pull it apart to swap new final drive gears in it. ... it feels pretty weak lately.

You can shim it.

You can get thicker washers.

You can mod the centre housing.