Quick question about gearboxes.

[Lawsy]

Hey fellas,

It seems no one actualy has really bothered to work a SOHC BP 1.8, as everyones reply to my 'how do I make it faster without blowing it up' questions seem to be 'trade it in, get a new one'.
So although there is some information about my following query, I'm more looking for advice to push me in either direction on this decision.

You see, my clutch is going to need replacing relatively soon, and I'm seriously considerig (probably in around 6 months to a year) buying a half cut from japan and putting a BPT motor in. I kinda have a bit of a plan and may have the means by then as well...

Lets say I can source a gearbox out of a DOHC that has relatively low KMs on it, which is sealed and in good condition. While I get the clutch done, would it be feasable to basically dump my crappy weak gearbox, and put the DOHC box and a clutch in, along with the larger input shaft diameter to suit obviously, almost like a first step in the right direction?

I guess I'm asking whether the DOHC box is what most of you guys are using, and since the gearbox has to come out anyway, do you think I might as well put a better one in now (if its easily enough to do), and take advantage of the better ratio's, etc for the time being?

Or are the turbo guys getting a gearbox that I haven't quite looked for yet?

Any help is much appreciated guys, and only if you can be bothered, with as much technical detail as possible, I'm trying to pick the collective brain of the forum ATM, and quite enjoying reading the progress of the forum

Cheers again,
Tim

[DavoAust]

http://www.astinagt.com/forums/showt...t=swap+gearbox

that might help. i would say from that that the SOHC box will fit with the BA BP (DOHC motor) and if it does that then if should fit the BPT.

however, i would say that most of the people that have done this conversion have gone DOHC -> BPT. i would think the DOHC box would have better ratios and might be able to handle more power.

[project.r.racing]

yeah it'll fit fine - but it is the weaker F series box and will break within 6 months.

the G series boxes is stronger from a DOHC Mazda 323 Astina 90-93 or Ford Laser 90-93 is much stronger and many have used it with success with turbo applications.

ryan

[boostedbatman]

If your not insanely boosted the F will still work fine
Took Dan The Man 193kw atw before he broke his
Learn too shift properly and not like a virgin teenager at his first sight of a naked leg and you will not have a problem on a mild BPT
Replace it if and when you break it

Personally I like the ratios of the F Series

[Lawsy]

Originally Posted by boostedbatman

If your not insanely boosted the F will still work fine
Took Dan The Man 193kw atw before he broke his
Learn too shift properly and not like a virgin teenager at his first sight of a naked leg and you will not have a problem on a mild BPT
Replace it if and when you break it

Personally I like the ratios of the F Series

Don't worry about that, I've done several motorkhana's, raced formula fords for a day and am of the mind that driving a manual is about finding that 'perfect' shift, so... No worries there..

The thing is, everyone else is saying that my particular gearbox will break just by using a HD clutch... And well, I don't disagree, it feels very flimsy (and I'm not talking about linkage slack, as I only have about 1cm of movement of my shifter when in gear, not 3 inches, I've fixed that issue).

Ok so everyone has kinda beated around the bush here...

If I get a box out of the SP, which is stronger and in my opinion has better ratio's, will I be able to mount the new clutch and gearbox to my current flywheel (after machining of course)? And what about on the output side of things? What happens there?

Thanks again

[Rupewrecht]

No, i never broke an F box with the 194kw setup.

Once i had the standard turbo on with the F series, i broke a few. It's the lowdown torque that kills them.

The BA versions of the F and G have different splines (26 vs 28) and most of the BG ones are the same (except for some early G series which were 26 spline...i think)...so no, you won't be able to use your clutch, and the flywheel is going to be a different size (bigger).

Think of it as having extras insurance against breakages if you've got a G!

It depends what sort of power you're looking to put through it, really.

Also, people have turboed the 1.8 SOHC in the US...but it's still easier to drop a BPT in.

[ROB-80E]

Originally Posted by Rupewrecht

The BA versions of the F and G have different splines (26 vs 28) and most of the BG ones are the same (except for some early G series which were 26 spline...i think)...so no, you won't be able to use your clutch, and the flywheel is going to be a different size (bigger).

Bit confused over your above statement there dan...? It's the early version of the BA G series that came out with the 28 spline diff. All the Mazda BG/Laser KF/KH G series boxes had a 26 spline diff. Off memory the F series CV input is 24 spline. I'd have to dig through my posts on fordlaser.com to confirm, as I know I've also posted measurements of the all the splines.

As Rupe said, you can't use a SOHC clutch with a DOHC gearbox. You'll have to change the flywheel otherwise your starter motor will not enguage. Clutch input splines also vary between the series. You can use either the 4wd G series fly or the the FWD G series fly...BUT you MUST use the appropriate clutch to match the fly.

So once you've chased up the mounts, gearbox, flywheel, clutch, metal clutch line, slave cyl and drive shafts, you're right to go.

Oh, the other thing to mention too is, the G series isn't indestructable. It needs to be treated with just as much respect as the F series. With the F, the whole diff yoke cracks, where as with the G, the spider gears themselves tend to shatter. Also, if your pushing over 220HP at the wheels, you should seriously consider a stronger 3rd gear, as that is also a ticking time bomb.

[Lawsy]

Originally Posted by ROB-80E

Bit confused over your above statement there dan...? It's the early version of the BA G series that came out with the 28 spline diff. All the Mazda BG/Laser KF/KH G series boxes had a 26 spline diff. Off memory the F series CV input is 24 spline. I'd have to dig through my posts on fordlaser.com to confirm, as I know I've also posted measurements of the all the splines.

As Rupe said, you can't use a SOHC clutch with a DOHC gearbox. You'll have to change the flywheel otherwise your starter motor will not enguage. Clutch input splines also vary between the series. You can use either the 4wd G series fly or the the FWD G series fly...BUT you MUST use the appropriate clutch to match the fly.

So once you've chased up the mounts, gearbox, flywheel, clutch, metal clutch line, slave cyl and drive shafts, you're right to go.

Oh, the other thing to mention too is, the G series isn't indestructable. It needs to be treated with just as much respect as the F series. With the F, the whole diff yoke cracks, where as with the G, the spider gears themselves tend to shatter. Also, if your pushing over 220HP at the wheels, you should seriously consider a stronger 3rd gear, as that is also a ticking time bomb.

Well its going to be a basic conversion to start with, nothing too serious.

And like I said, I need to do the clutch soon. I've been babying it now for 9 months and its just lasted me, but a few slightly lairy launches since putting the extractors on have put the bullet in (doh).

I just don't wanna have to get a clutch now and get another in a years time, I'd much prefere to have the right clutch ready to go, but with this gearbox, I don't particularly want to put a HD clutch in as I don't want to risk doing something stupid...

So the list is,
Flywheel
Clutch
Complete G series box (incl clutch cyl already mounted)
clutch line
Driveshafts (cv shafts? they'll get done soon anyway).


So what sort of cost would I normally be looking at here?

[FEM]

well, i got a new set of complete drive shafts and cvs and got change in 300 bux..

flywheel.. i should have one of them laying around if u need one.. prolly best to get it machined!

clutch.. i just got a new one with upgraded pressure plate.. set me back about 400ish.. i think a HD disc is rather $$ for the bg at around 150ish

thats all i know about atm.. hope it helps

DAn

[Rupewrecht]

Originally Posted by ROB-80E

Bit confused over your above statement there dan...? It's the early version of the BA G series that came out with the 28 spline diff. All the Mazda BG/Laser KF/KH G series boxes had a 26 spline diff. Off memory the F series CV input is 24 spline. I'd have to dig through my posts on fordlaser.com to confirm, as I know I've also posted measurements of the all the splines.

Ah knew i was something like that, but i wasn't positive on the BG stuff.
But BA F series is 26 spline.

Lawsy - you'll also need the gearbox mounts.

[Shaken]

Those of you with first hand experence please correct me if I'm wrong but I believe you will need the speedo cable and drive gear from the g-series box also.

In North America, the BGs that came with 1.6/1.8 SOHC engines and f-series trannies had a diferent speedo cable than the cars with 1.8 DOHC and g-series boxes.

[Lawsy]

Originally Posted by tinastar

well, i got a new set of complete drive shafts and cvs and got change in 300 bux..

flywheel.. i should have one of them laying around if u need one.. prolly best to get it machined!

clutch.. i just got a new one with upgraded pressure plate.. set me back about 400ish.. i think a HD disc is rather $$ for the bg at around 150ish

thats all i know about atm.. hope it helps

DAn

That does help thanks alot, I'll be finding out tomorrow from mazbits (the father of the joint knows everything about any mazda ever, its scary) of what my options are.

Also, Shelley's no more gaps... Can I pump my doors full of the stuff?.... I have this irritating rattle and I want to dominate it so it can never return; ever.

Thanks again, you guys are being very helpful and definately guiding me in the right direction.

Put it this way, if I can get this gearbox thingo done, then I'll definately have the starting point for a nice light turbo build up in around 6 or so months time. Hopefully I can get this off to a good start to more power And eventually I might give a standard rex a run for its money (around the 220whp mark I assume). Which would be funny

In the mean time, whiteline swaybars front and back and DBA slotted front rottors are on the cards in approximately 3 months.

Cheers
Tim

[DavoAust]

i would think that the wrx has more weight, and with 220whp you'd probably be pushing more power to the ground. just got to hope you don't lose traction.

hmm research shows the latest wrx weights around 1521kg, BG around 955kg.
latest wrx puts out around 293hp/213kw AT THE FLYWHEEL..

i would love to see a drag off between a 220whp BG and the wrx.

ps. interesting BG info on here

[Lawsy]

Ok well it seems I now understand what I need to do and here's my plan, I hope you like it.

What am I going to do now? Sway bars, possibly brakes... What am I not going to do now? Clutch and gearbox.

So the plan is this.

In 6 months time, working 40-50 hour weeks, I should be able to save enough money to invest half and spend 5 grand on being a big kid with my toys.

This involves a half cut from a reputable jap importer with a guarantee (so I'll spend a little more for it to be sure). And I'll do everything at the same time. It is just going to be way too much of a hassle to try and do half and half.

So for now, I want my car to handle and stop well, while I baby my clutch for 6 months until I can do the full conversion.

Then, when I've had fun with that, I'll think about running an EMS, bigger fuel pump and injectors and more boost. That should see me to around 180whp, right?

Then 6 months later, whatever needs doing to make 220whp will be done and I'll then drive it like I stole it.

Sounds good to me
For now, I'm just going to enjoy the wealth of knowledge that is on this forum as I prepare to get everything on the way (obviously thats not all I'm going to do for 6 months, geez...).

Cheers
Tim