BG Astina with DOHC Auto from Factory

[Fosgate]

Hey guys,

Has anyone seen a BG Astina with DOHC BP engine and Auto tranny? Not a conversion but from factory setup?

[TheMAN]

it doesn't exist... I believe this was only available in Japan and some other countries

[Fosgate]

Yeah thats what I thought as well... but couple of years back I bought auto tranny from someone locally in Sydney and that trany come of a BG Astina which had DOHC engine in it. The guy told me that he used to work for Mazda and there were some DOHC BG Astina produced and that was one of them. I end up getting the complete loom of him as well in case I needed for BPT Auto conversion ....

But wanted to see if anyone else has seen another one in flesh.

[project.r.racing]

none offically sold in australia.

[Fosgate]

must of been promotional vehicles or something ..... anyways looks like I'll be needing a SP then to convert it to Auto with a BPT engine.

Thanks guys

[phildough]

BG Astinas with BP Autos were sold in Japan.
http://www.cars-directory.net/specs/.../1993_2/15037/

The 1991 Mazda Familia GT 3 door hatch came out as a 1.8 DOHC auto.
I think there was a auto version of the GT sedan as well.

[TheMAN]

auto with BPT? are you insane? that gearbox wouldn't last a day!

[Fosgate]

Auto trannies are not that weak... they have same size front diff as in G type boxes plus I do know people who have BPTs in their lasers with Auto tranny... apart from shifting issues at high RPM (which can be overcomed) it runs quite well.

High compression BPT with a VF10 hybrid running stock 8-10psi should be quite nicely with longer ratio Auto box I recon.

phildough: Thanks for the info looks like they did come with DOHC 99KW J spec BP engine and auto tranny over there.... so another 30-40 odd KWs and alot more torque would be a nice combination.

[Mad Mat]

Like fosgate said, this has been done before. There was a member on here about 4 years ago that was asking the same questions, and did the swap himself. Cant remember his name tho

[project.r.racing]

Pete - I remeber being at this house and looking at the BG with the BP and auto in it, with anything else attached. I think that is as far as the project job. Was building it for his wife/girlfriend he had at the time.

Same as his KL-ZE into BG chassis. Engine got into chassis on mounts. But the project stopped there.

[Fosgate]

Brad (TX3BPT) from fl.com has done the conversion into his KH laser for his wife using 4 speed auto trany and BPT engine. Last time I spoke to him he said everything was pretty straight forward only problem he encountered was that gears would slip at high RPM when they up shifting, that was resolved by tightening the tranny cable going to the TB. Shifts are bit jerky now but it doesn't slip any longer.
Whats actually needed is an electronic BOV where it would release the boost pressure just before the changes or a way of retarding the timing before changes as it happens in the stock SOHC setup. Apparently there is a signal from the tranny to the engine (in SOHC model) to tell the ECU that tranny is about to upshift, I think that signal is used to retard the timing on the engine to make the shifting smoother. However that input is missing on the BPT ECU (as it was never designed to work with Automatic transmission).
So either electronic BOV needs to be installed using that signal or knock sensor needs to be triggered somehow for a split second to retard the timing before it up shifts.
Apart from that its a bolt in job.

[TheMAN]

if you go through with that, you may want to import the auto BP driveshafts from the US or Japan.... they're equalised with an intermediate shaft (mazda calls it a "joint shaft"), which is the short fixed piece bolted to the back of the engine you will see on the manual BPs

those driveshafts will be worth it as it'll greatly reduce torque steer

you definitely will want to buy a gearbox cooler for the auto too, and run synthetic ATF!

[Fosgate]

Yeah thats what we got on the Familias and lasers with BPT engines... I wonder how different the shafts are between Manual and auto boxes especially the G series boxes that go with BP DOHC engines.... Has anyone compared the two?
That would definitely help with torque steer.... so good point there.

Yeah cooler shouldn't be an issue can get one of these large oil coolers from another car .... and will be using Redline Synthetic ATF for sure.

[TheMAN]

I believe the splines and lengths are different
the auto is a F series auto

driveshafts are cheap here, the matter is finding the intermediate shaft from a wrecker or someone on the US forums

[Fosgate]

Yeah looks like thats what I have to do...
What about the shafts from BA Auto? were they a single piece same as what we got in BG models? I wonder if they would fit BG Auto.

[project.r.racing]

all ba models had a layshaft. the passenger side should be fine, it's the drivers side you may have to play with.

[TheMAN]

the BA auto box is different from the BG, I'm not sure it will fit

[Fosgate]

Fair enough .... well thanks for the confirmation

[TheMAN]

did the KH laser come with a BP and auto?

[Fosgate]

Originally Posted by project.r.racing

all ba models had a layshaft. the passenger side should be fine, it's the drivers side you may have to play with.

So the splin size is same between two models? Looks like I need to get a set of Auto BA shafts to compare.