The 70mod bellett owned by myself came standard with IRS 3.72 gears ,1600 , G161 engine twin hitachi s.u. type carby's , PR91 style dash & instrumentation, strip taillights vents in rear quarters & bonnet & black vinyl roof and factory alloy wheels as per PR91 a lsd style diff was available in this mod as well .

The chip sellers typically spend/spent long hours learning the finite details of tuning their own personal vehicle, or a main cash crop sales application. This is the one they use in their advertising as an example of their product's performance. Then they apply those techniques to the entire range of cars made by other companies and with a wide variety of unrelated electronics systems. 99% of those other cars they have never had on a dyno or tested to see if their product actually worked. They just bring in the ECU, pull the chip, guess what they think they can bump the curve to, slap it together, and that is the end of their concern. The six months of fine tuning that went into their example they made for their personal vehicle was never done on the rest of the cars they provide chips for. And none of this results in a chip that has been tested and certified for emissions compliance or fuel consumption as is required for auto manufacturers.

Holden's introduction of the Piazza was two or three years late (and for or five years after the US introduction). The UK distributor had already gone bankrupt twice. The car was never given a very warm reception in the motoring press.

What I am suggesting is that given the situation, and the amount of money and time that would have been required to bring the hot wire system into compliance or to work with the fuel and conditions of Australia, and the low number of projected sales, it makes more sense for Holden to have chosen the already available (Japanese market), lesser desirable fuel injection system for their market.

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My misreading of the first differential explanation had the five link Piazza and Bellett diffs as interchangeable. Very unfortunate to find this is not the case, I already had one located... So much for the easy way...

I don't know if this is 100% true.. it may just be. But if you want to tune your car get aftermarket programmable fuel injection and a wide band sensor and get on with your life.. with some (maybe all now) of the management systems the car will tune itself as you drive.


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What's the problem ratios, LSD, or both?

You could always put a supra diff in there.. would involve some kind of fabrication for the carrier and you would have to deal with bolting the axles to it, but they are nearly free, plentiful and have a bazillion cheap ratio and locker choices.

If the car is a road car, you don't want to be welding the rear... but I would consider it, as I hate open rear ends that much

I still don't see JT's point.
We are talking about "re-curving" an ignition system, not determining the curve (which these days is easy & automated as per Hudson, and may have been in 1980 else probably CAD/CASE or manual formula etc).

When the 1986 4ZC1-t was introduced, someone determined its ignition curve.
What I am saying is that it is easier to plug those values into an ECU (map; ROM etc) than manufacture another dizzy.
The ECU could also be a variable mapping rather than the general straight-line "curves" (usually 2) for each of the mechanical and vacuum advances.
Hence why did Isuzu go from a mapped ITEC system back to a mechanical distributor system some 5 years later?
GM/GMH did not develop the 4ZC1-t, its ECU nor its distributor (AFAIK).
And I think GM (Impulse) used the ITEC (as did NZ).

These days they are self learning - EMS, Autronic etc. No need for dynos. (Even CAS are not required - in principle, use an ionic sensing and you need not pre-map or config the ECU - except maybe whether 2 or 4 stroke, and the number of cylinders if you have a weak battery!).

I agree with GMH being too late on the Piazza. As I have said elsewhere, not only did they order the superseded chassis/body and smaller engine, but they mucked up its handling. In USA, Impulse got "car of the year" two years in succession. In Aus, it got lemon of the year.

I saw the Piazza at the 1980 Melbourne Motor Show. I was rapt - it was the only car I had seen with electronic dash (other than my own). And I liked its features - way ahead of its time. 3 "computers" (4 in autos). Climate control, vari-wipers etc. It took Ford over a decade to copy its door hinges. Its standard 1980-ish features were still options (if that) in many 1996 "quality" cars. IMO, it really was a production "concept" car.

Hudson - as to the diff, the Bellett carrier is totally different. You need the Bellett (GTR) LSD etc. Whereas in the "normal Isuzus" (ie, all except Gemini) all are interchangeable whether open or LSD. (ie till 4ZE1. In UBS17 4ZE1 Jackaroo & equiv Rodeo, the front diff is the same as older rear diff = Florian/Wasp/Piazza etc.)

No, rewriting the ignition and fuel curves.

Why did Holden order cars with the less desirable ignition system? Isuzu delivered whatever Holden ordered, not the other way around.
I've already explained. Too complicated to modify by Holden, likely without any aid from Isuzu. Too expensive to spend time and money developing for a production vehicle, which involves a lot more than selling an aftermarket chip. Too expensive to re certify to make legal with whatever the Australian equivalent is to DOT and EPA, both of which would require fuel consumption and emissions testing costing months and tens of thousands of dollars. All for a few hundred cars sold. What's the markup on a $12,000 car after import, duties, advertising, distribution, etc.? Not enough to cover re engineering the fuel injection and paying the government fees to make the modifications legal.
This may have less to do with understanding and more to do with a resistance to the content of the explanation.
If there is disagreement with the explanation, then just say so. We can agree to disagree and I can stop rewriting the same thing over and over.



The car was never awarded anything in the US.
It was among the cars considered by What Car (UK), and mentioned in the list by Motor Trend. But never received any award.

Not at all! I wasn't aware that Holden did the development of the 4ZC1-t or its mapping (both fuel and ignition obviously!). Your previous info stated "may have been" etc.
So it's as I suspected, Holden couldn't handle all-electronic systems (ha ha - my spin; noting however that Holden wanted to develop fuel injection back in the 1950s!)
But that then is the answer I was after - that it was Holden that wanted the dizzy and old mech stuff.

I know Holden didn't handle the more recent "wire" system to well. (Again, my LOL!)

Please don't take it as a refusal to accept. I usually do when I see a valid argument etc. I usually won't accept "well they must have had a good reason" - that's for the non-progressive.

So Holden rewrote the fuel curves for the 4CZ1 and placed that in an ECU (whether Japanese or not, but not "aftermarket").
And the recurved ignition was removed and placed in a mechanical dizzy. FIGJAM! (ie as I said originally, but for reasons unknown which you have now explaned.)

So we do/did concur. Or have I missed something?

So ... where do I get a LSD for project Bell ?

Cheers
Rob

i have a gtr lsd in my bellett but i had it fully rebuilt with the automatic 4:11 ratio as i have a 5 speed in mine so its accelerates real nice the 3.73 that was in with the 5 speed you would be cruising on the highway doing 110k's and the motor would be sitting on 2000rpm...probably could have had a very large top speed on her hehe

110 @ 2000rpm is a bit of an exageration here.
my cars that have had, or still do have, a 5 speed with the 3.73 diff sit on 110 @ 3000. 100 is about 2800.
a standard 4 speed Bellett with the 3.73 will do 100 @ 3400.

Rob, my race car had a home made LSD years ago (now has a locker). i had it rebuilt with springs fitted to push against the side/spider gears to put some pre-load onto them, making them hold their mesh tighter. while it's not a true LSD, it's as good as u'll get without the real parts and alot of money (i've seen the real stuff listed on auction sites at near enuf to the $1k mark...). i can't remember how strong those springs were, but they were the strongest the guy could get in there!! that made the diff very tight when turning the axles by hand (in that, they felt locked together), but it was still "free" enuf to drive normally once it was in the car. i only took it out because more power in the race car still had it spinning inside wheels more than what was exceptable, so a locked diff was the next step.
this LSD diff is now in another user on here's car, and he says that it definitly makes a difference. it really makes the car push out of corners much harder, but having said this, i'd strongly recommend front end work (for camber and castor) on a Bellett if fitting an LSD, as they understeer enuf without the added diff grip.
i'd think that any decent diff shop would be able to modify yours to the same as mine was.

Thanks for the info on the springs.
Yes the front end is set to get a look over very soon. Yep it under-steers, i keep saying in my head it pushes, but thats and old saying.
The toe settings are way out at the moment and probably the rack needs replacing, but all things one at a time.

Cheers
Rob

Now in the possession of a Jackaroo LSD rear axle.
Will be taking it apart to see what if any parts are interchangeable with the Bellett differential internals.

Cheers
Rob

Now not in possession of Jackaroo LSD rear axle.
Didn't get a chance to measure or check anything.