Original GTA T3 Turbo Specs

David, I always thought there was some problem about programmable ECU's for the early PRV engines (or did I miss something) all to do with the uneven firing cycle or somthing.....
How does this one get round that?

i think that because it is fully programmable (oops) this means that you can tell the ecu exactly when you want the spark, and to which cylinder.
this over comes the problem of odd fire.
hope thats the way of it, otherwise i am prepared to be told of by DG.

Any PRV that came with carbs or Bosch K-Jet mechanical fuel injection cannot be fitted with the ECU. All Renault 25, Safrane with the Renix/Bendix/Siemens electronic types ecus are even-fire arrangements. Basically any PRV v6 with even spacing between the electrodes in the distributor cap is even-fire.

There are some aftermarket ecus that can cope with even fire engines, but the engine needs to have run a cam angle sensor and a crank angle sensor which you cant do on the Alpine, and you's have to run full sequential firing, so only one injectors fires at a time...and because the old odd fire engines have different cam profiles from bank to bank its even more of a mess.

David, can you remind/educate me/us on what even and odd fire really mean, I guess in relation to one rotation of the dizzy? Thanks for the lesson in advance.

Right, its a little difficult to get your head round, but ill try and explain it as easy as possible.

Basically the engine should have been a V8, by the 90 degree V, but was modified to be a V6. This means that two pistons are missing from the original firing order.

The crank on an oddfire has 3 main jounals with two pistons/rods on each. The engine has to turn 90 degrees (on a v8) for each piston to fire.

For instance, the first piston goes up to top dead centre and fires, then crank then turns 90 degrees for the next piston (problem is that should have been piston 7 or but making the engine a 6 pot, we have made it become piston 4. The problem is at the next crank rotation, piston 4 isnt at TDC (as it wasnt its turn!), so we actually have to wait more degrees before it hits TDC, likewise, the next firing is at lesser degrees. That is why it is called oddfire, and this is why the points in the dizzy and not staggered equally.

The even fire crank has the journals split in two and staggered by what looks about 12mm for each piston/rod. So there for, on the second piston stroke, the piston is raised further up the bore to be at TDC and therefor equal firing every 60 degrees and evenly spaced dizzy points.

PROBLEMS!

Ecu based.....nothing ever goes simple on a GTA!

Seems the 'old' GTA ecu cannot be remapped with the new system. They phoned me today, and said the chip types are different and not compatible. They said the chips inside are so antiquated, most if it is transistorised.

..but there may be light at the end of the tunnel....

The R25 V6 2.8 ecu is the correct type fingers crossed (looking at circuit board photos)...so for the original price it wont be exchange, but ill supply an outright ecu. The only thing that would need changing on the car would be the throttle pot on the car to the 25 type (this is just two screws to change), and the good thing is the 25 ecu has lambda control as standard.

I have a 25 ecu and have tried it on the GTA and it works and runs, so therefore be reprogrammed to the turbo maps.

Im not going to talk anymore about it in case I jinx it.!

D'oh! How long will that lot set things back? Weeks...months??? Double D'oh!!!!

David, still confused......

The really easy bit, most V6s are 60deg with equal firing delay of 60 deg per pot, so the contacts are equally spaced in the dizzy, sounds balanced too.

PRV V6 should have been a V8, really or just because it is 90degs? I'd guess that a 90degs V engine should also have a lower overall height, for better centre of gravity too.

So simply(theoretically) fitting a V6 crank in a 90 deg block might allow the same dizzy to be used, just the timing on the cams would need to be different (just 1 bank could be advanced or delayed by 30deg)..... but that is just too simple I think you are gong to tell me?

So the PRV V6 has odd-firing, (seen by oddly spaced contacts) and would I assume that this means it is not evenly balanced for the firing tims between each pot too?

Perhaps it is all to do with firing on 1 pot while optimising the chances of not fighting against the hardest part of the compression stroke of another, and/or taking advantage of anoters power stroke?

Are there some interesting design books/sites available to read up on for this type of thing? All very complicated, but we know it works.

PRV V6 should have been a V8, really or just because it is 90degs?
when they (PRV) 1st set out to design a large engine it was to be a V8.
then i guess they had some DG style of problems
so the french being french (3 wheel nuts and all that!) decided to do a V6 and change none of the funamental design.........great!

David, still confused......

The really easy bit, most V6s are 60deg with equal firing delay of 60 deg per pot, so the contacts are equally spaced in the dizzy, sounds balanced too.

PRV V6 should have been a V8, really or just because it is 90degs? I'd guess that a 90degs V engine should also have a lower overall height, for better centre of gravity too.

So simply(theoretically) fitting a V6 crank in a 90 deg block might allow the same dizzy to be used, just the timing on the cams would need to be different (just 1 bank could be advanced or delayed by 30deg)..... but that is just too simple I think you are gong to tell me?

So the PRV V6 has odd-firing, (seen by oddly spaced contacts) and would I assume that this means it is not evenly balanced for the firing tims between each pot too?

Perhaps it is all to do with firing on 1 pot while optimising the chances of not fighting against the hardest part of the compression stroke of another, and/or taking advantage of anoters power stroke?

Are there some interesting design books/sites available to read up on for this type of thing? All very complicated, but we know it works.

Youve confused me now!. Yes, the engine was going to be a V8 when it was first designed, but becuase of the fuel crisis in the 70s they changed the design to a V6, but kept the design of the crank.

On an oddfire engine, you can convert it to evenfire, by fitting the crank and camshafts from an even fire lump.

You might understand what I mean from this pic. This is an even fire crank. You can see the stagered journals, so at a certain revolution, the piston is further up the bore at TDC than it would be on a normal crank with 3 journals. If the points were spaced equally using an Oddfire crank, the spark would fire well before TDC and cause massive cylinder pressures on top of the piston and kill it!



Heres a website that explains with pictures. Its about the Jeep V8 what was redesigned as a V6, but ended up being oddfire.

http://home.off-road.com/~merls_garage/oddfire.html

[Alpineandy]

If anyone still doesn't understand the phrase odd-fire, the way I explained it to a mate was as follows:
Imagine looking at a 4 cylinder crank from the end.
It looks like an X where each piston/rod moves up the bore one at a time.
Now cut off the section for one piston/rod and it looks something like a y, instead of even gaps between the throws there is an uneven gap.
Now expand that to a V8 -V6 situation

.

No.....youve confused me Andy....think I had it before but now its gone....oh god....odd fire will be haunting me for days now!!!!

Well David, it’s as clear as ice now, and I’m cool with it, many thanks.

Great link, I thought it was going to be a long night, but now I can explain odd-fire myself in 6 simple steps, given a few basic principles.

“It's actually fairly straight forward once you understand...” Well it is..., when I understand each step as I go and don’t jump to conclusions.

Myth: The V6 is simply a V8 that had two cylinders removed. It may be partially true but its absolutely no help when I'm trying to understand how the Alpine engine works. I put this myth out of my mind. However, the V6 block can be thought of as a shortened V8 block but with a different crankshaft, NOT a shortened V8 crank!!!

I remember that:
When I watch any 1 cylinder, all the rest do the same, but are just delayed by a certain number of degrees, in the order of the firing order.
The whole combustion cycle is 2 revs of the crank and 1 rev for the dizzy, from start to finish.
The 90 deg V6 firing order is 1-6-5-4-3-2, or even 6-5-4-3-2-1.

So in 6 simple steps……
1. I simply, think of the crank as a 3-cylinder crank with each journal double width and the journals are each shared by 2 con rods. Pot 1 and 2 share, 3 with 4 and 5 with 6.
2. The 3 journals are 120 deg away from each other, to be balanced and symmetrical.
3. Now, after cyl-6 fires, 5 fires 90 degs later, because we have a 90deg V between the banks.
4. This is the same for 4 and 3 as well as for 2 and 1, as they share journals too.
5. Simple maths, so the delay between say 5 and 4 is (720-(90+90+90))/3=150 degs.
6. This is the same for 3 to 2 as well as from 1 back to 6.

So as the crank is rotating the firing delay after cyl-6 is 90 to 5, then 150 to 4, etc 90-150-90-150.
Therefore on the dizzy, the spacing is 45-75-45-75-45-75.
That’s why upgrading and swapping dizzys can be troublesome and the reason why we can not swap heads or cams with even-fire engines, like the Atmo.

So, odd-fire means “odd” delays between firings, and even-fire is evenly spaced.

Now I fully understand the myth about a shortened V8, Block only, yeh?

If I split the 720 deg combustion cycle into 30 deg units, the firing looks like this:
6 . . . 5 . . . . . 4 . . . 3 . . . . . 2 . . .1 . . . . .

WHY, I may ask did they do this? ‘Cos they could and they did.
1 advantage of the PRV V6 set-up is that this adapted pseudo 3 cyl crank should be a lot stiffer and stronger than a 6 journal crank, with it's 6 separate journals, which would also look a lot more complicated. Our V6 crank may be more economical to manufacture, work on and balance.

However if the V was 60 degs, then we can still have the wide journal crank with pots paired up, but it should be even-fired, maybe as other V6s are.

Like all problems, easy when you know and understand the answer.

David, the Exhaust you supply i.e the twin race system, is that legal in the sense that if you took it for MOT would they moan! Or is the system strictly race? And so with the power upgrade business all I need 1st for the 1st step as in 230/240Bhp is the programable chip, and then any more power the larger stage 3 turbo? have I got that right, or is there any thing else. When will you be getting them?


[Emmerald green GTA[/quote]

The race system is alot better than the original in that it has the same diameter all the way through, and no silencer restrictions like the original. Its perfectly legal and alot lighter as there is not much too it!

Your right about the programmable ecu, once you have that you can do what you like. Im yet to see what the new ecu will do on even a basic upgrade such as raising the boost to 14psi on a standard engine. The piggyback chip sold previously increases the power at that boost to 230, but its still attached to the lo-tech old ecu...the new ecu at the same boost may make more power and torque, just because it can be fine tuned to your engine. You have to remember, factory ecus are programmed to work with engine conditions in the worst case scenario and the best fuel economy, and not always performance.

Even though the stage 1 package does provide 230bhp, the standard turbo is well beyond its limits and making alot of heat, so any turbo upgrade will be a benefit. The stage 2 turbo is basically the specification of the A610 turbocharger and good for 300bhp with still good efficiency.

Once the new ecu has been fully developed, ill try and work packages with certain fuel injectors to get certain power levels (fingers crossed)