AJP firing order?
Discussion
Dont quote me but found this....come on ex tvr worker what is it?
The reason the Ferrari V8s have that unique sound is because they are one of the few companies to use a flat-crank V8. If you take a Ferrari V8 crank out of it's block it appears much the same way a four cylinder crank does, except there is room enough for two rods per crank throw instead of one.
If you look at the Ferrari firing order it's the same as the Cosworth DFV, which both use the standard 1-3-4-2 on each bank, except interlaced. One bank takes it's turn, then the other bank takes it's turn except from the opposite end. They do this until it's time to repeat the firing order.
There are a few other cars that use a flat-crank with their 8 cylinder engines; there is the Lotus Esprit V8, the VW Passat W8, and the Cerbera AJP V8 (which we can't buy in the United States).
eta: try this link
www.autozine.org/technical_school/engine/smooth4.htm
The reason the Ferrari V8s have that unique sound is because they are one of the few companies to use a flat-crank V8. If you take a Ferrari V8 crank out of it's block it appears much the same way a four cylinder crank does, except there is room enough for two rods per crank throw instead of one.
If you look at the Ferrari firing order it's the same as the Cosworth DFV, which both use the standard 1-3-4-2 on each bank, except interlaced. One bank takes it's turn, then the other bank takes it's turn except from the opposite end. They do this until it's time to repeat the firing order.
There are a few other cars that use a flat-crank with their 8 cylinder engines; there is the Lotus Esprit V8, the VW Passat W8, and the Cerbera AJP V8 (which we can't buy in the United States).
eta: try this link
www.autozine.org/technical_school/engine/smooth4.htm
Edited by c3ber on Thursday 8th March 22:12
I should know this, because I was told. But I've forgotten.
But the AJP8, unlike most traditional V8s, fired two cyliners at once, hance it doesn't have that lovely deep burble that the Rover V8 and the Yank V8s do.
So assuming the previosu quotation is correct, it would be 1+8, 3+6, 4+5, 2+7.
But don't quote me. But I DO think that there is wasted spark going on, in that all plugs in each bank fire at once.
I'm really posting this to force someone who knows better to pipe up and definitively tell us!
A.
But the AJP8, unlike most traditional V8s, fired two cyliners at once, hance it doesn't have that lovely deep burble that the Rover V8 and the Yank V8s do.
So assuming the previosu quotation is correct, it would be 1+8, 3+6, 4+5, 2+7.
But don't quote me. But I DO think that there is wasted spark going on, in that all plugs in each bank fire at once.
I'm really posting this to force someone who knows better to pipe up and definitively tell us!
A.
alinton said:
But I DO think that there is wasted spark going on, in that all plugs in each bank fire at once.
My mate has been having a good look over my car and a read of the manual and he did point this out as well.
He said he reckoned the coil packs set-up fire all of them together.
And I think all the inujectors on each side squirt at the same time! There is only one wire from the ECU to each side's injectors.
Go figure.
Joolz at TCS explained it to me when I was there. It all made perfect sense when he said it but it went from my addled old mind shortly thereafter.
A.
Go figure.
Joolz at TCS explained it to me when I was there. It all made perfect sense when he said it but it went from my addled old mind shortly thereafter.
A.
This is all from memory a long time back when Joolz at TCS was explaining it all to me when I was investigating programming/mapping the MBE ECU.
So its possibly not entirely accurate.
The injectors are batch fired on each bank - the 4 all open at the same time. I think some fuel is pulled in from adjacent inlets to the cylinder on the inlet stroke but fuel also hangs around in the inlets until the cylinder is on its intake stroke.
The coil packs fire the plugs in pairs. Leads 4 an 6 were reversed on my 4.2 but it made no difference because they are both fired at the same time. The second spark is wasted because the cylinder is on its exhaust stroke.
But I can't remember what the actual firing order is
So its possibly not entirely accurate.
The injectors are batch fired on each bank - the 4 all open at the same time. I think some fuel is pulled in from adjacent inlets to the cylinder on the inlet stroke but fuel also hangs around in the inlets until the cylinder is on its intake stroke.
The coil packs fire the plugs in pairs. Leads 4 an 6 were reversed on my 4.2 but it made no difference because they are both fired at the same time. The second spark is wasted because the cylinder is on its exhaust stroke.
But I can't remember what the actual firing order is
I'm pretty sure it does not fire two cylinders at the same time. The 75 degree V is probably the reason why linked decat pipes appear to work on this, a flat plane cranked V8, where they aren't supposed to. The engine fires like a series of heart beats, ba-boom, ba-boom, ba-boom. In pairs yes but not together, and I believe this is why the Emerald for the AJP8 has different firmware to other Emeralds which run on traditional 2-plane cranked V8s, or 90 degree flat plane cranked V8s.
There are two coil packs, each consisting of a pair of coils, and each of the pair is connected to 2 cylinders. Wasted spark is used, but for every cylinder that fires, only one other has a spark presented to it (which is wasted). The whole bank is not presented with a spark at the same time. This unusual-for-a-flat-plane-cranked-V8 angle is also why the AJP8 does not sound like a modern Ferrari V8.
There are two coil packs, each consisting of a pair of coils, and each of the pair is connected to 2 cylinders. Wasted spark is used, but for every cylinder that fires, only one other has a spark presented to it (which is wasted). The whole bank is not presented with a spark at the same time. This unusual-for-a-flat-plane-cranked-V8 angle is also why the AJP8 does not sound like a modern Ferrari V8.
alinton said:
But the AJP8, unlike most traditional V8s, fired two cyliners at once, hance it doesn't have that lovely deep burble that the Rover V8 and the Yank V8s do.
I don't think that can be right. The flat plane engines run as two fours interlaced and the firings are equally spaced. The main reason you don't get the deep burble is that the firing order alternates between the two banks so you don't get that quarter frequency pulse that produces the characteristic rumble of a dual plane V8.
Batched injection can actually be a good thing. Dave Walker has tried sequential injection on 4-cyl engines with no performance benefit. In some engines sequential can be detrimental to performance. The main driver for sequential injection is economy. I've only seen comparisons between batched and sequential made on 4-cyl K-series engines and the economy factor was too small to attribute economy improvements entirely to sequential.
It might be interesting to see if the batching could be reduced to "pairs" rather than the current "bank" on the AJP8 to see if economy could benefit. The larger engine and number of cylinders might actually create an environment that can take advantage of such.
It might be interesting to see if the batching could be reduced to "pairs" rather than the current "bank" on the AJP8 to see if economy could benefit. The larger engine and number of cylinders might actually create an environment that can take advantage of such.
The AJP V8 is basically two 4 cylinder engines bolted together. Thats why when you set the engine up the optimum setting is 2 have both banks identical, so that both the '4' cylinder engines are in synch. And the fact that it is a flat plane crank is also precisely the reason why linked de-cats should NOT work. However it has been proved that the linked de-cats appear to work, but this is against all engine theory, one of those freaky things about the AJP V8 that make it such a brilliant engine, even now, as a nearly 15 year old design.
jensena said:
The AJP V8 is basically two 4 cylinder engines bolted together. Thats why when you set the engine up the optimum setting is 2 have both banks identical, so that both the '4' cylinder engines are in synch. And the fact that it is a flat plane crank is also precisely the reason why linked de-cats should NOT work. However it has been proved that the linked de-cats appear to work, but this is against all engine theory, one of those freaky things about the AJP V8 that make it such a brilliant engine, even now, as a nearly 15 year old design.
What do you mean by "the optimum setting is 2 have both banks identical, so that both the '4' cylinder engines are in synch"?
It may be effectively 2 x 4-cyl engines but they fire interlaced, not together.
I KNOW it's been proven that linked decats work. I have them to great effect (possibly the best of the lot) on my car. I was trying to offer an explanation as to WHY they work when convention says they shouldn't on a flat-plane-cranked V8. The AJP is different to every other available flat-plane-cranked V8 in its angle and the fact that the banks fire in pairs, like a heartbeat, as opposed to regular pulsing from a conventional 2-plane V8 or a conventionally-angled flat-plane-cranked V8.
mars said:
jensena said:
The AJP V8 is basically two 4 cylinder engines bolted together. Thats why when you set the engine up the optimum setting is 2 have both banks identical, so that both the '4' cylinder engines are in synch. And the fact that it is a flat plane crank is also precisely the reason why linked de-cats should NOT work. However it has been proved that the linked de-cats appear to work, but this is against all engine theory, one of those freaky things about the AJP V8 that make it such a brilliant engine, even now, as a nearly 15 year old design.
What do you mean by "the optimum setting is 2 have both banks identical, so that both the '4' cylinder engines are in synch"?
It may be effectively 2 x 4-cyl engines but they fire interlaced, not together.
I KNOW it's been proven that linked decats work. I have them to great effect (possibly the best of the lot) on my car. I was trying to offer an explanation as to WHY they work when convention says they shouldn't on a flat-plane-cranked V8. The AJP is different to every other available flat-plane-cranked V8 in its angle and the fact that the banks fire in pairs, like a heartbeat, as opposed to regular pulsing from a conventional 2-plane V8 or a conventionally-angled flat-plane-cranked V8.
In other words like two 4 cylinder engines
Not EXZCTLY obviously, but essentially that is what the flat plane crank V8 is. Anyway, heres someinfo from someone who knows more than I do......
"Flat-plane" means that the crank throws are all in a single plane - i.e. if you laid the crank on a desk it would be flat. Laying the crank of a conventional (twin-plane) V8 on a desk would result in a very three-dimensional wobbly thing sitting there. In both cases however, the desk will get very oily. With a twin plane you get eight evenly spaced firing intervals for every two complete engine revolutions, but the downside is that you can't take advantage of exhaust pulse extraction effects since the manifold design is prohibitive. The Cerbera's flat plane crank means that the engine (essentially) becomes two four cylinder engines operating on a common crankshaft, so the exhaust design is made like a traditional 4-2-1 set up to take advantage of pulse tuning effects.
Thus a flat-plane crank produces an engine that is more powerful but rougher in nature. It also means that the engine sounds like a pair of four cylinder engines together, rather than the classic "warble" of a V8 (e.g. the Rover engines used in Griffiths and Chimaeras). As a point of useless trivia, a four cylinder engine in a "boxer" configuration, as used by old Alfas, Beetles and of course the Subaru Impreza sounds like a classic V8.
The unusual exhaust sound is made even more weird by the "V" angle not being 90 degrees. Its 75 degree angle means the engine doesn't behave exactly like two four-cylinder engines since instead of the firing intervals being 90 + 90 degrees apart they are 75 + 105 degrees apart.
Edited by jensena on Friday 9th March 00:51
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