The Twin Spark theory
Discussion
Having read up on the Twin Spark engine, there doesn't seem to be any overwhelming evidence to suggest that it works.
Bias aside, can someone explain to me the benefits of the TS system? I find people asking why the need for 2 spark plugs, and I can't really answer the question!
Regards
Robsco
Bias aside, can someone explain to me the benefits of the TS system? I find people asking why the need for 2 spark plugs, and I can't really answer the question!
Regards
Robsco
Here goes my limited knowledge!
The logic behind having two spark plugs per cylinder is that, when the two plugs ignite simultaneously, they can burn the fuel/air mixture in the cylinder more quickly, and thus more efficiently, by igniting it in two places at once; making better use of the same amount of fuel and air. This could mean better fuel economy as less is wasted, or greater power outputs as each cylinder fires more explosively. This makes a pretty convincing argument for it being better, in every way, to have more than one plug per cylinder, but it does beg the question as to why other manufacturers haven't implemented similar ideas! In terms of it "working", of course, it will certainly bring gains in power/economy, the question is how much so.
The technology, I believe, originated long before the TS-engined road cars, and was used to up power in Alfa's race cars. The TS road cars, certainly, seem to use the technology for greater power more than anything else - bear in mind that 153bhp is a pretty impressive figure for a naturally-aspirated, indirect-injection two-litre four that still manages 140ft.lb of torque.
That said, how much benefit the TS idea actually brings doesn't seem to be directly measured anywhere - possibly because engines identical to the TwinSpark units were never used with single spark plugs per cylinder, so there's no direct comparison. At least, I don't know of such a thing, but maybe someone can correct me? One would have to assume that the advantage is slight, at best, because of it being unique to a relatively small number of Alfa engines. Alfa are surprisingly regular pioneers of engine technology (common rail diesel injection, MultiAir [which is absolute genius]), but this one hasn't caught on.
Still, at least you can answer the question now! More power without using more fuel.
Sam
The logic behind having two spark plugs per cylinder is that, when the two plugs ignite simultaneously, they can burn the fuel/air mixture in the cylinder more quickly, and thus more efficiently, by igniting it in two places at once; making better use of the same amount of fuel and air. This could mean better fuel economy as less is wasted, or greater power outputs as each cylinder fires more explosively. This makes a pretty convincing argument for it being better, in every way, to have more than one plug per cylinder, but it does beg the question as to why other manufacturers haven't implemented similar ideas! In terms of it "working", of course, it will certainly bring gains in power/economy, the question is how much so.
The technology, I believe, originated long before the TS-engined road cars, and was used to up power in Alfa's race cars. The TS road cars, certainly, seem to use the technology for greater power more than anything else - bear in mind that 153bhp is a pretty impressive figure for a naturally-aspirated, indirect-injection two-litre four that still manages 140ft.lb of torque.
That said, how much benefit the TS idea actually brings doesn't seem to be directly measured anywhere - possibly because engines identical to the TwinSpark units were never used with single spark plugs per cylinder, so there's no direct comparison. At least, I don't know of such a thing, but maybe someone can correct me? One would have to assume that the advantage is slight, at best, because of it being unique to a relatively small number of Alfa engines. Alfa are surprisingly regular pioneers of engine technology (common rail diesel injection, MultiAir [which is absolute genius]), but this one hasn't caught on.
Still, at least you can answer the question now! More power without using more fuel.
Sam
Edited by McSam on Tuesday 2nd February 20:22
I think using twin spark plugs was a bit of blind alley. The reason they started it in the first place, (pre war i think) was related to the speed the fuel burnt you could get a situation at high revs where the flame ignited at on side of the cylinder, but not the other, it simply didnt spread quickly enough. Later in the sixties they used twin plug heads on the GTA's, mainly because the valves were so big in the hemi spherical combustion chambers, they simply could not get a single plug in the middle, so again there was a risk of fuel not burning.
Fuel burns quicker these days so it's not such an issue.
I don't really think there was a compelling case for using the TS system on the later Fiat derived engines, granted they are lovely unit, but how much of that is down to having twin plugs I wouldn't like to say, not much I guess. It had to go for the JTS because there wasn't room to get them in with the direct injection.
I think Porsche used twin plugs, as also very recently did Honda in the Jazz, of all things. I remember looking around a Jazz at a Honda dealers and the salesman came out giving us all the blurb, he said something along the lines of 'these are the only cars to have twin spark plugs you know, Honda are always the first with stuff like this with engines'.... so I pointed out the little badge on the back of my 156
I didn't bother mentioning the variable cam timing on the 'old' Nord engines of the seventies....
Fuel burns quicker these days so it's not such an issue.
I don't really think there was a compelling case for using the TS system on the later Fiat derived engines, granted they are lovely unit, but how much of that is down to having twin plugs I wouldn't like to say, not much I guess. It had to go for the JTS because there wasn't room to get them in with the direct injection.
I think Porsche used twin plugs, as also very recently did Honda in the Jazz, of all things. I remember looking around a Jazz at a Honda dealers and the salesman came out giving us all the blurb, he said something along the lines of 'these are the only cars to have twin spark plugs you know, Honda are always the first with stuff like this with engines'.... so I pointed out the little badge on the back of my 156
I didn't bother mentioning the variable cam timing on the 'old' Nord engines of the seventies....
Try this,
http://www.berlinasportivo.org/marquespec/Alfa/pdf...
Explanation of the twin spark engine found in an old magazine.
http://www.berlinasportivo.org/marquespec/Alfa/pdf...
Explanation of the twin spark engine found in an old magazine.
Interesting, pretty much backs up what I thought too.
Notice here they are talking about the Nord engine in the 75. Mention is made of the better head design losing the Hemispherical combustion chambers.
This and the addition of fuel injection would account for a good chunk of the increase in BHP from the 130 in the old Carb fed Hemishirical single plug engine, to the 148BHP in the Twin plug.
Note this is only a twitter shy of the 155BHP (150 in later tune) of the 16V Twinspark.
Incidently think the situation in current Historic racing is that the power battle between the twin plug GTA engine and the Lotus Engine in the Cortina's is largly being won by the lotus, basicaly due to the inherent limit put on the GTA engine with it's Hemispherical chambers and twin plug. The flat top Pistons and single plug of the Lotus works better.
Notice here they are talking about the Nord engine in the 75. Mention is made of the better head design losing the Hemispherical combustion chambers.
This and the addition of fuel injection would account for a good chunk of the increase in BHP from the 130 in the old Carb fed Hemishirical single plug engine, to the 148BHP in the Twin plug.
Note this is only a twitter shy of the 155BHP (150 in later tune) of the 16V Twinspark.
Incidently think the situation in current Historic racing is that the power battle between the twin plug GTA engine and the Lotus Engine in the Cortina's is largly being won by the lotus, basicaly due to the inherent limit put on the GTA engine with it's Hemispherical chambers and twin plug. The flat top Pistons and single plug of the Lotus works better.
Didn't the original twin spark engines (also used in Ducati bikes by the way, hence the more interesting noise from them than their Japanese equivalents) not only have off set plugs, but also offset timing of the firing of those plugs? Something to do with igniting more of the combustion gases, almost a secondary explosion? I know that my twinnie has both plugs firing at once, so it's not a 'real' twin spark like the 80s/early 90s Alfas.
alfa pint said:
I know that my twinnie has both plugs firing at once, so it's not a 'real' twin spark like the 80s/early 90s Alfas.
I think you've got that the wrong way round. The later Twin Sparks (iron block) fired the plugs independently - the smaller one firing later more as a clean up than for power. The original Twin Sparks fired both together for one big bang.lpenn said:
Hi Guys
I think Alfa actually put the twin Spark engine in a Bi Plane first in the early 20's and the twin plugs where for relyability, I think the modern day twin spark evolved from there.
Aircraft engines pretty much always have had twin ignition for reliability. I think Alfa actually put the twin Spark engine in a Bi Plane first in the early 20's and the twin plugs where for relyability, I think the modern day twin spark evolved from there.
I know when I had 75 TS if one ignition pack died then the performance dropped quite dramatically so it made quite a difference.
RicksAlfas said:
alfa pint said:
I know that my twinnie has both plugs firing at once, so it's not a 'real' twin spark like the 80s/early 90s Alfas.
I think you've got that the wrong way round. The later Twin Sparks (iron block) fired the plugs independently - the smaller one firing later more as a clean up than for power. The original Twin Sparks fired both together for one big bang.The 75 Twinspark has two sets of plugs that fire together and yes, one set dropping out does reduce the power output (although the engine sounds smoother if they do!).
We built a race engine for a customer using a 75 TS motor but with only one set of plugs. He races and old 2000 GTV in Malaysia where his race regs allow "evolutions" of the original engine but not twin ignition. It came out a bit less powerful than a twin ignition one would have but only by a few bhp (on a 200+ bhp engine).
The later Fiat based twinsparks had the second set of plugs firing on the exhaust stroke to clean up the emissions although this sounds like marketing cobblers dreamed up so they could keep the "Twinspark" name.
The original GTA twin ignition engine has the same wide angle head as the single plug Nord engine fitted to more common (sorry Mitch) Alfas of the era. The main problems with tuning these are the poor combustion chamber shape and the need for heavily domed pistons which are quite weighty and cut down the allowable revs (and therefore ultimate power of the engine). You'll struggle to get more than 100 bhp/litre out of these. We've seen 168 bhp from a race GTA 1600 and about 205 from a single plug 2000 but this is as far as you'll get with an FIA legal engine. Autodelta claimed 170 bhp from their 60's Touring Car GTAs but I suspect that these were "Italian" horses...
There are plenty of people who will claim more than this from their engines (particularly the Yanks) but they're alway reluctant to show you a dyno printout. We had a "200 bhp" US engine arrive for rebuild in bits so had a good look inside. Our best guess for this collection of nuts and bolts was 180 bhp, the cams looked like something we'd fit to a road car and the "special" pistons looked capable of 11:1 CR at the most.
The Lotus twincam engine has a narrower head than the Alfa engine so can rev higher so there's more power potential. That aside, an FIA spec Lotus Cortina is allowed to run at about 820 Kg against the 870-ish you're stuck with if you race a Sprint GTA. Rumour has it that Colin Chapman got the cars weighed for homologation with no gearbox or axle internals in them so the kerb weight of a Lotus Cortina was always understated somewhat.
The differences between the "Nord" single plug engine and the related Twinspark 75 unit are-
1. 9:1 CR for the Nord, 10:1 for the TS
2. TS has VVT on the inlet cam so can use a "performance" inlet cam for higher top end power but still retain low end torque.
3. Narrow angle cylinder head with lighter flat top pistons so more revs allowed (rev limit is 5750 for a standard Nord 2000, 6200 for a TS) and the offset plugs allow bigger valves than you'll fit in a Nord (although the road cars didn't get these).
We've got 215 bhp from a road reliable 75 Twinspark 2000 unit and (cough cough, not allowed to say) from the one in the race car so it's easier to find the power in a TS. Not bad for an eight valve engine but it would have been better for all of us if Alfa had sprung for sixteen like everyone else did! The 148 bhp that the stock 1962cc 75 has isn't too shabby for a four door taxi even now.
We built a race engine for a customer using a 75 TS motor but with only one set of plugs. He races and old 2000 GTV in Malaysia where his race regs allow "evolutions" of the original engine but not twin ignition. It came out a bit less powerful than a twin ignition one would have but only by a few bhp (on a 200+ bhp engine).
The later Fiat based twinsparks had the second set of plugs firing on the exhaust stroke to clean up the emissions although this sounds like marketing cobblers dreamed up so they could keep the "Twinspark" name.
The original GTA twin ignition engine has the same wide angle head as the single plug Nord engine fitted to more common (sorry Mitch) Alfas of the era. The main problems with tuning these are the poor combustion chamber shape and the need for heavily domed pistons which are quite weighty and cut down the allowable revs (and therefore ultimate power of the engine). You'll struggle to get more than 100 bhp/litre out of these. We've seen 168 bhp from a race GTA 1600 and about 205 from a single plug 2000 but this is as far as you'll get with an FIA legal engine. Autodelta claimed 170 bhp from their 60's Touring Car GTAs but I suspect that these were "Italian" horses...
There are plenty of people who will claim more than this from their engines (particularly the Yanks) but they're alway reluctant to show you a dyno printout. We had a "200 bhp" US engine arrive for rebuild in bits so had a good look inside. Our best guess for this collection of nuts and bolts was 180 bhp, the cams looked like something we'd fit to a road car and the "special" pistons looked capable of 11:1 CR at the most.
The Lotus twincam engine has a narrower head than the Alfa engine so can rev higher so there's more power potential. That aside, an FIA spec Lotus Cortina is allowed to run at about 820 Kg against the 870-ish you're stuck with if you race a Sprint GTA. Rumour has it that Colin Chapman got the cars weighed for homologation with no gearbox or axle internals in them so the kerb weight of a Lotus Cortina was always understated somewhat.
The differences between the "Nord" single plug engine and the related Twinspark 75 unit are-
1. 9:1 CR for the Nord, 10:1 for the TS
2. TS has VVT on the inlet cam so can use a "performance" inlet cam for higher top end power but still retain low end torque.
3. Narrow angle cylinder head with lighter flat top pistons so more revs allowed (rev limit is 5750 for a standard Nord 2000, 6200 for a TS) and the offset plugs allow bigger valves than you'll fit in a Nord (although the road cars didn't get these).
We've got 215 bhp from a road reliable 75 Twinspark 2000 unit and (cough cough, not allowed to say) from the one in the race car so it's easier to find the power in a TS. Not bad for an eight valve engine but it would have been better for all of us if Alfa had sprung for sixteen like everyone else did! The 148 bhp that the stock 1962cc 75 has isn't too shabby for a four door taxi even now.
Edited by Mound Dawg on Saturday 6th February 18:27
Just another small point, the Smart Roadster has twin spark plugs in a three cylinder engine - so six plugs in all. However they didn't think about the design too much, as to change all the plugs you needed to remove the complete rear of the car. Consequently many roadsters have only had half their plugs changed....
- does that remind you of any other manufacturer??
Mike
- does that remind you of any other manufacturer??
Mike
Mound Dawg said:
The later Fiat based twinsparks had the second set of plugs firing on the exhaust stroke to clean up the emissions although this sounds like marketing cobblers dreamed up so they could keep the "Twinspark" name.
I thought both plugs fired twice, giving the so called "wasted spark" during exhaust which makes the ignition simpler & cheaper by sharing coil packs between cylinders.Still marketing cobblers though
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