In motorcycling you can get cams that change the firing order and time from a traditional 1,3,4,2. It's was very common in American road racing in the 1990's to hear 4 Cylinder engines that sounded like two cylinder v-twins.

The way these guys did it and ultimately popularized this configuration for awhile was to essentially cut the cams in half at the center and rotate one side 180 degrees and weld them back together. This first try wasn't reliable for obvious reasons but you know how racers are and what they will do to get an advantage.

This configuration became known as the big bang engine. On a 180 degree crank 1 and 4 would fire at the same time and 2 and 3 would then fire at the same time 180 degrees later in the rotation. This allowed for v-twin low end torque numbers to increase (big debate on that actually) AND since it was a well balanced 4 cylinder engine it would still get those incredible rev's up in the 12,000 plus range.

The primary objective for this config is the bottom end power curve is much steeper and levels off earlier to peak horsepower. It makes the motor feel like a two stroke in many ways.

Since that time I've built a couple of these engines with cams that are now available, a bit rare, but available. I can tell you they're super fun and sound awesome.

Finally, onto my question

  1. Do any of the four cylinder car guys out there run this configuration?

  2. If they do, what would they call those cams?

  3. In particular, I'm really curious, are there any similar solutions for Subaru platforms like the 2008 or 2009 WRX Boxer motor?

I consider myself a pretty good googler but when it comes to finding car mod solutions I fall in a hole and frankly many of the sites out there offering components are klugy and poorly put together using fancy terminology that my motorcycle brain doesn't comprehend. Any help will be greatly appreciated.


Here are some linkss regarding this and similar configurations with motorcycles.

Wikipedia on the big bang engine.

This is similar but it is done at the crank. It's called a crossplane crankshaft where the offset journals are at every 90 degrees. Chevy uses a crossplane configuration in many of it's ICE platforms.

Another good explanation, this one really nails it and breaks down the big bang engine.

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    This (IMHO) is definitely on-topic. Commented Mar 21, 2015 at 12:49
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    While I could see someone would be able to do this, I'm still not understanding the why, other than the curiosity factor. Seems you'd be making a good, sooth, running engine into something which would run lopey. I don't see how you'd gain all but maybe a pittance of torque out of the matter, mainly because the only way you are really going to gain anything there is through either greater displacement (usually by longer stroke). I think you'd lose engine revving and top engine speed by doing so. Commented Mar 27, 2015 at 1:09
  • @Paulster2 - Reasons why. More bottom end power to get out of a corner quicker. Time gap between power pulse for more mechanical grip. I typically defer to a shorter stroke (oversquare bore) with larger valves and higher RPM. Torque isn't necessarily the big winner in my mind. Commented Mar 27, 2015 at 20:56
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    Bottom line: IMHO - It won't work like you think it's going to work, but by all means, expend your funds to figure it out. Commented Mar 30, 2015 at 20:58
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    Big bang in automobiles? It's called a wreck.
    – anonymous2
    Commented Sep 21, 2016 at 12:16

3 Answers 3


Surely, to get a Subaru (or any true boxer engine) to run in this kind of configuration is relatively easy. Bear in mind that you are talking about an engine with two horizontally opposed cylinder heads and a four stroke so for each revolution of the camshaft, there are two revolutions of the crankshaft. Each piston hits it's "top" of it's travel twice, once after it's compression stroke and once after it's exhaust stroke.

In usual four stroke applications, one piston will be on it's compression stoke, one on it's combustion stroke, one on it's exhaust stroke and one on it's inlet stroke. Cam timing events are set so that the exhaust valve is open during the exhaust stroke and the inlet valve is open on the inlet stroke. During combustion and compression, they're both closed. With me so far?

Now, look at an engine like the Alfa Romeo boxer engine and you'll notice that it has two timing belts.Alfa Boxer 16V timing exploded diagram

Imagine what would happen if the timing belt was fitted incorrectly such that the timing marks on just one bank of the engine (cam wheels) were 180 degrees away from where they should be. The effect would be that bank one and bank two would now be on their compression or whatever strokes at the self same time. Of course there is the slight issue that the spark plug would now be firing 180 degrees out of step with bank two. However, imagine you could connect the spark plugs from cylinder three to that of cylinder two and that of cylinder four to cylinder one. You'd now have two cylinders on firing their plugs at the same time. If you had a carburettor engine, you can stop now as you've achieved your goal.

For fuel injected engines, you'd have to tie the firing of the injector up across the two cylinder banks too. However, this wouldn't be a massive undertaking either as all you would need to do is tie the bank that's 180 degrees out to the injector event of the bank that is timed correctly. All of a sudden, you've got an engine that behaves as your described.

Real world implementation would mean either willfully fitting the timing belt 180 degrees out or removing the keyway from the camshaft (or using a modified set of pulleys) so that the cam was 180 degrees out compared to the cam wheel. On a fuel injected car you could reprogram the ECU to move the bank two injection and ignition events to be the same as bank one or you could physically disconnect the wiring from the fuel injectors and coil pack from the bank two loom and bridge them to the bank one connectors (I'd rather do this in the ECU software and bridging the connectors would be a bit of a "hack" but no reason why it wouldn't work provided the harness and any relays you used were up to the job).

For boxer applications, I think that is pretty much all and everything you'd have to do.

  • Interesting. I'd imagine the only minor issue with wiring the fuel injector banks together as opposed to doing it in sw is if there were some non-ideal differences between the cylinders or whatever in the two banks, the fuel trims for the master bank might be inappropriate for the slave.
    – Jason C
    Commented Sep 22, 2016 at 3:16
  • @JasonC basically, yes. You'd have to control each injector as a pair (like in the old Mini MPI engines which only had two fuel injectors for four cylinders). That's probably why the better way would be to do it in software but in theory it could run with a bridged out loom, albiet slightly less than perfectly. Commented Sep 22, 2016 at 10:36
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    @SteveMatthews You're over 10K now. Congrats!. TY for the answer. Commented Sep 27, 2016 at 16:37
  • Thanks @DucatiKiller, I checked and it appears that the Subaru cams are fitted with a keyway. Simply machining this off the cam would allow it to be assembled at 180 degrees out (you'd have to make sure the cam wheel was quite tight though). I do know some motorsport guys who run without a keyway because it effectively allows them to use standard equipment (as per their regs) as a vernier cam wheel. Thanks again for pushing me over 10K. Commented Sep 28, 2016 at 9:31

Do any of the four cylinder car guys out there run this configuration?

Not that I can find, with the simulated exception of some "scatter cams" referenced by @Steve Matthews, and given a great answer by @Paulster2. Although these are not really "Big Bang" by strict definition.

Here is a link to a really good read even though it's only marginally appropos!

If they do, what would they call those cams?

They don't, so I'm gonna say Ghostphantasie Offset Vaporbang Unheardof Cams (GOVUC)

In particular, I'm really curious, are there any similar solutions for Subaru platforms like the 2008 or 2009 WRX Boxer motor?

The Subie scene is the one I can comment on with the most veracity and alacrity. And the answer is just plain "no". I don't care what anyone "believes", it's not happening. It doesn't seem that the large power pulse available with the Big Bang configuration would provide any help to a car. There's some complex physics I came across that establishes how the pulses distort the carcass of the tire on motorcycles, yielding wicked pulsing corner escape velocity (with a very skilled rider), and thus the surge in popularity for a while home-brewing these beasts.

The same has no application in cars. In fact, with sooper-genius radial tire technology in motorcycles, I think most of the utility is now gone from that application as well. The "pugilist" motor enjoys a fine balance and a low center of gravity. I've seen methanol, E85, and a whole gamut of turbos applied to EJ series engines, along with every trick in the book and some that aren't. (500+ AWD Hp on 2 liters, 750+ AWD Hp on a 2.5) But no GOVUC on Subaru.

Cutting and rotating Subie cams (2 on some, 4 on others) is simply not in the cards. And it's not wasted spark, either, so that's an issue. Along with the FI. But you could rig it simply enough, by just ganging the 1-4 and 2-3 spark and FI together, as @Steve Matthews suggested. But those costly cams are gonna be worthless, and I think an overall detriment to producing torque, power, or corner exit speeds.

So that's not much of an answer, but it is an answer nonetheless. In the meantime, here's a great article I found that describes a lot of the torsional input on a crankshaft given various configurations and timings. (In other words, doesn't answer the question one lick, but is still a nice read -- and provides a lot of the background info necessary to cogitate fully on this question...)

Crankshaft Torque Various Configurations and Timings

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    I love the answer. Thank you. I especially like this piece of literary expression, "Ghostphantasie Offset Vaporbang Unheardof Cams". +1 Commented Sep 23, 2016 at 21:28

There are 2 main firing orders in use, they are called screamer and big bang, the difference doesnt lay in the firing order, it lays in the time between the firings of the pistons. The notorious sound of a superbike, that high pitched scream is a screamer engine, it fires in a sequential way, one piston after the other in a regular way, however the bigbang engine does it firing 2 of the pistons at the same time, giving it that lumpy sound, thats why the yamaha r1 with its crankplane sounds as it sounds, way different than a ninja or a cbr or a bmw s1000rr. You have to take into account that this difference in firing doesnt really change the torque or the power chart in a dynamometer report, the difference is more notorious in a bike with a 4 cylinder engine, because the big bang engine gives more time to the tires between power strokes to cope up with the power and grip with the ground, as opposite to the screamer engine, it just fires in a sequential way and doesnt give enough time to the tire to cope with the power when there is too much power, thats the reason why Mick Doohan became so famous in the superbike racing scene, in the 90s when no one wanted the screamer engine, when every rider was scared and complaining about the sudden way those bikes delivered the power, he was the only one who stayed with the screamer, everyone else raced the big bang, and he won the championship with the screamer engine, showing how good he was and how better the screamer engine is if you know how to give it gas, constantly smoking the tires, drifting some corners and leaving everyone in the dust.

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    This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
    – SteveRacer
    Commented Aug 29, 2016 at 17:42
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    Can't seem to escape this beast. "the difference doesnt lay in the firing order, it lays in the time between the firings of the pistons" I have no idea what this means, as if I should. The DIFFERENCE has to do with the orientation of the crankshaft, nothing more. The ultimate effects have yet to be determined in this challenge.
    – SteveRacer
    Commented Sep 21, 2016 at 4:36
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    @SteveRacer I presume he's referring more to the cam period relative to crank duration. In the old Austin A series engine, "Scatter Cams" could be used which had different points of maximum duration for different cylinders. This worked in part due to the siamese port configuration of the head where the centre two cylinders shared one port for exhaust and the were only two inlet ports. I don't know if this would work the same on an 8-port 4-cyl engine. Commented Sep 21, 2016 at 9:02
  • @SteveRacer this thread contains more info, it's slightly unrelated... mechanics.stackexchange.com/questions/23939/… Commented Sep 21, 2016 at 9:03

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