What's it take to get two (car) engines to run together in tandem. That is, two engines, working together. From the probably very warranted advice from my father, I get the impression that it won't work. He said that they'd have to be perfectly similer (as far as output torque/hp) otherwise the stronger one would be doing most of the work. Just like all four carburators have to be extremely in sync on a 4-banger motorcycle or it'll run horribly. But in the two engine setup it seems to me like if the stronger one pulled against the load, the load would reduce the powerful engine's force and then the second engine would support it--so they'd still work together.

The thing with all of this, is that it's been done before. Go Karts in the 60's ran 2, 3, or even 4 single-cylinder engines in tandem. They were considered a nightmare to get balanced, but it's still possible. Additionally, there have been many multi-engine drag racers and tractor pull race cars throughout history (more so of the latter category).

So... what do they do? You can't just link the suckers together, I imagine the gears would warp, shred, and die a horrible death. I want long-term durability (not 300,000 miles, but long term), since it's a decent investment of money. Another point to consider is that each engine that I have puts out 140 HP. So the design proposals have to be able to take ~280 HP.

• Go Karts ran the engines directly together with chains. I doubt that it will take 280 HP being coupled even with racing motorcycle chains (drag chains?).

• Some sort of fluid coupling could be used to absorb shock differences between the engines.

• Running one engine FWD and another RWD would also absorb shock loads, but I'm not sure about power differences. A Hundai was run with two 300 HP engines (317+- RWD and 308+- FWD) and I assume it ran at least one pass. But the durability factor comes into play.

Now... here's the kicker on top of this madness: The engines are motorcycle engines with integrated transmissions. So I could bypass the transmissions, run a fluid coupling (as a shock load absorbing medium) and then run to a real transmission. Or, I can run them together anyway. But given that, the transmissions will have minute differences (.005inch clutch engagement differences, etc) so that will also have to be perfectly synced (crazy hard) or a shock absorber used (better idea). The latter will introduce delays in drive-feel, but I bet I could have it less than 500ms, so it wouldn't be bad.

I don't know. RWD/FWD sounds like a good idea from its natural shock absorbing characteristics.

There's the basic proposal with some possible solutions. Any ideas?

Having one engine for the front wheels and one for the back would be simple and effective. Some military vehicles and fire-trucks do it (presumably for backup purposes as much as anything).

The obvious way to do it would be to start with a FWD, and use the back axle off a RWD

It doesn't really matter if they aren't balanced right, as it can't be more unbalanced than normal 2WD. You could even use an automatic on the rear which would simplify the gear-stick linkage. (and with 2 motorcycle engines, I would be tempted to have the rear one shifted by servos, so it electonically attempts to stay in the same gear as the front one. This is from experience with old worn motorbikes where the gear pedal needs several kicks for one change, or makes 2 changes with one kick)

I've thought about having electric drive for the rear, as this gives instant grunt at go, and wouldn't take up as much space. You wouldn't need nearly as much battery as a pure electric. (and there may be tax/insurance benefits if it's registered as a hybrid)

FINAL EDIT: or, you could make 2 go karts. paint 1 red and the other blue, and have friends around for races (print up some liability disclaimer forms)

They are connected through the friction with the road. The unpowered wheels are effectively driven by the road. OK, being freewheeling they respond quicker to speed changes, but you still have them being driven at a speed different from their rest state (stationary). You'll probably get more tyre wear if it's powered, but it'll work and drive fine.

I think the crankshafts are hard linked giving an effective V16.

You could model this all in Blender now it has a physics lib built in. One of the demos is a simple vehicle.

Your deathwish might just become reality. A kart with a single bike engine is already crazy fast (check out these vids)and with two and 4wd it'll be probably just simply, too quick.

Your ratio is off. The extra engine will add weight to the car probably upwards of 500 - 1000 lbs.

On top of that, the modifications would probably cost $100000+ and be mostly custom. They would probably weaken the drivetrain to the point of constant repairs and I also wouldn't be surprised if the modifications made your car illegal on the street. It's just not a good idea. Besides, you could just buy a performance engine and beef it up with performance components, aspiration mods, etc., and in turn would add less weight to the car.

This two engine idea doesn't fit your model. If you want more performance look into turbo chargers and exhaust kits. Personally I would save my money and get a much better car.

Nope. An iron engine and transmission weighs 400+ lbs. Old Big blocks weighed over 760 lbs just for the engine. These motorcycle engines weigh less than 130 lbs each including transmission! So the car might lose weight.

I'm not sure how two differentials add up to $100,000... unless they're made of gold or broken dreams. Because two differentials and two front drive-trains (CV joints, shocks, hubs and arms) aren't going to cost that much. Especially coming from a beater car.

It's only 140 HP. My Talon comes stock with 135. The Turbo Model comes stock with 190.

I can't think of any reason why equipping a car with road-tested engines would outlaw it.

No... you see that's where it gets expensive. Even if I start with a tank of an engine that's free (because I own it), the 4G63 which can take 450 HP off the stock bottom end, it still adds up to more money than this project. A bigger turbo, a better intercooler, a new ECU, fuel injectors, fuel pump, and exhaust system (to just name a few) are more than simply buying two stock motorcycle engines. And I'm still stuck with a 3000 lb car.

A Festiva like I want will set me back $300 top. I have one GSXR engine, and one more will cost ~$1000. Two differentials $100 / pop, and full rear/front end, I can get for $100. So even if I went hog wild, it's still $1500. Which is thousands less than the 4G63 route.

[appenderized!]
Well, it seems (at this point) that the biggest problem is changing the rear-end to allow driven wheels. (Metro's and Festivas are FWD only.) The best idea I've seen so far is mounting a front-end on the back. That way the brakes, calipers, hubs, and so on are the same. That'll also give the car 4-wheel independent suspension, which is just awesome from a tunability stand-point. Just throw 2 anti-roll bars on and stiffer springs, and it'll handle like a dream. But it also has to fit and mount up. There's some fabrication time.

I'll just have to wait and see what Festivas and Metros become available for sale.