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Twin Engine V12 or 2x60°V6

Twin Engine V12 or 2x60°V6

Twin Engine V12 or 2x60°V6

(OP)
I'm going to attempt to mate two modern FWD GM engines into a longitudinal V12. As the title states, they're 60° V6 engines that can be pretty easily setup for RWD applications. With FWD accessories, they should fit together tidily enough.

My understanding is dragsters coupled engines like this would two sprockets and a double strand chain, but I'm looking for something that'll last longer, and ideally I could decouple the front engine to run as a V6. The standalone tuning to allow this will be difficult. I've read of different options but perhaps someone here could recommend something. Ideally this coupler could fit 6 or 12 different ways to allow different timing combinations of the engines for testing. Any ideas for a reliable coupler/decoupler would be appreciated.

The balancers in these engines I need to learn more about, but I'm curious if you can eliminate the need for a secondary harmonic balancer if coupled correctly. Probably not worth pursuing in this case. Constructing an exhaust system that's capable of sounding like a balanced V12 would be nice. I'm honestly not even sure what effects aside from sound would be present, given the engines are each balanced.

The routing for coolant through two engines seems a bit redundant when I want to turn one off, but maybe possible still. I could eliminate one of the thermostats maybe or use an electric water pump on the dead engine to assist with this. Ideas here are also appreciated.

I've been told not to combine the oil system into one, and though I don't totally understand why not, it does seem safer not to.

What am I missing here?

RE: Twin Engine V12 or 2x60°V6

(OP)
I think a good question I should go ahead and ask to help with the balance thing is such: While a 90° V4 is inherently shaky I'm told, could it be on the nose of a V8 to only add power and balance to the two? Admittedly I don't know much about V4's aside from motorcycles and homemade projects from years ago, but it seems you could smoothen the NVH on a V8 theoretically by just having a properly timed V4 on the front of it. While this would be harder than what I'm trying to do as far as sourcing parts goes, it may help me better understand the fundamental harmonics at work here.

RE: Twin Engine V12 or 2x60°V6

You want to couple the engines front to back (the flywheel end of one driving the front pulley end of the other)?

The front pulley connection is normally not designed to transmit full rated power of the engine. The rest of the crankshaft of the rear engine probably isn't designed to transmit the power of two engines.

The chain and sprocket method allows the flywheel end of both engines to do all of the power output without having to go through the front pulley. It also means the front end of each engine can operate all of its own accessories just like it normally does. It also provides some degree of "give" to allow for mechanical vibrations and torque fluctuations.

If you want to be able to shut one engine down, you will need a clutch to do that. There will not be any synchronization on re-engagement, nor does there need to be.

Keep it simple. Let each engine operate stand-alone completely independent of the other one aside from the throttles being mechanically connected. Each one is mechanically balanced on its own, each one does its own oil system, each one does its own ignition and fuel delivery.

A V8 + V4 probably isn't a good idea. A V8 has 90 degree firing intervals. An even-firing V12 has 60 degree firing intervals. A V4 with 90 degree bank angle and single crank pins has uneven 90-270-90-270 firing intervals. There's no way to stick that onto an even-firing V8 without resulting in uneven firing intervals without completely redesigning everything - which is, of course, the correct way to do what you are attempting to do as opposed to butchering something together that was never meant to work together ...

RE: Twin Engine V12 or 2x60°V6

(OP)
The engines would be rear to front. My understanding is tractor pullers and industrial hydraulic pumps may have couplers like what I'm after. Perhaps you could clutch the front engine and use the ignition system to bring it back in time. Unifying the exhaust and using that to each engine's advantage is part of the exhibition here, but running them separately is neat too.

The really terrible approach would be to spin the front engine dead for the sake of fuel economy, I'd think. Hence the idea to decouple. A somewhat efficient "sleeper" is part of the theme, I guess.

RE: Twin Engine V12 or 2x60°V6

Coupling the exhaust system of a running engine to the exhaust system of one that's not running is a
>>>>>>>>>>>>>> REALLY BAD IDEA, <<<<<<<<<<<<<<
because the exhaust gases will destroy the idle engine's cylinder bores in a matter of hours.

The crank nose of a (sturdy) John Deere 6.3 liter Diesel is rated for something like 75HP @1800rpm. I assume that tractor pullers add extra keyways and/or shrink disks and/or custom cranks, and still don't expect much in terms of lifetime.

If you want a V12, just buy one.

Mike Halloran
Pembroke Pines, FL, USA

RE: Twin Engine V12 or 2x60°V6

It's unclear what the original poster's objectives are. If the objective is simply "more power", that's what turbochargers are for. Or ditch the V6 and simply use a modern V8 like everyone else including GM themselves do. I'm not sure what two coupled V6 engines will do that can't be done with a supercharged V8 like the one GM supplies in some versions of the Corvette and Camaro, complete with a warranty.

"Because we can" ... sure, but not all ideas are good ideas ...

RE: Twin Engine V12 or 2x60°V6

(OP)
wink I'd rather dig a start digging a foundry with a shovel than buy a V12.

If it's that ill-advised maybe I should try to fuse two blocks together and make a crank. Seems like a breeze, no?

RE: Twin Engine V12 or 2x60°V6

I worked on a supercar that was to have a V12. We couldn't get the sums to work unless we took the power off the middle of the crank, ie we effectively ran two V6s back to back. One trouble with trying to run them nose to tail is that the second crank is carrying twice the torque it was designed for, and another is that the torsional vibration resonances would be very low frequency. All of these problems are solvable, it just depends on your constraints and targets.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Twin Engine V12 or 2x60°V6

It would be best to have a special crankshaft made for the rear engine, like mentioned it will be looking at twice what
it was meant to take for torque.

RE: Twin Engine V12 or 2x60°V6

(OP)

Quote (GregLocock)

I worked on a supercar that was to have a V12. We couldn't get the sums to work unless we took the power off the middle of the crank, ie we effectively ran two V6s back to back. One trouble with trying to run them nose to tail is that the second crank is carrying twice the torque it was designed for, and another is that the torsional vibration resonances would be very low frequency. All of these problems are solvable, it just depends on your constraints and targets.

Now this is an interesting idea. How did all the ancillaries work, and more importantly, how did the drivetrain all come together in this case? A V-drive or some sort of splitter or transfer case could be useful here maybe. The ability to split the power for all wheel drive while keeping one transmission would be dandy and could maybe be integrated in a tail to tail setup like this.

RE: Twin Engine V12 or 2x60°V6

I think it was a chain drive to a transaxle, but might have been Mini style drop gears. Yes it was AWD. It never got much further than stroking the program manager's ego, but we did get some nice cars to play with.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Twin Engine V12 or 2x60°V6

(OP)
I need to understand the architecture of this engine block better, but I'm starting to give in to the idea of cutting and welding two engines together, at least the blocks if not the heads, then line-bore and get everything squared back up. Actually cutting and welding this much material seems daunting, as I'm not sure what would be necessary, but I know it's doable for a one-off.

RE: Twin Engine V12 or 2x60°V6

I which case you are probably better off starting with two V8 blocks and cut the front 2 cylinders off one and the rear 2 off the other. A few people have done it successfully - https://www.youtube.com/watch?v=4ssA_O4GGhA

je suis charlie

RE: Twin Engine V12 or 2x60°V6

(OP)
The V12 LS engine is part of my reasoning here, but I'd rather use the 60 degree engine and not cut right down the bore if I can help it. If I'm lucky with the coolant and oil galleys it may be feasible. GM was going to do this at one point but abandoned it, if I recall.

The idea of using the GM Atlas I6 to do a twin inline six has crossed my mind, but once again, I'd be unsure how to join them with the transmission. Probably easier to do reliably than my first idea, but very large. Great for a marine application. Maybe a landyacht, but the small v6 is what I'm still curious about.

RE: Twin Engine V12 or 2x60°V6

Might Google GMC V12 which had one piece block and crank, the rest from the V6

RE: Twin Engine V12 or 2x60°V6

Those GM 3.8 V6's are pretty amazing. The engine has a history that spans from the 60's to the early 2000's. GM sold the rights to Jeep then bought them back. They came up with the split pin crank that made it even fire and then went on to turbo and supercharge them. You can take the supercharger off of one of the modern L67's, add 20psi of boost with a turbo and be into the 400hp range at the crank. I put one in the back of a VW rabbit a couple years ago.



I think you need to make the front of the rear crank as strong as the back. I don't know if there were steel cranks available for these, but if so, maybe you could weld on a hub that would be big enough to transmit the power from the front engine to the back. Hell, they've done just about everything else with these engines, it can probably do this too.

As far as a longitudinal transaxle, maybe you could use the TH425. It will be the 90 degree bellhousing pattern, where yours is the 60 degree pattern (although it's a 90 degree engine)

RE: Twin Engine V12 or 2x60°V6

Oh I missed the 60 degree part. The 3.8's are 90 degree. I think the 60 degree engines are the 2.8's, 3.1's and 3.4's, which came in dohc. But the 3.8 is the Daddy.

RE: Twin Engine V12 or 2x60°V6

(OP)
The Buick V6 was a great engine, but it's had its day. To me, any 90° V6 is just inherently messy from a balance standpoint. The 60° versions displace as much as 3.9 liters now from GM I believe, and make just as much power under boost with a lighter rotating assembly. Less torque, higher revs, lighter weight, same displacement. It should work out, apparently it does.

RE: Twin Engine V12 or 2x60°V6

(OP)
Just to be fair, the 90° V6 from GM is still alive, barely, as the 4.3, though I believe it's branded as Ecotec now. Most of us are perhaps more accustomed to the old nomenclature, most recently Vortec, I believe. Only used in 1500 series trucks now, if I recall.

RE: Twin Engine V12 or 2x60°V6

I find it interesting that a 90 degree V2 can be balanced, first and second order, so it's possible to just sort of stack them end to end to make a 90 degree V engine with an arbitrary even number of cylinders.

That doesn't mean it's easy.

I recall a particular yacht whose owner removed the original Cat I6 engines, and replaced them with more powerful V10 engines from another manufacturer, because he wanted his displacement hull to go faster, and only that manufacturer would guarantee the engines for unlimited operation at WOT.

What he didn't know at first was that the engines ran on only five cylinders at RPMs below 1400, and shook the bejeezus out of the boat. I observed the (sturdy) handrails wobbling side to side maybe a foot under those conditions.

I understand he had special fuel pumps made that ran the engines on all 10 cylinders all the time, but the smoke was intolerable, so he put the original pumps back on, and then he died. I was asked to propose some magical exhaust system to fix the problem; not possible at my skill level.

I have no idea what his widow did to solve the problem and/or sell the boat.

Mike Halloran
Pembroke Pines, FL, USA

RE: Twin Engine V12 or 2x60°V6

The 90 degree V6s are fairly nasty balance wise. As I remember they have a strong 1.5 order (inertial) couple. Designing the engine mounts to bring that down to an acceptable level for a European cruiser was beyond me 31 years ago.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Twin Engine V12 or 2x60°V6

(OP)
That is my primary or perhaps seconday issue with them tongue. Not a great pun given the 1.5. The other issue is the width in a narrow application such as mine. It's not a huge problem and even has its advantages, but the internal balance just makes the power and torque curves that I'm after harder to achieve safely, in the long-term even more-so. You can make them do more, but the cost is there.

I've often wondered about the tradeoff in engine longevity regarding high revs vs hard balancing. The 90° V6 versus, say, an I6. The power of the V6 is made at relatively low (albeit rough on the rotating assembly) revolutions, which I'd think would mean you'd wear away less cylinder bore, valvetrain and bearings while making the same power, over time. The moment of inertia wears away as well, though, not to mention the "dead spot" most engines have at low RPM (maybe more common on I4's but I'm not as familiar with it). I don't know enough about lubrication or metallurgy to be sure which wins though.

RE: Twin Engine V12 or 2x60°V6

Are the definitions of first and second order vibrations universally agreed upon? I think there are very few truly balanced engine designs. Some say an inline 6 is, but the fact that the piston travels faster on the top part of the stroke than on the bottom (or is it the other way around) negates this I believe. Even a boxer engine has a couple imbalance, unless the opposing cylinder bores are aligned, which can be accomplished with a Harley style fork and tang connecting rod. Although referencing a Harley V twin in a sentence about engine balance is pretty ironic.

In practice, though, inherently bad designs can achieve acceptable balance related behaviors and perform amazingly well, like a Honda inline 4 with a redline in the 8's. I think the talk about engine balance is over rated. I think any engine sold for automotive use in a 1st world country in the last 30 years is pretty well balanced.

RE: Twin Engine V12 or 2x60°V6

(OP)
I'd agree, but one has to consider all the different aspects of engine balancing, from piston travel to crankshaft connection, ignition timing, fuel maps, angular moments and so on... but I think the part I'm interested in is "static" balance as well as rotational. Offset crank pins seems like a band-aid, but better than balancers in some cases. Though I do quite enjoy an I4 or even an I5, it feels like the more "naturally" balanced just has a more rewarding powerband as it wakes up, well beyond 8K for smaller I4's and beyond 20,000rpm for the smallest of I6's. It's horses for courses, of course, but this is mine right now.

Pardon the poor terminology on my part, it's been awhile. I always thought, contrary to the folks who said "there's no replacement for displacement", I have to argue that, actually, clever cylinder arrangement can be a fine substitute.

RE: Twin Engine V12 or 2x60°V6

I'm using engine designer terminology for orders, others may use what they will.

Nope, 3.8 litre 90 deg V6 has enormous inertial couple at 1.5 order, and is still currently sold. They may have fitted 1.5 order balance shafts but I doubt it very much.

Also no, an I6 has (virtually) zero inertial second order. The various cylinders cancel out. The only 2nd order that is left is due to mismatch in piston weights and things like that.

Engine balance is not overrated, you as a consumer benefit from a lot of hard work by people who know what they are talking about, so that you can think it is 'overrated'. Try riding a motorbike with a 500cc single cylinder engine with no balancer shafts and then say it is overrated.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Twin Engine V12 or 2x60°V6

I'm sure you're right and you know more than me, but isn't it true that max piston speed is achieved somewhere around 75 degrees before and after TDC for most common engines. If that's true, the piston(s) that will be "balancing" that one/those ones that is/are traveling in the opposite direction won't be traveling at the same speed nor have the same acceleration, so it won't be perfect balance, right? Also, what about the front to rear imbalance because cylinder bores aren't aligned in an inline engine?

And yes you are certainly right, that balance is important and that a lot of engineering goes into it. I was directing my comments toward a conversation that seemed to have evolved into whether or not off the shelf engines were balanced acceptably well, and I was trying to point out that they are.

RE: Twin Engine V12 or 2x60°V6

The GM/Buick 3.8 V6 has a balance shaft since 1988 or so. It was born as 3/4 of a Buick V8.
The GM 4.3 is a different engine family, based on the Chevrolet V8. There may be different series 4.3s, I don't know.
GM finally stopped building the 3.8 in the US around 2008, I think.
The newer GM 60 degree V6 motor seems to run pretty strong. (I have 2012 Impala with 3.6, feels considerably stronger than the '02 3.8 I had)
My project car still has a 1987 3.8 in it. Last year without a balance shaft. Not super smooth at idle. Being a transverse may reduce the imbalance effects?
It has been unreasonably durable, but am looking forward to installing the newer 3.8 I have for it.

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Twin Engine V12 or 2x60°V6

The GM 3.6 is probably the "high feature" V6 with DOHC, variable valve timing, and 4 valves per cylinder. The 3.8 is the old pushrod 2 valve per cylinder engine. I said "probably" because the 60 degree pushrod V6 was built in more displacements than I've kept track of. I don't think the HFV6 is related to the pushrod design in any way.

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