Twin Engine V12 or 2x60°V6 1

[assquatch20]

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?

 

[assquatch20]

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.

 

[assquatch20]

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.

 

[MikeHalloran]

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

 

[GregLocock]

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


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[assquatch20]

That is my primary or perhaps seconday issue with them . 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.

 

[carwhisperer]

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.

 

[assquatch20]

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.

 

[GregLocock]

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


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[carwhisperer]

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.

 

[GregLocock]

You have to do the maths on the I6 to see that it cancels . Yes it is true, the piston speed is different, here's an article explaining why

https://en.wikipedia.org/wiki/Pisto...espect_to_angular_position_.28Angle_Domain.29

Of course for forces we are interested in accelerations not velocities.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[JayMaechtlen]

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

 

[BrianPetersen]

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.

 

[JayMaechtlen]

That's my understanding - the 3.6 has all the fancy stuff, and none of the pushrods.


Jay Maechtlen

http://www.laserpubs.com/techcomm