Can two engines in tandem share one exhaust manifold?

[LDO]

Let’s imagine a pair of Oldsmobile Quad-4 engines inline. Can they share an 8 into 1 log manifold...with no weird side effects? The goal would be something that looks like this. 

[iBorg]

What you'd have to do is join the two four cylinders into one eight cylinder. The issue would be to get the crankshafts synchronised so no two cylinders would fire together. If you got the cylinder firing in proper order, which might require a custom crankshaft and cam shaft, it should work.

[Ace-Garageguy]

No problem.

You simply orient the second crank just as it would be in a straight eight engine, and make certain to orient the cams so that when two pistons are both at the top of their strokes, one is at TDC firing, and the other is at TDC overlap.

No magic custom crank or cams required.

This is a conventional straight eight crank. The solution should be obvious.

 

Edited June 25, 2020 by Ace-Garageguy

[iBorg]

You're right. I forgot its a four stroke.

[Ace-Garageguy]

19 minutes ago, iBorg said:

You're right. I forgot its a four stroke.

But I'm also wrong.

A 4-cylinder inline crank is not half of a straight eight crank.

 

 

Edited June 25, 2020 by Ace-Garageguy

[Ace-Garageguy]

HOWEVER...if we can assume the engines can be independently balanced, the stock cranks could be oriented 90 degrees from each other to even out the exhaust pulses, and avoid any two cylinders exhausting at the same time.

But let me think this all the way through...   

[Muncie]

The crankcases would need to be rigidly connected to each other.  Flex between the engines will damage or crack a single cast exhaust manifold or single header - unless the flex was accounted for with some type of flexible coupler in the exhaust.  Frames twist and flex. 

Two quad fours would make an awesome straight eight.

Thinking out loud - wondering if two blocks could be cut down and fitted to a common crankcase...

[Deuces ll]

Check out the twin inline small block motor on the net... Also GMC had a 702 twin v-6 setup in their trucks back in the early '60s......

[Ace-Garageguy]

54 minutes ago, Muncie said:

...Thinking out loud - wondering if two blocks could be cut down and fitted to a common crankcase...

No reason why not. Crosley, for one, used a crankcase fabricated from steel sheet and plate, oven brazed together...something like this general idea:

A custom-cast block isn't impossible either. The most difficult problem to overcome is where to put the necessary flywheels.

Edited June 25, 2020 by Ace-Garageguy

[Ace-Garageguy]

How about a straight-eight Lada?

 

[Mark]

The Chrysler Atlantic concept (Lindberg did a kit, no engine detail though) was powered by a straight eight made by linking two Neon engines.  Guys have been doing it forever; I've seen photos and stories about Model T-based straight eights.

[stitchdup]

I've seen it done with diesel tractors, mostly the ones i saw were home conversions

[sfhess]

Way too much overthinking here.  Just glue 'em up and go.

[Snake45]

15 minutes ago, sfhess said:

Way too much overthinking here.  Just glue 'em up and go.

I agree. It ain't rocket surgery, it's only plastic. 

[Ace-Garageguy]

3 hours ago, Mark said:

The Chrysler Atlantic concept (Lindberg did a kit, no engine detail though) was powered by a straight eight made by linking two Neon engines...

While the Atlantic engine is indeed based on two 2-liter Neon blocks, it's a lot more than just sticking a couple of engines together. 

At the moment, I can't find the full engineering details of the Atlantic engine, but I recall this:

The Atlantic straight eight derivative is a DOHC engine, with a custom 8-chamber cylinder head that supplies considerable rigidity to the unit. Kindof a big deal from an engineering standpoint.

Look closely, you'll see the plug spacing between 4 and 5 is significantly wider than the others. This is most likely to allow space, lengthwise, for the flywheel of the front crankshaft.

Edited June 26, 2020 by Ace-Garageguy

[LDO]

1 hour ago, Snake45 said:

I agree. It ain't rocket surgery, it's only plastic. 

True, but I also wonder if it could done real world. I have this crazy idea of a custom car inspired by the Duesenberg “Mudd Coupe” (owned by Dr Seeley Mudd). It would absolutely have to have that beautiful eight into one exhaust. 

 

[Ace-Garageguy]

15 minutes ago, LDO said:

True, but I also wonder if it could done real world...

Yes. Absolutely. 100%. Guaranteed.

[LDO]

23 minutes ago, Ace-Garageguy said:

Yes. Absolutely. 100%. Guaranteed.

Could we discuss this offline? I tried sending a PM but it says you can’t receive them.

Thanks. Lee

[Ace-Garageguy]

11 hours ago, LDO said:

Could we discuss this offline? I tried sending a PM but it says you can’t receive them.

Thanks. Lee

Glad to. Box was full; now it's not.

[Classicgas]

14 hours ago, Snake45 said:

I agree. It ain't rocket surgery, it's only plastic. 

True but if one is trying to model something that could feasibly be driven in the real world for the sake of realism it matters.

[peteski]

There were plenty of inline-8 engines early in the 20th Century (in the '30s).  They had single exhaust (and often the intake) manifold.  I don't see why this could not be done on a inline-8 made up from 2 4-culinder engines.  You just have to couple the crankshafts in such a way that only one exhaust cycle is taking place at any give time. I think that is one of the basic design criteria anyway (especially if the new engine has a single distributor, this will occur by default).

Edited June 26, 2020 by peteski

[Carmak]

On 6/25/2020 at 2:51 PM, Ace-Garageguy said:

No reason why not. Crosley, for one, used a crankcase fabricated from steel sheet and plate, oven brazed together...something like this general idea:

A custom-cast block isn't impossible either. The most difficult problem to overcome is where to put the necessary flywheels.

We have a local hard core Crosley guy and hes displays a straight 6 Crosley he welded up from 4 cylinder parts. I runs good and doesn't shake. His name is Paul Gorrell, google him, he has made many interesting engine configurations from Crosley parts.