Do you have a girdle?

[N54SG]

This is getting pretty common on big horsepower engines. It seems to make sense in my book, and I'm tempted to make some of my own.

Like on this supercharged 780:





Or this Turbo Charged 720:




Big compression loads divided over more than 1 head, that is all I need to know about it.

[Low Pass]

Sure like the added options of baffling attachment/integration and accessory connection!

[Bob Kuykendall]

Originally Posted by Ironflight

Just what I was thinking. Anytime you constrain motion that has worked for a couple of million hours, you are going to transfer that stress somewhere....

I'm also pretty nervous about stuff like this executed by folks without access to the original engineering data. These days I see a lot of parts made with CNC and 3D printing that look very pretty, but demonstrate a distinct absence of engineering wisdom.

Thanks, Bob K.

[RVDan]

Re the 780 "girdle". If I assume the aluminum girdle is 24" from the inside point of the end heads, the expansion with just 100 degrees F change in temp is .0295". That means that it is trying to separate the end heads that about far. If you assume a 0 deg F to 200 degree operating range that is .061" of movement. Seems like a lot of preload stress to the end cylinders to me, even for just a 100 degree change. But maybe the vibratory loads are much higher. Interesting. Love to see a FEA on the engine.

[DanH]

Originally Posted by RVDan

Re the 780 "girdle". If I assume the aluminum girdle is 24" from the inside point of the end heads, the expansion with just 100 degrees F change in temp is .0295".

Good point, but the cylinder bases move apart too...the case has a similar thermal expansion.

[rbibb]

I'm sitting about 5 miles from their location and am tempted to drive over in the morning and take a look?

As far as producing hp - sure these things don't do that. But it take a fair amount of energy to move those cylinders around. If you can stop some of the energy produced by combustion from being wasted bending the cylinder back and forth that energy can then be used to turn the crank. I believe that to be the basis for the claim. Their instrumentation readouts seem to show some significant improvement in reducing that movement. Now how much hp that equates to would take some math work and access to the data that I"m not even going to attempt right now.

My beer would just get warm and that would be waste of another valuable energy resource?.

[RVDan]

DanH good point. Wonder how close the case temp is to the girdle temp? Great stabilizer though. The SS bog bone links are also interesting. Wonder why they are needed.

[LifeofReiley]

I've got ocean front property in Arizona if anyone is interested...

[380mxc]

Most air cooled car engines have the heads tied together in one way or another and a lot of motorcycle engines do.

Can any body show an example of an engine besides aircraft that threads the head on to the cylinder similar to Lycoming?

[Toobuilder]

A bit off topic, but along the lines of "controversy" - anyone notice the NXT pictured has header wrap installed on the exhaust and intake?