Carrera 4 cam exhaust

[Vic Skirmants]

Fletcher's exhaust "augmentor" was not successful. Aside from hellacious noise levels, it did not cool well enough. None of that was used on the 550s.

[Jeff Adams]

Only the first two cars had pushrod engines from the factory, as the cars were ready before the 4 cam engine was fully developed and built. The exhaust systems were nothing exotic, some closeups and details can be seen in Ludvigsen's picture book. All the other cars, 550-03 to 90, had four cams and exhaust systems like the one in Brad's drawing. Later on, many cars were "updated" with Sebring systems or some other homemade contraption that DIY's thought were better then the original factory setup.

A customer of ours built a replica 550 with a pushrod engine, the exhaust looked similar to Greg's 90faux system except with a 4 into 1 instead of a muffler. This car had a full bellypan like a real car, and we had an overheating problem. The issue was having exposed header pipes inside the enclosed engine and transmission compartment, which radiated a lot of heat that got sucked into the cooling fan. The four cam cars did not have this problem, as the header pipes exited the bottom of the engine through lower air shrouds that were sealed off by the bellypan with a rubber surround.

The problem was mostly solved by using a fiber insulating wrap on the header pipes anywhere they were exposed inside the engine compartment. If I remember right, the first two factory 550's were also done this way and can be seen in the picture book.

[Ron LaDow]

Fletcher's exhaust "augmentor" was not successful. Aside from hellacious noise levels, it did not cool well enough. None of that was used on the 550s.

Nor was it successful in GA; none of the builders used it to reduce the intake air drag, and I'm sure they all took a look at it.

[Vic Skirmants]

I used exhaust wrap in my Dolphin to help with heat management. Seems to have helped.

[Wes Bender]

Fletcher Aviation owned Rosemead Airport in SoCal back in the fifties. I was at Rosemead in CAP at the time. There was a Ryan Navion there that had the Fletcher "Jet Cooling System" on it. If I remember correctly, the pilot said that, while it helped cooling slightly while on the ground by drawing more cooling air across the cylinders, the difference wasn't noticeable in flight. The consensus was that it was an interesting concept, but not worth the trouble or cost.

[Martin Benade]

What was the augmentor? It made lots of noise from the cooling air? And Ron, what is the GA reference?

[Jay Laifman]

It was a larger tube around the exhaust tube. And the exhaust tube ended inside the larger tube. So the flowing hot air blowing out the end of the larger tube would suck through the cooler air inside the larger tube - thus pulling it from the other side where the engine was.

[Jay Laifman]

I've thought about that very heat separation issue. Even back when I had my 356, I knew that the pan around the engine was critical to keep the heat away from the engine cooling. I remember it was not uncommon on this site (or maybe the email list) that people would criticize a car for not having the pan. So I was wondering what to do for the race car.

I did see that some of the 4 cams had aluminum running the full length of the exhaust pipes in a number of pictures.

The factory cars above with the 356 engine seemed to have something like that too - and wrap around the parts of the J tubes that were above the lower sheet.

And, yes, I did see that Vic is running wrap and a heat shield separator as well, just below the air intake.

[Jay Laifman]

I've been reading about tuning headers, and that the primary tube length and ID impact when the pulse gets back to the head. We need the pulse to be timed to get back at exactly the right time to help suck out the exhausts, and not show up when the new fuel is entering the chamber.

Back to my comment before, how do mere humans do this? What sort of shops can help?

[Martin Benade]

I think tuning for high rpm calls for a much shorter pipe than what fits a 550. Being sort of slow to understand, could you explain the augmentor a bit more? Are the aforementioned exhaust tubes part of the cooling air exhaust, or the combustion chamber burned gasses type exhaust? And how does it make it noisy?

[Ron LaDow]

[...]And Ron, what is the GA reference?

GA (General Aviation) is what the FAA calls all the guys puttering in Cessnas or Pipers

[Alan Hall]

The augmentor was an ejector device using the exhaust gas as a primary flow and creating a negative pressure at the ejector inlet which would suck secondary flow over the cooling system. The combined flow would then go through a diffuser to exhaust to ambient pressure. With a piston engine you really don't have enough primary flow (engine exhaust) to accomplish much pumping. The ejector concept can work well with turbine engines with huge volumes of exhaust flow. In the 70's I designed a number of infrared suppression exhaust systems for military helicopters that used ejector systems to pump cooling air for cooling the exhaust metal as well as diluting and cooling the hot exhaust gasses to make the helicopter "invisible" to heat seeking missiles. Don't really know why the Fletcher system was supposed to be so noisy, an ejector system that mixed the exhaust with the pumped cooling air actually should have been quieter than an open pipe exhaust.

[Jay Laifman]

Here is a picture of a system that shows the basics.

[Jay Laifman]

I just noticed that the Glockler Porsches ran mid engined pushrod engines. Anyone have any information on their exhaust set ups?

[Jay Laifman]

FWIW, I spoke with someone who worked on the early 550 cars with 356 engines while they were restored. He said from looking at the exhausts - at least how they were when he saw them - he did not think the factory did any tuning, other than to make the pipes fit in the limited space, with no attempt to even out the pipes or tune them. He did not think tuning exhausts was particularly a point of focus then.

And of all things, he did offer up a suggestion of pipe sizing - which is exactly what Vic suggests on his website (but of course).