Exhaust Ideas

[Frankenpacer]

In the spirit of sharing ideas, here's a few pictures of an exhaust system I built for my Hiperbipe. It has worked so well that I will duplicate the same thing for Frankenpacer.

Based upon the EAA CAFE research, the lengths of the primaries is 40 inches. Also based upon the same research, this system adds 8-10 HP on a 180 Lycoming over the standard 8 inch straight stacks!

The muffler shown in the first picture failed pretty early on due to sustained high temperature. The turndown tip is the way to go!


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[Student Pilot]

I had one made up the same as a twin Commanche set up. There seemed to be no increase in static revs or cruise speed. Because it was there was more noise I went back to the original system. For me a Pacer shouldn't sound like a Pitts. :mrgreen:

[Frankenpacer]

The Twinkie exhaust is not an equal length, 4-into 1, is it? I'm not sure if I have ever even seen one... Anyway, what hot rodders and racers have known for decades, airplane people are just now starting to learn - The exhaust is among the most important elements of naturally aspirated engine performance. NASCAR engines deliver better than 125% volumetric efficiency, and they could never do that without a very carefully constructed exhaust.

As far as it being loud, Well, it's certainly not quiet, but the 4 into 1 makes for a pleasing note. The Pacer exhaust was quiet, but I'm certain it was strangling the engine. That was one of the first things to go into the scrap pile!

[Student Pilot]

Just had another look at your piccies, somebody stole your carburetor. :mrgreen:

You would think that even though you don't have equal length headers there would be some performance gains if the pipes were straight through. This system was two front cylinders out one side and the two back cyl's out the other, straight through. Much the same as a Maule set up.

[Frankenpacer]

Yep, no carburetor on this baby; they don't like running upside down! :shock: Pictured is an IO-360-B1E.

I can think of a couple reasons why you did not see an improvement. For one, it's possible that the Pacer exhaust is not as restrictive as it seems. Two, after looking at Steve's hot rod pacer picture in the gallery, it occurs to me that the tubes are not even close to the same length and are tied at a "Y" junction, which is not optimal. It certainly works, but if you are looking for the best, that's not it. Most production aircraft exhaust systems are an afterthought; merely a way to get the exhaust gasses overboard as quickly as possible while meeting noise specifications. There is more to an effective exhaust than simply minimizing backpressure. After all, the factory engines are rated with a "neutral" exhaust system - individual 8 inch long straight stacks. That has to be the ultimate in backpressure reduction! But a 4 into 1 system with "tuned" length primaries can produce NEGATIVE pressure at the valve face the instant the exhaust valve opens for each cylinder. This evacuates the cylinder and allows more complete filling with a "fresh" charge. This is why you will see a HP increase.

[Stephen]

The Sutton exhaust which is approved for the SC, is simple, light and it is a reasonally priced at about $1700. It may have some hp increase.

[Frankenpacer]

$1,700! :o Ouch! I have about $300 wrapped up in mine, not including about 8 hours of labor or the Jet Hot coating.

[stevesaircraft(Bri)]

Frankenpacer,

Yes our exhaust is not optimal for maximum performance.
BUT, our exhaust is part of our STC for the 0-360 A1P coversion and is a STC/PMA part.
You also have to consider that our exhaust system had to pass "MULTIPLE" FAA tests including maximum decible levels for noise and carb heat temperature rises. The FAA wants a 90 deg temp rise in the carb heat to pass thier tests. We barely got there with this system. Considering the stock system, our exhaust is definatly a better system.

As far as experimental aircraft exhaust systems, the 4 into 1 system is the best for overall performance. Look at the formula 1 Reno racers and just about all of them have that type of exhaust.

Brian.