powerflow exhaust surprise

[neverquit]

"turbosuperchargers" = full name for what we call a turbo

Sooo...Dust, you're still years ahead of me.

Got this from forums/pimprig.com of all places...
When the screw charger / blower was invented the gear driven supercharger was all but abandoned because it was not as efficient of a design till paxton brought it back. The supercharger then became solely the screw type blower and because people couldn't keep them straight the turbosupercharger got the chop down to just turbo. The P-51 mustang used a gear driven supercharger, The B-17, B-25 bombers and the P-38 lightning all used turbo's.

Born with four tires and a shifter. Still learning about this aircraft powerplant thing. Keep me staight Dust and get the bugs out before I fly...heheh

[Riseguy]

I did not use tuffs of yarn. I did use dirty oil. There is a lot of confused air back there.
The other plus for using short pipes is there is not as much hot air to get out of the engine compartment. Cyl head temps never get above 390 degrees F even when outside air temps are in the high 90's, and full throttle climb out to 8,000 feet. This is with the std. P-51 scoop. no extra baffeling.
As for the back pressure thing and valves. You are right. Now if I can just get this Lycoming to turn 4,000+ RPM to make it happen. Heck I would be happy to get 2,900 RPM.
The Lycoming book says never exceed 2,700 MAX. The Canard experts tell me 2,900 is OK. My ear and wallet tell me 2,500 is just fine. That comes to 150 knots indicated, and 6.5 GHP.
KISS is COOL!

[Dust]

Originally Posted by DJ Rise

There is a lot of confused air back there.

Had to make sense, but, your performance and cooling sounds great.

So..... 2+2 still equels 4

[Glos]

"Tunning" the exhaust on a normally aspirated engine is planned around several factors.

1) The distance from the exhaust valve seat to the exit point (The length of the pipe.)
2) The diameter of the pipe/pipes
3) The size and shape of the intake port runners
4) The size of the carb butterflies

"Tunning" as it were achives two things. Increase in rpm or increase in torque
Play with any of these and you get the desired changes. This was known back in the late fifties and early 60's in drag racing.

Gas velocity, while true, must go along with volume the larger factor. That is, a 360 cubic inch engine at any given RPM will only pump a given cubic feet per second, no more. The easiest way to increase velocity is to increase rpm.


Short, large diameter pipes produced higher RPM. Longer , smaller diameter pipes produced higher torque. These were the general rules of thumb. But don't expect massive changes to either Hp or torque. This is for the guy looking for that last once of performance to be squeezed out.

Expansion chamber pipes worked very well on higher rpm two stroke engines but not big bore four strokes. But all of this was easy to quantify.
Simply mount the engine up on a dyno and start playing away. Not something that is easy for us to do.

Turbos or supercharged engines didn't care. The fuel/ air mix was being jammed down into the cyclinders. This extra voume required immediate exit.

On supercharged engines like top fuel drag racers you see only short stubby exhaust pipes.

Lastly cam timming and overlap of the intake and exhaust strokes are an additional factor.

We have big bore big stroke engines relatively speaking. These big block muscle cars were running up to 7,000 to 8,000 rpm and not < 3,000 rpm.

[Riseguy]

YA, thats it! Lycosorus= 290 Cu. Inch 2,650 RPM all day, MA3SPA carb, Just like grampa's Model A!

[Waiter]

When I had my CAM (O-320) reworked a couple years ago. I spent a lot of time talking to Mr Elgin (Elgin Cams - San Mateo). He seemed to feel that tuned exhaust was a waste of time until the RPMs started getting up past 5,000 or so. At that point, the CAM geometry would start playing a factor in the exhaust tuning.

Neat shop, and learned a lot about CAMs.

Waiter

[Glos]

Originally Posted by Waiter

He seemed to feel that tuned exhaust was a waste of time until the RPMs started getting up past 5,000 or so.

Waiter

Exactly, he was correct. If I remember correctly the Torque curve started around 4500 to 5500 and the RPM above 6,000.

[Lynn Erickson]

I can't tell you I seem to feel that it is a waste of time. I can only tell you what the dino says and how it flys.

IO-360 Angle valve Lycoming run at 2700 RPM

6" long straight 1 3/4" dia. factory test pipes =202 HP

18" long straight 1 3/4" dia. test pipes =192 HP

18" to 23" different length 1 3/4" (long eze type) pipes = 188 HP

Equal length 1 3/4" tuned 4 into 1 with collector = 213 HP

In my aircraft that is 200 Kts true at 9500 ft. at 2680 RPM
On my return trip from No. Cal today we had a slight tail wind and the GPS was showing 222 KTS. at 8.2 Gph

[Glos]

Interesting and impressive.

We couldn't get a 25 Hp swing on 427 chevy "rat" motors over any rpm spread
and we were trying to squeeze ever once of power from it. Best performance was 42" pipes equal length into a collector. The pipes were like snakes and for all that we got only about 18 to 20 Hp.

Of course everything else was addressed prior, pistons, cam, intake,ports matched,and parts balanced. Maybe there is a point of diminising returns.

These are good numbers if the load was properly applied on the dyno.
Almost too good. But to a fellow canard flyer, I will put my faith in what you say over someone else.

You did not say what the final length of the equal pipes were. How did you find the room?

[Lynn Erickson]

The pipe length tuning got us about 50 percent of the improvement the rest is the collector and reverse cone size. the outlet size is where we gained the the most HP and best of all is the leaning. we can lean way past peak egt and it still runs smooth. one of the times where smaller is better

[Lynn Erickson]

Looking closer, only 11 HP was gained over the stock lycoming 202 hp recorded with the factory test pipes. but a decrease of 14 HP below stock HP when we install a set of stock type long eze pipes. the combination of very tight double bends and unequal length straight pipes just killed the HP

[neverquit]

Anyone talked to Jack about his ERacer? The design is somewhat similar concept but two plenums.