Aircraft vs Car

[Ramcharger90]

So out of curiosity and a lack of a way to articulate this in a google search this maybe one of you will know.


Since an aircraft normally has such a short header or exhaust manifold, Since the beginning of powered flight with radial or piston driven engines one thing puzzles me.

How do aircraft not burn valves regularly?

Why would a car with an open manifold or too short of header burn a valve?

How short can a header be on a car without burning a valve?

Zoomies are pretty short, sure they have atleast 2 bends but still, I haven't found an answer that breaks this down scientifically.....

 

[Shran]

I am certainly no expert here but I would expect a couple reasons - probably has to do with the way the exhaust exits.

Noise isn't so much of an issue in the air as it is in a residential neighborhood and air rushing past an open header can pull exhaust out? vs in theory just swirling around in an enclosed engine bay, assuming an open header in a car. It would be more difficult to put a full muffled exhaust system on an aircraft and back in the day when piston engines were used a lot in aircraft, emissions and stuff were also not a factor.

Fuel mixture probably plays some part in it too. Burnt valves in vehicles used to be pretty common. I kinda feel like very short headers on a car engine would in theory probably be fine, the main thing would be to get heat away from the engine.

Fires would be another concern with vehicles - watch just about any video of an engine running with no manifolds and you'll see it spit sparks occasionally. No problem if you're flying in the air... big problem if you're on the ground.

 

[Ramcharger90]

1st a joke I dont live in California.

But in all seriousness I wonder how it would work say in a open engine bay roadster? Noise isn't to much of my concern lol thats the neighbors.....

I just wasn't sure

 

[RonD]

Never bought into the short exhaust causing burnt valves

Back in the carb days shorty exhausts could cause leaner burn so burnt valves if you didn't richen the mix
Maybe it came from that, and valve material has gotten much better

Airplanes, motorcycles even your lawn mower have very short exhausts, yet no common burnt valves happening

Some eluded to the "cold air" coming in after engine is off and warping an open exhaust valve, not gonna happen
First the cold air can't come in, there is no "flow", intake valve is closed if exhaust valve is open, and there is COLDER air in the intake usually, so if intake valve was open we would have warped exhaust valve like crazy, or intake valves, lol

If you get burnt exhaust valves in an engine I wouldn't look at shorty exhaust system as the culprit


Exhaust valves burn because they stop rotating, valve and seat don't have matching angles, so less heat transfer, lean HOT cylinder temps(EGR removed), that's all that comes off the top of my head
But nothing from shorty exhaust

 

[Dirtman]

Aircraft and marine engines run at a single relatively high RPM the entire time so the head and exhaust is tuned to run at that relatively small window of RPM range, car engines need to run well from idle to red line. Aircraft also have the benefit of cruising along at high speed where the air is flowing over the exhaust pipes and literally sucking the air out of the pipes. There is no need for scavenging systems on these engines so no need for long complex headers. And no need for noise or emissions nonsense either. But nothing to do with burnt valves, that's just from the engine running too lean.

 

[Ramcharger90]

So the next question is how short can I go?

I have a love for the P51D mustang and want to stick with a theme on the Model A.

I had an idea for zoomie style headers that curved back up to exit the side panels but it may be a fools errand with fitment even with a 32 grill which would make my hood wider.

 

[RonD]

Well on cars you can have people walking by when engine is running and exhaust temp coming out of a short pipe will be 700-800deg at idle, over 1,000deg under load
So that's a concern

Up facing exhaust is a concern for rain/water unless kept inside all the time or you put plugs in pipes when its not being used

You could certainly make pipes that "look like" P51 exhaust but use them for intake air or just show

 

[Ramcharger90]

No no..... this certain vehicle is suppose to be a flame throwing monster....

It wouldn't be a hotrod if it wasn't "hot" then it would be just a rod.... and that sounds lame.... lol

 

[Ramcharger90]

 

[Dirtman]

If you wanna stick with the theme then the car needs a Merlin V12 there's no other way around it...

 

[RonD]

Sounds good

So you are not doing just to burn the paint off peoples cars in a parking lot

There are several ways to do the "flame thrower" effect

 

[Ramcharger90]

I know a guy with a few old packard twin sixs so..... yeah it isnt out of the realm of possibility.

 

[Ramcharger90]

Sounds good

So you are not doing just to burn the paint off peoples cars in a parking lot

I never said I didnt have ulterior motives.... lol

 

[19Walt93]

There was an old guy (older than me) named George Barber that used to race a flathead on oval tracks in NH and Vt with the exhaust blowing straight out of the block- no pipes at all- and he made it work.

 

[Ramcharger90]

There was an old guy (older than me) named George Barber that used to race a flathead on oval tracks in NH and Vt with the exhaust blowing straight out of the block- no pipes at all- and he made it work.

Thats interesting to me. Was it dirt or clay oval?