teknicalissue

i just read this article on rockets and the vacuum space:
http://www.straightdope.com/columns/...acuum-of-space

basically.. the way rockets move in space is by pushing itself using the exhaust as a launching mechanism

soo... what if we add some kind of mechanical fan to our exhaust systems that expel (by pulling and pushing) the exhaust air faster and narrow our exhaust narrowing????

idk but i feel im up to something, let me hear your opinions please.

EHondaJDM

isnt a muffler mounted turbo kinda like that? the momentum of the turbo from the exhaust keeps the exhaust gases coming out

teknicalissue

I didn't know you could mount a turbo to an exhaust but yes, the idea is still the same. push out the air faster while narrowing the muffler so it can create a strong and efficient "push" effect

EHondaJDM

its been done many times, mainly on cars like corvettes cause theres no room inder the hood, seen it done at the mid pipe and exhaust.
this is what the vette setups usually look like...

EHondaJDM

i dont think youll get the desired effect from just a 4 cyl exhaust

watch this vid, might be a setup for you!

http://www.youtube.com/watch?v=uS_p4...eature=related

teknicalissue

hm, pretty interesting. the gas turbine is actually another interesting concept that can be added to cars..

so theoretically, if i were to put a small fan inside my exhaust piping, and have it blow out air along with a narrow exhaust, i would not see gains in a 4cyl car?

im also noticing that with turbo cars, the bigger piping the better.. why is that? wouldn't it be better to have narrow piping? or atleast a narrow muffler for that "push"

EHondaJDM

no the turbo needs bigger exhaust for less restriction

i dont see a small 2 1/4' pipe running from the exhaust from a 4 cyl putting out enough pressure to make any difference, no

also if you narrow the exhaust the back pressure will be too much and will decrease hp in the motor where it counts

newtron63h

well a good cam, with a header that is well suited to the cam profile/s, a good PnP, and port matching is going to scavenge about as well as can be expected from a non-race engine. if you add some negative pressure to the exhaust flow, you might over-scavenge or pull clean fuel-air mixture out through the exhaust port before the valve closes.........which is not helping power or economy.

during overlap the intake air and exhaust gases mix some, so there will always be either some exhaust gases trapped in the compression stroke, or intake air/fuel going out the exhaust unburned.......or some combination of both. what this means is that if you add more negative pressure(more than a header provides) you might be pulling a significant amount of air/fuel past the exhaust valve which means 2 things......you have a more powerful intake charge trapped in the cylinder for cumbustion.....but you are also wasting energy because the engine has pulled in the clean air that is now traveling out the exhaust without being useful.

and on top of that, the O2 sensor/s will pick up the oxygen in the exhaust and add more fuel............further decreasing economy and decreasing performance. also this scenario will be keep increasing fuel until it cant add anymore......probably setting a code.

to do this correctly, you would have to do alot of tuning (and in the end i think you might find that adding any vacuum beyond what a header does is hurting more than helping), and the negative pressure would have to vary directly with rpm.......AND in hondas case youd have to account for the extra flow when vtec kicks in. in order to do that i think youd have to have an extra control module(or maybe you could program an extra channel of something like a AEM standalone to control the fan). its also going to have to be a fan that can handle very high temps.

newtron63h

turbos need alot of flow, otherwise the exhaust gets backed up, exhaust temps get really high especially in the turbine side of the turbo, which can cook the oil flowing through it, and performance goes down because the turbo isnt spinning freely.

newtron63h

yup, ive seen trucks with bed mounted turbos.

the problem with remote mounted turbos is lag, you stomp the throttle and it takes time for the exhsut gases to get back to the turbos and spool them up, and then there is a large column of uncompressed air in the intake lines going back to the engine that takes even more time to compress. so in alot of cases what you end up with is "stomp the gas, nothing, nothing, nothing, nothing, nothing, AHHHHHHHHHHH!" BUT fortunately thats where displacement comes in, the powerful engine in something like a corvette means theres still considerable power even when its not in boost.

EHondaJDM

So to sum this thread up,

No

Our honda powerplants are not good for exhaust thrust

hondamark35

basically, if you can find that the thrust gained is worth the power lost.. go for it!

...find the exit diameter and nozzle velocity of a jet engine or rocket that would provide.. say 50lbs of thrust. working back from that you should be able to calculate the needed RPM to provide the same flow of air from your tail pipe. i'm guessing the resulting RPM will be astronomical... pun definitely intended . it's not rocket science without a bunch of super fun math, right?

i will add that many racing teams (Formula 1 for sure) direct the exhaust out the back for whatever thrust it does provide. but with an F1 motor, 2.4L (i think) at 19k RPM... they've got some big flow from the exhaust!

newtron63h

OHHHHHHHHHHH WOW, yeah i completely overlooked the OPs question. can you make the exhaust push out with enough force to add to the forward force?

yeah not a very workable idea.

teknicalissue

lol thanks for all the theories. so.... no you can't push out exhaust with enough force to add a forward force... but this brings up another question...

would it be cost effective to put a turbo on the exhaust AND turbo under the hood??

EHondaJDM

Are you high?

tasco

Or you could put a fan in the exhaust piping to suck all the exhaust out of the engine. Eliminating the need for a nicely tuned aftermarket exhaust system.

unusual71

man in space there is no friction to slow you down and the exhaust from the rocket is not like exhaust from an internal combustion engine but an enormous amount of energy being released from a huge chemical reaction.

EHondaJDM

I think apexi has a muffler with a fan inside it. Its spun by the initial exhaust then helps to suck air out.

Yea we already established our powerplants couldn't produce the amount of energy needed.
The friction doesn't help matters but it don't stop us from using a exhaust for forward thrust. Take a look at the video I posted earlier in the thread

newtron63h

except that a properly tuned exaust system is just that "properly tuned" so that its making things happen at the right time. a fan in the exhaust would create negative pressure(or at least lower the positive pressure) in the stock system. the stock system is not tuned, therefore the negative pressure would be helping evacuation........BUT it wouldnt be doing things at the right time nor would it be doing it at the proper rate.

make sense?

newtron63h

x2

a rocket engine and a turbine engine provide thrust in the same basic way.

newtron63h

no i dont see any advantage to that setup............the ONLY advantage i see to a remote mounted turbo is lower exhaust temps at the turbine housing, lower temps is usually better........BUT im sure turbo manufacturers engineer their turbos with a certain temp range in mind so they can account for the expansion of parts and have proper clearances(which is why its a bad idea to hammer on a cold turbo). which could mean that lower temps is NOT good.

newtron63h

also just for some added information, in a rocket engine, its not JUST about the nozzle diameter/thrust ratio.............there is a certain shape to the nozzle. so you would have to have that shape right, along with the diameter. ALSO this idea would only work at a specific rpm range, under than range and the pressure differential wont be enough, over that range and youll just be choking the engine...........in fact the engine might not rev beyond that range because of the exhaust restriction.

tasco

Other than timeing the exhaust pulses together to try and pull the exhaust out of the cylinder with a tuned exhaust, what kind of timing or exhaust rate are you talking about that is needed to make more power? BTW i was not being serious about the fan, the rate the fan would have to flow to actually make a negative pressure in the exhaust would be hard to get.

newtron63h

thats exactly what im talking about, header diameter and length is designed to maximize scavenging. they determine when and how fast the exhaust gases are pulled out of the cylinder. so with a fan on the stock exhaust system.......all you are doing is creating a pressure differential which could help some.......but not as much as if the exhaust system were tuned.

also something to consider is that a header is designed to scavenge all by itself, so if you were to add a fan that helps that.......it throws off the tuning of the header. so it would have to a be a header tuned FOR that kinda setup.

and its not really nessesary to create a negative pressure in the exhaust, just creating a pressure differential is enough to increase the velocity of the gases.