Negative pressure on exhaust?

[ConnClark]

Why not just look at data from a test to settle this debate.

http://aerade.cranfield.ac.uk/ara/1947/naca-tn-1367.pdf

Okay, they don't touch fuel economy directly but they do show power output increases when you have only 7 psia in the exhaust vs 14.7psia

[gone-ot]

...that Allison V-1710 cid engine was supercharged, most all of our cars aren't.

[ConnClark]

If you look at figure 4 it has the inlet manifold at 30 inches of mercury which is about 14.7 psia or about atmospheric presure.

[jakobnev]

In the graphs it looks like power increases about three times as much as charge air flow. *cue dramatic music*


Ecky should definitely dust off his shop vac and duct tape.

[Ecky]

I believe what I have right now is ~2.5" pipe to a low-restriction muffler. 2.5" is definitely not optimal, does anyone know the stock pipe size for an Integra LS/GS/DA?

Anyhow, neither attaching the vac nor restricting the exhaust to ~1/4 size seemed to do anything to my idle speed, and I'm going to need a friend if I want to test at higher rpms. One unexpected side effect was that with the vac attached, the exhaust went completely silent.

Will report back after I test.

[ps2fixer]

Interesting concept similar to what my co-worker thought of. He refered to it as the air sprayer effect, basically paint is pulled up when air pressure is passed over a straw creating a vacuum on the straw. Since the highest airflow is going over the car, having the end of the exhaust pipe end in the direction of the top air flow of the car and just slightly into the air flow would create enough vacuum with out slowing the car down more than the benefit.

If you have a way to check instant MPG, couldn't you throw an extra battery + inverter (need a higher grade one for motors) in the trunk, hook all the hosese etc, and check MPG change at steady speed with vac on/off with out changing any draw on the engine etc? Really would love to see some results . I could see those with the alt delete adding more batteries for a vacuum lol.

[pete c]

A high enough vacuum might act as a reverse turbo of sorts, but, as someone has mentioned, where do you get this vacuum from?

[ncwa]

I have to agree in that by pulling the exhaust gases out, the volumetric efficiency will increase.

Any ideas on a high suction / flow device that will also hold up to the exhaust temperatures? Most shop vacuums will pull less than 1 psi of vacuum and I would rather pull more than 5 psi to really see a difference.

I might be the ideal person to try this out as my car won't need an extension cord and I don't use all of my battery pack's 2.9kwhs during my drives.

I appreciate the device tips as I sure can't find an affordable device that meets the bill!

[t vago]

You might could use a jet pump, along with a turbocharger configured as a jet engine. Hook up the turbo exhaust to the nozzle of the jet pump, and connect the car exhaust to the jet pump inlet.

Jet pump


Turbocharger jet engine


I'll leave it as an exercise to the reader as to how practical this device would be.

Update: Make sure also that you provide some sort of correction factor to your O2 sensor outputs. They were designed to work at around atmospheric pressure (or slightly above on the exhaust stream side). Subjecting the exhaust stream to vacuum will cause your O2 sensors to start reading richer than actual, due to the way O2 sensors work.

[oil pan 4]

Originally Posted by drmiller100

No, There absolutely are things you can do which improve both low RPM part throttle efficiency and WOT.

Get a diesel engine.

You can get 110% volumemetric efficiency if you have room for it.
http://ecomodder.com/forum/showthrea...els-23234.html
(this was originally developed for gas engines to go fast, burn more fuel, yes I know immature stuff I was maybe 23 at the time I made this)