Tail pipe restrictor test - Page 2 - Fuelly Forums

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Old 11-12-2007, 09:08 PM   #11
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Quote:
Originally Posted by 8307c4 View Post
As for the air, it really doesn't matter whether you increase the in or the out flow
Hrmmm.... So I can take more than I put in

Or put more in than I take out

I believe we have violated some fundamental physics

Quote:
...for best results enhance both.
Define "best results" -- we're generally not looking for more power or more airflow... We're looking for less air flow and therefore less power And ideally, without adverse running problems
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Old 11-13-2007, 06:03 PM   #12
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Quote:
Originally Posted by Erik View Post
Noise- about the same at idle, definitely quieter at 60 mph.

Driveablility- not noticeable around town, a little less power on long steep hills

Other differences- when pulling a long steep hill, I could see the engine temp coming up noticeably even when outside temps were cold. It usually stays within 1/3 and 1/2, on a few hills it went up to maybe 60%. The temp doesn't rise this much without the mod when driving the same hills in warmer weather.

(By the way, I know I was no where close to boiling over. I overheated the engine several months ago and recall that it happens at the edge of the red zone- or at about 95% up the gauge).

I could also tell that the cooling fan was running more even when in city traffic. This makes sense because probably more of the hot exhaust gasses were remaining in the engine.
Remember:

...a 60 HP engine only needs ~ a 1.1" ID exhaust...believe it or not.

60HP (at the crank) per square inch of (cross-sectional) flow area needed

PI*r2

Got 90 HP? Need 1.5 square inch flow area or 1.4" ID?

.........

A dime is only 3/4" ID. At 76 HP you might need around 1.25"? Or somewhere between 3/4" and 1.25"?

If it was overheating and the fan was running in cool weather...that isn't a good thing. Fan uses fuel to run. Try 1" to 1.1"?
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Old 11-13-2007, 09:41 PM   #13
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exaust gasses are acting as a fluid, and the fluid dynamics in the exaust system, and changes in the exaust pipe need to be made to the entire exaust system, not just the tip of the pipe, the honda insite, and the crx hf both have extreamly small exaust pipes, running the whole langth of the vehicle, smooth transitions, fewest number of seams possible (early crx hf's like I have have almost 8 feet of seamless small diameter exaust pipe), with my understanding of exaust systems, after reading a number of books on engine design, and exaust system design, what you are doing should have no positive affects, but of course you are welcome to proove me wrong.
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Old 11-14-2007, 02:26 AM   #14
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Originally Posted by Ryland View Post
what you are doing should have no positive affects, but of course you are welcome to prove me wrong.
The idea is that it might reduce reversion of exhaust gases due to valve overlap. ..increasing engine efficiency. But it is like everything else...the devil and the best results are in the details?
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Old 11-14-2007, 03:51 AM   #15
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I think it is too late to affect valve overlap at the tip of the tailpipe...needs to happen at the exhaust manifold or close to there for a street machine. If you were running at WOT (like a race car) then tube lengths ect. would affect the intake/exhaust characteristics in the valve train or ports (rotary engines/2 stroke). Once the exhaust has passed the half way point or so, you want them to exit as fast as possible IMO.

Now if you made a "flapper valve" near the front of the exhaust that you could control...that might help. You would close it down at slower speeds and open it up at higher loads. All just a guess tho!
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Old 11-14-2007, 05:49 AM   #16
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I appreciate the comments (positive and negative) as well as new ideas .

I got this idea from 3 separate past experiences.

1. I put a free flowing exhaust system on a Yamaha 850 3 cylinder bike and it ran awful without the stock exhaust back pressure. Had to reinstall the stock system to fix it.

2. I had an 85 Nissan Pulsar with a 1.6L and 5 speed. Typical mileage was is in the mid/upper 30's. I made a long trip just before my cat converter melted and plugged itself up (my max speed was 50 mph when this happened). My mileage on the tank before it plugged was up into the low 40's- very atypical

3. My 87 Integra had a bad exhaust pipe (the pipe that runs up over the rear axle) so I moved the muffler up under the center of the car just behind the cat. The car was much louder and my mileage went down. So I added another muffler in series with the first. Still loud. Next, as a crazy idea, I rolled up some steel screenwire and stuffed it into the last muffler's outlet. Ran quieter and mileage went up with little difference in power.

I know that these are 3 anecdotal events and that all vehicles are different, but I figured I might try to see if there could possibly be a benefit on my current vehicle.

I'll definitely test the spring loaded flapper valve, but I want to get 1-2 more baseline tanks first in the colder weather with winter gas.

I do have a way to put a restrictor just downstream of the exhaust manifold, but I don't believe that I could control it with a cable without drilling a hole in the pipe and creating a leak.

Good point on the cooling fan running more often, that is hurting any gains that might be made by increased backpressure.
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Old 11-14-2007, 11:28 AM   #17
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Quote:
Originally Posted by Erik View Post
I appreciate the comments (positive and negative) as well as new ideas .

I got this idea from 3 separate past experiences.

1. I put a free flowing exhaust system on a Yamaha 850 3 cylinder bike and it ran awful without the stock exhaust back pressure. Had to reinstall the stock system to fix it.

2. I had an 85 Nissan Pulsar with a 1.6L and 5 speed. Typical mileage was is in the mid/upper 30's. I made a long trip just before my cat converter melted and plugged itself up (my max speed was 50 mph when this happened). My mileage on the tank before it plugged was up into the low 40's- very atypical

3. My 87 Integra had a bad exhaust pipe (the pipe that runs up over the rear axle) so I moved the muffler up under the center of the car just behind the cat. The car was much louder and my mileage went down. So I added another muffler in series with the first. Still loud. Next, as a crazy idea, I rolled up some steel screenwire and stuffed it into the last muffler's outlet. Ran quieter and mileage went up with little difference in power.

.
1) Opening up an exhaust on a motorcycle like that means you have to rejet for the new system. Also, a very open exhaust like that would lose low end but help midrange and really help up top.

2) Since you could not duplicate driving with previous speeds, you might get the better mileage going 50mpg (limited by clogged cat). I would bet that you would have had the same or better if you ran no faster than 50mpg with an unclogged cat.

3) Louder most likely because the end of the exhaust was no longer exiting the 'back" of the car. As for mileage, without real testing ... it is still just a guess.

Gotta try new ideas nonetheless...you might come up with a good combination for your vehicle and driving style.
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Old 11-15-2007, 03:16 AM   #18
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Quote:
Originally Posted by Erik View Post
I know that these are 3 anecdotal events and that all vehicles are different, but I figured I might try to see if there could possibly be a benefit on my current vehicle.

I'll definitely test the spring loaded flapper valve, but I want to get 1-2 more baseline tanks first in the colder weather with winter gas.

I do have a way to put a restrictor just downstream of the exhaust manifold, but I don't believe that I could control it with a cable without drilling a hole in the pipe and creating a leak.

Good point on the cooling fan running more often, that is hurting any gains that might be made by increased backpressure.
The fact that it's getting hot is an indication that it is too restricted.

I think you are on to something. At least you test things and pay attention to the results....looking for clues.

Two different commercial restriction type exhaust tips that I know of...and your results.

Could use the bypass valve that Jegs sells? Operated by cable...just block off the open bypass and use it as an adjustable restrictor?

http://www.jegs.com/webapp/wcs/store...44831_-1_11529

Remember...there are a lot of people on this forum who waste their own and others time explaining ad nauseum as to why something won't work....and don't test things. New forum needed: whysh*twon'twork.com :-)
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Old 11-15-2007, 11:45 AM   #19
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Originally Posted by theclencher View Post
feel free to start the sucker forum, where the laws of physics don't apply
youtube?
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Old 11-15-2007, 05:19 PM   #20
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The exhaust throttle idea interests me. If you a in charge of how open the throttle it might be able to show a benefit.
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