Posted at that "other" place... No Pressure Line Necessary!

[olds97_lss]

Well, I got into a discussion at traxxas and then mods shut it down after a couple of days.

Derek Buono (from XRC Mag) posted that a pressure line isn't needed in the RC world and has dyno results to prove it. Apparently, there's an article in XRC that I haven't seen yet about it.

Here's a few posts from the thread:

I don't know where you guys get your information but the pressure is NOT the driving force of the system. The Venturi and the cycle of the engine is what draws the fuel into the engine. Your lawn mower and weed whacker don't have pressure lines.

Removing the pressure line is something that is run in lots of other RC applications.

And if you read the article it explains why it works and what you have to do to run without the pressure line. The dyno graph also shows there is no "lean condition" from running without.

The method doesn't "smooth" out the bottom it actually increase power in the low end region. In the article it also explains that we had to richen the engine about a half turn on top and an hour on the bottom, and it returned to the performance with the pressure.

I know you guys think people make things up but this is something that is used by some racers and has been used in the past. You'll also see an interesting new device coming out soon because of the data we got from the dyno.

And another after some "talk" had gone on about his above post and other posts:

First off, it is not like removing the pipe or like anything else. The pipe is responsible for the scanange and draw of the fuel through the engine. The pressure line is there for "consistent" pressure and nothing else.

Fortunately I actually talked to engine tuners and racers about the subject and did testing on the dyno, which shows performance and where you can see "lean" conditions.


And I'm sorry acceer guy but if you do some research outside of cars you'll see that "pressure lines" are just as uncommon as common.


And for those interested in actually seeing some researched "facts" and not what is just "a thought on the Internet" removing the pressure and richening the mixture results in more power down low (not always desireable). The "downside" is that at high RPM the peak HP (which was about the same) was at a lower RPM and a little bouncey.

The new device coming out is nothing more than some common sense when it comes to engine tuning.

I'll look up the issue tomorrow and post which it was in for those who want to actually read it.

But how about you guys try it and actually see before you try and act like things don't work. Sometimes Internet talk can be disproven. And since I have more to loose than people posting anonymous posters on the Internet if I was reading this thread and was interested I think I'd chose the magazine with a reputation.

Like when I ate my shorts about the Nitrous Express kit actually working.

Superchargers...they are another story.


Those who would like to learn more about why and how feel free to comment here or directly to me. My email is posted on the magazine's website.

This is intended in no way to bash Derek. Just posting what his experience with this has been. Also, I'm curious what your thoughts are on the matter. How many of you run without a pressure line? I thought it was a necessity, but apparently not.

 

[Lessen]

I figure it like this...

the fuel tank has an extra nipple

the pipe has a nipple

?????

unless there is hard evidence that running w/o a pressure line is drastically BETTER I see absolutely no reason to run without one.

 

[DerekB]

Read The Article.

Not more than a few years ago you had to drill your own pressure line.

 

[ImBroken]

Thats pretty interesting... About a year ago, my uncle who races Nitro boats, asked me what that line was for. I looked at him like he was retarded..

Awesome mag by the way... :thumbsup:

 

[olds97_lss]

Read The Article.

Not more than a few years ago you had to drill your own pressure line.

I'll be sure to read it when I get the mag. The last one I have is April. I thought I normally get the next month a lot sooner.

 

[Monkey Wrench]

I'll read the article, but regardless, so long as the pipe and the tank have fittings for a pressure line, I'll continue to use them. Have to wonder, though, why they are still included if they are not needed? Also, dyno testing, while a great tool, is not real world use.

It is a fantastic magazine! I'm looking forward to reviewing the article!

 

[HeartBreak]

I was always under the impression that the 'pressure' line was actually a vent line, routed from the pipe to the tank to help cut down on crud sucked in by the vent. The "vent line" was needed to help the engine draw fuel (easier, since it isn't fighting against a sealed container), and to prevent the tank from trying to implode (like a juice box).

 

[digger]

I'm trying to keep an open mind here and real interested. No way I'm losing the pressure line, but I would like to see the article.

The way I see it, the pressure line going into the tank acts as fuel pump?
Not much pressure there, but enough to keep fuel to the carb.
Take away the pressure line, you still have to vent the tank, right?


I'm confused. Can't see where any power would be gained. The pressure line is a simple set up. Why screw with it?

 

[neobart]

Try this little experiment. If you put your finger over the carb, and turn over the engine. You'll fell how much suction these engines make.

 

[Lessen]

Not more than a few years ago you had to drill your own pressure line.

really?... guess I havn't been around long enough. Anyhow, I'm just saying if it's there I might as well use it. As far as it being necessary.. well, I'm no engineer. I've always been under the impression that a pressure line was just that, a pressure line. I've always just assumed that from being around here. It is interesting though for sure

 

[Plaidfish]

the key line and wording I believe alot are over looking was
"The pressure line is there for "consistent" pressure and nothing else."
in onroad I could see you not really needing a pressure line until you got into cars doing like 80 and the G forces would affect fuel positioning for longer periods.....but in offroad I think you could get alot more inconsistent temps from slightly leaning out periodically while bouncing around.....

 

[rocknbil]

This is correct, technically the pressure line is not needed, it only ASSISTS the fuel going into the engine, which is actually drawn by the vaccum created by the engine.

However - most engines/carbs are designed to have this "assistance". As you all know the sweet spot for any given engine is a very narrow band, you have to have the tuning, compression, and glow plug all set correctly or you will be here posting "what's wrong with my engine?" So while running an out of box engine without the pressure line can probably be done (by just enriching fuel mixture,) it would probably show some problems.

 

[DerekB]

If you read the article it's very clear where the power is, and if you understand the graph you'll see tht it creates more power in more of an "electric" powerband (more linear) with a pressure line you get a "ramp up" of power later which is what is called a "rubber band effect".

The place where the pressure line helps is at high RPM where even with a pressure line more fuel is needed, which this is also explained in the article. The "device" that I can't mention was tested on a .12 and a gain of 7,000 rpm was achieved (49,000). It's still being tested and developed, but if you understand engines the pressure line and no pressure line will make sense.

 

[robriguez]

Were just discussing things here Derek. Were not bashing the idea.

But since you have chimed in, has this article been published/released yet or is it in an upcomming release? Either way, what volume/month/release/whatever can someone who is not familiar with the mag (like myself) find the article? Is there an online version that you could provide a link to for us?

I for one would love to read the results.

 

[WoodiE]

DerekB,

I'd also like to read this article and would be interested in which issue it's in or URL.

I do have two questions however:

1. Your first post in this thread said that just a few years back we had to drill our own pressure lines - why do you think the reasoning is that every pipe now days come with that line is there already?

2. Why can't you tell us what the tested "device" was? I for one am very cautious about anyone that can't disclose their testings.



-Michael

 

[DerekB]

It's in the May issue with the T-Maxx 3.3.

Woodie, Pressure lines were an option. With engines revving higher and higher, more fuel at the top is needed and a pressure line does help (CVEC Pipes vary the pressure for this reason).

2. I can't tell you because the company is doing something nobody is and is doing the leg work of this. So instead of ruining their work I can just avoid who and what it is until they feel comfortable. It's a very simple idea, which works at this point, but they have to test it more. No use pumping something up until it's tested. We did that with this test, which is why I'm explaining why it works, and it's downside...which is not ruining your engine.

 

[FastEddy]

I have read a lot on this over the years and the conclusion I have come to is a pressure line seems to make it easier to get an all around smoother power band and a larger sweet-spot for the average user. For the average user it helps keep the temps in line and the performance more even across the RPM spread. When you look at the typical RC hobbyist the manufacturers and engineers are trying to please the masses.

Ill have to assume this “Device” is either a fixed or variable rate fuel pressure / pump (?) unit. We all know what Ass-U-Me means.

 

[DerekB]

Fast, it's not really hard to figure out what it is, and I'm not going to spoil how they are doing it.

From my testing without a pressure line the engine was no harder to tune and the "window" wasn't smaller. But that can vary on engines greatly since there are some that are very narrow and others that aren't.

 

[Clintd]

I just scanned through this post quick. but I noticed the lawn mower was called into play. Anyway there is 2 types of fuel delivery systems for most lawn mowers. 1 is gravity feed which just has the tank mounted above the carb and the other is diaphragm feed which has the carb connected directly to the top of the fuel tank. The diaphragm feed uses the pulse from the crankcase vent to actuate a diaphragm pump between the tank and carb. so in other words. It also needs a pressure line.

I'm fairly certain that you could run a nitro engine with a gravity feed system. But then you would be raising the center of gravity due to the tank having to be higher then the carb.

 

[WoodiE]

DerekB,

What engine(s) did you use for your test?


-Michael