SportsFans

2[sm=thumbs_up.gif][sm=thumbs_up.gif]'s up!!!!!

saxy174

I tested all 4 of my savy's before and after the fuel line change and what a difference. "Thanks" for the savings! My temps have come down. I re-tuned the motors and I'm getting consistancey temps all through the tank of fuel. Thanks Again!

DawgBone

I have a Savage XL, and I haven't seen any half tank leaness....at least no more than any other RC I've owned...
I just tune my trucks from a half tank as I do all my RC's....and temps come out exactly where I tuned them for at an empty tank....

It's a little sluggish on a full tank, but nothing a couple of WOT runs, doesn't take care of within a minute or so....It's nice to know it won't run lean though...

twomanytoys

Yes you could tune at half tank like HPI told me to do but its a dog until half tank then it really comes alive. Doing the short fuel line makes consistant performance and temps from top to bottom. My sons X does not have this problem so I left his stock. His temps dont get above 250 and it runs strong from top to bottom unlike my X SS did until the mod.

DawgBone

Doesn't make a bit of sense to me....

I guess the only thing that would make me believe that there is a half tank lean issue...(which I don't know a RC vehicle that doesn't(even airplanes) would be if the pressure feed or fuel feed nipples where clogged or the pressure feed was too small for the fuel feed...
regardless if they're clunk style tanks or non-filtered....all nitros run lean on the bottom half of the tank...

I don't and have not owned a SS...So take my comments with a grain of salt....I have owned a .25 and a XL....
[edit] well a Tmaxx 2.5, Revo 2.5, LST, LST2, Muggy, and an 8T.....just to add injury to insult...

twomanytoys

I understand that most all nitros will run leaner as the tank gets lower. Have you read the thousands and thousands of posts about the half tank lean? Google it and you will have reading all day long. Its because of the way the tank is made. It has the shelf and once it reaches the half tank when the shelf drops the pressure dramaticly drops and then temps go way up. Temps go up about 30-40 degrees and once it gets down to about 1/4 tank the temps start to go down. This is not just something that someone pulled out of thier butt. HPI knows about it and they dont have a fix nor do they plan on having a fix because they would have to redesign the tank. I have been doing nitro rc for over 15yrs and have never had a tank lean like I have on my Savage. I did all the reading and read about all the mods and figured there has to be an easier fix. So thats what my post was for. So far everyone that has tried it has had good luck and all have seen temperature drops, easier starting and more consistant tune. That does not mean that it does not run lean as the tank drops but the effect is decreased to where you no longer have to worry about running too hot. My temps only go up about 15 degrees now. You may not see the half tank lean on your XL because that 5.9 puts out alot of pressure so pressurizing the tank is no problem.

Argess

Yes, it seems to work. The engine temp may rise a bit as the fuel level drops, but it's hard to tell if it's leaning, or just continuing to warm up. I did run two tanks in a row to try to get rid of the "warm-up" phase and it seemed pretty consistent after that. But that's in my buggy which wasn't too bad anyway.

er.....I'll probably take heat for this, but it's not the step that seems to be the problem with the stock Savage tank.....it's just the oveall depth (height) that seems to be a problem. At least that's what makes sense if you go by the static theory of less fuel ='s less pressure at the pick-up. "Static" meaning constant rpm's, i.e. such as WOT. The one-way valve and "T" fitting mod addresses this situation (modified uniflow mod).

If you subscribe to the dynamic theory that as the airspace in the tank increases, it takes longer to pressurize (during acceleration), then the step may have some effect as the airspace appears "too quickly" as the level drops. It's not uniform. Shortening the pressure line addresses this problem. It appears that shortening the fuel line also addresses this problem.

Continuing to speculate, the real truth is that it's probably a combination of both and that's why so many different approaches help or cure the problem.

But there's nothing like results, and in this case, improvement to complete success has been found. Speculation can only do so much. It's a good thing when people come back to report their results. Always fun to find a theory that meets the facts (which you're not supposed to do....should be "find facts to support a theory".....LOL).

twomanytoys

I have also read that when the tank is full the fuel level is even with the carb. Once it gets to half tank the fuel is below the carb. When the carb is full it does not need as much pressure because gravity works with it but once it gets to half tank it needs more pressure and gravity works against it. Like blowing water through a hose. Put one end of a hose on a second story building and see how much water you can blow if you were on the ground. Now put the hose on the ground or level with your head and it will pretty much flow by itself. Im sure if you raise the tank above the carb you would never have the half tank lean.

kurtf5

Why is it good to make the pressure line shorter as well?

Argess

Actually,, until Twomanytoys discovered shortening the fuel line, all I ever did was shorten the pressure line, and it helped quite a bit.

Imagine an almost full tank of fuel. You are at an idle. Now you nail it. As the muffler pressure goes up, the tank pressurizes quite quickly and everything is fine.

Now imagine an almost empty fuel tank. You are at idle. Now you nail it. The muffler pressure goes up, but it takes longer to pressurize this large air space in the tank, so the engine runs lean during acceleration. In order to help reduce this, you shorten the pressure line to help get the tank pressurized more quickly.

This is a "dynamic" situation, which means something is happening as things change.

The "static" situation means somthing happens during a steady-state situation, like at WOT. The static situation, is that when there is less fuel in the tank, there is less pressure to the carb at any particular rpm, not a changing rpm. Shortening lines doesn't have any affect here as you are looking at a long-term situation.

I have always felt the dynamic situation (leaning during acceleration) was the biggest factor. This is because the static situation (fuel pressure changing with fuel level) isn't that significant, but it turns out both situaitions come into play. I had calculated out the % change of pressure between an almost full tank, and an almost empty tank, and it was around 1%, so I dismissed it. Turns out I was basing this on muffler pressure of about 6 psi, but I measured it and it was only about 1 psi. Re-calculating, the % change rose to about 7%, which is more significant. This also explains why some engines seem worse than others for half tank leaning. The engines that generate higher muuffler pressures (or pipes that have higher muffler pressures) arn't as affected as much by half tank lean.

Basically, shortening the pressure line helps reduce the leaning problem. Turns out shortening the fuel line does too. When you do both, the problem may be still there, but it is reduced so much, it is no longer noticeable.

There....more of an answer than you probably wanted, and mostly speculation on my part as I've never measured the pressure at the carb, tank, muffler, etc. at various engine speeds, acceleration, etc. Pretty hard to do with available gauges as the pressures are so small. You need manometers, and I don't have any.

saxy174

This is one very useful and easy mod. All 4 of my units have this and my temps dropped. thanks to "toomanytoys" for his findings and thanks to "argess" for his efforts as well.

This is one main reason i am on this site. To learn, create different designs and share for all to benifit from.

Thanks again you all!

canopy

When tank is full(above half), the area of fuel is big. when the tank is below half, the area of fuel is only half size. and therefore the pressure from the muffler is only working on the half area of fuel. that means that you get lower pressure in the lines.. bigger area of fuel means higher pressure.

Hordsak

Why doesn't someone remedy this, and design a micro fuel pump. Problem solved for everyone.

Argess

Hordsak: They do make them...well "regulatorss". Both CLine and IronBay. See links:

http://www.ironbaymodelcompany.com/i...es/Page438.htm

http://www.billsroom.com/pcfs/produc...uelsysdesc.htm

They also make fuel pumps, but I havn't heard good things about them:

http://www3.towerhobbies.com/cgi-bin...?&I=LXDG59&P=7

Canopy: I think you're confusing pressure and force.

twomanytoys

Some more asking on this mod.

Super Mud

My Feedback: (1)

I just got a Savage21 tank from my lhs for a replacement. I'm gonna run my fuel lines the same and see if it is better or not. Then try this mod. Yea on my truck it would go from run rich to pulling wheelies on half tank lean lol.

twomanytoys

Do this mod and it will run consistant through the whole tank.

sb13

My Feedback: (52)

Awsome mod you came up with. I'll be sure to use it when I get my new Savage. Thanks for sharing it with everyone.

twomanytoys

No problem. It works great.

sdh1391

How bout posting some pics of this mod twomanytoys. This might be a little easier to understand on how to do.

twomanytoys

I will get a pic up later today.

sdh1391

How about them pics twomanytoys.

twomanytoys

Ok here is a pic of what you need to do with the fuel lines. For the exhaust make it as short as you can but its not as important as teh fuel line. The fuel line is only about 4.5-5 inches. Turn the brass fitting facing the tank and tighten. Then run the short line fron brass fitting to tank in front of the engine. I have not noticed any effects from the engine with the line but you can put some of that heat tubing that traxxas uses on thier trucks. Here is a pic of what it should look like. I have been running both my savages every weekend like this since the beginning of this post and it has worked awsome. So here you go.

zztommis

Okay, wait a minute. In the picture, it looks like you have the fuel line wrapped through the tank lid?? I have 2 questions:
1. Why?
2. How do you fill the tank?

twomanytoys

Comon expand the picture and really look. The fuel line is not wrapped through the tank lid. Thats the pull thingy to open the tank lid. Look at the zip tie on the end. The fuel line is on the back side of that.