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Old 01-26-2011, 08:39 PM   #1
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Default Exhaust tubing length

hi,
just wondering: i've heard that using longer length of tubing from pipe to tank is equal to having a 'exhaust/boost' chamber between the pipe and tank.

if it's true, what length of tubing is required to be equal to a boost chamber?

what's the effect of having a too long of the tubing? what length is considered too long or too short?
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Old 01-26-2011, 08:45 PM   #2
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long tubes will give you more torque at low revs but they tend to create lots of back pressure at high revs and you lose torque there.
opposite applies to short tubes.
i really don't know what length they should be. i don't even own a nitro car yet but i do know that length is important and if you go too much or too little, the engine simply won't work.
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Old 01-26-2011, 09:59 PM   #3
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Using a longer exhaust tubing doesn't really make the effect of the cooler or boost thing you talk about, the only reason I can think of (in on-road racing) is having a loop of that tube around the tank lid so that during refuelling the fuel doesn't make its way up there and then cause the engine to run lean when it goes through a turn - because of the force in the corner, the fuel in that tube pulls its way out, effectively making a vacuum in the tank instead of keeping it pressurised.
Understand what Im trying to say here? I hope it didn't confuse you
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Old 01-26-2011, 10:30 PM   #4
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ooops! i think i misunderstood the question. i thought the OP meant the actual length of the exhaust pipe. My bad
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Old 01-27-2011, 12:48 AM   #5
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The longer the fuel line the lower the pressure into the tank (resistance), You have to re-adjust the engine what will result in other characteristics.

Finally what we have seen is that short lines will give a faster responding engine.
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Old 01-27-2011, 01:12 AM   #6
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Originally Posted by Roelof View Post
The longer the fuel line the lower the pressure into the tank (resistance), You have to re-adjust the engine what will result in other characteristics.

Finally what we have seen is that short lines will give a faster responding engine.
so is there any 'optimal' length? better to have a short length with pressure chamber or just longer length? any difference?
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Old 01-27-2011, 03:44 AM   #7
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Quote:
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so is there any 'optimal' length? better to have a short length with pressure chamber or just longer length? any difference?
The difference would be very slight.
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Old 01-27-2011, 03:50 AM   #8
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Quote:
Originally Posted by NitroWD View Post
so is there any 'optimal' length? better to have a short length with pressure chamber or just longer length? any difference?
I heard 15cm is the optimal length.

I dont know the reason why 15cm.
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Old 01-27-2011, 03:50 AM   #9
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Quote:
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The difference would be very slight.
Depending the fueltube and the length. Some tubes have a 1.8mm hole and others 2.4mm and a short 10cm tube or wraping arround the car first to get 30cm does make a difference. What is ideal? I do not know. One thing I do know is that a lower pressure can give a much leaner bottom end without bogging what can give longer runtimes.

The same effect can be get using an exhaust cooler with an attached needle to adjust the pressure.
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Old 01-27-2011, 01:27 PM   #10
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guy at a LHS who is a pretty good tuner once said that the general rule is 1.5 times the length of the exhaust for the pressure line ... i think it was just the chamber.

I've been roughly going off that ever since and everything has been running alright.
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Old 01-27-2011, 01:48 PM   #11
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Originally Posted by NitoriousRC View Post
guy at a LHS who is a pretty good tuner once said that the general rule is 1.5 times the length of the exhaust for the pressure line ... i think it was just the chamber.

I've been roughly going off that ever since and everything has been running alright.
Does he has an explenation why? I wonder if there is some scientific background.... Also with which size of hole in the tube.
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Old 01-27-2011, 02:36 PM   #12
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Default pressure line length

I have tried short and long fuel tubing length and I never could tell too much difference. However I could tell a difference between the medium and large diameter tubing.

I have always run large diameter on my car for between the tank and carb and between the pipe and tank.

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Old 01-27-2011, 03:16 PM   #13
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I don't think there is a general ideal fuel tube length.
Fast motors normally put more pressure on the exhaust system.
Also it can be used as a tool to make runtime, and make an engine fit the drivers preferences.

Normally I always try to go as short as possible because I like an engine which reacts almost instant since I also steer the car with throttle input.
But with the engines I'm running recently I had to lengthen the pressure system quite a bit (30cm of tubing + RB cooler) to reduce the pressure.
The pressure was so high it lifted the fuel tank lid by just blipping the throttle.
Took me some time to figure that one out.
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Old 01-27-2011, 10:52 PM   #14
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Quote:
Originally Posted by Roelof View Post
Does he has an explenation why? I wonder if there is some scientific background.... Also with which size of hole in the tube.
Nope, i think it's a general "rule of thumb" thing.


I've read here people talking about the pressure chambers ,,,, i take it thats the same as the thing i call a fuel cooler yeah??

Will they add extra pressure?

Mate has a big one on his and the other week he gave it a few little revs whilst i was refueling and gosh it was blowing fuel all over the place!! Had to get him to cut the throttle
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Old 01-28-2011, 12:37 AM   #15
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No, most coolers are just small pipes with cooling ribs and has no chamber.

A pressure chamber is a larger room and has as function to flat out the pressure peak pulses making the pressure more constantly.
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