jdoug

I just wanted to start a thread on how people tune and find the right pipe length. One question I have is if your engine isn't revving up like it should, then how does one know if the pipe length is the culprit or it just needs some tuning. On my WT .18 I just put my pipe length to 8.5 in. to the convergent cone and tuned from there. I got that measurement from Ron O. Yes, it screams, but, how do I know that's all I'll get? I suppose I could buy another header and start over with an engine that seems to be tuned in. Another question would be...If I change my pipe length wether its longer or shorter, on an engine that's tuned, would I have to retune with the new pipe length?

Dan S

Here's some info:

A SHORTER PIPE LENGTH WILL RAISE THE R.P.M. or more exactly it will raise the RPM point where maximum power is produced.

A LONGER PIPE LENGTH WILL LOWER THE R.P.M. or more exactly it will lower the RPM point where maximum power is produced



Adjustment
1. Fix the manifold and pipe in position at the length required for your engine, making sure that there are no steps or leaks in the manifold to engine joint.
2. Run the boat on the normal propeller and set the needle valve for the best straight-line performance.
3. Turn the boat in 90-degree turns. If the motor loads or slows considerably then the pipe length is too short or the propeller is too big. If the motor slows a little or not at all then shorten the manifold slightly or try the next size up propeller
4. Shorten or lengthen the manifold until the best balance in performance is obtained between turns and straight-line speed.

This information can be found here: http://www.nimrifmodels.co.uk/setup.html

Dan.

Sean Bowf

Do you own a GPS you can run in the boat?? If so, do you have a little room between your header and pipe?? Mark the pipes length in some way, so you know where it is now. Run the boat a couple times and write down the speeds you are getting. Now lengthen the pipe just a little (quarter inch or so), and run it again. See if the boat sped up or slowed down. If it slowed down, go the other direction (shorter) and run it again. I would think that different props, hull styles, etc, would tune in at different pipe lengths (need a different balance between the RPMs you get with a shorter tune, and the power you get with a longer tune). I am running a little shorter tuned length than you are with my .18 CVRM. Not saying my pipe length is optimal, or would work for you, but you might want to try it a little shorter. When possible, I cut the header instead of the pipe, because headers are cheaper than tuned pipes. So if I do mess it up (go too short) it is just a matter of buying another header.

EDIT: By tuned length, I am talking about measuring from the center of the glow plug down the center of the header and pipe, to the widest part of the pipe. I know I have seen at least one other person refer to the physical length of the pipe by itself. I don't think you can go by this because...as an example, the MV has at least 3 different header lengths I have seen. The version 1, Version 2, and one you buy by itself.

Sean

Hesco Racing

Before saying go shorter or longer on the tune length it must be understood what is actually happening when you change this.

moparbarn

if it MUST be understood, then why didn't you explain it? pressure waves, convergent cones, divergent cones........ who cares, unless you are building pipes or are a tech freak. as long as you know what longer and shorter cause, then it's all good. the info given here is good, and all you REALLY need to tune a pipe. you may have to try a few different pipes to find what works for your setup, driving style, and boat. two "identical" boat/motor combos may not like the same pipe, in the hands of different drivers. just another excuse to go burn more nitro!

Pete48

I think Dan hit the nail on the head. Funny, the first tuned pipe was actually an accident. I remember reading an article where an old fashioned motor cycle had crashed. During the crash, the exhaust bent, creating a shorter pipe. The shorter pipe created more power at a higher RPM and the cyclist had more top end.

I am not an expert, but apparently the exhaust pressure wave hits the end of the pipe and travels back to the combustion chamber to "stuff" more mixture in. Unfortunately, the pipes are only tuned for ONE specific RPM. Not a bad thing for our boats I guess since we run WOT all the time.

I believe CVEC or some RC car company tried to create a pipe with a spring such that the back pressure was adjusted, but I don't know if it worked or not.

kevinsburns

Tuned pipes don't turn on and stay on, they have low and max rpm ranges.

The short pipe is for low end power. A short pipe is short so the sound wave has a shorter distance to travel back to the engine so a short pipe will come on at lower RPM and turn off sooner too, top end suffers because the short distance and higher RPM the pipe becomes ineffective and out of time/tune.

A longer pipe the sound wave takes longer to get back to the engine thus the pipe comes on at higher RPM and stays on longer, low end suffers because the longer length is out of time/tune for the lower RPM.
Short is low end power good for short race courses
Long is top end power good for long race courses where you wouldn't want the pipe to pipe out too soon.
Back in the day we had pipe sliders that adjusted the length in sync with the throttle. Off throttle the pipe would be at the shortest length for low end power, and as the engine was throttled up the pipe would lengthen for top end.
Pretty much like the ceeva pipe someone else mentioned except the sliding pipe the whole pipe slid using a ceramic slider
Sealed, also a myth. The raw glasses that the sound wave forces back into the engine just before TDC hangs out at the exhaust port and never really enters the pipe, only the hot oil goes into the pipe so the sound wave doesn't care if it's sealed or not 100% the sound wave will force the glasses back in.
People do play around with the stinger to fine tune a pipe too. A pipe that's slightly larger someone will ventury down the stinger to help keep pipe pressure up to scavenge the hot oil from the engine.

1QwkSport2.5r

You have it backwards. Short pipes are for high rpm and long pipes are for low rpm. The higher the rpm the faster the pressure wave travels. If load is too high (rpm too low) for the pipe length, it won’t get on the pipe. If the load is too light (rpm too fast) for the pipe length, it’ll get on the pipe early and fall off early. When tuning a pipe, usually one will start out long and work shorter in small increments until no gain is had. This is your ideal setting for the given load. Anytime the load is changed (prop size up or down), the pipe length must be changed. A lighter load will require a shorter system. A higher load a longer system. (Sometimes adding one or two sections previously removed can be reinstalled in the coupler to add the necessary length.

A friend of mine is a tuned pipe guru. I usually ask him his advice on a starting point for pipe length, but I know there are basic rules of thumb that will get you started. What those are escapes me at the moment.