Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

tuning a pipe

Reply

Old 10-08-2006, 04:51 PM
  #1  
lbarnes
Senior Member
Thread Starter
 
Join Date: Sep 2003
Location: de forest, WI
Posts: 672
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default tuning a pipe

Trying to use a Macs pipe on a Mecoa 45.

This is my first pipe experience and I'm learning alot about lean, hot and burning up glow plugs. I was told at one time that the average length of the pipe should be about 9 inches from glow plug to the first hump in the pipe for a 40 size engine.

When trying this measurement the engine seems to respond nice but getting less rpm than the stock muffler. Have a 10 x 5 prop and with the stock muffler at full throttle I was getting 12000rpm. With the pipe I am getting about 9-10k.

The tuning info on the Mac's website states to start at 4" length on the header pipe for most 45 size engines.

I also notied that with the stock muffler the needle valve is open about 1.5 turns, with the pipe I opened it up about 3 turns.

Any suggestions?

Larry Barnes
lbarnes is offline  
Reply With Quote
Old 10-08-2006, 06:04 PM
  #2  
kamakazie frank
My Feedback: (2)
 
kamakazie frank's Avatar
 
Join Date: Jun 2002
Location: Sewell, NJ
Posts: 155
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: tuning a pipe

Hey Larry:

On the standard tuned pipes, my rule of thumb, for a 45 is to start at 11.5 inches from the plug and 11.75" for a 60, to the widest point on the pipe, usually were the pressure fitting is mounted. No wonder you are blowing plugs and running hot. I really think the 9 inches is way too short.

Frank
kamakazie frank is offline  
Reply With Quote
Old 10-08-2006, 08:09 PM
  #3  
lbarnes
Senior Member
Thread Starter
 
Join Date: Sep 2003
Location: de forest, WI
Posts: 672
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: tuning a pipe

Thanks for the info.

I guess the engine/header chart on the Mac's website is incorrect. I every .40 size header they suggest is from 4.25 to 3.35" in length.

I saved the pice i cut off and can add it back on using tubing.

Will give it a try and see what happens.

Larry Barnes
lbarnes is offline  
Reply With Quote
Old 10-08-2006, 09:16 PM
  #4  
johnfly
Senior Member
 
Join Date: Jul 2004
Location: Arkansas city, KS
Posts: 141
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: tuning a pipe

this info was copied and pasted right from dub jetts website..... read it and learn..... he has allllot of info on his site. hope this helps. and i hope dub doesn't mind me pasting this info from his site..... >>>>> the motor god>>>http://www.jettengineering.com/

Tuning your full tuned pipe is normally very easy if a few simple rules are observed:

Your engine must be in good condition and be timed for full tuned pipes.

You must have a good carburetor and tank system--if your engine is not running properly on its stock muffler, it certainly will not run on a full pipe.

You must have some idea of the rpm range you can expect with your chosen prop - if you think you should be turning 20000 rpm, but the engine is actually only capable of 16000, then you will surely fail to get the tuning correct.

You should do your tuning on a test bench with good fuel and plug--use at least 20% oil, which means adding 4-6 oz. to standard sport mix.

Make sure your engine is well broken in before running these tests.

Run pipe pressure, placing the tap at the front part of the largest section of the pipe (at the rear of the divergent cone). Ignore bulges toward the rear of the pipe.
Follow these steps:

Choose the propeller you wish to tune, eg. 10x6, then get a propeller with 1" more pitch, eg. 10x7. Start with the bigger prop

Determine the expected rpm range by running your engine on its standard muffler. You will very seldom obtain more than 1500-2000 extra rpm with a full tuned pipe. In the case of JETTs, where the standard muffler is also tuned, then the expected rpm increase may be only a few hundred. If the prop is very large, out of the recommended range for the JETT, then you may obtain larger than expected boosts with the full pipe. For example, a JETT .46 will not pull a 11x6 very well in its stock condition, and you may find that it turns the prop only 12000. With the full pipe, tuned properly, it turns 13500. However, the same .46 will only turn 300 more with the 10x6. (these are examples only)

Using the larger prop, install the pipe at its longest length (nothing cut off) and run the engine up to peak. (peak is where the engine will not go any faster when you continue to screw in the high speed needle--it sags and drops off rapidly) open the needle rapidly after peaking to avoid hurting the piston and liner. Record the rpm. Let the engine cool. Cut the pipe or header by 1/2" (12 mm) and repeat the test. The engine rpm should increase. Cut the header again, and repeat the test. Continue at ever decreasing amounts cut off until the engine does not pick up any more rpm, or it actually drops off slightly. At this point, your system should be tuned for the size smaller prop, as you have cut off the pipe too much for the larger prop.
This method is not foolproof, but will work well if all other systems are in good shape. You are looking for a system that will run smoothly as you advance the throttle. Pipes that are too short have difficulty "jumping" up on the pipe and will struggle, overheat and blow plugs when operating at full throttle--use smaller props until the engine stays on the pipe, even at rich settings. If you are blowing plugs, something is wrong--look!!!!!!

Pipes that are too long show little or no jump when coming on the pipe, ie., they are always on the pipe. This jump is usually at about 2000-3000 rpm below peak. Eg., as you advance the throttle slowly to, say, 12000, the engine suddenly jumps to 13500 and will not run steadily between 12000 and 13500. The amount of jump determines the boost of the system. The more boost, the more problems you will have.

Try to keep the "jump" or boost to a minimum while producing the power you need.

JETT engineering 9-16-98

If you have any questions, feel free to call or email us. When in doubt, check it out!


Send your email to techsupport@jettengineering.com
johnfly is offline  
Reply With Quote
Old 10-08-2006, 09:27 PM
  #5  
combatpigg
Senior Member
My Feedback: (3)
 
combatpigg's Avatar
 
Join Date: Nov 2003
Location: arlington, WA
Posts: 19,891
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: tuning a pipe

First you get a baseline reading with open exhaust. Be prepared to start out with the NV opened up alot. If the venturi is too big, then you would need to use a bladder feed or pressure tap to get adequate fuel draw. The open exhaust reading is your benchmark, the reading through the stock muffler is meaningless, unless it is a very well designed muffler. If you know what the practical RPM limits of your engine are [usually stated by the manufacturer], then you can approximate which prop you want to tune the engine for. I would say 90% of your .45 sized applications would do well with a 9x7 or 9x8 prop. MACs says to chop 1/4" off the header at a time until no improvement is noticed. The extra boost of power will also require you to shim the head or open up the chamber slightly if you are blowing plugs every run. No way is the header 9 inches long or longer on a .40-.50 sized setup.
combatpigg is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service