R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Nitro Off-Road

Reply
 
Thread Tools Search this Thread
Old 09-18-2009, 07:18 AM   #1
Tech Rookie
 
Join Date: Aug 2009
Posts: 16
Default Fuel pressure question

Does exhaust from the pipe soley provide fuel pressure, or is there any vacuum generated by a running engine that also sucks in the fuel? I'd figure that if I open the tank to refuel, the engine would stall because loss of pressure but it doesnt?
un4gvn is offline   Reply With Quote
Old 09-18-2009, 07:27 AM   #2
Tech Elite
 
Zerodefect's Avatar
 
Join Date: Apr 2008
Location: Underground, Ohio
Posts: 4,305
Default

Yup, it has vacuum.
Zerodefect is offline   Reply With Quote
Old 09-18-2009, 08:28 AM   #3
Tech Regular
 
coviello's Avatar
 
Join Date: May 2009
Location: goshen ny
Posts: 357
Trader Rating: 6 (100%+)
Default

its a little of both. more of the pressure though
__________________
Barnstormers RC - Mugen Seiki - Hitec - EB Mods - Pro-line Racing - Lucky 7 RC

"Plug and play, Is not the way"
coviello is offline   Reply With Quote
Old 09-18-2009, 09:36 AM   #4
Tech Elite
 
mblgjr's Avatar
 
Join Date: Sep 2006
Location: AL
Posts: 2,173
Trader Rating: 86 (100%+)
Default

A good engine needs very little fuel pressure at all.

And unless you're already running excessive pressure or have a worn sleeve; the engine won't stall just because you leave the lid up.
__________________
Team Associated Reedy JConcepts.net FusionX USA
mblgjr is offline   Reply With Quote
Old 09-18-2009, 09:55 AM   #5
Tech Elite
 
Join Date: Mar 2009
Location: Aurora, Colorado
Posts: 3,644
Default

And engine NEEDS the pressure lie from the pipe, If not it will not run.
__________________
TLR - Spektrum - Horizon - TLR 8ight 4.0 - TLR 8ight-T 4.0 - TLR 22 4.0 - Orion
token is offline   Reply With Quote
Old 09-18-2009, 10:10 AM   #6
Tech Elite
 
Zerodefect's Avatar
 
Join Date: Apr 2008
Location: Underground, Ohio
Posts: 4,305
Default

You can tune them to run without the pressure line. Its more of a tank breather than a psi line. Did it all the time with airplane engines. There really isn't much pressure in that pipe. Allthough the engine is desighned to have a pressure line, my cars run decent with the tank open for a little while.

Quick test for fun, remove your pipe. put a 2' fuel line on the pressure tap hold it like a U, kinda like a sinks trap with the open end if the line going vertical. Fill pressure line patially with water so that both sides of the U have plenty of fluid in them.

Blow into the pipes inlet, notice how much that water moves. If the water moves up your fuel line about 1.5-2" thats close to 1 or 2 once of pressure.
Google "manometer" to see how this works.

You can try this on your car as well to see exactly what pressures you have when the engine is running. It ain't much.
Zerodefect is offline   Reply With Quote
Old 09-18-2009, 10:20 AM   #7
Tech Elite
 
PTP Racing's Avatar
 
Join Date: May 2003
Posts: 2,699
Trader Rating: 2 (100%+)
Default

I view it like this. The pressure from the pipe is like the accelerator pump in a real vehicle carb. At idle your engine is tuned to run on very little pressure since the pipe pressure is relatively low at idle. As soon as you start opening the throttle and rpm rise the pressure in the pipe also rises increasing fuel flow to the carb. I think this also has a lot to do with why different pipes run so differently on the same engine.

If your engine stalls when the lid is open you are way too lean on the bottom end and if you have a problem stalling after a fuel stop you are too rich on the bottom end.
__________________
Paycheck to Paycheck Racing
Jason Miller
PTP Racing is offline   Reply With Quote
Old 09-18-2009, 11:53 AM   #8
Tech Master
 
scwrod's Avatar
 
Join Date: Apr 2008
Posts: 1,421
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by token View Post
And engine NEEDS the pressure lie from the pipe, If not it will not run.

This is not 100% true.
I ran my GT2 w/ DPS.12 with no pressure line
__________________
hbracing.com tritonrc.com raceaka.com
scwrod is offline   Reply With Quote
Old 09-18-2009, 12:02 PM   #9
Tech Elite
 
Join Date: Mar 2009
Location: Aurora, Colorado
Posts: 3,644
Default

Quote:
Originally Posted by scwrod View Post
This is not 100% true.
I ran my GT2 w/ DPS.12 with no pressure line
ok
__________________
TLR - Spektrum - Horizon - TLR 8ight 4.0 - TLR 8ight-T 4.0 - TLR 22 4.0 - Orion
token is offline   Reply With Quote
Old 09-18-2009, 12:34 PM   #10
Tech Elite
 
Zerodefect's Avatar
 
Join Date: Apr 2008
Location: Underground, Ohio
Posts: 4,305
Default

Even though two strokes don't have much vacuum, the venturi effect of the carb also has the ability to draw fuel from the tank.
Zerodefect is offline   Reply With Quote
Old 09-18-2009, 12:46 PM   #11
Tech Addict
 
Jesse Robbers's Avatar
 
Join Date: Aug 2001
Location: Cincinnati, OH
Posts: 600
Send a message via AIM to Jesse Robbers
Default

Our r/c 2-stroke engines don't need the pressure line to run. I use to run my 1/10 gas truck without a pressure line all of the time. It made the throttle super smooth and a lot more linear/easier to drive. You need to run a pressure line from the tank's lid and secure the other end of the line (that normally goes onto the pipe) but position so when the car is upside down the end of this lins is above the bottom of the tank so fuel doesn't spil out when you're upside down. The take a 1" or so long piece of tubing, put it on tank with a screw or some plug on the end of it. Richen motor top & bottom between 1/4-1/2 turn and good to go. You do lose the ability to prime the engine/fuel line which can cause problems for re-starting after flameouts. If engine is super hot/vapor lock, it might not start/draw the fuel.
__________________
Sponsored by: O.S. Speed, KO Propo, Sidewinder, Tekin, Thunder Power, Lunsford, Skipgear.com, Fioroni, Avid R/C, GMK Supply, Competition Heat, Dialed Inc., LiveRC.com, DE Racing, CIG2O, ANDROID Nitro Runtime Calculator App
Jesse Robbers is offline   Reply With Quote
Old 09-18-2009, 12:52 PM   #12
Tech Elite
 
allan42r's Avatar
 
Join Date: Jun 2008
Location: OSWEGO IL.
Posts: 2,602
Default

yep no pressure line was a hot setup on the gas trucks "back in the day"lol
__________________
Pinky kisses better than mason's mom
allan42r is offline   Reply With Quote
Old 09-18-2009, 12:54 PM   #13
Tech Elite
 
allan42r's Avatar
 
Join Date: Jun 2008
Location: OSWEGO IL.
Posts: 2,602
Default

Quote:
Originally Posted by token View Post
And engine NEEDS the pressure lie from the pipe, If not it will not run.
wronge
you lose
you get nothing
good day sir!
lolololololol
__________________
Pinky kisses better than mason's mom
allan42r is offline   Reply With Quote
Old 09-18-2009, 12:54 PM   #14
Tech Elite
 
R/C Lidz's Avatar
 
Join Date: Dec 2003
Location: Clayton, NC
Posts: 2,696
Trader Rating: 53 (100%+)
Send a message via MSN to R/C Lidz
Default

Jesse thanks for posting, empirical data from pros is priceless on an ordinarily not-so-certain forum.


Kinwald also used to run his Losi's without a pressure line to the engine.
__________________
Josh Langness
RC8T/ OS Speed/ 2060
RC8/ OS Speed/ 2060
FTGT/ MT12
BLitZ/ Castle SCT
R/C Lidz is offline   Reply With Quote
Old 09-18-2009, 01:27 PM   #15
Tech Elite
 
Join Date: Mar 2009
Location: Aurora, Colorado
Posts: 3,644
Default

Quote:
Originally Posted by allan42r View Post
wronge
you lose
you get nothing
good day sir!
lolololololol
ok - if you are a racer are care about performance - YOU NEED THE PRESSURE LINE -

If its not needed why is it there, why does it make such a huge difference in tuning. I have worked on way to many engines solving problems and it turns out it would not stay running becuase the line had a whole or the nipple on the pipe was broken.

Go head take your 1/8 to the track a TRY to run with out that line. better yet try to start with out the line. I will be here Monday to hear the results. - until then ladies
__________________
TLR - Spektrum - Horizon - TLR 8ight 4.0 - TLR 8ight-T 4.0 - TLR 22 4.0 - Orion
token is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Fuel consumption question. charlesd Onroad Nitro Engine Zone 12 10-18-2007 04:33 AM
Need help with no fuel pressure problem pumpkinfish Nitro Off-Road 12 08-05-2007 09:44 AM
fuel pressure problem 32819toon Onroad Nitro Engine Zone 17 05-06-2007 07:19 AM
I got a Question. NS[]D[]RT Rookie Zone 31 09-02-2005 06:25 PM
Question for parking lot basher running belts... puma1824 Nitro On-Road 17 04-01-2003 05:30 PM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 08:42 AM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net