Bus Conversions dot Com Bulletin Board
September 02, 2014, 02:47:30 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
News: If you had an E-Mag Subscription: It arrives at least two weeks before the First Class printed magazine.
   Home   Help Forum Rules Search Calendar Login Register BCM Home Page Contact BCM  
Pages: [1]   Go Down
  Print  
Author Topic: smoke at full power  (Read 1866 times)
bevans6
Hero Member
*****
Offline Offline

Posts: 4600


1980 MCI MC-5C




Ignore
« on: December 06, 2012, 05:29:15 AM »

My ex-military 8V-71T has oodles of power, but does smoke solidly at full power.  I can make/not make smoke like turning a switch on and off.  It has N80 injectors, so it's really just an over-fueling condition.  I could change injectors, but that's expensive and these are fresh. I could probably put a turbo on that puts in more air, but that's expensive too.   My question is - does the engine make more power while it's over-fueling and smoking, or is there a plateau that you reach where the extra fuel is wasted and doesn't result in more power?  If that's so, then I can do a poor-mans fix by installing a throttle pedal stop that just doesn't let the engine get the extra bit of pedal that results in the smoke.

Brian
Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
Utahclaimjumper
Hero Member
*****
Offline Offline

Posts: 837




Ignore
« Reply #1 on: December 06, 2012, 05:56:56 AM »

 An easy "fix" is to route the exhaust out the lower left side so you can see it and adjust your foot,, excessive smoke is dollars out the door with little increase in power.>>>Dan
Logged

Utahclaimjumper 
 EX 4106 (presently SOB)
Cedar City, Ut.
 72 VW Baja towed
luvrbus
Hero Member
*****
Offline Offline

Posts: 12329




Ignore
« Reply #2 on: December 06, 2012, 06:51:18 AM »

That is a military turbo it was designed to run full throttle with the 80 injectors change the turbo to a TV 8511 with a A/R of 120 to .99  The.99 A/R will get you out of the gate faster with less smoke but will cost a little on top end in torque  

If you don't want to change to 70's injectors adjust your settings reducing the fuel also check the drive ratio on the blower there are 3+ drive ratios and 15 different blowers and I have no Idea what you have it is a real simple process on a 2 stroke match the air with fuel and no smoke


good luck
« Last Edit: December 06, 2012, 07:02:08 AM by luvrbus » Logged

Life is short drink the good wine first
lostagain
Hero Member
*****
Offline Offline

Posts: 1526


MC5C




Ignore
« Reply #3 on: December 06, 2012, 06:53:08 AM »

All I know is that from empirical experience, I can feel a plateau somewhere around when it starts smoking. So say going up a hill, when it starts smoking, I pull my foot back a little and I still get the same power. If I pull back a little more it will fall off noticeably. So I still don't know exactly where it is. It is mostly a feel for it and being familiar with your bus thing.

There you have my non scientific definitive answer...

JC
Logged

JC
Invermere, BC
1977 MC5C, 6V92/HT740
Len Silva
Hero Member
*****
Offline Offline

Posts: 4084


Angle Parked in a Parallel Universe


WWW

Ignore
« Reply #4 on: December 06, 2012, 09:09:47 AM »

The solution is simple (applies to life as well as buses):  If you do something that has an unwanted reaction, stop doing it.
Logged


Hand Made Gifts

Ignorance is only bliss to the ignorant.
gus
Hero Member
*****
Offline Offline

Posts: 3507





Ignore
« Reply #5 on: December 06, 2012, 01:03:55 PM »

The best gage for a DD when climbing a grade is to add power until there is no acceleration, then you know you have all you can get in that gear. Any more throttle will take more fuel for no more power and probably smoke.
Logged

PD4107-152
PD4104-1274
Ash Flat, AR
roger dolan
Newbie
*
Offline Offline

Posts: 32




Ignore
« Reply #6 on: December 06, 2012, 05:05:54 PM »

In the days of the first diesels the practice was to have a mirror so that you could see the exhaust pipe. If she was smoking to much you eased off alittle till there was just a wisp of smoke, that was all you were going to get. now if you wanted to impress the other drivers ,keep it floored and you might get a foot of fire, if you werent paying the fuel bill that would ok.   
       
                                                                                                rd4106 
Logged
TomC
Hero Member
*****
Offline Offline

Posts: 6751





Ignore
« Reply #7 on: December 06, 2012, 10:32:53 PM »

The last on highway version of the 8V-71TA (aftercooled) from Detroit used 80 injectors for 400hp with 1200lb/ft torque-so the injectors are not to big. Quite possibly-when you have smoke at the top end, it usually means you're not getting enough air. Maybe you're air cleaner isn't big enough. Try running it for a short drive without the air cleaner and see if you still get smoking. That will answer whether you have a big enough air cleaner, or need a bigger boost from the turbo.  Good Luck, TomC
Logged

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
robertglines1
steam nut
Hero Member
*****
Offline Offline

Posts: 3994





Ignore
« Reply #8 on: December 07, 2012, 06:42:22 AM »

Tom: you just might have hit it!  did the air supply increase match the increase supply demand over original engine.     Sometimes simple slips right by.  I have misses the little-major things before.   Bob
Logged

Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
Sam 4106
Hero Member
*****
Offline Offline

Posts: 645





Ignore
« Reply #9 on: December 07, 2012, 06:48:55 AM »

There is also a possibility that you aren't getting enough air because the stock bus air intake into the filter isn't large enough for your turbo'd engine. I had to cut a hole in the side of our MCI 8 for that reason. Thanks to Fred Hobe for that solution. Do you have a filter minder in the intake? That might tell you something, if you have one or install one.

Good luck, Sam
Logged

1976 MCI-8TA with 8V92 DDEC II and Allison HT740
luvrbus
Hero Member
*****
Offline Offline

Posts: 12329




Ignore
« Reply #10 on: December 07, 2012, 07:12:02 AM »

Ok guys the the 8v71 without some type air cooler never came with 80 injectors fwiw and the liner port height also comes into play along with cfm on the air cleaner,exhaust and the exhaust temperature in short he has work to do but he will figure it out

 He is never going to stop the excess smoke with his present setup if he left the pre heater in the engine it will need to be removed he is dealing with a military engine

CFM

1300 cfm air cleaner
3000  cfm for exhaust
850 to 900 degrees exhaust temperature 

good luck
« Last Edit: December 07, 2012, 07:18:54 AM by luvrbus » Logged

Life is short drink the good wine first
TomC
Hero Member
*****
Offline Offline

Posts: 6751





Ignore
« Reply #11 on: December 07, 2012, 08:30:47 AM »

When I turbo'ed my 8V-71, I also had smoking problems at full throttle. After measuring things, I changed my 6" intake to a 7" intake with a new air cleaner. I measured the opening on the side of the bus for intake and discovered it wasn't big enough. I added a 8"x4" vent that brought it up to the correct sq/in of opening required. Good Luck, TomC
Logged

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
bevans6
Hero Member
*****
Offline Offline

Posts: 4600


1980 MCI MC-5C




Ignore
« Reply #12 on: December 07, 2012, 03:46:54 PM »

I have about the largest Eco air filter that will fit. From memory it is 7" in, 7" out and 1600 CFM.  I think that Clifford is right, it is mostly the turbo, I was told it wouldn't work well from the start.  I do still have the stock MCI exhaust system, that might get upgraded.   What I saw was that I could pull monster hills without smoke (or without military grade smoke, put it that way...) by just holding a steady throttle pedal, you could really hear the engine take up the load and it would pull a 6% to 9% grade (Buswarrior knows the roads I am talking about) without serious smoke, but it was hard to modulate, easy to give it a little too much, hence the down-rate with the throttle stop idea.  At the end of the day I will probably change the turbo, since I know it's not right and I get this itch to do things right...  This is in a 26K lb MC-5C, so it's a little light weight for 400 rated HP.

Thanks for the ideas, I'll keep thinking on this - winter here, no bus for me!   Grin

Brian
Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
lostagain
Hero Member
*****
Offline Offline

Posts: 1526


MC5C




Ignore
« Reply #13 on: December 07, 2012, 07:45:38 PM »

Tom C is right about not enough air. I have the same problem I will address after new year. You, like me, have to find out what is the right turbo that will feed enough air to satisfy the injectors. How much boost are you seeing? I am only getting around 10 psi, and  I can really roll on some coal by stepping on it. So the right turbo should produce some power without too much smoke.
JC
Logged

JC
Invermere, BC
1977 MC5C, 6V92/HT740
Scott Bennett
Scott & Heather MCI-9
Hero Member
*****
Offline Offline

Posts: 1273


Scott & Heather


WWW

Ignore
« Reply #14 on: December 09, 2012, 08:26:38 PM »

Another vote for TomC on this one. We ended up cutting a hole in the body where the intake for the filter housing was. Made a noticeable difference.


Sent from iPhone via Tapatalk
Logged

Scott & Heather
1984 MCI9 6V92-turbo with 9 inch roof raise & conversion in progress.
http://www.scottmichaelbennett.com/p/our-bus.html
˙ǝɯoɔlǝʍ suoıʇɐuop ˙snq ʍǝu ɐ pǝǝu ʎlqɐqoɹd ll,ǝʍ 'sıɥʇ pɐǝɹ uɐɔ noʎ ɟı
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.18 | SMF © 2013, Simple Machines Valid XHTML 1.0! Valid CSS!