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Author Topic: Can a 8-71 get too much air??  (Read 1959 times)
Larry B
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« on: April 15, 2013, 08:45:32 PM »

   I have an 8-71 non turbo in an MCI-5b. Last summer I added a set of trial air scoops to the air intake for the engine rads. These where made of several leftover pieces of aluminum . They where made in a hurry and not to pleaseing to the eye, but they did seem to help with my overheating issue. I am in process of making new ones (one piece) and then paint. On the driver side the air intake to the engine blower is throught the same screen as the air to radiator. This air scoop thing got me to wondering if a smaller scoop at the front of the screen to help the air make the 180 degree corner to get started into the suction side of the engine blower would help engine performance when the bus is in motion. The inlet to the blower is 2"x2o" in the wall of the bus and I plan on making the blower scoop about the same size. Half the air scoop would be on the out side of the screen and half on the inside to make 180degree corner.  Is this a good idea or a bad one? Can I push too much air into the suction side of the blower? (non turbo engine)
     While I have the attention of the two stroke people I have one more question. After I got back my first engine oil analyisis back after rebuild it warned of high silicone content and listed possible causes as plugged air filter and gasket sealant.Air filter was not plugged and no holes. I did use silicone as a sealing agent on gaskets and I am hoping that is all it was. But the mechanic at the shop that sent the sample away for me suggested I check the blower intake gaskets for leaks. To check he said start the engine, leave it idle. and spraay starting fluid around the blower intake and listen for increase in engine rpm. RPM increase = leak . Is this a common and safe thing to do? I would thik you would not want your engine smoking hot and use either sparingly. I have not heard of this check before, I do not post often but have read for  over two years. Would it be ok to try? Thanks again for all your time and patience. 
             Larry B
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1977 MCI-5B---
8V71- 4speed man
hargreaves
1987 MCI 102A3
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« Reply #1 on: April 15, 2013, 09:08:06 PM »

The more air you can feed that sucker the better, you will probably have to be going about 100 miles an hour to do any good though.    Cheers , Gerry
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now as of Feb 2012 series 50 B400  . Sunshine Coast British Columbia
Lin
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« Reply #2 on: April 15, 2013, 09:20:55 PM »

Yeah, but if you were going 100 mph, you'd be using all that extra air just to keep going.

I just added some scoops to my 5a as per Fred Hobie's website.  I can't say yet if they will do any good since it is not hot.  I did find that making a jig to keep the rear doors open a bit did reduce hear.  I also think that adding a full width flap behind the rear wheels helped too.  I know that there are some very skilled people that do not like these kind of fixes, but they look like they work to me.

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You don't have to believe everything you think.
wg4t50
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« Reply #3 on: April 15, 2013, 11:25:51 PM »

A couple points,
1-I never use ether, perfer carb cleaner, much less damageing
2-No such thing as too much air
3-The later plumbing setup works much better than the origional on my MC7, where the origional ran both thermostat outlets into one box on top, from there a line to each radiator, the newer setup uses each thermostat outlet ran to A radiator with a small balance line between the radiators, this puts the equal amount of hot water into each radiator, the origional setup had the majority using the left radiator, the right side did much less cooling as it had a longer distance to flow/more restrictive, less cooling flow.
FWIW
Dave M
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MCI7 20+ Yrs
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niles500
Niles500
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ROSIE




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« Reply #4 on: April 15, 2013, 11:52:47 PM »

No such thing as too much air (O2) let the puppy breathe  Grin
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bevans6
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« Reply #5 on: April 16, 2013, 05:28:30 AM »

The scoop won't make a difference to the engine one way or the other, although a little dam right ahead of the air intake might.  That part of the bus is a high pressure area, and air tumbles in to the cavity that is the air intake to the radiator and where the air intake to the engine draws from.  A little dam, maybe 1/2" tall, will encourage that tumbling a bit.  A scoop at the rear of the area will tend to retain the air in the cavity and create a little higher pressure there. 

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
lostagain
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« Reply #6 on: April 16, 2013, 07:15:38 AM »

My 5C came with rad air scoops from the PO. Ugly IMO, looks like an old tired church or sports team bus. I removed them after a while and found no difference in running temp. My bus has, from the factory, a lip about 1/2" tall along the front of the rad openings. I don't see that it serves any purpose other than to help air flow into the cavity toward the rads. Do all 5s, 7s, 8s and 9s have that?

What will make a difference is the smaller pulley for the cooling fans, and bigger said squirrel cages to move more air through the rads. IIRC, that set up comes from an MC9. I don't remember the size, but could measure if you want.

I also removed the pan at the bottom right of the engine, for better air circulation down to the ground. There was none on the left. And have a full width flap between the wheel mud flaps. For really hot weather, I have a piece of wood and a bungee cord to keep the engine doors open.

I also installed a 8" diameter hose from the air filter to an opening high on the side of the bus just below the roof line. The purpose of that is to suck in less dust into the filter. Works quite well. We live on a dirt road that is either muddy or dusty.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
Ed Hackenbruch
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« Reply #7 on: April 16, 2013, 07:54:27 AM »

JC, my 5A doesn't have a lip in front of the radiator intake.
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
Ed Hackenbruch
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« Reply #8 on: April 16, 2013, 08:23:09 AM »

Just looked at the pics from the rally and the other 2 5As that were there don't have the lip either,....one of them does have the scoops at the back though.
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
treeplanter
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« Reply #9 on: April 16, 2013, 09:47:09 AM »

I too am in the process of expeirimenting with air intake on my 8V-71, i have a old squirrel cage fan from a 12v. heater i took apart i was planing to install it in the air intake hole ahead of the filter and see what it would do, my bus wont start without a burst of starter fluid when cold and even with the block warmer on, many miles on her i guess, dont have $20,000 to rebuild the Detroit D.
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Timothy
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« Reply #10 on: April 16, 2013, 10:22:00 AM »


I do not have a MCI. I have an Eagle. But I will attempt to answer your questions based upon my experience.

I think you need a little clarity.

Unless you have a turbo, you are not "pushing" air into the blower. The blower "sucks" air.
A larger intake than was designed for your engine probably won't do anything for you.
If later, you add a larger turboed engine, you will need greater air capacity.
Make sure your filtration is functioning correctly. keep it clean and make sure it doesn't leak downstream of the filter.
Silicon indicates dirty air.
The mechanic gave you some good advice. However; as pointed out, ether is pretty volatile. Use some other accelerant
like wd40. It won't take much. Be very sparing with it. If you have a leak the engine will rapidly accelerate on a very small
bit of spray. It would be nice if mechanics issued some caveats with their advice.

IMO, The addition of air scoops do nothing but dirty up the coach. Theoretically, they are needed most when the greater
power is needed. That would be at lower speeds when the engine is using greater horsepower. You would be too slow to
get any ram air benefit. If you are going fast enough to generate any ram air, you are cruising at a reduced horsepower
and would not need additional air circulation.

Most of us went through the same learning curve.

The engineers turned out a vehicle to do the job intended. It was state of the art for the intended purpose and time.
It was very different from what we as converters want.
If we wish to do our will with their design, we must make some concessions concerning weight and performance.
If we are unable to accept those principals, we must spend a lot of money to adapt the vehicle to our specs.
Experience teaches it is best to buy a bus with the performance features we expect instead of the usually very expensive
modifications.

Of course if you want a powerful Model T roadster......
   
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Joe Laird
'78 Eagle
Huron, South Dakota
lostagain
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« Reply #11 on: April 16, 2013, 11:09:01 AM »

Ed, I'll take a picture of that lip in front of the rad opening. Probably on Friday when we get back home. In Alberta now without the bus.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
bevans6
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« Reply #12 on: April 16, 2013, 11:36:55 AM »

Putting a squirrel cage fan in the air intake to the engine will really restrict air flow and won't help the engine at all.  May as well just put duct tape over the air intake, cheaper.

Brian
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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
treeplanter
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the grey ghost,1971 GMC 5305A




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« Reply #13 on: April 16, 2013, 11:55:28 AM »

Ok, well i am always trying to make something work better!
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Timothy
Larry B
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« Reply #14 on: April 16, 2013, 07:59:19 PM »

  Thanks everyone for the replies, some good food for thought. I removed the old scoops today and I will have to admit the bus looks better without them. I am getting the impression that it is likely a waste of time building new ones. If I add new scoops I will make them removeable. I also have run with rear doors held open with bungie cords. I have a set of small louvers that I am going to cut into the rear doors and repaint doors. Behind each rear tire are side access doors with louvers that can manually be opened or closed. Has anyone tried adding a 12 volt fan at these doors, mounted inside and blowing out threw the louvers? Many smaller vehicles use  12 volt cooling fans on their rads and I am sure a set could easily be found at a wrecker. Would these fans not help remove air that the squirrel cages just pushed into the engine compartment and in effect increase air flow through the rads? If adding air scoops will not help to "push" air though the rads is it possible that 12 volt fans mounted at louvers on side access doors would "suck" more air threw rads? 
    I appreciate the advise of using WD40 over starting fluid. The idea of spraying an engine that is already running with some thing as volitile as starting fluid made me think nervous thoughts, that is why I asked the question.
    Thanks for everything -----Larry B
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1977 MCI-5B---
8V71- 4speed man
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