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BMC (Bluebird Motor Coach Unique Issues) If you have a unique issue with your BMC coach and it can't be answered in one of the other forums here, then this is where you can list it.....List your BMC Parts here too.

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  #11  
Old 02-06-2010
AC7880 AC7880 is offline
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I've been giving the dyno results some thought. It is reverse of what I figured would happen, I gained at the bottom and lost at the top end. I figured it would lose on the bottom and gain at the top with more air flow, less back pressure. That seems to be what I saw on gasoline motorcycles and cars with mods for more air flow.

Perhaps it has too much air and too little fuel at higher rpms?

The coach will accelerate faster now than before - up to 65 mph or so, but when the allison downshifts and pulls higher cummins rpm -- it is a net loss.

Sounds like I'll need a lighter foot on hills and grades, and should run the economy mode on the allison. In economy mode, it upshifts earlier, and downshifts later - which will work better to stay in the power band.

I pretty much blew my maintainance budget on this for now. Otherwise, a higher rear axle ratio to run lower rpms would keep me in the power band more, and also get better mpg. Also changing the fuel plate for more fuel "might" help. The 8.3 in BMCs are mechanical - no electronics to re-program the fuel curves.

I'll also look at the banks kits results for power band just to see what their kit does - shift power down the rpm scale, up the scale, or across the board. Banks kit is out of my budget for now.

I don't have a boost gauge nor a egt gauge on the 94 BMC.

I've been reading on the forum that a few guys are doing a muffler delete straight pipe, or straight thru muffler designs. Unless this is a fluke - might give that a second thought.

I am also considering running the toad back down the road and pulling the original muffler out of the metal bin just in case I decide to re-mount it.

Opinions?
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Last edited by AC7880; 02-10-2010 at 01:35 AM.
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  #12  
Old 02-06-2010
AC7880 AC7880 is offline
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Thanks Brad,
Fixed the dup -115 entry. I too am concerned about the loss 1900 to 2200 rpm.

Quote:
Originally Posted by bwinter1946 View Post
Well two things:

In post #9 the RPM scale has 9 entries and the torque entry has 10 entries. I'll assume the -115 is a duplicate entry.

My personal opinion is I would be concerned about the torque loss at or above 1800 RPM. That is where "I" prefer to climb.

I prefer to spin the engine at about 1900-2200 RPM at a reduced power setting (lower gear) than run it at 1500-1700 RPM. I think it is better for the engine and trans for two reasons. I am fearful of lugging the engine and I want to ensure adequate cooling for both the engine and transmission.

Someone more knowledgeablre than me may jump in here and tell me I am all wet but that is my opinion.
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  #13  
Old 02-06-2010
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those numbers are weird,I'm thinking more fuel would be a good thing,also your governor springs just may be weak,I got great results from changing the Gov. springs and sliding the fuel plate forward on several trucks that I've had.
But,its a motorhome,not a hotrod pickup,most guys would leave it be.
That list does not include Woody,Mike H,or me.

I wonder about the air intake,and fuel delivery,do you have an electric lift pump?
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  #14  
Old 02-06-2010
AC7880 AC7880 is offline
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I've self help modded Harleys and cars successfully for power and suspension, but don't know what I'm doing on a deisel (lack of knowledge).

51,500 miles on the coach/cummins, valves adjusted correctly, replaced stock turbo a couple years back (with new stock turbo) as the turbine fins had a couple of knicks found when changing air filter.

Big air filter with nice size air intake on side of coach. Air filter changed about 5,000 miles ago, and looks clean inside - "gauge" on intake showing fine for any restriction.

I successfully played with the governor on my previous 83 FC35 cat 3208 for more fuel and rpm based on advice on the forums, but don't even know where it is located on the cummins (never occurred to me to look for it). Sad to say I don't know where the fuel plate is either, or how hard it is to access - I have never looked at the cummins with that in mind so didn't pay attention to the intake system other than changing air filters myself and having cummins replace the turbo for me. I do know where the fuel cuttof solonoid is, incoming fuel filters, pac brake, etc.

How hard is it to access the fuel plate - how much dis-assembly to get to it? If I mod the governor springs and fuel plate, how do I tell if it helped or not without springing for a dyno run - preferrably on the same dyno I already have numbers from.

I can turn a wrench on autos/bikes - but don't get into heavy mods like motor rebuilds and trannies -- have done clutches etc. Have rebuilt a carb, repaced ignition systems, etc.

On the Bluebirds I have done thinks like shocks, waterpump, air dryer rebuild, solar installs, 12 volt mods of various types, etc. In other words I lack knowledge on the deisel, know my limitations, but am still somewhat capable as shade tree mechanic.

My best bet since I don't want to spend much more money for quite a while would be to put the stock muffler back on if the recycler hasn't dumped the metal bin yet (I'm only 15 miles north of the shop where it's at for the next couple of days). If an easy fix recommendation like governor springs and maybe fuel plate mod may help - - I'd be willing to try that with some advice and guidance from someon smarter on that then me. Problem is it would be hard to ensure the results without another dyno run to be sure.

Would you have expected like I did that the power curve should have increased at the higher rpm range versus lower? Would you have guessed it would increase across the entire range? I find it strange the bottom end picked up and the top end fell off.


Quote:
Originally Posted by Randy Dupree View Post
those numbers are weird,I'm thinking more fuel would be a good thing,also your governor springs just may be weak,I got great results from changing the Gov. springs and sliding the fuel plate forward on several trucks that I've had.
But,its a motorhome,not a hotrod pickup,most guys would leave it be.
That list does not include Woody,Mike H,or me.

I wonder about the air intake,and fuel delivery,do you have an electric lift pump?
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  #15  
Old 02-06-2010
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hmmm,i don't think I would attempt to mod this stuff without someone on hand to help,someone that has done it before,your a long way from any of us,(Mike,Woody or me)
After all,this is your house.
If you had a boost gauge it would sure hepl,you may have an air leak that shows up at high RPM,where you should have higher boost,check all of the charge air cooler hose and clamps,they may be leaking boost.
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  #16  
Old 02-06-2010
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I personnally would not modify the fuel curve without a boost and an exhaust temp guage. You can get the engine to hot if not careful.

I could better understand the weird numbers if you had them going in before any work was done but since the only "engine" work they did was replace the muffler I have to assume it is restrictive at higher RPMs than stock. Don't know if that is true but I would guess it is restricting exhaust flow and you are losing boost. Turbos do not like restriction down stream.

Here is a link to the Banks Stinger for our 8.3 it shows the fuel cam plate on page 8. Temp warnings are on page 9. http://assets.bankspower.com/manuals/45/96381.pdf

Not sure if this helps............
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  #17  
Old 02-06-2010
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I second your opinion Brad. The Aero Muffler must be creating a standing wave at Dan's exhaust flow rates and velocities. The Areo might be tuned for higher rpm pickup truck engines (less flow, but higher velocities). I sure would like to see the inside of it.
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  #18  
Old 02-06-2010
jnxmas jnxmas is offline
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Could it be you'r back pressure is to low ?
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  #19  
Old 02-06-2010
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Quote:
Originally Posted by jnxmas View Post
Could it be you'r back pressure is to low ?
I don't think there is such a thing as too low in a turbo charged diesel engine.

The muffler seems too small, dimension wise; tuned for a different frequency band and flow rate. Tuning sounds odd, but that's what Aero Muffler brags about on their web page. The marketing blurb is something about outer gas flows and inner gas flows and mimicking jet engine concepts... vortices, positive interference, etc.
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  #20  
Old 02-06-2010
AC7880 AC7880 is offline
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I found pics on line on another guys website.
The one on my coach is the 4040XL resonated:
http://www.aeroexhaust.com/index.php...l-exhaust.html

The fellows pics of the "guts" of this same 4040XL:
http://i226.photobucket.com/albums/d...y/IMG_0829.jpg


It is a 4" inlet outlet, and indeed there are "some" restrictions inside - but the inner core is straight thru...


Quote:
Originally Posted by davidmbrady View Post
I second your opinion Brad. The Aero Muffler must be creating a standing wave at Dan's exhaust flow rates and velocities. The Areo might be tuned for higher rpm pickup truck engines (less flow, but higher velocities). I sure would like to see the inside of it.
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Last edited by AC7880; 02-10-2010 at 01:38 AM.
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