Only 8 psi of turbo boost

[lostagain]

Last week, I installed a turbo  boost gauge at the dash. Ran a 1/8" line from the horn on top of the blower to the front. It is not easy to find a way over the rear axle, but I finally found an unused AC coolant line that I pushed my line through.

This weekend we drove to Coeur d'Alene, ID, about 5 hours away. The most pressure I saw is 8 psi. Going down on the flat highway, I see 4, 5 psi. Shouldn't I get pressure in the 20s ?

I have black smoke really easy if I push the pedal too hard, and I always felt that the 6V92, although in great shape, never had as much power as it should. This is mostly the reason why I installed the gauge. The engine and HT740 were swapped in '87 IIRC by a "professional" shop in California. Evidently they put on the wrong turbo. I works good, meaning I have had the intake off and the wheel feels good. I don't know what kind of turbo it is now. I plan to remove it this winter, so I can see what it is. Another thing is that it is mounted on the side, with one long exhaust pipe from the right bank, although it is quite responsive. The pressure goes up right away when I push the pedal.

I will be back with this subject in a couple of month with questions about what kind of turbo to put in. I can't wait until next summer after I tweaked it to run right, LOL...

JC

[luvrbus]

May not be the wrong turbo JC you can set those engines up so many different ways sound to me like yours is setup for high end torque when you get it off check the A/R on the hot side inside the housing the cold side is embossed on the housing and is easy to read 

Let me know I have plenty of hot housings of different A/R you should be getting 20lbs under a heavy pull even with a 1.34

[lostagain]

Thanks Clifford,

I will let you know what I have when I get it off. I just don't have time to get into it now. Too many other projects. Plus I use the bus quite regularly till the end of October.

JC

[Geoff]

If I was running a turbo boost gauge I certainly would not run a 1/8" line to the front of the bus.  That setup might work for trucks with the engine in front but not on a 35-40' bus.  You not only only need a an electrical boost gauge, but you need to account for the drop in voltage with the electrical gauge that you are going to lose running the wires 40 feet.  I had a similar problem with an electrical oil pressure gauge and I ended up using a different sending unit than came with the temp gauge thanks to my laser temperature gun, now I am right on temperature at the dash.

The accuracy of a turbo boost gauge is a little harder to check-- since you need to be driving the bus you need a second person at the rear of the bus with a short connection to see what the loss in pressure readings is between the front and the  back.

--Geoff

[luvrbus]

I stay out of the 1/4 vs 1 /8 debate but I use 1/4 dot tubing easy to check I check at the horn then connect it at the horn then check the pressure at the dash so far never saw a drop

good luck

[lostagain]

Geoff,

the line is continuous with no leaks. The pressure at the dash gauge should be the same as at the other end coming out of the turbo. I have done the same installation in 2 buses now, and I can say that the response showing at the gauge is instantaneous when you press the accelerator pedal, and when you let it off. It should be like the water pressure at the kitchen tap, it doesn't matter if you are 10 miles from the water tower, the pressure is the same as determined by the head. The only limiting factor would be the friction in the water line. In the air line to a gauge, there is no friction because there is no flow. The only variable that I could see is that air is compressible, so it would affect the response time, which I have observed is quite negligible.

How is my reasoning?

JC 

[Sam 4106]

I recently installed a boost pressure gauge using 1/8" tubing in our MC8 because Hard Headed Ken, Clifford, and probably others suggested it. Even if the pressure at the air horn is different than at the dash, after I establish the readings under different conditions, I will still know when there is a change due to an obstructed air filter, blown exhaust manifold gasket, loose exhaust pipe connection before the turbo, bad turbo, or anything else that causes a drop in boost pressure. Once I have a basis I will know if there is a problem if the boost pressure drops. That is what I'm interested in, not whether the gauge is accurate to the gnats a$$. Thanks JC for the suggestion of using the old A/C line as a route for the tubing. It was easy to fish the tubing from the engine compartment to the dash using an electricians fish tape. It's nice to have a retired electrical contractor as a neighbor and friend to help with these projects.

I removed the old dash air evaporator and that allowed me to put some foam insulation against the front bus panel and still have air flow to the defroster. That should make the copilot area a little warmer in the winter.

Good luck, Sam

[rgwilliams]

JC

I have a DDEC2 6V92 in my 4104 and I use Silverleaf's VMSPc to monitor.  At cruise on the flat at 95 kmh, towing a 4X4 Ranger,  it pulls about 4-6 psi.  Max boost about 24 psi at 2150. At 1625 the max boost is only about 18-20 psi when going up a hill.These are from (an old) memory.  The engine is a stock "transit package" at 277hp.  I can email you exact figures on the next trip but management hasn't informed me when that is.

Rob

[lostagain]

Thank you Rob,

your boost numbers is what I expect to attain with the correct turbo and other tweaks that I will do this winter.

I have met some really good mechanics on this board that will give me expert advice on what to do.

Don Fairchild and I spoke about this in the spring when I visited him in Bakersfield.

Clifford Luvrbus will also have some solutions for me.

I will post more about this subject when I get into it, probably not till November. I welcome any advice from anybody, it will all help. I can do the install, I need to find out what to use to make this engine rock.

JC