Tom C need Turbo info

[mrcrafty]

We recently had our 8V71 rebuilt and turbo charged. The engine is back in the bus, however the turbo is not developing enough boost pressure and its blowing a black smoke cloud. So far the mechanic has replaced the newly installed injectors, retuned the engine, replaced the turbo charger, checked the blower, checked the after cooler, checked the muffler, clamed that one head may have a right hand cam in a left hand engine, and the latest reason for the poor performance is our Alison V730 transmission. The tranny was just rebuilt and I drove the bus on its first new engine test drive and the tranny shifted at the same speeds as always. According to the mechanic the tranny is not allowing the engine to spool up enough for the turbo to work.
I'm no expert, but even if the tranny wasn't shifting correctly and was stuck in 2nd shouldn't the engine still develop max RPM and produce enough exhaust pressure to spin the turbo.
The boost pressure is being measured before the blower and air box pressure after the blower.
With no load boost pressure will rise to a max of 2lbs and the air box goes to 9. Out on the road boost is 5 or 6 lbs and the air box 11 lbs. Can anyone help us out with this problem?

[TomC]

There are many different models of turbos that you can use-for the same engine-and within the same turbo-by just changing the snail housing on either the exhaust or pressure side.  To me it sounds like you need a smaller exhaust snail to allow the turbo to spine up faster.  On my AMGeneral Transit, the 8V-71N was available with either N55 or N65 injectors, or turbo from the factory-and this is with the V730.  On my turbo conversion I installed a custom air to air intercooler, by pass blower kit, 9G75 injectors, but with the same cam timing, early Series 60 turbo with waste gate.  Did you also install a fuel modulator?  It installs on the left head (lower) and prevents the injection rack from opening until turbo boost is sensed.  Before I installed the fuel modulator, it looked like a locomotive starting out.  Now it has about 10% smoke and then quickly clears up with the turbo spooling up.  With the fuel modulator, from a stop, it is a bit lethargic, but when you only get to 10mph starts picking up quickly then kicks pretty good.  I had to rebuild the radiator from a 5 row straight fin to a 6 row serpentine fin, go to a turbo muffler, and increase the air cleaner from a 6" to a 7" opening (same sized can). Since my radiator is new, and has the biggest core, it is still overheating on over 90 degree weather.  I have installed misters that I plumbed into my water system and use a 12v solenoid to operate it (considering most bus operators running from LA to Las Vegas year round have misters). I used the old emergency shut down wiring and switch on the dash since turbo engines do not have the emergency shut down.  Also have bought a 19"x24" trans cooler with a 12v fan to put in between the hot outlet and the existing shell cooler to take more heat away.  Also, discovered this weekend that the fan creates lots of pressure in the engine compartment when revved up, so I'm having custom louvers made for the rear door.  If all this still doesn't cool it, I'll just have to go slower on hot days, but hoping not.  Good Luck, TomC

[JackConrad]

Tom C,
   I am curious, do you have any boost gauges on your bus?  Just wondering what kinda numbers you are seeing under different conditions.  Jack

[donnreeves]

Need more information.What injectors are you running? What turbo? If you have big injectors with only 5# of boost, it will smoke.You should have 20#+.As Tom said, if you don't have a fuel modulator, it will smoke untill it comes up to boost,which in your case you don't have.  Donn

[TomC]

While I don't have a boost gauge, when on the dyno, it was putting out 15 psi of turbo boost before the blower.  And with the bypass valve on the blower, once it opens, the blower essentially is just free wheeling, so no additional boost is provided by the blower when turbo boost is above 5 psi (the blower only puts out 3-5 psi).  I didn't want more than 15 psi since I still have the higher compression ratio (18.7:1) pistons compared to the turbo pistons (17:1).  Good Luck, TomC

[mrcrafty]

Thaks every one I took all your questions and suggestions and sent them to the mechanic. Hopefully he will fidure it out.
Thanks Russ

[NJT 5573]

I'm not tomc but if I was going to go the route you have, why not build to 8V71T specs and have a dependable proven unit. I have one of these engines and can furnish a serial number if you want. Why build a morphadite that only one person can work on that is under powered and is going to never match up to a real 8V71T?

[gg04]

not enough information to even start on turbo...need at least a compressor map....will agree on t update much better than smoke turbo..not even sure why intercooler on smoke turbo..not enough boost to build enough temp to build hp....(1 degree cooling of intake air normally good for around 1/2 hp)not really needed at low boost to clear up over fueling...turbo on bus ,street rod, and street car..gg04