Turbo Boost Gauge?

Mike in GA · March 27, 2017, 10:17:26 AM

A couple of respected Bus Nuts have been telling me of the value of having a turbo boost gauge on my dash, even though my vintage MCI didn't come with one ('85 MC96a3 – 8v92 TA). They say it is a great indicator of engine health, performance, etc.
I have room for one on my dash. My questions are, is it worth it, and if so should I go mechanical vs electronic.
It seems that 40 feet of tubing for the mechanical version is a lot. But I have been told that disused pipes for the over-the-road AC that go from the engine compartment to the condenser bay can be used with fishtape or something similar to feed the tubing forward. Question: is this as easy as it sounds? Which pipe goes to the condenser vs the center radiator/heat exchanger? Incidentally, the AC hasn't been used in 10 years and was blowing warm last time so I don't think there is any freon to abuse the environment.
The alternative is using an electronic gauge that uses wire off an engine compartment sending unit. I have been told that I can hitchhike on a disused wire in the rear junction box to get this signal up to the front, to the driver's side electrical panel, and thence to the dash. (Maybe use one of the over-the-road AC control wires?!)
Your comments on the whole idea will be welcome.
Thanks in advance!
Mike in GA

lostagain · March 27, 2017, 12:39:42 PM

A turbo boost gauge is nice to have. I used an oil filled 0 to 30 psi pressure gauge. I ran 40 feet of 1/4" air line from a port on the air intake horn on top of the blower to the gauge at the dash. The first 2 or 3 feet inside the engine bay is actually oil line to withstand the heat. I cannot remember where I routed it, although it seems to me I went up an empty pipe from the engine compartment to the condenser bay behind the left front wheel well. It is very responsive. You wouldn't know there is 40 feet of air line. It is fun to watch going up a hill. I get 23 psi under ideal conditions: cold outside air, full rpms, and full load. You get to know how much pressure there should be under certain conditions, and you would notice if you didn't see that. A malfunctioning turbo, or a leak between the turbo and the blower, or an exhaust leak upstream from the turbo. All the old equipment like trucks and buses with mechanical engines had lots of gauges for the driver to monitor everything. Now with electronic engines and sensors everywhere, there is hardly any gauges on the trucks and buses dash. Last year I was driving a Freightliner Cascadia semi, and all it had on the dash was a speedo, tach, air pressure gauges, coolant temp, and oil pressure. And a phone number for road side assistance.

JC

HB of CJ · March 27, 2017, 01:49:37 PM

A comparison? Back in about 1970 my daily driver school bus had a SW mechanical turbo boost gage. 1963 Crown Supercoach 40 foot 10 wheeler. Went up and down the Grape Vine Ridge Route every school day. The mill was a 220 743 T Cummings slightly stepped up. Ran about 10 pounds boost.

The shops had some issues with oil leaks. Also the OP, tack and speedo were SW mechanical gages with the long encased cables spinning. Long runs and twists to the dash board. The mechanical gages created headaches for the mechanics. A oil seep shop rag was engine space dedicated to clean up.

Everything seeped or slightly leaked oil and grease.

luvrbus · March 27, 2017, 05:22:15 PM

I think when installing a gauge the EGT gauge is more beneficial to you than a boost gauge JMO ,anyways I did sorta of drive by my boost gauge when it was up around 20# I knew the 8v92 was sucking some fuel

lostagain · March 28, 2017, 06:53:10 AM

Exhaust Gas Temperature and turbo boost go hand in hand. The hotter the exhaust when the engine is working hard, the more boost is produced by the turbo. That usually happens at higher rpms. Hot exhaust and boost also heat up the radiators, a concern with 2 stroke Detroits. The probe for EGT on my 6
V92TA is after the turbo, so it only shows around 300F on the flats, and can go up to 400F going up a hill. One day I would like to move it to the other side to see what temperature is really like. But what if the probe broke... I have one upstream of the turbo on a 6 liter Powerstroke. It has never broke.

JC

luvrbus · March 28, 2017, 07:30:20 AM

Quote from: lostagain on March 28, 2017, 06:53:10 AM
Exhaust Gas Temperature and turbo boost go hand in hand. The hotter the exhaust when the engine is working hard, the more boost is produced by the turbo. That usually happens at higher rpms. Hot exhaust and boost also heat up the radiators, a concern with 2 stroke Detroits. The probe for EGT on my 6
V92TA is after the turbo, so it only shows around 300F on the flats, and can go up to 400F going up a hill. One day I would like to move it to the other side to see what temperature is really like. But what if the probe broke... I have one upstream of the turbo on a 6 liter Powerstroke. It has never broke.

JC

It is way off JC you should be 800 EGT+ on a heavy pull

lostagain · March 28, 2017, 07:34:07 AM

Clifford the probe is downstream (after) from the turbo, that's why. If I moved it to the other side on the upstream side of the exhaust I would see 800 right?

luvrbus · March 28, 2017, 07:39:39 AM

Quote from: lostagain on March 28, 2017, 07:34:07 AM
Clifford the probe is downstream (after) from the turbo, that's why. If I moved it to the other side on the upstream side of the exhaust I would see 800 right?

Under a load with your 9G90 you should, 595 degrees @ 2100 no load is the normal EGT for 6v92 TA with 9G90 injectors on a 350 hp engine

TomC · March 28, 2017, 08:21:14 AM

Most truck/bus diesel engines with turbos have the pyrometer after the turbo. I once saw a sign on a boat with twin Perkins turbo 160's reading "over 1200 degrees cost money".
Only time I've seen pyrometer before the turbo was on a giant Diesel generator-they had one pyrometer per cylinder (straight 8 Wartsilla), overall pyrometer, and even a tachometer on the turbocharger. Good Luck, TomC

luvrbus · March 28, 2017, 08:37:00 AM

Quote from: TomC on March 28, 2017, 08:21:14 AM
Most truck/bus diesel engines with turbos have the pyrometer after the turbo. I once saw a sign on a boat with twin Perkins turbo 160's reading "over 1200 degrees cost money".
Only time I've seen pyrometer before the turbo was on a giant Diesel generator-they had one pyrometer per cylinder (straight 8 Wartsilla), overall pyrometer, and even a tachometer on the turbocharger. Good Luck, TomC

92 series have tap , plate or a boss to drill and tap for the probes on the manifolds you read the egt at the manifolds on a 2 stroke and that is from the DD bible

akroyaleagle · March 28, 2017, 09:05:49 AM

I too used the 1/4" tubing for the boost gauge. It has worked great for over 21 years. I can get 26# with the 8V92TA with 9A98 injectors.

My pyrometer probe is just after the turbo. It is around 300 normally but can indicate over 800 when working hard.

I believe in old school. No such thing as too much information if you know what it is telling you.

Probably an affliction of all us old pilots!

Good Luck

lostagain · March 28, 2017, 09:44:27 AM

I should move mine before the turbo. How often do they break?

JC

luvrbus · March 28, 2017, 10:24:05 AM

It's possible but never saw 1 break before ,I have twisted a few off though

Iceni John · March 28, 2017, 08:32:23 PM

I put in a VDO 30 PSI boost gauge a few years ago, and it uses almost 45 feet of 1/4" non-DOT plastic air tubing and a few feet of 1/4" refrigeration copper tube. I underestimated how hot the air is after the turbo and melted the DOT push-in fitting's O-ring and the plastic tubing, so now I have a compression fitting there for the copper tube: no more plastic to melt! The gauge reads almost instantly, proving that using air line is OK even in a 40 foot bus.

I like to use the boost gauge when climbing long grades. I can comfortably climb a steady 6% grade in 3rd gear at 1900 RPM with about 18 PSI of boost on a 3/4 pedal, but if I work the engine harder the temperature will rise.

John