How loud should a turbo be? - Page 2

Honeydipped · 10-30-2020, 08:45 AM

Quote:

Originally Posted by CHEESE_WAGON

Guess my hearing isn't all that great, all I heard was differential gears and tires. Of course, I was on mostly level ground with the cruise set at 70, running about 2100-2200. Turbo probably wasn't spooling much. Windows weren't open either, as I have severe asthma and allergies.

It actually depends on the application and emissions equipment. Here is a TSB I downloaded.

Service Bulletin Cummins® Engine Oil and Oil Analysis Recommendations

I wouldn’t discredit your hearing too much, there were a couple of big differences between our trips! I was on some moderate grades on I-80 and cruising at a much lower rpm (around 1800). AND I had all my windows down because it was mid August and I was sweating in parts I like to keep dry

Thanks for posting that service bulletin! That will come in handy for sure. I didn’t see anything regarding zinc except for the natural gas applications, but I’m also at work and couldn’t do a proper read through. Thanks again!

Take care,
R

Kota Fox · 10-30-2020, 11:39 AM

Well my speedometer is off by 7-8mph at times. And on some of the downhills on the highway my tach was reaching 3400 rpm at 75mph max (from waze). I now know that is stupid fast rpm, but I was trying to keep up with traffic mainly at night, and secondly see what she could do as it was my first trip. I guess if it actually was 3400rpm the engine would have blown apart from what Ive been reading, but shes seems to have held up fine.

cadillackid · 10-30-2020, 11:53 AM

Very possible that by running it flat out that on a downhill you were over revving it and it won’t last long nor will you for driving down a hill at 75 in traffic.. ever thought how you’d stop a bus careening down a hill if the traffic. Slowed or someone cut you off? It’s a school bus. Slow it down, the traffic expects it to be going slow..
Get your tire size and rear gear ratio fo determine your tach accuracy. Use a GPS speedometer and run up to 60 and check your tach, through knowing gears and speed and tire size you can calc what the real engine RPM would be

Kota Fox · 10-30-2020, 11:12 PM

Quote:

Originally Posted by cadillackid

Very possible that by running it flat out that on a downhill you were over revving it and it won’t last long nor will you for driving down a hill at 75 in traffic.. ever thought how you’d stop a bus careening down a hill if the traffic. Slowed or someone cut you off? It’s a school bus. Slow it down, the traffic expects it to be going slow..
Get your tire size and rear gear ratio fo determine your tach accuracy. Use a GPS speedometer and run up to 60 and check your tach, through knowing gears and speed and tire size you can calc what the real engine RPM would be

Ok thanks, Ill definitely be taking it easier

Jolly Roger bus 223 · 10-31-2020, 02:50 PM

it was posted on here several years ago about an app called sommething like accoustitach that was supposed to be pretty decent.
i remember because i dont have a tach and want to know my rpm. plus many more things i work on with faulty tachs.

cadillackid · 10-31-2020, 05:08 PM

theres a couple different tach apps.. one of them you chalk a mark on the harmonic balancer and then you use your phone at night to adjust a strobing light till the mark stops in place and the display shows your RPM.. so you can compare with your tach.. ie you set high idle and then go get a reading with your phone / compare it to your dash gauge

CHEESE_WAGON · 10-31-2020, 05:16 PM

Speedwise, way too fast. Your bus will need about 500-600 feet, perhaps more, to stop at 55-65. There is a lag in air brakes, and they aren't going to stop as quick as a car either, something I've discussed in a few other threads here. Diesels, as I've mentioned, are not tolerant of higher rpm. Keep your 8.3 below 2400, that's as high as I would push it, only because Cummins rates it at sage to 2750. I've found that these are happiest at 1500-2200, and most efficient at 1500-1800.

55 zone I recommend 50.
60-65 zone, I recommend 58.
65-70 zone, I recommend 63.

cadillackid · 11-01-2020, 07:02 AM

Quote:

Originally Posted by CHEESE_WAGON

Speedwise, way too fast. Your bus will need about 500-600 feet, perhaps more, to stop at 55-65. There is a lag in air brakes, and they aren't going to stop as quick as a car either, something I've discussed in a few other threads here. Diesels, as I've mentioned, are not tolerant of higher rpm. Keep your 8.3 below 2400, that's as high as I would push it, only because Cummins rates it at sage to 2750. I've found that these are happiest at 1500-2200, and most efficient at 1500-1800.

55 zone I recommend 50.
60-65 zone, I recommend 58.
65-70 zone, I recommend 63.

pretty much it right there!!

Kubla · 11-01-2020, 10:13 AM

Floor it and go LOL

CHEESE_WAGON · 11-01-2020, 01:05 PM

Quote:

Originally Posted by Kubla

Floor it and go LOL

Exactly the kind of advice that gets people into trouble.

Ronnie · 11-01-2020, 06:31 PM

about 1200 ppm of zinc is what is generally recommended for flat tappet cams.

Speed, come on now how many trucks pass me going well over 70, and me around 65. Just know your stopping distance and give yourself room.

CHEESE_WAGON · 11-01-2020, 06:38 PM

Quote:

Originally Posted by Ronnie

Speed, come on now how many trucks pass me going well over 70, and me around 65. Just know your stopping distance and give yourself room.

Those trucks have at least 2-3 times as many forward gears, wide brake shoes / drums, better springs, and those are also the guys you see piled up into twelve cars in a traffic backup because they can't stop in time. We professional drivers call them supertruckers because they think they know everything. Just because you CAN do something, doesn't mean you SHOULD. They learn the hard way eventually. CDL courses teach fifteen-second following distance and slower than the flow of traffic for a reason.

Ronnie · 11-01-2020, 07:15 PM

well I guess they all must have been supertruckers the other night. It was kind of nice almost no "4 wheelers" on the road all trucks and me.

Just as a comparison my International flatbed truck has one hydravac( brake booster), and one wheel cylinder per brake shoe, and my bus with the same chassis has two Hydravacs, two wheel cylinders per brake shoe, and dual brake lines. So better braking then the same size truck. I have stopped at traffic lights and had someone slide around me.

My trailers I expect the brakes to be good enough to stop the trailer, so the bus is only stopping itself.

CHEESE_WAGON · 11-01-2020, 07:19 PM

I won't say I've never done 70-75 to get ahead of someone who wouldn't maintain speed in order to avoid a bad situation, but otherwise I generally cruised at the speeds I've mentioned per speed zones. Lots easier on the nerves.

Ronnie · 11-01-2020, 07:39 PM

Must say I am usually a bit less then the speed of traffic in the bus.

cadillackid · 11-02-2020, 06:50 AM

my DEV bus maxxes at about 68-70 if i run it flat-out.. I played with its brakes one late night.. I ran it up to max and then I mashed the brakes.. hard enough I had to modulate the pedal a bit to keeo the rear wheels spinning..

thje weight shift in an empty bus is real.. my front brakes were Hot.. not smoking but enough to smell them.. i lost a lot of my rear braking power during that hard stop.. I could feel a bit of fade toward the end.. i didnt measure the distance

another time i did a "half mash" I call it.. while my stopping distance was definitely longer none of my brakes smelled ..they were all good and warm but none hot..

my conclusion was that I wouldnt regear that bus to ev er go any faster.. it just wouldnt have the brakes to stop it in a panic stop...

my normal spoeed is 55-60 in it and stopping is much comfortable..

the red bus has hydraulic disc ABS.. its top speed is mathematically to the moon (100+).. its tires are rated at 75 so i did the same tests with it.. ran it up to 75 and mashed it.. hard enough to let the ABS tag the rear wheels a couple times during the initial weight shift.. that one stopped quick.. MUCH quicker than the DEV bus.. (its also much lighter).. again the front brakes took the brunt but not as much.. more even heat among the brakes. .. slight fade toward the end..

its cruising speed is 65-70.. at 75 I feel i was pushing the brakes to their max effective limit... the factory design speed of that bus was 70-72 with its AT545.. the engine power increase and new trans made it a Hotrod that i'd never be able to safely drive at 80+ (even if you could find tires to take those speeds)..

Ronnie · 11-02-2020, 07:20 AM

A lot has to do with not only braking but what road you are on. The interstates out west with 80 mph speed limits, long sight lines and little traffic, by all means let it roll. Crowded east coast, rush hour around cities, etc much slower. Once clear of Washington dc and its traffic RT 95 is mostly 70 mph speed limit, and traffic is mostly around 75. I think it is unreasonable to go 55-60. The bottleneck that causes is dangerous by itself. Those that want( or can not) to go slower get off the interstates.

Christopher, Interesting observations on your brakes. My old dump truck I could overheat the brakes and get brake fade if I was not careful. Did that once in the west Virginia mountains, went through a small town rather fast.... Only happened once. I was trying to get as many loads in a day as possible, so I could get the job done and go home. Never have liked staying in motels. It was about two weeks on this job.

This is where knowing how each vehicle is differant and what it can or can not do is really important.

Something else to be mindful of when on smaller roads is people expect school buses to be going slow. So many will pull in front of you thinking you are just poking along. Just be prepared.

FAC · 11-02-2020, 10:38 AM

Since this turned into a braking discussion I have some things I’ve been thinking about.

I agree that safe speed is situational.

And I have also noticed how people see my bus coming down the highway and seem
To instantly need to pull out in front of me. It seems the worst in rural areas.

Regarding brake fade I do great in town and full stops don’t heat them up enough to smell them but on long grades like the grapevine I have a hard time keeping them cool. I usually go in the truck lane and “stab and glide” doing about 25- 35 mph glides. Using 3rd on my md3060 but I can smell them at the bottom every time. Which I don’t like.

So I tried it faster last time because traffic was very light. Doing stab and glide 45-55mph the brakes didn’t get hot enough to smell. Possibly the extra wind cooling them? Or the extra drag from the frontal area being an air brake?

Bottom line though was if there were any need for an emergency stop it would have been unsafe.

I guess I’m curious as ways to keep them cool on long grades

CHEESE_WAGON · 11-02-2020, 10:49 AM

Stab braking is actually a common technique used by semi drivers for exactly that purpose. It's not advisable on ABS systems or in slick weather, but it does work and can be done in bad conditions if you know what you're doing. Saved my bacon on a icy downhill grade three months out of CDL school with a 41,000 lb load behind me. In a rig with ABS on both the tractor and trailer, no less. Maximum braking in that instant with minimal heat buildup is the name of the game. Use with discretion, it is not advisable for all situations.

Ronnie · 11-02-2020, 11:06 AM

I have a manual trans and a gas engine, so with that I can pick a gear that would hold me back and not even touch the brakes on long grades, usually top gear on the trans and low on the rear for the steeper ones on interstates. Mountain two lane 3rd and high, maybe even drop to 3rd and low.

I do not care for an automatic in the mountains, so I can not say with any real autority what is best for your bus. I do think that you are on to something with a little higher speed keeping them cool, and wind resistance is helping too.

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