Thomas Followed Me Home Today

[golfersmurf57]

Most of what I see coming in down there are short bus freightliner cab and chassis. 4 or 5 decked up for transporting. Is that where you delivered?

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[cadillackid]

thomas is near I-77 ? I nerver knew that.. ive driven I-77 from ohio to its end at 26 many a time.. ive seen lots of new busses along that route... of course when I go I-75 i always see brand new bluebirds from ft valley in georgia..

1998, is that 8.3 engine electronic where a scangauge D will do you good? or is the diagnostic connector just for the allison?

seems hard to believe an electronic engine wouldve allowed the REV limiter deleted if in facts revving that high.

as for the tach being off.. it will likely be a percentage.. ive no idea on cummins and thomas.. but I know on international there are different amount of teeth on the flywheel for the tach to get reading from. on my older bus its a dip switch on my gauge cluster to set that number.. so if for instance your tach is set up for a different engin e than whats in the bus it would read a percentage off .. say the en gine has 132 teeth on the flywheel but the tach thinks theres ionly 117 teeth on the flywheel. the tach would think 1 revolution is 117.. and the engine hasnt yet finished that revolutuon.. result is the tach is going to read higher than what the actual engine speed is.. by a percentage.. so it might be 200 RPM at idle. but would be much higher at a higher RPM..

if the engine is electroniuc then yes your scanguage should help you out. otherwise you can use a strobe light as a guide.

your smart phone may be able to use an app with a camera flash that you can shine at a pulley at night.. "strobe tachometer" is what you are looking for..

the idea being that you make a chalk mark on your main engine pulley from inside by the hub to the endge of the pulley so its bright and visible.

start the engine ,shine your phone at the pulley, and then you adjust the strobe slider on your app until you see that pulley and chalk mark appear close to stationary. the app should tell you your current RPM. it may jiggle back and forth a bit as RPMs vary slightly.. you just dont want to see it rotating. the app will tell you the RPM of the pulley.

then trip the high idle switch and do it again. you'll get a new reading. compare those readings with your tach, you can deduce the percentage if any that your tach is inaccurate.. and calculate real RPM vs displayed for even higher RPMs.
-Christopher

[Twigg]

Thomas told me that the bus was shipped with a 5.38 rear axle.

It does not have that now! I'll be able to be more definitive when I get th Scangauge, but early calculations suggest it has been fitted with 7.12. The tags are missing.

The first problemthat creates is that Thomas are not going to agree to release 6th gear if they think it has a 5.38 rear axle. That would make it a 98 mph bus!

Oh well, I'll figure it out.

[Twigg]

I think by '98 all Cummins engines were electronic. That strobe ide is an excellent suggestion, thank you.

Scangauge should be here by Wednesday and there is a 9-pin connector in the electrical panel.

[cadillackid]

Originally Posted by Twigg

Thomas told me that the bus was shipped with a 5.38 rear axle.

It does not have that now! I'll be able to be more definitive when I get th Scangauge, but early calculations suggest it has been fitted with 7.12. The tags are missing.

The first problemthat creates is that Thomas are not going to agree to release 6th gear if they think it has a 5.38 rear axle. That would make it a 98 mph bus!

Oh well, I'll figure it out.

that or your tach is WAY off.. which if its an electronic engine id suspect, I really didnt think an 8.3 was physically capable of spinning at 3200 RPM.. many of these engines will float the valves way before then...

-Christopher

[Twigg]

Originally Posted by cadillackid

that or your tach is WAY off.. which if its an electronic engine id suspect, I really didnt think an 8.3 was physically capable of spinning at 3200 RPM.. many of these engines will float the valves way before then...

-Christopher

It would be good news if the tacho was way off.

It's showing over 900 rpm at idle, and 1200 at high idle.

[Tango]

3200 is near the limit on old 2 stroke DD "screamers". Can't imagine any other diesel happy turning that fast.

[cadillackid]

Originally Posted by Twigg

It would be good news if the tacho was way off.

It's showing over 900 rpm at idle, and 1200 at high idle.

try the strobe app.. if its cloudy out and youyr phone flash is bright enough you might be able to do it in the daytime. esp if you close the hatch down as much as you can. the idea is to make the pulley look like its standing still..

[cadillackid]

Originally Posted by Tango

3200 is near the limit on old 2 stroke DD "screamers". Can't imagine any other diesel happy turning that fast.

on any long stroke engine piston speed becomes an issue at the middle of the stroke, as well as the inertia of the piston esp on the exhaust stroke.. you have to slow that piston down to zero at the top and bottom of the stroke. on the exhaust stroke you have nothing holding it back exceot the rod... at high RPMs rod stretch is real.. too fast you you slap the piston into the head or a valve if the valve floats..

valve float is determined by the valve spring and the cam lobe profile along with the weight of the valve and any pressures it is overcoming. plus tolerances to allow for wear.. where a valve might stick ever so slightly in a worn guide.

I dont know the 8.3 specifically.. I do know what the navistar books say about the navistar 360 and 466..

they state that spinning a DT360 at 3200 RPM is the maxmimum "safe" no load RPM.. (3100 loaded). meaning it wont explode at that.. HOWEVER they state that longevity is reduced GREATLY by spinning it at anything above 2800 RPM non loaded.. suggested is 2700 RPM max loaded, for longest Life.. the books were to the point that 40-50% less longevity could be expected by spinning it at 3200 vs 2800.. that foes along with what you say about semi trucks running at 1500-1600 down the highway for 750k miles maybe more befiore being worn out.. again NOT-LUGGED being a key also..

the DT-466 ratings were a couple hindered RPM below the DT360 ratings in my books.. biugger engine lower RPM..

my books dont say anything about my T-444E (powerstroke 7.3).. {same engine cept for a few parts} my computer limits that engine to 2700 RPM.. ford spins em up to 3400. different cam and different head gasket.. ford wanted to win the consumer pickup-truck Horsepower wars... Navistar wanted them to last forever as commercial truck engines..

im among the spin slower last-forever crowd when it comes to my diesel engine.. if I want to win the consumner Horsepower wars ive got a nice Dodge HEMI pickup with a "tweaked" computer that does nicely for that.

-Christopher

[Tango]

Hey Chris...have you looked into pumping a little nitrous into one of your rigs? Has anyone ever on a diesel?

[Twigg]

Originally Posted by Tango

Hey Chris...have you looked into pumping a little nitrous into one of your rigs? Has anyone ever on a diesel?

They pump propane into diesels

[Tango]

Familiar with propane but have to wonder about what an NOS would do.

[M1031A1]

Originally Posted by Tango

Familiar with propane but have to wonder about what an NOS would do.

I'm not so sure I'd like to be around to find out......

M

[Robin97396]

That depends on who's bus it is with the NOS. I'd like to see it. Not willing to try it.

[Twigg]

Originally Posted by Robin97396

That depends on who's bus it is with the NOS. I'd like to see it. Not willing to try it.

Won't be mine. I'm happy with the 250 hp I have.

[cadillackid]

NOS by itself wont do anything.. you still need to fuel more.. the NOS itself isnt fuel, but when its heated in the cylinder oxygen comes out of the breakdown. so you still need to add fuel.. the issue with most of the medium duty diesels with computers is that you cant up the fuel. wit ha mechanical you would need a way to inject more fuel into the cylinder at the right time for the NOS toi be effective. so on a mechanical you would still need some type of way to widen the injector pulse or up the pressure on a moments notice when you hit the 'Go Baby' button.

yeah maybe you inject propane with the NOS if you can time the shot? im not that familiar with making hot-diesels.. im sure the guys on the pulling forums would have lots to say about it.. they build insane rigs for sled-pulling..

-Christopher

[Twigg]

I've been number-crunching since I got that unexpected email from Thomas.

The email said that the bus left the factory with a final drive ratio of 5.38.

As you know, this does not jive with the numbers I was getting from the speedo, tacho and GPS. The speedometer and GPS broadly agree on the speed. The tacho seems to be a problem child.

If the tacho is accurate, the FD ratio is around 7.12, which makes no sense for two reasons. First, who would spec that in an Activity bus unless it has been replaced. There are no data-plates on the axle to say either way, but it hasn't been replaced recently (which might have prompted a sale). The second reason is that Cummins are clear. The engine should be rev-limited to either 2200 or 2400 rpm. HArd to tell which because there were variations, but let's be kind to the tacho and assume 2400.

When I was driving home I hit 70 mph at an indicated 3100 rpm. That's absurd, the engine would be on the point of self-destructing and it was showing no signs of strain. So being kind to the tacho, assume for a moment that the actual rpm was 2400.

2400 rpm, in 5th gear with a 5.38 final drive ratio would be 70.21 mph if the tire height is 41.4".

That sounds very plausible. All I need to do now is confirm it.

[EastCoastCB]

If that's the ratio it left the factory with, then I'd bet you dollars to donuts that your tach is WAY off...
Like I told you the other day!

[Twigg]

Originally Posted by EastCoastCB

If that's the ratio it left the factory with, then I'd bet you dollars to donuts that your tach is WAY off...
Like I told you the other day!

I never thought it could be 30% off.

I'll find out Thursday when the Scangauge arrives.

[golfersmurf57]

I have a photo tachometer comes with a stick on strip you attach to crank pulley
Also has physical rotation piece in end so you can manually sample be careful. It is rather pricey though. I'm pretty sure there's a way to test the factory tach. Usually they either work or not.

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