Mating a Cat to the Allison HT755

[luvrbus]

The 450LXI Blue Bird offered the ISX 15 Cummins 600 hp they easy to bump to 700 hp .I don't why you would need any thing larger my ISX 15 Cummins pushing a 45 ft  weighing 48,000 lbs down the high way and up mountains and the Allision never drops below 4th gear and averages 7 to 7.8 MPG 

[waterlodge]

The 8V92 was a dog too. It did ok in Texas at low altitude and rolling hills. But in Colorado 25mph up the hill, and on the steeper hills it flat out would not move at all. I'd have to back down the hill and make a long run for it. Happened several times in the one vacation we got with it.

[dtcerrato]

The 8V92 was a dog too. It did ok in Texas at low altitude and rolling hills. But in Colorado 25mph up the hill, and on the steeper hills it flat out would not move at all. I'd have to back down the hill and make a long run for it. Happened several times in the one vacation we got with it.

If it weren't for our four down toad(s) we too would have not been able to get the bus either up some hills or into some precarious pristine spots. The wife has that move (in the toad) down pat. Walky talky & no hand on the steering wheel in the toad! 

[luvrbus]

The 8V92 was a dog too. It did ok in Texas at low altitude and rolling hills. But in Colorado 25mph up the hill, and on the steeper hills it flat out would not move at all. I'd have to back down the hill and make a long run for it. Happened several times in the one vacation we got with it.

That was a easy fix you should have had someone adjust the fuel delay (modulator) or replace it ,I ran my 8v82TA in my Eagle all over the Rockies for 15 years lol I could average 48 MPH  on I 17 from Phoenix to Flagstaff and that is a long climb when you leave Black Canyon.I have a dislike for for fuel modulators on a 2 stroke I have barrel full I have removed from the Detroit's go figure they don't take fuel if the turbo is not  boosting and the turbo will not boost without fuel,you have the same problem with the DDEC 8v92's     

[6805eagleguy]

Not all Cummins are the v8/903 has been around a long time and I never understood why it was a dog ,a few buses had the left turning Cummins 903 and were dogs too

hehe  ::)clifford i was only joking. How ever the isx 15 is the only cummins i have ever seen that is not a dog

[luvrbus]

hehe  ::)clifford i was only joking. How ever the isx 15 is the only cummins i have ever seen that is not a dog

The ISX likes to work they are kin to the old 2 strokes when it comes to idling they do not like idle with their EGR system,they are new to me but I have Kevin (Azdieselman) and my buddy at Cummins in Phoenix that guide me lol 

[niles500]

Clifford,  could the fuel modulator on My DDEC2 be the cause of the turbo not spooling and the coach not moving when starting from a full stop  at 6 degree plus grades? Tac just pegs at 1000 rpm

[niles500]

BTW I don't even know that I have one 😅

[luvrbus]

Clifford,  could the fuel modulator on My DDEC2 be the cause of the turbo not spooling and the coach not moving when starting from a full stop  at 6 degree plus grades? Tac just pegs at 1000 rpm
[/quote

DDEC  don't use the modulator they have a boost sensor if the 1/4 inch hose has cracks or broken or if the sensor is bad the DDEC 11 can be a real pain we have Vans DDEC ii spooling up check the hose and the BAR rating on the sensor the sensor is not exspensive and 1 does go bad over time some just jump the sensor and forget about it I don't like to do that myself

[waterlodge]

Clifford,  could the fuel modulator on My DDEC2 be the cause of the turbo not spooling and the coach not moving when starting from a full stop  at 6 degree plus grades? Tac just pegs at 1000 rpm
[/quote

DDEC  don't use the modulator they have a boost sensor if the 1/4 inch hose has cracks or broken or if the sensor is bad the DDEC 11 can be a real pain we have Vans DDEC ii spooling up check the hose and the BAR rating on the sensor the sensor is not exspensive and 1 does go bad over time some just jump the sensor and forget about it I don't like to do that myself

On mine the hose was ok but still no power off idle. I had the same issue, 1000 rpm and no go. It would be blowing a hint of black smoke so that's just all the air it got. Replaced air and fuel filters to no avail.
Once it hit 1600 rpm it would start boosting and take off. The boost would peak around 2000-2100 rpm at about 22 psi. IIRC the gauge only went to 25 so it would be almost pegged.

I agree rigging sensors sucks although blowing smoke for a few seconds might get you over the hump. Maybe make a "knight rider" style boost button on the dash LOL.

It's worse on the higher HP models. I had a 1989 Setra S-215 with , I think, a 430 or 450 HP 8V92 and it did better off idle than the 500HP one. The 500HP has a huge turbo that doesn't make any boost off idle.

[niles500]

Thanks for the replies, I did replace the sensor but I'll check the hose for cracks or leaks

[luvrbus]

Check the hose to the bypass on the blower to,not knowing the mileage the bypass valve may need cleaning or replaced they stick and then depend on the turbo for all the air just the opposite of the way they were design to work 

[TomC]

My truck has the Caterpillar 3406B 400hp mechanically controlled with Allison HT740 mechanically controlled. I picked the HT740 since the 4000 series 6 speed would have been twice the money and then have electronics. With my 11R-24.5 rubber (476rpm) and 3.55 rear axle ratio, I have a comfortable cruising rpm of 1690 @ 60mph, 1830 @ 65mph, 1971 @ 70 mph, 2112 @ 75, 2253 @ 80. Considering my normal cruise is 60-65, I'm right in the correct rpm range. Good Luck, TomC