1993 Prevost xl40 vs 1964 MCI mc5

Dreadnought · November 06, 2024, 07:44:43 PM

I test drove a Prevost xl40 with a 500 bhp 8v92 and an Allison transmission. It felt very slow to take off compared to my 1964 MCI mc5 (with 8v71 and manual spicer 8245). Is this normal? I don't know what to expect. Does the auto trans make a bus feel sluggish at to take off?

Even with 40,000 lbs plus I expected 500 bhp to feel more peppy. My usual MCI mc5 has about 280 bhp only and weights maybe 26,000-30,000

The engine diagnostic light was on but I didn't have a ddec2 code reader.

The prevost rode very well but it is heavier.

plyonsMC9 · November 06, 2024, 09:28:49 PM

Good evening!

Is the Prevost just slow to take off before the turbo kicks in? I'm guessing the Prevost w/ Turbo & 8v92 would take more time to "take off" than a smaller standard transmissions bus. However once the turbo kicks in there should be strong acceleration.

Disclaimer: I've never driven a bus w/a standard transmission.

Kind Regards, Phil

luvrbus · November 07, 2024, 05:46:49 AM

Depends on the Allision ? with the 755 CR 5 speed Allison they get out of gate good with the older Allision some start off in 2nd gear and you need to manually down shift for 1st gear start, the DDEC ll will have the older Allison ATEC ,I would ? the 500 hp rating on a DDEC ll`

muldoonman · November 07, 2024, 01:52:15 PM

The 1991 (Turned up to 500HP with a 755CR Allison) Prevost XL (40,000 pounds) I owned for many moon's hauled azz when you pushed the pedal at a stand still. No lag what so ever. Maintained good speed on hills also. If a turd at start,, Might start looking for problems.

Tom Y · November 09, 2024, 08:57:37 AM

My 5C weighs in at 26,700 lbs. So saving some.

Busted Knuckle · November 11, 2024, 07:43:51 PM

Could also be a bad boost sensor, or loosing boost at a clamp somewhere.
I had an 8V92 in one of our older Setra's that took off like a scalded dawg most of the time. But something happened and it was a SNAIL. I called Don Fairchild and we did some talking and after he had me check a few things he told me to go get boost sensor # yada yada and see what happens. I did and was happy to call him back and tell him he was spot on!
I've also seen loose clamps cause low boost/slow starts too!

BK

Dreadnought · January 25, 2025, 08:36:52 AM

Just found out that compression on cylinder 7 on that Prevost is down.

Taking the heads off that Prevost with engine in situ is possible I believe but a major undertaking.

It's off my list now

lvmci · January 25, 2025, 09:01:54 AM

Good idea , more options out there...

luvrbus · January 25, 2025, 09:36:49 AM

Quote from: Dreadnought on January 25, 2025, 08:36:52 AM
Just found out that compression on cylinder 7 on that Prevost is down.

Taking the heads off that Prevost with engine in situ is possible I believe but a major undertaking.

It's off my list now

How was the compression test taken,you can not do a compression test on the 8v92 with out the engine running @ 900 rpm,spining one with starter dosen't do it ,running a compression test on a 2 stroke right is a all day job and it costs

Dreadnought · January 25, 2025, 10:24:10 AM

Quote from: luvrbus on January 25, 2025, 09:36:49 AM

How was the compression test taken,you can not do a compression test on the 8v92 with out the engine running @ 900 rpm,spining one with starter dosen't do it ,running a compression test on a 2 stroke right is a all day job and it costs

I'm not sure, that's what the dealership said they did. It was a trade in. They don't claim to know anything about it and would like to get rid of it. I think it scares them. Their own technician is used to sticks n staples and refuses to touch it! I found the honesty of that dealership refreshing tbh.

I didn't know that about a compression test on a 2 stroke.