BIG EDIT

I think turbo is bad. Big exhaust leak where turbo connects to exhaust, and from actual seam of turbo and where the actuator arm exits turbo coupled with loud whooshing noise.

 

You mentioned GVWR, have you run this across a scale to see how much it actually weighs?

10 ply load range E tires would help you out I think.

Steve

 

Fixing the exhaust leak on my truck made a big difference, in both power and coolant temp. I also would take the radiator out and blow all the crap out of it if you haven't already. Does it build coolant pressure?

 

Make sure your cooling system is in top shape, hills + boost can quickly raise temps.

Check your vacuum pump if your turbo is not boosting - could be an easy fix. Not a bad idea to grab a cheap boost gauge and install to have an eye on what is going on.

Move PMD to somewhere cool on the bus.

Swapping out the muffler for something straight through will gain quite a bit of mid-range power and lower temps. This would also shave off a small amount of weight.

A chemical intercooler (water or alcohol, injection, etc.) might be a good option for the steep hills.

 

For the suspension. Looks to me you are overloaded on the stock springs. if you dont whnt to buy HD springs. Try a set of Helwig Load Pro helper springs. fairly easy install. They really will help a Lot with your heavy load and reduce sway
Its not a bus, but I have a set on my 1/2 ton. They made a big difference when hauling my Lance self contained camper in the back and towing my fishing boat boat or toy. Truck rides good unloaded too.
For tires I run 285- 75- 17" AT

 

ETA
Derp, many of my chassis suggestions do/may not apply to your van. Sorry.

If you haven't changed the water pump with the later H(igh)O(utput) design, you'll probably want to. Higher flow that's also more balanced from side to side.

Also, if you have dual thermostats, ensure you have the "heater bypass orifice."

>>>>>>>>>>>>>>>>>>>>>

OK, we have a lot of ground to cover here, so let's just DIVE RIGHT IN.

2002 gmc Savana 3500 6.5L
4 window shortbus
20 ft long with bumper extension
145k miles
NICE, LOW CHASSIS MILES BUT PROBABLY MANY IDLING HOURS ON THE ENGINE.

weight: 10,500
(1000 above GVWR)

Front axel:4100
I'VE NO IDEA HOW STOUT YOUR SOLID FRONT IS, BUT US INDEPENDENT FOLK ARE SUPPOSED TO GO EASY ON THE FRONT.

Rear axel 6400
(300 above axel rating)
(300 above current rear tire rating)
I CAN'T FIND THE REFERENCE AT THIS INSTANT, BUT THE CORPORATE 10.5" IS A SOLID PIECE OF KIT--RATED FOR 8,600 AXLE LOAD. NOW YER, SPRINGS, TIRES, AND FRAME MAY NOT BE, BUT THE AXLE, GTG.

Current tire size 245/75 r16
"EASY" TO STEP UP TO 265 (WHAT I RUN, 4X4 IFS) OR EVEN 285

I have put at least 25k into the conversion and mechanical work combined. I love this rig and want it to last as long as physically possible. I didn’t pay attention to weight as I was doing the build clearly lol. Don’t suggest a different engine or avoiding steep grades or lowering weight, it is what it is at this point I’m not rebuilding the rig.
I'D SUGGEST MAKING SURE YOU'RE PROPERLY INSURED. STATEALL WILL GIVE YOU $1,300 OR SIMILAR GARBAGE FOR A TOTAL LOSS (I HAVE HAGERTY, AGREED VALUE $12k, AGREED TOTAL HULK BUYBACK $1k, SO i CAN AT LEAST KEEP THE "NEW" ENGINE AND TRANS. YEARLY PREMIUM IS $209. YES, TWO HUNDRED).

Things I’ve installed/replaced since I purchased at 128k;

power steering pump
injectors and injector pump
brake lines
wheel bearings (after almost losing a tire)
starter
Metal injector lines
Valve cover seals

Main issues:

1.) Lack of power going uphill (sometimes can’t go over 20 when flooring it) (about to fix exhaust leak, unknown how much of a difference that will make)
LACK OF FUEL (CLOGGED FILTER(S), WEAK LIFT PUMP, ETC) OR LACK OF BOOST (BAD VACUUM PUMP/WASTEGATE, BAD TURBO, EXHAUST LEAK(S) ON THE HOT SIDE OF THE TURBO SYSTEM, ETC)

2.) high temps when going uphill (260 F)
DO NOT EVER DO THIS AGAIN.
I RUN AT NO MORE THAN 225, Y LONGEVITY MV. CHECK THAT YOUR COOLING STACK IS CLEAN/CLEAR (SPIDER WEBS AND TUMBLEWEEDS BETWEEN THE AC CONDENSER AND RADIATOR, OIL COOLERS ETC). YOU SHOULD HAVE ENOUGH FAN, BUT MAKE SURE YOUR CLUTCH IS ENGAGING PROPERLY--FAN SHOULD BE REALLY LOUD WHEN WORKING.

3.) brake fade/ smoking brakes despite engine braking
FOR 15K MILES I'VE BEEN HAPPY WITH 18A489SD AND CERAMIC PADS. INCLUDES GETTYSBURG-MEMPHIS-LA-BOISE-GETTYSBURG TRIP AT 19k GCVW.

ONE ALLEGEDLY "EASY" UPGRADE MAY BE A LATER REAR END, WITH DISK BRAKES.

A BIT "OUT THERE," BUT IF YOU NEED MORE ENGINE DRAG, ADDING A 4X4 TRANSFER CASE WILL GIVE, WHAT, 2.3:1 MULTIPLICATION OF SUCH.

Questions:

A. Any advice for longevity given my continuous heavy load.

b. I’m upgrading brake pads to be bendix semi metallic and rotors to R1 drilled and slotted and brake fluid to dot 5.1 because my brakes have smoked a few times and pedal has gotten spongy even with as much engine braking as I can do when going down mountain passes. What’s max speed I should go engine braking in first gear?

I DON'T GO ABOVE 3600, BUT WILL RUN THERE "CONTINUOUSLY" WITHOUT FEAR (LIKE 10-30 MINUTES, NOT ACROSS THE SAHARA). PER MR HEATH BACK IN THE DAY, "6.5 IS A REVVER, NOT A TORQUER. ESPECIALLY WHEN CLIMBING, ALWAYS DOWNSHIFT "EARLY" TO LOWER EGT AND INCREASE COOLANT PUMPING, ALLOW MAX AIR AVAILABILITY FOR THE FAN CLUTCH."

Should I go locking or limited slip?

I PREFER LOCKING (LIKE MY G80, OR AN AIR LOCKER ETC). WITH A LIMITED, IN MY EXPERIENCE, "DRIFTING" IS FAR TOO COMMON.

Should I switch to a different vehicles axle for better clearance? Pumpkin sits really low.

IF YOU GO FROM 245 TO 285, YOU'LL PICK UP OVER AN INCH OF GROUND CLEARANCE ( ( 285 - 245 )mm * 0.75 = 30 mm. IT'S TOUGH ... BIG RING GEAR, BIG PUMPKIN.

 

OK, we have a lot of ground to cover here, so let's just DIVE RIGHT IN.

I think this Savana is a 4x2 so he's got IFS in front just like the 4x2 pickup trucks. AFAIK no Savana got the P chassis beam axle setup like GMT455.

IMO the cutaway vans rear suspension lack the travel of the truck chassis cabs, the frames are humped at the rear axle and there's not a lot of room for travel. On longer buses they used to fit a bagged trailing axle for extra support when fully loaded, that typically bumped the GVWR up to (or close to) 15,000, but still the unit would be a Class III vehicle.

Bags in the rear might not be a bad idea for this since it's running heavy AND has that big box obstruction mounted on the roof in front, which doesn't help with aerodynamics. I wonder how much power that slab up front steals?

Steve

 

Personally I'd go with Firestone air bags wih an on board pump and cab controller. You'll never have to worry about springs and can adjust to the load. It'll ride better than over springing especially when the load is lighter.