1991 Cummins Suburban

[Spur]

I'm surprised at the weight too. I was expecting 9-10k. When I had it stripped down (only one seat, no flooring, etc.) it was about 6500 lbs. I want to get a dry weight as well without anything in the back. Figure it will be somewhere between 7500 and 8000.

I know I've said this before but just to reiterate, I've got 37" tires, 4:10 gears.

Interesting comments about the boost. I'll have to look into. I had a long conversation with a very experienced diesel mechanic. He seemed to think the boost was good. But he builds race trucks so his perspective might be different.

Right now I've got my starwheel and smoke screw backed all the way out flush to deal with 9000 ft of altitude. Only way I could get the smoke under control.

 

[Spur]

Thought y'all might like to see my new work truck and daily driver. Signed the papers today.

2006 Dodge 2500 4x4 5.9L 24v Cummins. 6-speed manual transmission. Short bed, 4 door, Silver. Only 46k miles . It is pretty much exactly the truck I wanted and I feel lucky to have found one with such low miles. I really wanted a 5.9 and not the new 6.7. It has a couples dings here and there but mechanically it's in super shape.

 

[Metcalf]

M&H sells a spacer that give you a little more retraction on the fuel pin, or you can mill the cover a bit to give you a little less fuel.

If your making that much boost your probably pushing the fuel pin down allowing more fuel. The factory truck makes about 15psi max so I would suspect that the spring in the AFC is tuned for those pressures.

Now that I have a gauge ( no matter how crude ) in the truck I will try and record what I am running for boost on my truck. I think you have a hx35 on your truck right? That is going to build boost much quicker than stock.

I think you can flip the starwheel over to gain a little more preload on the spring also.

If you haven't, replace the flat head screws on the AFC with some allen heads. I had the flat heads start to strip messing with stuff.

 

[Spur]

Good advice. Thanks metcalf. I've already had those screws start to strip too.

You're correct in that I have an HX35. I also have an 18 cm housing. Still I'd like to find a way to have a little less turbo lag.

 

[chasespeed]

Okay..... I see boost at highway speeds.... just the nature of the beast.

It has to do with many factors.

I am usually cruising around 1800 rpms... boost... 3-10psi(I really dont watch my boost gauge, until it gets 45psi or higher...) I try to keep my EGTs around 600* or less for best mileage.

I have used my pyro for more than a few years, on several diesels, for the best mileage, and it always works. Its the only REAL tell tale of how much fuel you are using. Boost is relative.

My avg mileage, not towing, and not driving hard, is 19-20. I have seen 24mpg on long highway trips.

Running 35s, and 3.55 gears with a NV4500 trans....

Keep your EGTs down, and the mileage will go up for any given speed, load, etc.... that is when your engine is running just the way it wants to.

And your buddy is right BTW. Though, the type of engines he prefers to build is irrelevant. The guy who did my pump, and a few other odds and ends, builds race trucks, sled pullers, etc... but, also works on heavy equipment... BIG shop.

Another thing I would look at is your timing. That alone can be a big deal on a p-pumped engine....

Chase

EDIT, for less turbo lag, try a 14cm housing.... I will check around, and see if I have one.... I dont know if I sold the last one with the turbo or not....

 

[Metcalf]

You can always change the exhaust housing, but that is probably going to make even more boost and add a little more fuel. I'm going the HE351 route, that gives me a 9cm wastegated exhaust housing and a 60mm compressor wheel.

Another idea, install a 'valet' switch on the air line going to the AFC. This would allow you to turn 'off' the AFC at will. I have been wanting to try this. I think this would help a lot with long distance mileage, and full power would be available with just a flip of a switch for passing/mountains/fun. This would limit fuel to the base pin setting of the AFC.

 

[Spur]

My EGTs really depend on driving conditions obviously. Normal driving on flat ground is about 6-700. Normal hilly driving is about 800. I can hit 1000 on mountain passes. I once hit 1100 towing a trailer over a pass. But that was before I had my starwheel and smoke screw turned down.

I mostly think the truck is running really well right now. I'm happy with the power and the mpg's. One thing I'm worried about is the water temp. Back before all the upgrades it ran a solid 180 F. Now it runs at 190 F and can easily creep up to 200 F. It has gone up to 205 F a couple time on particularly steep mountain passes. When it hits 205, I usually slow down or pull over to let it cool down. I'll get a very worrisome smell in the cabin like burning plastic. I've looked all over to see if I can find anything that is melting but have never found anything (doesn't mean it's not there though). My thought is that it's overheated coolant that I'm smelling but I don't know.

My plan is to replace the mechanical fan with dual electrics, each one set to a different thermostat. What temp thermostats do you think I should use? One mechanic told me I should use a 190 and a 205 but that didn't make any sense to me.

 

[chasespeed]

I dont exactly remember how the truck drove stock, or with the small turbo.. BUT, cruising manners are the same, and the EGTs are pretty close too.... just need to be MUCH MUCH more conscious of the foot input...

Chase

 

[Spur]

I dont exactly remember how the truck drove stock, or with the small turbo.. BUT, cruising manners are the same, and the EGTs are pretty close too.... just need to be MUCH MUCH more conscious of the foot input...

Chase

Sorry but I'm not following what you mean. I need to be lighter on the throttle? I drive like an old man as it is. Only time I rev it up is shifting from 4th to 5th. It is a lot easier to keep momentum when i get it up to 2000 rpm for that shift, especially if there's any kind of incline.

 

[Metcalf]

Did you use the factory 1st gen fan and clutch? There is a replacement HD clutch and beefy fan with larger blades and more twist. I don't think electric fans are the way to go. Do you have a shroud on the fan? What radiator?

 

[Spur]

Did you use the factory 1st gen fan and clutch? There is a replacement HD clutch and beefy fan with larger blades and more twist. I don't think electric fans are the way to go. Do you have a shroud on the fan? What radiator?

Factory fan. Replaced the clutch but don't think it was HD. Radiator is a replacement aluminum. No shroud. Fan blades had to be trimmed to allow for clearance with the hood (even with a very thin hood pad.)

Temps aren't the only reason I want electrics. A couple pages back I posted about an incident with the fan and the radiator. There is very little clearance between the fan and the the radiator. Even though the frame has been boxed there is still a tiny bit of flex. When I was doing some off-road driving, the frame flexed a bit and the fan kissed the radiator. Made a little quarter-arc imprint on the back of the radiator, flattening the fins. It's very minor but could possibly be part of the reason why my temps are now higher.

 

[chasespeed]

Did you use the factory 1st gen fan and clutch? There is a replacement HD clutch and beefy fan with larger blades and more twist. I don't think electric fans are the way to go. Do you have a shroud on the fan? What radiator?

If you are running that warm, that bother with electric fans. I use the stock mechanical fan, and fan clutch... have towed 15k without the temp going over 215. Check and make sure you are getting good airflow, and the fan is the right depth in the shroud.

If you are smelling cooked plastic... check your heater box....

What I am saying to the above... if you are getting 18-20 without really trying, that is about par for the course with a 12v. Actually with 37s... yeah, I would say you are okay. Boost isnt the determining factor. 600-700 cruising isnt that bad.... I would find a spot, and see if you can even maintain speed while keeping your temps down to the 400-600 range... you might not be able to....

Do you have a P-pump? Or a VE rotary?

Have your buddy bump the timing up a few ticks... I was running 20* before this pump... running 19* now....

You can always try to get more mileage... but, remember, you ARE driving an 8k BRICK down the road... with the areodynamics of a building.... factor that with the height and size of running 37s.........

Chase

EDIT... ignore what I said about the fans... in your case, it will probably solve your cooling problems.

 

[Spur]

Like I said, I'm fine with the mpg's. But it's fun to play around with. Part of the joy of owning a 1st gen is fiddling with the knobs

I'll check the heater box. So am I correct in assuming that 205 isn't really overheating? What temp thermostats would make the most sense? Maybe 190 and 205 would be the way to go? That's assuming that I can track down the weird burning plastic smell and it isn't a problem.

It's a VE pump from PDR. It's turned up a bit. If I remember correctly it flows 205. They call it their "hot rod" pump. It has their mildest fuel pin, but still a bit more aggressive than stock. Also Bosch 190 injectors.

 

[Metcalf]

If your fan is THAT close to the radiator...mmmmm. Can you move the radiator forward? While electric fans look like a good clearance option, I have never seen them last that long, unless they are OEM electric fans with proper gauge wiring, HD OEM relays, and OEM temp control. All the aftermarket stuff I have seen/used has failed and left friends stranded.

You can get a 'fin' comb and straighten the radiator a bit, or spend a LOT of time with a small screwdriver

How much did you trim off the fan. The 1st gen fans ( stock ) are nothing special. The HD replacement has a wider blade that might do better after you trim it for hood clearance.

You need to get a shroud on that thing. If your trimming the fan for clearance you are going to have a hard time fitting a proper shroud. A shroud will help A LOT though. Could you run a fiberglass hood with a scoop/blister in the middle for more clearance. That might give you enough room without having to trim the fan....and allow a proper shroud.

Also. I didn't look back to see what size radiator you used, but I remembered that GM factory diesel trucks from the 80s came with a SUPER wide radiator. I can't remember if it was core support specific, but it might be something to look into.

On the plastic smell. I would vote the turbo being close to the heater or a/c box on a GM in the engine compartment?

 

[chasespeed]

If your fan is THAT close to the radiator...mmmmm. Can you move the radiator forward? While electric fans look like a good clearance option, I have never seen them last that long, unless they are OEM electric fans with proper gauge wiring, HD OEM relays, and OEM temp control. All the aftermarket stuff I have seen/used has failed and left friends stranded.

You can get a 'fin' comb and straighten the radiator a bit, or spend a LOT of time with a small screwdriver

How much did you trim off the fan. The 1st gen fans ( stock ) are nothing special. The HD replacement has a wider blade that might do better after you trim it for hood clearance.

You need to get a shroud on that thing. If your trimming the fan for clearance you are going to have a hard time fitting a proper shroud. A shroud will help A LOT though. Could you run a fiberglass hood with a scoop/blister in the middle for more clearance. That might give you enough room without having to trim the fan....and allow a proper shroud.

Also. I didn't look back to see what size radiator you used, but I remembered that GM factory diesel trucks from the 80s came with a SUPER wide radiator. I can't remember if it was core support specific, but it might be something to look into.

On the plastic smell. I would vote the turbo being close to the heater or a/c box on a GM in the engine compartment?

Not a big fan of electrics either. What I have done in the past, is use OEM fans. Say you probably want 5500CFM.... find some OEM fans that are about close to that.... or, get creative, and run 3... 2 primary, and a 3rd set to kick on at the upper limit of your "comfort zone".....

There are always solutions.... in my Bronco, I ran 2 Taurus electric fans.... controlled at different temperatures....

Chase