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Noob with too much truck?

3058 Views 28 Replies 11 Participants Last post by  Chrisco148, 
Chrisco148
Hi all, i just bought a cummins and as it turns out it my be too much motor for my goals!! I'm trying to get as best mpg as I can with this truck but am not sure what a realistic goal is, 18-20? Here's what I am working with,
1996 ext cab dually 4x4 315/65/16 tires, (haven't confirmed my gears).
3000 miles on rebuilt motor and tranny.
BW turbo (was told s300 66mm)
200# injectors
60# springs
3 angle valve job
4k gov spring
18* timing
4" exhaust to 6" single stack
No fuel plate. Maxed out star wheel, smoke screw and Afc full forward.
Gorend triple disc converter
Suncoast valve body
Bilit input.

Ok, my first goal is to confirm as much as this as I can, I did confirm no fuel plate, I backed the smoke screw out two turns as well as slid the Afc housing toward the firewall an slightly adjusted the wheel. Currently this truck rolls so much smoke before the turbo spools it's insane, after spool it clears out to a haze and hold on!! These adjustments didn't help too much, I still see $$ pouring from the stack.

I have only had the truck for a few days and since the fuel gauge Is currently not working (horay!!) I'm fearing getting 4mpg right now!!

Ok enough rambling, before I get knee deep into this project do I have too much motor? I've never had anything that I had to detune but am willing to put in the work if it's achievable.

I have learned more about tuning for power in the past two days on this forum than I have in the 18 years as a diesel mechanic, I appreciate the time put into this forum and hope I can help someone in the future. It's what it's all about...
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7
Good to hear you're loving your truck except for the fuel mileage. As always, I must remind the foot is the biggest mpg control :hehe: First thing I would adjust is your sw. Here is a link for that which will answer all your questions. http://www.cumminsforum.com/forum/9...pre-boost-smoke-screw-waste-gate-answers.html

Secondly I would think you have to get some smaller injectors. Are they 7x.014?
18-20 is reasonable depending on the terrain you drive. Mixed driving I would say you can get that anywhere but in town unless you keep your foot out of it and are on flat ground it will be harder to get that. Hope this helps!
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mitchell78749
do the 12v get better milage than cr motors?
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mitchell78749 said:
do the 12v get better milage than cr motors?
Click to expand...

Stock yes the 12 valves generally get better fuel mileage. Now that being said truck owners generally want power... since 12 valves are mechanical you can't adjust "on the fly" like you can with a cr. It will cost more money to modify a cr for much power or economy but you can choose between the two at anytime, within reason. Several of my friends who have CRs and have modified them do better than I do on fuel mileage. I can get 18-20 in town with a light foot but if my foot gets heavy so does the fuel mileage... all the way to 14-16.
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'89dodge
i might be wrong but your injectors might be a little big.

you can do twin turbo set up to help cut smoke and improve your mpg some since your spool up would be better.

fix your fuel gauge should be the sender unit in the tank thats messing up. then report back with some mpg,

and like whats been said keep your foot out of the thing, and those 35" dont help towards your mpg goal.

what stall is the converter do you know? a low stall is very efficient that might help some
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S
Not much you can do about the dually, 4x4, 315/65/16 tires part of your equation (without big money) and those are substantial. If you have 4.10 gears, there is another substantial MPG hit that is significant. Sounds like it may not have been the right truck if MPG was high on the importance list.
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T
Chrisco148 said:
Hi all, i just bought a cummins and as it turns out it my be too much motor for my goals!! I'm trying to get as best mpg as I can with this truck but am not sure what a realistic goal is, 18-20? Here's what I am working with,
1996 ext cab dually 4x4 315/65/16 tires, (haven't confirmed my gears).
3000 miles on rebuilt motor and tranny.
BW turbo (was told s300 66mm)
200# injectors
60# springs
3 angle valve job
4k gov spring
18* timing
4" exhaust to 6" single stack
No fuel plate. Maxed out star wheel, smoke screw and Afc full forward.
Gorend triple disc converter
Suncoast valve body
Bilit input.

Ok, my first goal is to confirm as much as this as I can, I did confirm no fuel plate, I backed the smoke screw out two turns as well as slid the Afc housing toward the firewall an slightly adjusted the wheel. Currently this truck rolls so much smoke before the turbo spools it's insane, after spool it clears out to a haze and hold on!! These adjustments didn't help too much, I still see $$ pouring from the stack.

I have only had the truck for a few days and since the fuel gauge Is currently not working (horay!!) I'm fearing getting 4mpg right now!!

Ok enough rambling, before I get knee deep into this project do I have too much motor? I've never had anything that I had to detune but am willing to put in the work if it's achievable.

I have learned more about tuning for power in the past two days on this forum than I have in the 18 years as a diesel mechanic, I appreciate the time put into this forum and hope I can help someone in the future. It's what it's all about...
Click to expand...
I dont know that with a 4x4 Dually Auto you can expect to see 18+, It might be possible, doesnt seem likely... Just my not so humble opinion.

Once you get some of the smoke out the lower end you will find your turbo spools faster, and obviously you will improve the fuel economy. Just start backing the star wheel and smoke screw out till you have no smoke, then slowly add smoke screw. Once you have just a little haze off the line, you’re most likely good. Then adjust the star wheel to give you a little more fuel till you have a light haze at the mid RPM.

The other thing to pay attention to is how the Turbo spools now. You should be able to tune a lot of the smoke out without loosing that spool time. (Maybe even spool it faster)

If you really want to dial it back for max fuel economy and don’t mind loosing power, then smaller injectors might serve you well. With smaller injectors you may not be able to spool the turbo, but there are lots of options on that too.

The engine mods will have no real effect on fuel economy. Star wheel/smoke screw mods only affect fuel consumption during hard acceleration; they have absolutely no effect on freeway fuel economy. Fuel economy while maintaining a speed is only going to be changed by a few things such as:

  • Modifying how much drag the vehicle has (Aero dynamics/weight)
  • Parasitic loss due to backpressure or accessories driven by the belt (Turbo could affect this)
  • Fuel spray angle and atomization levels (Injectors)

Compare a truck with a gutted AFC and a truck with a very conservatively adjusted AFC, all other factors the same, will get the same freeway fuel economy, if you can keep your foot out of it.
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J
too much truck, I wish I had that problem
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GAmes
If you back the timing off to 16 the turbo will spool up easier and solve a little of the rolling smoke problem.
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Chrisco148
All n all I like what I'm hearing, it seems 18-20 may a push but not impossible. I did find the tag on the rear that says 3:54 but both pumpkins have sealant so still need to verify.

As far as the spool now it seems real laggy until 2k ish, then it takes off like a bat outa he!!. Kee in mind I don't have a good base line for comparison, I need to find someone with a stocker and make friends with him weather he likes it or not!!

As far as the injectors, this one I am not having luck with finding out how to verify what they are. There are 3 didgit numbers on each. 256? Any help on this one would be awsome.

As far as stall speed, I don't think there is.

I found a thread talking about turning the sw and smoke screw out all the way, no smoke, no power. Then turn them back in until your where you need to be. What it doesn't say is how far to back them off, can I go to far?

Today we took the truck out to a deserted road and opened it up, the boost hit 58psi and still climbing!!!! This doesn't seem good to me, what boost psi is safe? But I guess that's what you get with no fuel plate and non gated turbo.

Thanks again for all the replies!!!!
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Chrisco148
I am game at setting the timing to 16* but will need to wait for the tool kit! I will see snap on next week. 18* also seems high! is that safe for a daily driver?
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J
I run 18* on stock head gaskets pushing 300k
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T
Chrisco148 said:
All n all I like what I'm hearing, it seems 18-20 may a push but not impossible. I did find the tag on the rear that says 3:54 but both pumpkins have sealant so still need to verify.

As far as the spool now it seems real laggy until 2k ish, then it takes off like a bat outa he!!. Kee in mind I don't have a good base line for comparison, I need to find someone with a stocker and make friends with him weather he likes it or not!!

As far as the injectors, this one I am not having luck with finding out how to verify what they are. There are 3 didgit numbers on each. 256? Any help on this one would be awsome.

As far as stall speed, I don't think there is.

I found a thread talking about turning the sw and smoke screw out all the way, no smoke, no power. Then turn them back in until your where you need to be. What it doesn't say is how far to back them off, can I go to far?

Today we took the truck out to a deserted road and opened it up, the boost hit 58psi and still climbing!!!! This doesn't seem good to me, what boost psi is safe? But I guess that's what you get with no fuel plate and non gated turbo.

Thanks again for all the replies!!!!
Click to expand...
If the AFC is all the way back towards the firewall, and you take the smoke screw too far back, your truck may stall when trying to leave parking spots due to NO rack travel. Once the truck is completely smoke free your back far enough.

(Again, based only on my research)
With a stock head gasket you should be good for 35-40PSI.
Add studs you are fine to 50PSI.
O-rings bring you to the 70-75 range
Firerings can be good to 100 PSI.
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The_Joe said:
If the AFC is all the way back towards the firewall, and you take the smoke screw too far back, your truck may stall when trying to leave parking spots due to NO rack travel. Once the truck is completely smoke free your back far enough.

(Again, based only on my research)
With a stock head gasket you should be good for 35-40PSI.
Add studs you are fine to 50PSI.
O-rings bring you to the 70-75 range
Firerings can be good to 100 PSI.
Click to expand...
I have go agree with The_Joe on this one. If you keep running that much boost on a stock head, it is only a matter of time before you'll blow the head. :banghead: The most I personally ran on mine before doing the head was 16 degrees but I have several friends who have run 18 degrees before on a stock one, just not that much boost. Keep it up! Let us know how it turns out.
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GAmes
Under the hood, next to the latch, should be a tag with the differential gear ratio, paint code(s) and some other info.
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Nor'Easter
Don't need a fuel gauge to check mileage.


Sent from AutoGuide.com Free App
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Chrisco148
I forgot to add the arp head studs, and it is not a stock gasket. Full upper end rebuild 3000 miles ago. So I can't not control boost since I do not have a waste gate correct? Can I add one? Or can I control the boost if I put a fuel plate back in? This makes sense in my head, if I control the max limit of fuel I control boost....

As far as not needing a fuel gauge to figure out my mpg I agree, but I also don't know if I'm getting 16mpg or 4!!!! Mpg becomes more accurate with more miles so if I want an accurate figure I need to travel farther than 100 miles between fueling.

Anyway to verify what injectors I have?
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'89dodge
fuel plates only limit wot fueling instead of allowing the pump to give it all she got.

i say go 200miles and fill up.

i am not sure on injectors.
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Acm home
I have similar truck with 4.10's and 235/85r16's 5 speed. Getting 17mpg in town.
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builtcummins
light foot is all i can say. seems normal that a 66 has a bit of smoke and dosent light untill 2k..
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