How do you get "free power" out of a 3.9 Cummins?

[Tigger4X]

With a gasser you can port the intake and match the exhaust to your headers, cold air intake and such, but being new to black smoke I have only heard stuff about getting free power out of a diesel mill. Some of the things I have heard have been about using jet or cerami-coating on intake and exhaust parts, turning up the pump, using higher rated internal springs, etc.


My main goal is to get the best MPGs, like around 30 or so, out of the 3.9 Cummins in an extended J-truck. I'm looking to dispell myth from actual cold, hard facts. There are plenty of high performance diesel magazines out there, but I'm looking for the best bang for my buck mods that will support really good MPGs.


Anybody have real world street knowledge or non-high modded diesel dyno info :confused:

[68_Gladiator]

ill be interested in this, although not the 3.9 ive always wanted a 5.9 in my 67' and one day maybe ill have it

[Mikel]

If you go to www.4btswaps.com (http://www.4btswaps.com) you'll find many write-ups on increasing power. Getting up to 180HP is just a matter of turning a few screws. Going over that requires some expenditures.

30MPG in a FSJ with a 4BT is a bit unrealistic. Most people with 4BT's in full size trucks get low to mid 20's (I get about 24 in my J300).

[710 Burner]

Turning up the power = turning down fuel economy.

[El_Diablo]

UNLESS you do so by increasing ease of air flow in and air flow out

black smoke is a bandaid for cooling a diesel motor, its just wasted fuel and nothing more, contrary to what many think it is not required to make power with a diesel, your just throwing that potential fuel power out the exhaust

[Mikel]

Turning up the power = turning down fuel economy.

I've gone from 105HP to about 180 and my mileage hasn't noticeably changed. This is because 95% of the driving occurs at the same power levels.

[gotmike]

up your horsepower, lower your gear ratio's... maybe add a nitrous drip for off the line there was a guy in the diesel power challenge who had it on all the time... and if it were rigged up to only comeon during the initial depressing of the pedal then it would act more like a sequential turbo setup without using ton's of nitrous and that would help your fuel mileage... but only to the extent of how often you have to change out bottles... then there's CNG... which can be compressed at home or bought from filling stations and would probably get you that 30 mpg mark...

[lifted-04-lj]

Do you have a rotary or inline pump?

advance the timing a bit. You'll burn the fuel you put in more completely.

rotary pumps.... tighten the linkage and turn the screws a bit. 60 hp injectors do wonders (see 1st gen CTD). Just big enough for more power but have good atomization.

Inline pumps (see 2nd gen 12V CTD). Grind the plate, bump the timing, Mild injectors.

I've heard of using HY-9 turbos from a 3rd gen CTD for better midrange and top end.

Propane in VERY small quantities(<10%) works as a catalyst to diesel.. burns the fuel faster and a byproduct is N2O ;):cool: Propane for power buys head gaskets.. in bulk:eek:

Mileage is driven by the right foot.. more powerful diesels get better mileage if driven properly.

[YJ-4BT]

If you go to www.4btswaps.com (http://www.4btswaps.com) you'll find many write-ups on increasing power. Getting up to 180HP is just a matter of turning a few screws. Going over that requires some expenditures.

30MPG in a FSJ with a 4BT is a bit unrealistic. Most people with 4BT's in full size trucks get low to mid 20's (I get about 24 in my J300).

X2 :thumbsup:

[auzjtruck]

Hi, if you want more power and milage on deisel, the best way to go is [LPG], Propane,you will get atleast 30% more power and milage , the system is electronic injected and is about 30% injection of LPG, you can get more info if you google Injected Propane Deisel, all the best mate ,Joey:drivin:

[Mikel]

up your horsepower, lower your gear ratio's... maybe add a nitrous drip for off the line there was a guy in the diesel power challenge who had it on all the time... and if it were rigged up to only comeon during the initial depressing of the pedal then it would act more like a sequential turbo setup without using ton's of nitrous and that would help your fuel mileage... but only to the extent of how often you have to change out bottles... then there's CNG... which can be compressed at home or bought from filling stations and would probably get you that 30 mpg mark...

Adding other fuels kinda defeats the purpopse of having a numerically higher MPG. That has to be factored in too ;)

[gotmike]

actually the compressed natural gas is super cheap... so even factoring that in makes for awesome numbers... the one guy was getting 45-50 mpg in a built duramax...

http://www.dieselpowermag.com/tech/0905dp_natruell_cng_conversion_kit/index.html