Kennedy Boost Valve yields MPG increase under heavy tow

[Mark Rinker]

Ran an 1,100 mile trip last weekend with the Kennedy Boost Valve installed for the first time. I ran the whole trip with the Predator set on 'tow' 40hp tune. Added a moderate propane injection rate (20hp?) on the return trip to help run the hills better.

Made a few adjustments until I was getting a solid 7-8lbs unloaded (empty trailer) at 70mph. Mileage was 14.5, with lots of construction areas and Chicago toll booths. Definate increase in power and mileage after the very first tank. EGTs were steady in the 700-750 degree range.

On the way home with a 29' boat (total of 10,000#...and a HUGE wind drag) I averaged around 65mph and was making 14-18lbs boost with the same BV setting. EGTs in the 900 range with a few peaks over 1100. One of the nicest attributes: No downshifts from high gear, even on some moderate to steep grades in hilly Wisconsin west of the Dells.

Amazing what the right boost curve can do! The extra air to burn really made the stack work under load. It was basically 'pick your speed, set the cruise, and forget that you have a 10,000# object bigger than your truck behind you."

My average combined whole trip (#2 + propane) MPG was well over 12, with a reduced average fuel cost of ~$2.50/gal. This was a time pressured 'thrash' with no attempt to conserve on fuel. With that as a goal, and a lighter foot, I think a 14mpg trip average could have been attained.

I cannot tell you how fun it is to play with traffic up long steep grades with a boat of this size in tow. :)

[Kennedy]

Awesome! I would not have expected the increase to come at such moderate boost levels, but that's really great!

[Mark Rinker]

(EDITED LATER: My boost observations are an 'observed average' from my digital gauges - but I suspect they actually are reading lower than actual. Boost levels before the BV were 2-3 unloaded and 6-8 loaded. This seems low for a stock LB7. The MSD software reads significantly higher. Interesting, the MSD is pre-intercooler, digital gauges is post-intercooler...)


JK, given the extra fueling described, and your knowledge of my towing, what would you recommend as nominal and peak boost levels at 2K rpms (cruise) with 8-12K in tow?

BTW - I am running a K&N filter, but bone stock (cat-less 2001) exhaust and muffler. Probably time to upgrade...it never ends once you start the quest for MP... :)

[DmaxMaverick]

You're gonna run outa tranny before you get much further, especially towing.

[Mark Rinker]

I expect you are right, DMax. In the mean time, I use my right foot as the moderator. I have limped it with a loaded trailer on a hill with the cruise control set.

Noticed today that after the boat and trailer were removed, it took awhile for the Allison to relearn its shift points. Had some harsh shifts in T/H, but turning it off smoothed things out until it adapted to no load.

[mark45678]

I expect you are right, DMax. In the mean time, I use my right foot as the moderator. I have limped it with a loaded trailer on a hill with the cruise control set.

Noticed today that after the boat and trailer were removed, it took awhile for the Allison to relearn its shift points. Had some harsh shifts in T/H, but turning it off smoothed things out until it adapted to no load.


I think all the early duramax trucks ran good but the trans tune limited how much power you could throw at them. The lly truck I had would deal with more HP then the 2001 , the 01 after removing the juice shifted harsh and the 2004.5 lly shifted normal right away. Makes you wander if you swaped the TCM out of a newer truck how would the lb7 act?

[Mark Rinker]

Been wondering EXACTLY the same thing.

Oddly, I have been towing heavy, daily, for over 3,000 miles with 40 extra HP of diesel (Predator Tow Tune) and probably 40 extra HP of propane (only on when trailer is loaded).

Either my right foot, my TCM, or a little of both have learned not to slip, and no more problems with 'limp mode'. Occasionally I will have a harsh shift, but usually find that I didn't have tow/haul on, and should have.

[redvette33]

what's the diff between the KD and the PPE boost valves? Or is it just a matter of preference?

[dieseldummy]

The KD boost valve has a spring loaded diaphram that is adjustable. The PPE is a simple little thing that bleed off boost so the actuator doesn't see full manifold PSI. The PPE is at best a crude device and doesn't work very well IMO. I would have sprung for the KD valve, but it must be gold plated looking at what it costs...

[Kennedy]

It's actually solid gold. :rolleyes:

[Mark Rinker]

I have a PPG valve laying around somewhere. Worthless. I think if you drilled it out a bit, you might be able to smoke hooch out of it, but other than that, its a waste of aluminum, IMO. :)

JKs BV works, and its variable for your application and amount of fuel being added over stock.

You get what you pay for. I paid for both. DOHHH! (Homer Simpson)

[VA_Dmax]

Is the boost valve something that is really only beneficial if you have a programmer to add more fuel?

Or is there any benefit by just adding the boost valve, with the only mods being intake and exhaust mods, and no programmer/chip?

[Mark Rinker]

I would think with intake and exhaust flowing free(r) than stock, you might get some performance gain and/or lower average EGTs with a bit more boost.

Couldn't hurt, unless you cranked it up and set overboost codes. Personally, I'd add gauges first and establish a baseline of data to see where 'stock' boost and EGTs are.

[Kennedy]

The boost valve will do best when you are running with enough load to cross 10-12 psi and should work regardless of engine tuning. The factory fueling will make it difficult to run higher boost levels w/o dropping out of OD though...