Timing for DD and MPG.

i have searched through several pages of this section and all the threads that i come across about timing and daily drivers or fuel mileage seem to get hijacked and away from the subject. below is my current set up on the truck with the fuel cut back to 450cc. i also have a set of .020 DVs also that were originally in the pump when i got it. its also an SO motor with an auto trans and 3.54 gears

my situation is that if i run the truck in OD down the road at 1800 rpms the egts run between 800* and 1000*. if i kick it out of OD and run it up to 2400 rpms it will run between 400* and 600*. IMO i think the timing set at 24* is too high and requires me to run higher in the rpms to get better fuel mileage and to run cooler on egts. i have also noticed that everyone seems to say that these motors like higher rpms, but not sure if thats for the racing/pulling set ups or for a daily driver.


Hamilton 181/210 cam
Hamilton 110# valve springs
Hamilton heavy duty pushrods
S366 bullseye turbo (66/71 .88 AR)
Stainless Diesel T4 manifold
DTT transmission with billet input and output shafts
JL Machine 7x12 injectors set to 250bar
215 ppump benched by diesel performance engineering and set at 600cc
.084 conversion ppump lines
181 DVs

thanks

michael

Correction with OD kicked out its between 600* and 800* and i found this out yesterday pulling a trailer hauling a truck around in the city. I was thinking of dropping it down to between 18* - 20* timing but want to see what everyone is running for daily drivers. Also another thing is my horrible fuel mileage i am getting between 10-13 mpg right now just daily driving.

I would try injectors with higher pop pressure, 250 bar seems too low for optimum fuel economy.

24 valves run a lot of timing when cruising down the road at the right conditions. I'd try more timing with about 290 Bar pop pressure on the injectors. I say try, because all you can do is test, tune, evaluate, over and over till you find what produces the best fuel economy.

alright ill give that a try and see what i can come up with. maybe its not my timing thats the issue its a lower pop off pressure. other than the turbo swap and smaller dv's the truck came set up like this.

that turbo isnt going to be a good mileage turbo either, and those injectors again arent mileage oriented.. need a tighter housing to burn more fuel at lower rpms that will also cool those egts, smaller holes with higher pop off will attomise better..

well i went with this turbo thinking it would be a hell of a lot better than the S472 that was on there. thought with the set up on injectors and pump that i didnt want to go too small.

oh im sure the smaller turbo is better for dd and prolly didnt loose that much power.. but you understand how much smaller and efficient the stocker is for mileage. also consider that a stock 215hp 12 valve injector thats pretty much accepted as one of the best mileage injector is only 5x.010 and your running a lower popoff with more and bigger holes.. just saying.. its hard to balance any kind of descent mileage with higher hp turbos and injectors.
im happy with my combo and 430 gears im getting mid 13's mpg's.. i also have a 12housing for the bottom end on my hp turbo with bigger gates for the top end.. this gives me anywhere from 7+ psi cruising and 650*egt cruising down the highway

i run like 2-5 psi just cruising down the road. i do understand the whole bigger hole and more holes deal with the injector. i just want to get the egts down and which sounds like i need to up the pop off pressure first before i change any timing.

Chevycummins said:

i run like 2-5 psi just cruising down the road. i do understand the whole bigger hole and more holes deal with the injector. i just want to get the egts down and which sounds like i need to up the pop off pressure first before i change any timing.

Click to expand...

And a smaller a/r housing.

yep i would set those injectors to around 300 bar and see about finding a smaller a/r housing and you will prolly pick up more than a couple mpgs and loose zero hp..

Is there a smaller housing for a T4 flange? Or am i gonna have to get a new manifold?

got the injectors re-set to 300 bar and truck has better throttle response but i still set at about 800* cruising 70-75 mph at approx 1800 rpm's. if i kick out over drive i run at about 500* cruising between 60-65 mph at approx 2200 rpms. if i leave over drive engaged it will climb back up to 800* cruising at 60-65 mph. at approx 1600-1700 rpm's. also i do carry a little more boost during cruising speeds, closer to 5 psi instead of approx 2-3 psi i was before. gonna check with chris at ED to see if i can get a smaller housing for this turbo with a T4 flange to keep from buying a new manifold and to see what my options are.

with my old combo(granted 12 with a drop in cam) i was in the exact same boat, high egts and low mileage.. i changed me exhaust housing on my super b special(64/71/14) to a 12cm housing, mileage climbed so did boost, egts came down, a lot! I made the difference between having to tow in 4th and 5th..

yeah like i said i will see what chris can do at ED otherwise i can get the new billet wheel from Bullseye that makes this turbo respond like a 64mm version. it sucks that they dont offer a smaller housing for this turbo but i am sure chris can do something cause its a borg warner turbo.

for the rest of that combo i was running 32* timing with 370 injectors and 191's. made right at 540 like that on drakes superflow..

i am wondering if i need more timing since i run cooler at higher rpms. i know in theory that i am of course moving more air and spinning the turbo faster. i wonder what higher timing would do or would i just waste my time going to like 28-30*

or maybe put the 020 DV's back in and run it. the pump has 181 DV's now and plate is set at approx 450 cc's.

you will be spraying out of the bowl at 28-30. however, with the same size injectors and 30* and full cuts, i got 21 MPG highway and ran about 800* EGT in a 2wd FWiW

i thought with the SO motors you were able to go higher on timing???

Mine is an SO and at 30* it was out of the bowl, I have the melted pistons I could show how much.