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Proper Final Ratio

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  • Owner

I know this a common issues for guys adding wheels and oversized tires but to show a quick clip of running down the pavement semi-flat ground at 66 MPH and the tach shows a prefect 2,000 RPM's. The EGT floats today about 600*F, and boost is about 3-5 PSI. Had to try mounting to the side window and see if the GoPro could do it. I found out the LED lighting screws with the frame rate with the flashing displays which its not actually doing.



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  • Owner

I just had a good conversation with @Hutch24v just a bit ago. He's looking to squeak out just a bit more MPGs out of his truck. Again he's another person with improper ratios and EGT's are higher and fuel usage as well. He's running 285's and 47RE transmission which 4th gear is 0.68 vs. my 5 speed at 0.75 so it down lower in the final ratio. I'm going to try and help out and look at both of his tunes and hopefully get him the MPG he need to survive the "Biden Energy Crisis" which is affecting all of us like here its $6.029 for diesel in New Meadows when I rolled through this morning. 


For optimal cruising RPM for 65 should be close to 2,000 RPM's. Like I mention to Hutch24v if your EGT's are below 600*F your doing better than 20 MPG. If your EGT's are higher than 600*F then your lower than 20 MPG. Just a rule of thumb for guessimate on MPG. Just consider at 65 MPH your consuming at least 3.25 gallons of fuel per hour for 20 MPG

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What is the ratio to aim for? 3.5-.7? Thought I saw that number somewhere. And when calculating for ratios, do you start at the 245/75r16 on the door panel for 3.55 gears, or with the optional 265/75r16? Thanks!

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  • Owner

3.73 is about the best you can get for towing and daily use economy wise. 3.55 is good but getting wee bit low for cruising RPM personally. I don't per se race so top speed doesn't matter. What does matter is being close to 2,000 RPM at 65 MPH. Just for info Thor is a true 3.73 on stock 265/75 R16 so it's about 2100 RPM at 65 MPH.

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So 2 part question. As this best relates to economy. What numbers do you look for in your data log and then which parameters are then adjusted? Timing vs egt, etc?

Ill post a datalog just took, as HW try to do a doc graph, still not great at it. Also the ECO is quads way of tracking MPG?


2nd part relates to the larger injector theory. Read a lot about the .010 with the higher pop pressure. Shorter duration, precise fuel. Im trying to calculate that to crankshaft degrees. Microseconds is a small unit. For (rounded) max canbus and wiretap (~6000us). Im getting 1.2*. Does that sound right? When adjusting the timing parameters, the event STARTS at the desired value, and ends when duration complete?

Sv275 ii.csv

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2000 RPM is close to 75 for me. Not great with wind drag. This is with 3.55 275/65R18. (Essentially a 275/75r16) 47re. RV275. Already stepped down a tire size, and it improved, but don't want to go much smaller. Would consider 3.73 but lots of work for a 4x4.


First attempt at graph, wish could get 2nd axis as a bar instead of line. Didnt include boost, its mostly 0-1 psi. A 64/64.


I dont think its bad, but unsure where to try tweaking or improving. Any pointers would be greatly appreciated!


Current daily,


Levels: 6



Fuel Load Timing: 0

Low PSI Timing Reduct: 4.5

Timing Reduct Scaling: 90

Light Throttle Timing Adv: 6.0

Light Throttle Timing Load Limit: 37


Timing vs rpm

1500: 16.5

2000: 19.5

2500: 23

3000: 25

Timing Max: 26


Pump Stretch: 1900

TPS Pump max: 100

TPS Pump Min 50

Minimum Pump Tap Fueling Percentage: 0

Pump Low Boost Scale PSI: 15


Boost Scaling: 40


RPM Limit: 3400


Power Reduction:


PSI %:115

PSI %:116

PSI %:117

PSI %:120

PSI %:122

PSI %:124

PSI %:125

PSI %:125

PSI %:125

PSI %:126

10 PSI %:127

11 PSI %:129

12 PSI %:131

13 PSI %:135

14 PSI %:137

15 PSI %:140

16 PSI %:145

18 PSI %:150

20 PSI %:

22 PSI %:

24 PSI %:

26 PSI %:

28 PSI %:

30 PSI %:


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I wouldn't set my CANBUS to 115% right at 1 PSI, that's a big jump from 0 PSI, and you do have slightly larger injectors, too.


Some will say your 1500 RPM timing is too advanced and won't spool the turbo real good, but you have the Low PSI timing reduction set at 4.5⁰ which is what I believe allows setting that 1500 setting higher.


I don't run wiretap so can't comment on that section.

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  • Owner

Economy speaking you shouldn't be over 100% till after 15 PSI at the earliest kind of like running the secondary on a carb all the time (not efficient). Timing is all wrong too and over advanced creating negative torque being that advanced. (Again not efficient) No retarding state so spooling is poor. 

Edited by Mopar1973Man
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Thanks for taking a look. Im figuring with this setup is only 1 step larger on tires and injectors, shouldn’t be too hard to find something good. The larger turbo may make it trickier. 


I thought there was some good info posted here. From 2019 and back then 2.99$ was ‘high’!

When running .010 about 82% where was starting. Theres no smoke @ 115%. The truck doesn’t take off well for sure though, @LorenS. One thing Im fighting is load, or perceived load. Data time cruise was about 22-25 with the 150s. I have to put load limit up high for these..


Id start lower on the 1500 timing, but big jump to cruise.. I find it ‘bounces’ between 16-22*. Ill start with lowering the CANBus.

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@ThreadzyI am totally, 100% open to suggestions. Had quad less than year now, so still new to me. Before that was the original edge JWA!


When I went down in tire size, I didnt see the load decrease much. But could definitely notice it with other gauges, and acceleration/gearing.

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with rv275's I don't know that 115 is too much offidle.   its a % of stock table and your right foot still controls the scale from idle to WOT at a given psi.   


My go to method for find the 0 psi setting is setting it to a given % then going snap from idle to WOT from a stop does it light grey haze at 0 psi?  black? no smoke?  black means take it down a few % no smoke bump it up. light grey is perfect.  

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tone it down to like 110 at 0 psi then work up by 1% until 4 psi then go by 2% then bump that up to %5 at 10-15 psi.  throw as much fuel at WOT as you can at it without smoke then use your right foot to drive nice and get good mpg.   then repeat the process if no smoke at snap wot take off then bump fuel by %2 across the board until happy.


for timing you def want to retard the timing when under load.

Edited by Me78569
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@Me78569Okay, thank you. Done, and put load timing reduction to 1 for now. Also can adjust base. Ill post another log later, or try another graph, if those sensors are most valid.


Anyone want to take a stab at injection event in degrees from uSec? Ive read a lot of research from you all, its all been fascinating and helpful. :thumb1:


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Here’s what I would try on your timing. 
Fuel load 2-3

Reduction 4-5

scaling 50% 

Light load cruise 2-3 roughly about 20-21 degrees total

1500- 14


2500- 22/23

3000- 27/28

max -30 

As been said your tire size is hurting your load %.  I keep my truck in drive up to 55 - 60 mph. At 55mph my EGTS float around 550-600 on level ground.  Rpms are about 2,100. I want to say my load is about 25%.  Anything much above 55 mph I turn the over drive on. 
My brother in laws 02 has rv275’s and an HX35.  I’ve got his canbus starting around the mid 90’s. Still blows black on take off and under lower psi boost. I need to cut more. 

Edited by Threadzy
Fixed some spelling
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