Super duper MPG 6.4 help!

So as everyone knows I always like to max out the possible MPG when building an engine for myself, well I am putting together an engine for my 2011 ram 2500. What I have for it is a BGE short block 5.7 eagle cam and eagle heads, intake, exhaust... I am thinking about cheating and using one layer of the factory head gasket (about .010 thick) to bump the compression and quench a little more (11.75 VS 11.16) . My current truck has a SRT8 6.4 short block and cam with eagle heads (12.3 compression) and runs fine on premium (.050ish quench) but the bigger cam is obviously bleeding a little more compression that the 5.7 cam I want to use in this one to bring the RPM down a tad. My question is what is the maximum advanced intake closing point ABC position of both cams? I can't really find cold hard specs for either, the compression calculators want to know the .050 intake closing plus add 15 degrees. I want to make sure I end up at the same or very slightly less dynamic compression in the BGE engine with the 5.7 cam as I have in the SRT engine with the SRT cam.

With these specs on these 2 cams what degree is the intake valve closed down to .050?

215/221 @ .050"
.353"/.333" lobe lift
.574"/.541" valve lift
121 LSA
108 ICL

186/208 @ .050"
499/493
115LSA

this is the 1st one , need the icl for the 2nd one

Thanks!

I found 101 ICL on the second one

#2

Very awesome thanks!

So it seems the dynamic compression will only be .1 lower with the stock head gaskets in my new engine than my old engine. If I went with the single steel shim head gasket I would be nearly .5 higher and since I am borderline on my compression already and now with less overlap with the 5.7 cam to dilute the charge I will be using the stock gaskets.

I really wish we had e-85 local, I would have put in a set of SRT pistons AND run the thin head gasket.

So I got it about ready to fire up and had to take a break, the final combo for now is basically a BGE short block, 5.7 MDS cam, Eagle heads slightly ported, fully radiused and mirror pollished exhaust valves to help keep them from being a hot spot in the chamber and the intakes got an "almost" regular 3 angle valve job but I made the cut on the outer edge of the valve (the one parallel to the stem) as clean and sharp as possible and is actually about 5* off parallel to the stem to make the edge even sharper to help break up fuel droplets as it passes over. I chickened out on the single layer head gasket mostly because I think I would just have a little too much cylinder pressure for pump fuel with the small cam, I used a factory 6.4 head gasket.

I will keep bothering the local gas stations to start carrying e-85, if they ever do it then I will swap in SRT8 pistons and the thin head gasket... or maybe build a 5.7 about 14 to 1 with early 5.7 pistons and milled eagle heads!

Well I been driving it last night and this morning and dang it is smooth, torquey and very throttle responsive. Fuel trim seems to be needing to add a lot of fuel, I have seen it near 25% a lot but has not set any lean codes "yet", I have a set of SRT8 injectors I may throw on to see if that helps keep it closer.

It has 3/4 tank of who knows what kind of fuel that is probably a year or two old (I bought it 6 months ago and it looked like it had been sitting a long time even then) but no knock sensor activity at all so maybe I could have gotten away with more compression. It runs very smooth even with old gas. I will run this tank out and run it with fresh fuel before postin any MPG results.

For a huge truck it has lots of TQ, crew cab 8 foot bed 4X4 3.73 gears and limited slip rear and a bed full of firewood right now and no problem barking the big 20" tires on dry pavement. There is a lot more TQ down low that the SRT8 in my 1500 but not as much at higher RPM.

Did I mention this thing is extremely smooth? With my head under the hood at idle it is smooth like a lexus V8, very weird, not even the slightest quiver.

I don't know if anyone is reading these or not butt I did get lean on both banks codes but the trim was very close on both sides so I put in a set or 392SRT8 injectors and that brought the trim numbers down a ton and made it even more responsive, it will flat go sideways with the 8 foot bed full of firewood!

You have at least one reader.


Bank to bank trim is an improvement but I wish there was a way to dial it in cylinder by cylinder, especially at highway cruise part throttle.

You changed 8 injector to get “in the ballpark.”
It would be good for MPG to give each cylinder the capacity injector it needs.

Having used an un-lit propane torch to find vacuum leaks,
I have wondered in the past whether adding a cheap flow gauge on a propane bottle, then tapping a small test port into each runner to add a measured stream of extra fuel when at highway cruise would allow finding rich or lean cylinders. Keep increasing propane flow until that bank’s Oxygen sensor registers a change.

Having a threaded test port on a individual runner also makes in possible to screw in a “ Flow restricter” to do the opposite: reduce airflow a bit to balance AFR in each cylinder.

Getting each cylinder near to 14.7 AFR would help MPG,
but taking all cylinders to 21 AFR would improve MPG even more.
Remember at +20 AFR tendency to ping or detonate goes WAY DOWN, just like running AFR below 10 suppresses pinging.

I'm reading your post, I just don't know what to make of them. I do enjoy the information. What do you use to tune everything? I do have custom tune on my 12 durango but I feel like it could use some help.

I read them

If you are running headers, you could use a temp sensor gun to identify lean cylinders. Lean ones would be hotter. Could also weld bungs into each tube to test with wideband AFR gauge set up.

As usual I am reading HRD. Always appreciate the out of the box thinking to get the most out of factory parts. It is what hot rodding is all about.

Hey Dave,

Following along, tried to send PM but your mailbox is full

I have not done any empty testing with it yet, loaned it out before I got to fill it and check it, they put some gas in and screwed up my numbers, so far the only solid numbers I have got was pulling an 8000LB skid steer one way on a 20ft deck over flatbed and a 1/2 ton 4x4 2011 ram the other way and got 11MPG so I was a little disapointed with that but the TQ pulling the big hills was very nice. It never triggered any knock sensor activity on the 89 octane I filled it with before I left.

On a side note I used it to haul a 500 gallon water tank when fighting the forest fire here and when the tank was full it only squated about 1/2 inch and still rode very stiff, parked next to a single wheel one ton 18 ram diesel and noticed someone has added thicker leafs than his truck has and air bags, I have no idea what they were doing with this truck but evidently something very heavy.

Another update, finnaly got to make a round trip on the highway with the truck basically unloaded, 18.5 MPG or about 2 mpg less than my 1/2 ton with a 6.4 SRT8 would have gotten on the same trip. It never pings audibly or on the knock sensors in the data stream even on 87 octane and heavy loads where the SRT8 would rattle on anything less than quality premium fuel.

The 1/2 ton had 3.55 gears, less weight, less aeromatic drag, more compression, more cam and MDS

I really wish I would have run single layer real thin head gaskets to get more compression but it runs really nice as is. Much more low speed TQ with less high speed passing power.

What computer are you running? What tuning if any? That reads like possibly something is at least logging data?

I'm running the stock 5.7 computer and watching the live data stream on a regular scanner. I had to run 6.4 SRT8 injectors to get enough fuel with the 5.7 computer, it kept setting lean codes before that.

If you dont have one/two already, I'd get at least one wide-band. I've used Innovate motorsports programmable* LC1 before to replace upstream narrow band sensors and also data log. What this will help even without ECM tuning is determining exactly where open loop is AND because its a heavy truck, where COT (catalytic over temp) is. If you have access to tuning software you can find out your target AFR... hint it almost certainly is not 14.7:1. In 2003-2009(?) NGC computers it is something like ~14.4. Moving that up will increase MPG, note the LC1 can do that even if you cannot tune the PCM.

Its been a few years, I have *no idea* about 6000lb truck tuning but the scheme on about every vehicle under heavy load that i had a wide-band in will eventually start dumping fuel to cool off the cat and keep it from melting. I don't know what wizardy they do with your gen computer these days but I'd imagine a heavy truck gets into openloop quite often and when towing probably can get into COT often. You can see this on a large hill with a wide-band 02 sensor output where your cruising at part throttle closed loop at the target AFR, then as throttle increases (TPS v) the computer will switch to open loop tables and there will be a noticeable drop down to 12-13AFR for a period of time. With enough load for long enough and then BAM suddenly drop AFR to 10:1 or richer (COT) until you let off the enough on the throttle. Knowing those points that can get you a couple MPG just by changing your foot habits. I suspect you are getting into open loop a bunch and thats were the tune will help.

Not quite sure I follow on what the LC1 will do without tuning and how it works with a computer programmed to function with a narrow band O2, is it taking a reading and sending the computer a fake signal to get the desired AFR?

I understand about the cat over temp, I am not too worried about the cats honestly, selling them will just about pay for a set of long tube headers...

I really wish I could afford tuning the truck, idle timing is not very steady and way too late and I suspect it could stand more advance everywhere, I would like to be able to use the shift button to lock it into a gear like the old "auto stick" would do, there are still plenty of un-nessacary down shifts. I could also just tell it to run 14.7 or even leaner until I hit WOT. I am also thinking about adding a bigger throttle body and modifying a vararam to feed more air at lower throttle angles so it don't downshift as much.

Yes, the LC1 wide-bands have an programmable output emulate a narrow-band. You can keep output strictly to emulate the narrow band signal or skew it in any way you want. including for e85 (would need a tune unless flexfuel). **The skew would only ever affect part throttle closed loop.** Somewhere more than part throttle the PCM uses tables and your going to get a programed/modeled AFR regardless. Data-logging from from the wideband will help you determine those points and actually tell you if its getting too lean/rich and where. At WOT in your combination, your PCM never did have any idea where AFR is and it wouldn't even if the engine was completely stock. Seriously. There are actually a couple outputs on the LC1, e.g. you can send an output to a gauge or datalogger like a diablo trinity while still using the narrow band emulator for the PCM.

You mentioned e85; you will need to do your own math to figure at what price-point that makes any sense and a wideband (unless your PCM is flexfuel compatible). Its not likely, but it might be if cheap enough.


My point is that the PCM literally has no idea they exist and will dump raw fuel anyways in certain situations...ALOT of fuel actually. Speaking of the catalytic, this is oversimplified but the downstream o2 sensor exists to know if the catalytic is 'working'. It tests for a difference in O2 from the upstream sensor before the catalytic vs after. The only way to get a less free o2 in that measurement is for there to be unburnt fuel going into the catalytic . Burning more of that fuel in the engine will get more MPG... and possibly higher egts



Seems like you spent plenty on whatever this experiment is. I'm just trying to enable you to finish it out.

I certainly apreciate the help, that LC1 sounds like a very fun and useful tool I had never heard of, I'll have to look into it. SO just to be clear, I could set it to something like 15. AFR and it will send a signal to the computer that would trick it into thinking 15.5 was actually 14.7 during closed loop?

WOT open loop I am sure it is trying to dump more fuel but like you said it is not able to tell anything and I am now pumping a lot more air through it also, it could actually be lean, I am sure it is a total crapshoot at this point but a tuner is what $1000 more plus paying someone that knows how to do it right and not a hack like me and the cost of the LC1... I am terrible with computer stuff, heck I can't even post a picture on moparts! I have been working on dodge stuff for well over 20 years, ASE master certified (for whatever thats worth) so I do have a basic Idea how the stuff works to diagnose cars but programming is beyond me.


As for cost, I don't really have much into this project, I bought an entire burned 2014 6.4 truck for $300 and sold the cats for more than that and also the trans. The truck I put it all in was dirt cheap because it had a blown up 5.7 in it and actually came with another super low miles complete 5.7 engine and new lifters, head bolts, gaskets and a ton of other stuff I have used to get customers vehicles fixed. I do all the work myself with my 9 kids. This is the only way a guy with 9 kids can accomplish stuff like this. I don't know a low buck way around the tuning issue besides what I've already done though I am going to look into the LC1 more now and see what I can do with it...

I just did a bit of a hypermiledge test with this truck, cruise set on 62 MPH on a 100 mile all flat ground round trip with nothing in the bed but 3 fishing poles AC cranking and got 22.7 MPG. Even my 318 2wd dakota won't do that, heck the closest I came was doing 65 MPH AC off and got about 17 MPG, even though I have to use premium in the giant 3/4 ton it is cheaper to operate... (I still prefer driving the dakota though).

What trans is behind your 6.4?

545rfe

I have been watching all your posts, also. Most of my trucks end up getting fixed and sold to support my hobby, my kids are all grown up. When I find a nice 2500 or 3500, then Id like to try the modified 6.4 in it. I am surprised the the 5.\7 PCM works, I always figured they would have pulled timing out of the bigger motor, as well as compression. Kind of like what they used to do on the 3 series truck motors from the 60's and 70's. As someone else mentioned, your an out of the box thinker and doer. Always need more of them. Jim.

The 6.4 is lower compression than the 5.7, that's why I put eagle heads on it, they take 10 CC out of the combustion chamber. Also both BGE and SRT8 6.4 cams has slightly more duration so I used a 5.7 cam to give it a tiny bit more time to push on the crank before the exhaust valve opens and the intake valve closes a tiny bit earlier to build even more cylinder pressure. Also the 6.4 uses EGR and the 5.7 don't so when you put a 6.4 in a 5.7 truck you get a free EGR delete.

I am going to sell this truck and build an engine for my newly aquired 2015, going to put in SRT8 pistons and zero deck em, BGE heads, 5.7 cam for real high cylinder pressure and hopefully keep it out of detonation. If I had access to e-85 I would run the SRT8 pistons, zero deck em and run the 5.7 cam and eagle heads for super high cylinder pressure. I think this would be hands down the cheapest way to run a 3/4 ton truck.

I just put a bid in on 4 RAM trucks today, One of the 2500's looks like a keeper, Ill be in touch. Jim.

Well I sold it and moving onto another one, a friend with a 2010 cummins borrowed it when his truck was down and just had to have it. For a replacement I bought a 2015 5.7 4 door 4x4 long bed, same basic truck but all stock with 5.7, drove it 400 miles this weekend and got 2 MPG less than the 6.4 truck did on a same trip and I was trying real hard to get good MPG. It did cost less to operate because it can run 87 octane but not a lot of difference. I was babying it to try and squeeze more MPG out of it and keep it from downshifting all the time... It had to down shift a ton more to get up hills and never had anywhere near the TQ the 6.4 had.

I have another 6.4 to build for this one and this looks like the recipe I will be following.

BGE heads shaved .025, I will do the same thing with the valves, mirror polish the entire exhaust valve head in the drill press, machine the margin on the intake valve to a very sharp edge to break up the fuel drops and minor porting on the heads along with porting the intake to more closely match the heads.

SRT8 short block

Can't decide on 5.7 or BGE cam, I feel the BGE cam will give me more power as the RPM go up but the 5.7 will give more MPG, also the switch from eagle to BGE heads will give it just a little more power as the RPM goes up and it will have a hair more compression... I thought about retarding the 5.7 cam a few degrees to give it just a tiny bit more time to push on the piston before the ex valve opens. Anyone know how much I can retard the cam timing before I get a computer code?


The other option I been considering is an eagle 5.7 with a piston swap to the early pistons, not gonna have the TQ of the 6.4 but could possibly do better MPG again with premium fuel only of course and I can easily sell the 6.4 to buy long tube headers and a vararam...

Thats funny, had a 4.7 Dakota that I liked for a daily beater, a fellow showed up today and had to have it. Gotta sell when the money is good. Picked up an Eco-Diesel to drive in the meantime. Keep up the posting. Jim.

Well I sold it, bought another 2015 with 5.7 long bed 4x4 4 door, same configuration same gear ratios (3.73) same trans and well it gets significantly worse MPG. On the same run with the cruise set at the same speed yesterday I was only able to manage 18MPG with this one so I got some work to do. I know it may be a tiny bit cheaper to operate this one as it runs perfect on low grade gas but the TQ has taken a huge hit with this 5.7. Even towing, or normal driving it is sucking more fuel than the 6.4 truck did with a lot less TQ.

I have another 6.4 just sitting around and like I mentioned before I am trying to decide exactly how to configure it, I am leaning toward SRT8 pistons, BGE heads and 5.7 cam, exhaust and intake... should give me a tiny bit more compression and a little more airflow thru the heads and extend the RPM up a tiny bit without hurting the bottom end TQ.

For better engine efficiency the “low hanging fruit” is to go from a factory air/fuel ratio of 14.7 to 20 to 1 or more.

That probably means an aftermarket fuel injection system or open source Megasquirt.

To convince yourself of this buy
an old carb single cylinder generator,
a wide range O2 sensor,
and run the generator engine at 14.7 and 20 using an electric air heater to load down the generator.

I know y’all talking truck but my 15 SRT 392 just got 28 mpg on a trip to Hilton head (75 mph) down and back. Lie guage was same as fuel-miles added up. The 4 cylinder drop out really makes a difference.

The best my 2020 T/A 392 has gotten was 22mpg, with the wife driving, that was in eco mode.

Just read a review of the 2024 model Honda Accord where it is mentioned that the I-4 gasoline engine static compression ratio is 13.9 to 1 and
-surprise- the air to fuel ratio is lean.

Not sure how Honda does that lean trick and still meets NOx standard.

I know people don't want to hear it but generally anything leaner than about 14.7 burns cooler not hotter.

When talking performance engines they tend to make best power around 12.5 or so because of the cooling effect of the extra fuel and yes running leaner than that gets hotter but only up to around stoich and equally important to hot rodders the 14.7 makes less power so running leaner than 12.5 gets hotter and makes less power so not a good idea under WOT. WOT at about 14.7 AFR is as hot as you can get the burn to be and that is when pistons melt not 17 to 1 AFR.


However part throttle is a different story at say 17 to 1 would run cooler than 14.7, it is just science that it would make less NOX. A lean mix vs stoich plus EGR will provide better odds of the fuel molecules combining with an oxygen molecule. EGR molecules just get in the way of a complete reaction. I think the reason companies have not typically done very lean mix instead of EGR is that it is not as easy to keep the cat lit and functioning properly with very lean mixtures VS richer with EGR. Maybe honda fingered out a way to clean up the lean mix in the exhaust with a new fangled cat or something.


If I was designing an engine from scratch I would shoot for something around 14 to compression with maybe a slightly retarded cam timing to bleed off just a tiny bit of the compression and allow for a longer push on the piston before releasing cylinder pressure into the exhaust and it would also have a much better expansion ratio. And yes I would run a very lean mix at part throttle.


I am curious do you know how lean they are claiming it is running? Also is it direct injected?

Yep, “way out there” on the lean graph a very high compression ratio does not knock
like this 2016 post shows in the Porsche graph by a guy named Gruden

https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2182726/1994-5-9-magnum-upgrades.html

same graph shows that a “pig rich” mixture does not knock

another
look at how the NOx curve “brown line” drops with lean-ness to near zero percent just past 16.3
but the graph uses “percent”
which is way bigger than “parts per million”
and ppm would getting to EPA levels,
which legally are grams per mile.

On a side note,
notice the news articles
about Death Row executions
carried out “painlessly”
with pure nitrogen.