Tuning Rb25S For Eflex And E85 .

[AngryRB]

From memory

6900 - rev limit

1100 - fast idle. when you back off the engine will sit at this RPM for a couple of seconds before going back to idle

1200 - Injector pickup, ie. when you back off the injectors cut out untill this RPM

800 - idle speed

850 - air con idle

If you increase the 1200 to say 1300 you will notice that when the revs drop they will come down softer, ie. the last 200 RPM will be more gradual. Adjust this if it seems to be overshooting too far below the fast idle.

I could have the 1200 and 1100 around the wrong way, it has been 5 years since I've touched a PFC. It is very easy to figure out when you know what to look for

cool thanks, ill try adjusting them and see what happens..

[rob82]

I think its more a case of knowing what they mean as in elec load vs no elec lod load fuel resumption revs and elec load vs no elec load idle speed .

I had the Tech Edge wide band back in mine today and as I thought it was running a little lean in the light load low to medium engine speed areas .

I richened up the very low engine speed areas when loaded ie 400 and 800 rev colums at higher airflow rates . Thhis makes the idle torquier and less likely to stall with very small throttle openings when moving off . With the fuel resuming at 12-1300 revs nothing I did fixed the bucking kangarooing problems I had .

ATM I'm idling at 1.01 - 1.02 Lambda but it can go lean towards 1.08 at hot restarts which doesn't give any drivability issues . Light load cruise is around 0.98 to 1.00 L . As the load ramps up its falls to 0.95 and around boost it gets into the 0.92 to 0.85 range . If I go WOT as it comes on boost it gets to 0.80 L and I had to look up petrol L/AFR to see what it equates to .

To save you looking the tables I found show this

Lambda .....Petrol AFR .... E85 AFR

0.75 ...........11.03 ............. 7.32

0.80 ...........11.76 ............. 7.81

0.85 ...........12.50 ............. 8.30

0.90 ...........13.23 ............. 8.79

0.95 ...........13.97 ............. 9.28

1.00 .......... 14.70 ............. 9.77

1.05 .......... 15.00

I'm getting a better handle on what the E85 Lambda numbers mean but I had to go back and search for some petrol Lambda numbers to see what the corresponded with in petrol AFR . I did go to start a new thread on Lambda vs AFR but I didn't think too many would be interested a didn't post it .

Something I would be interested to knoe is Lambda numbers with E70 because most of the tables and calculators only show E85 and Lambda = 1 or 9.77:1 AFR . Logically E70s chemically correct mixture would be a slightly higher AFR number because of its higher petrol content .

The difference wouldn't be huge but if we could gain a slight consumption edge thats not a bad thing .

Just on cost I love paying $1.15.9 for Eflex when its cheap compared to Ultimate 98 at $1.70.9 when its not . I think in rough terms I'm paying 2/3 the price of Ultimate was a while back and getting 3/4 of the consumption I used to get though my petrol tune wasn't real good . Eventually I will go back to Ultimate just to clean my petrol tune up but overall I prefer the Eflex E70 .

Ongoing , cheers A .

I'm not sure your getting what lambda means... I think what your really searching for is the leanest mixture you can run without causing drivability issues or engine component failure?

I think what you really need to do is to compare egt's vs lambda and find the sweet spot it will vary more so with load.

[discopotato03]

No what I was looking for some sort of Lambda reference to petrol AFRs which had some meaning for me . I'm not interested in being any richer than does any good in the light load areas because that costs money for zip .

I can tell you that leanish mixtures under load feel weird with this fuel and not really like a leanish petrol situation . No cough spit or rattle just a torque fluctuation from probably low combustion temps and pressures .

Being able to read EGTs would be great but how many normal people have access to the gear or even know what the ideal temps are ?

Yesterday I put more fuel back into the low medium load areas which helped made more torque and put the Lambda numbers up to what I now think they need to be . Later today I will do the same a bit higher up the engines rev range because I'm getting to know what leanish mixtures feel like to drive with but the wide band will show for sure .

I think this is going to be one of those times where adding more fuel in the right places gives better consumption because lean isn't always economical .

Also going to have to resort to a serial cable because this laptop is doing blue screens with Datalogit when the engine is running , seems ok with the ignition on and the engine not running with their supplied USB converter cable .

A .

Edited September 24, 2012 by discopotato03

[rob82]

No what I was looking for some sort of Lambda reference to petrol AFRs which had some meaning for me . I'm not interested in being any richer than does any good in the light load areas because that costs money for zip .

I can tell you that leanish mixtures under load feel weird with this fuel and not really like a leanish petrol situation . No cough spit or rattle just a torque fluctuation from probably low combustion temps and pressures .

Being able to read EGTs would be great but how many normal people have access to the gear or even know what the ideal temps are ?

Yesterday I put more fuel back into the low medium load areas which helped made more torque and put the Lambda numbers up to what I now think they need to be . Later today I will do the same a bit higher up the engines rev range because I'm getting to know what leanish mixtures feel like to drive with but the wide band will show for sure .

I think this is going to be one of those times where adding more fuel in the right places gives better consumption because lean isn't always economical .

Also going to have to resort to a serial cable because this laptop is doing blue screens with Datalogit when the engine is running , seems ok with the ignition on and the engine not running with their supplied USB converter cable .

A .

Being on the lean side in a SI engine will generally always improve fuel efficiency as your reducing your pumping losses. I would be looking running around 1.1-1.2 lambda and see what you get. Yes the engine will feel less responsive but you will increase your fuel economy. I would also run the largest spark plug gap you can to help complete the burn.

[discopotato03]

Well my most recent experience shows that being lean was not economical and adding a bit more fuel in certain places gave it a tad better consumption and it runs better too .

I don't think ethanol burns much like petrol at all and the fact that it can run lean and not detonate (speaking same Lambda numbers petrol/E70) means lean with less heat and pressure and I reckon less torque and agro because of it .

It would be real interesting to compare EGTs with both fuels running the same Lambda numbers to see if high ethanol content lean means lower combustion temps by comparison . We know a lean running diesel has lower combustion temps where petrol engines tend to have to a degree higher combustion temps when lean and I reckon high eth content fueled engines are a bit more like a spark ignition diesel in some ways .

I can see the difference in the turbo not spooling as early or as easily when mixtures have been lean in these areas , throwing in more fuel makes a noticable difference here . Turbos are driven by thermally driven exhaust gasses and generally if the gas is not as hot it doesn't have as much energy (velocity) to drive the turbine with .

I'm not splitting hairs but I'm not really sure how a wide gap would make any difference to the end of the burn phase .

Outa time cheers A .

[scotty nm35]

Larger gap = better burn = more power. I had no issue running 2.5mm gap on melted iridiums and VQ coils, it felt very strong still.

I have run many lean cruise tunes, up over 18:1. The exhaust temps are higher but still under 700 degrees from my experience. It does feel quite soggy as you lean it off, forcing you to feed on the throttle more and probably using a similar amount of fuel.

The best way to gain back the low end would be higher compression, 8.5:1 is never going to feel good NA with e85. 12:1 would be perfect I believe, with 15-20psi keeping the turbo in its highest efficiency.

[AngryRB]

so is having the 0.8mm gap no good with the ethanol use..? 2.5mm sounds like a huge gap.. should i change my gap to say 1.1mm or will that effect the tune.?

[discopotato03]

I haven't seen inside a VQ but I imagine being a later design its burn characteristics are a bit different to most RB25/26 engines . Except for Neo 25s I don't seem to remember the 25/26 chamber design changing much if at all . I don't think they were intended to be ultra low emissions engines and probably don't cope super well with lean overall mixtures . Obviously Nissan put some extra development into 25 Neos to get them to run reliably as a ULEV engine .

Big plug gaps tend to like very high voltage ignition systems and thats probably what it takes to fire lean mixtures reliably , always assuming the engine doesn't detonate with the higher associated combustion temps .

I have limited experience with these high ethanol content fuels but from what I can hear and feel ethanol fires quite easily . Perhaps the greatest difference between E70-85 and 98+ octane petrol is that its a higher octane fuel but unlike high octane petrol its not hard to light up . The detonation resistant properties of high octane petrol actually work against it when it comes to lighting the fire .

Anyway back to my goals , economy at all cost is not what I seek best torque at all engine speeds and loads is . My aim is to not use any fuel beyond getting the most torque I can everywhere .

A .

[rob82]

I haven't seen inside a VQ but I imagine being a later design its burn characteristics are a bit different to most RB25/26 engines . Except for Neo 25s I don't seem to remember the 25/26 chamber design changing much if at all . I don't think they were intended to be ultra low emissions engines and probably don't cope super well with lean overall mixtures . Obviously Nissan put some extra development into 25 Neos to get them to run reliably as a ULEV engine .

Big plug gaps tend to like very high voltage ignition systems and thats probably what it takes to fire lean mixtures reliably , always assuming the engine doesn't detonate with the higher associated combustion temps .

I have limited experience with these high ethanol content fuels but from what I can hear and feel ethanol fires quite easily . Perhaps the greatest difference between E70-85 and 98+ octane petrol is that its a higher octane fuel but unlike high octane petrol its not hard to light up . The detonation resistant properties of high octane petrol actually work against it when it comes to lighting the fire .

Anyway back to my goals , economy at all cost is not what I seek best torque at all engine speeds and loads is . My aim is to not use any fuel beyond getting the most torque I can everywhere .

A .

Your correct, generally big gaps require larger peak secondary voltages due to the increase resistance and yes as the equivalence ratio decreases the ch3 ion reduces meaning it's even harder to fire. Don't assume that the chamber temps will go up with lowering equivalence ratios as it normally not the case but can be so on slow burning chambers.

Unfortunately though ethanol based fuels do have a lower Reid vapor pressure and high flash point than normal 98oct fuel meaning that it is harder to ignition or less volatile - hence the reason cold starts are difficult under 12 degrees c.

[discopotato03]

Well for whatever reasons my car fires up fine even cold when the PFC has the settings it likes .

I found a thread here started by Joeyjoejoe about his E85 Tuning Adventures and it mentioned a few interesting things I didn't know

For example I think either Paul33 or Cubes mentioned that R33s have 55L fuel tank where I thought they were 60 and typical GTS25T mileage was ~ 400 on PULP and possibly 300ish on E85 ? I think the figures worked out to 14/100 and 18/100 .

I don't suppose anyone knows any difference mileage wise with a Neo RB25DET compared to the R33 version ?

Joeys power numbers also looked pretty good at 320Kw on a 0.68 AR GT2835 , someone else mentioned numbers like 270 odd on a GTRS too .

http://www.skylinesa...ng-adventutres/

Woolverine as well must have cottoned onto something good with the 2835 Pro S and the ethanol seems to make them very streetable . I guess these kits come up second hand in good condition at times ...

Cheers A .

Edited September 29, 2012 by discopotato03

[GTSBoy]

I have properly calculated records of the mileage on every tank of fuel that has been through my car since 2000. RB20 used to average about 13.5 L/100km. 25Neo is running about 12.5. This is in an R32 though, so less weight than the later naval vessels. Neo is running stock tune and boost for the moment. I expect (want) to be able to pull at least 1 L/100km off that consumption when it is boosted and tuned.

Trying to calculate consumption of tank volume and distance travelled per tank is hopeless. You never run the tank out, have no idea how much is really left, etc etc. Comparing between people/cars is also fairly hopeless. Everyone's usage pattern is different. Some drive to work through heavy traffic, others only ever take it out on longer runs through the hills. Some have no idea that if you relax your right ankle you can save a lot of juice without losing a lot of time, others drive like there's a great big spike sticking out of the accelerator pedal. Some drive for economy when they can and have no problem with belting it when they want a laugh.

I think the concensus is that E85 needs 50+% more fuel when running hard but seems to only add an extra 20-30% to the total consumption when you include more cruise driving into the mix. Tends to suggest that you can tune even more lean and advanced at cruise conditions on E85; enough to eke out of the consumption to be far better than the difference in stoichiometric air requirement (and hence calorific value) would suggest.

[discopotato03]

Yeah I was just curious to know what Nissan actually achieved with the Neo 25 differences . A bit of extra power is always good for marketing when releasing an updated model ie R34GTt and if they can get a bit better consumption thats good too . Cleaner emissions would have been a must and not something Nissan probably had much say in .

I am still interested to see if adding a bit more fuel in places will get me a little more performance and same or better consumption .

A .

[GTSBoy]

Again, that will come down to how you drive it. If you need good transient response from lean cruise because you drive in more traffic, then going as lean as possible might not help. But if you did most of your miles in a steady lean cruise mode, then you'd obviously get the best overall consumption from leaning everything out as far as you can.

I'm of the opinion that making the car unenjoyable to drive is a stupid exercise. So lean it up as far as you can without interfering with how well it picks up speed and consider any improvements in economy you get to be a bonus.

Edited September 29, 2012 by GTSBoy

[discopotato03]

I think you missed the point with the neo 25 . Obviously Nissan intended it to be a petrol rather than E85 engine and they changed things like chamber volume and piston crown design and used different cam profiles . Late engines tend to run better on lean mixtures than older designs , part of this is making them more detonation resistant so they don't have to retard the timing as much to make it reliable .

Stop start traffic driving is never going to give good consumption no matter what you do . If an engine is an efficient design , combustion wise , it doesn't need much fuel for small throttle transients . I don't know too many people that would deliberatly set this area lean enough to have drivability problems because that often increases rather than decreases consumption .

I do understand what you are saying about how you drive and consumption b ecause big fluctuations in throttle opening mean extra fuel hosed in just to maintain acceptable AFRs .

I believe that if you can run best torque timing and the engine is capable of efficient combustion it should make good torque at fairly small throttle openings and thats good enough to get around town much of the time .

I stuck a reasonable amount of extra fuel into my PFCs table tis afternoon to see if I could get it to show rich on the Tech Edge wide band but it doesn't seem to show much richer lambda numbers . It makes great part throttle torque and the lower end drivabilityis really good . I topped up my tank which I don't like doing at more than 1/4 just to see how the fuel usage will be . It seems to fire up with the temp gauge on the peg first go atm .

I had a think about fuel trims and PFCs and I'm not sure they change anything accel enrichment wise so I again raised the increase and sustain and it seems to like that as well .

Anyway to round off with the limited tuning I've done over the years I find that mixtures lean enough to cause drivability problems make consumption worse not better . I think its the steady state mixtures that have the most say consumption wise and particularly at smallish throttle openings . This always assumes you don't boot you car everywhere ans stupidly expect good consumption figures .

RBs are not exactly a modern engine but they are not really agricultural either . They escaped out of the late 1980's and engine design has changed quite a bit in the last 22 years . Also 90s era Skylines are not exactly light for their size .

A .

[discopotato03]

Yesterday evening went out on the expressway with the medium load range mixtures a bit richer to see what butt dyno said . It didn't really achieve anything and it makes me think an issue with E70 etc is that it allows you to run richer advanced settings without drivability problems though best torque isn't there .

I made up maps with a little less advance and leaned some areas out a bit to see if its a bit torquier in those areas and I'll try that today .

My car really needs a dyno tune so its known exactly whats going on in controlled conditions and everything is measurable .

I think a problem with Ethanol in high percentages it that it allows wide variations in mixture and timing without the engine really acting up . I guess with experience real tuners get to know what different engines like and have the dyno gear to dial it all in .

A .

[simpletool]

OK I finally read through the entire thread. Thought I might make some comments - but I'm not a professional tuner just a chemist who tunes his own car on 98.

TIMING:

Timing can be higher than 40 for light load (less than 5psi ABSOLUTE - ie 10psi vacuum) from 2800, 3200, 3600, 4000. My maps on 98ron are 43deg, so you should be 46 at least. See my map for 98ron. This is on a stock R25 with Apexi AX53B70 (very similar sized turbo to GTRS - just bigger turbine housing).

Load 80 = 15psi boost (30psi absolute), 40 = transition/ zero boost.

These light load areas may not sound like much but they help response between gears when short-shifting. Which you probably do a lot of with a small turbo on an RB25. If you are running 13psi then that is load 74. So 25degrees at full load is quite a bit of timing even for E85. The fuel economy is gained mostly from timing load 25 to 40 from 2000rpm up to 3600rpm. That is 90% of daily driving and every 1 degree of timing here will be reflected in fuel economy. I guess for E85 you should be at least 3 degrees over these numbers, probably 4 or 5.

FUEL vs temp:

You mentioned it would be interesting to see if temps were lower with E85 at the same lambda as 98. From everything I have read (not practised) that would be true for PRE-combustion. EGT might not show it ??? but pre-combustion should be lower. This is because you have a higher thermal mass of liquid entering the chamber for a given Lambda which will absorb more heat from cylinder walls and head. However since the power is greater for E85 then more heat is likely to be produced for a given lambda which means EGT might not show the difference. Just my thoughts on the subject. Also this higher liquid mass causing lower pre-combustion temps one of the reasons that lambda does not need to be as rich as 98RON for sustained high loads. ie. You shouldn't need to go below 0.82 lambda even for track work.

Edited October 5, 2012 by simpletool

[discopotato03]

I have to go out now but will get back to this in a while . My timing table looks very different to that , is that from a PFC as I've not seen load reference numbers like that .

My finding with E70 is that it's very easy to advance the timing past the point where you get maximum torque and going beyond is effectively going backwards performance wise . I'm not sure going much higher than 40ish does much at light loads as in enough to drive rather than just coast on a feathered throttle .

My experience is that very low revs and light loads don't like lots of ignition advance probably because with low cylinder filling and low fuel requirements make it easy to time the combustion pressure spike later in the cycle than it needs to be .

People have to realise that its this timing thats critical and different fuels burn at different speeds sp a slow burning one needs its fire lit earlier than a fast burning one to get the thermal pressure rise where it needs to be .

I think the charge temperature advantage is purely one of more fluid evaporating and reducing the temperature of the air going into the cylinders .

A .

[Race__24]

In the Guilty Toy e85 thread he mentions that his measured EGTs were much lower with the e85. I can't remember the details, you'll have to go have a look.

[simpletool]

Yeah Guilt-Toys E85 thread is awesome.

[simpletool]

I have to go out now but will get back to this in a while . My timing table looks very different to that , is that from a PFC as I've not seen load reference numbers like that .

My finding with E70 is that it's very easy to advance the timing past the point where you get maximum torque and going beyond is effectively going backwards performance wise . I'm not sure going much higher than 40ish does much at light loads as in enough to drive rather than just coast on a feathered throttle .

My experience is that very low revs and light loads don't like lots of ignition advance probably because with low cylinder filling and low fuel requirements make it easy to time the combustion pressure spike later in the cycle than it needs to be .

People have to realise that its this timing thats critical and different fuels burn at different speeds sp a slow burning one needs its fire lit earlier than a fast burning one to get the thermal pressure rise where it needs to be .

I think the charge temperature advantage is purely one of more fluid evaporating and reducing the temperature of the air going into the cylinders .

A .

It's a Nistune table - it's sideways compared to PFC. The loads numbers are proportional to AFM output (and completely configurable).

I have no experience on E85 but I'd be surprised if you don't get benefit above 40 degree. It will help with transition from off-boost during gear changes - akin to having a slightly lighter flywheel. But yep, there is a point of negative return. E70/85 reaches MBT before knock - usually even under boost.

And yes, 1 degree makes a bigger difference at low revs, since it's triple the relative difference between 12 and 13 than between 36 and 37.

Edited October 5, 2012 by simpletool