How do I add/remove fuel in PE mode?

Should I change the VE table or is it PE% vs RPM?
(+ more fuel, - less fuel or???)

Going to take the car to a dyno soon and I like to know what I should adjust because the people who works there havent reprogrammed any GM cars(TC).......

thx/N.

 

There's different theories on tuning WOT with SD cars. My theory is as follows...

1) Make sure your VE curves are pretty close to yielding 14.7:1 ... even at 100kPa.
2) Use %AFR vs. RPM to smooth the AFR and get it even across the board at WOT. Obviously a WideBand will be necessary.
3) Use the %AFR vs. Coolant to raise or lower the AFR across the board at WOT.

Another thing I like to do is that whenever I get a good deal of fuel addition or subtraction at ALL RPMs in the AFR vs. RPM table I then globally lower or raise the values in that table and then make the corresponding inverse changes in the coolant table. Example ....

If the RPM table has 10% across the board (with some being 13%, some at 15%, some at 11%, etc), then I will subtract 10% from the RPM table to give me more room to work around with that table. I will then add 10% to all points on the Coolant table. This keeps the RPM table pretty close to zero at the minimum points.

Tim

 

I disagree, with the, even at 100 K/Pa.

At 100 K/Pa and regions close to that especially at the higher RPMs, you need the fuel for in cylinder cooling. And for the new guys, that can be expensive in the ATTEMPTING to get there.

There are numerous posting about broken rings, locking ring end gaps, knocking corners off of pistons, etc, etc.. Which are caused by localized overheating in the piston crown.

Given some specific combos, and high level of experience with plug readings, MAYBE. But as general advise on an open forum, nope, I wouldn't even suggest going there.

And for those the try and are using a oem O2 sensor, your sensor goes to dodo reading wise due to backpressure and at the higher RPMs, you can't count on that as being accurate.

And don't forget gas is getting to be more and more reformulated. and less and less of what you think your getting.

I've been seeing more and more devergence in the NB to WB readings on some tanks of gas, on more then one WB setup.

Fully relying on O2 sensors, and Knock sensors is getting more and more dicey, IMO.

 

so whats the tip here?

 

When tuning 100 KPa at higher RPM's make sure that the ECM is in PE mode. This makes sure that the INT is locked at 128 & learn is off. Now tune for 12.0 to 12.8 AFR or such as the engine requires.

Other then stoich don't use a NB O2 sensor.

RBob.

 

Not sure if it matters, but I like to flatten out the PE RPM table and tune only vie the VE . The way I see it you never want to be at 80 kpa or anywhere above and be at 14.7. So therefor I tune PE only from the VE because it makes it easier to see where your peaks are.
Now sometimes you must use the PE RPM table like when above 5600 if your last VE value is not what yuou want to carry through.

 

OK.....thanks

In the PE%change A/F is + more fuel or less?

 

positive number = more

 

The reason I like to nail down the upper VE curve close to 14.7 is because the $8D assumes the VE table values produce 14.7 when no other modifiers are active (PE, highway, etc). The $8D pushes AFR to the ALDL stream. This AFR is the target AFR that the ECM is shooting for. If you can get the VE values close to 14.7 then the AFR pushed via the ALDL will be pretty close to the real world AFR as viewed with the WideBand ... this is through personal experience.

... I am not saying that this is the safest way. I agree with what has been said in previous posts about this being dangerous for the newbie. However, *if* you can nail it down according to what I said then you will be programming it according to the original design. I posted about calculating the AFR a few years ago ...

https://www.thirdgen.org/techbb2/sho...threadid=37236

The code assumes 14.7 and then changes the AFR according to the PE modifiers.

Tim

 

As well as it could 14.2, 13.7. or any other number.

And remember lean, needs more timing.
So not only is you fueling off, and dangerously lean, but your off on the wrong track timing wise.

Why tune or even attempt to tune going too lean, and with too much timing?.

Like I've a couple thousand times, tune for what the engine wants. Tuning to get a specific AFR, number of degrees timing, or running the most timing possible, can be terribly misleading.

 

Fact is - you are never at 100kPa unless you are in PE anyhow. So, it's a moot point. That's why 14.7 ... because it doesn't matter. You are still giving the motor what it wants. You are just doing it through PE. Like I said before - the VE tables were designed for 14.7. If you don't want to take advantage of this feature then you might as well run an aftermarket ECM. They don't have PE and dump all their fueling in the VE tables ... even WOT fueling. I consider PE a nice feature of the GM ECMs.

Furthermore, in all my experience LEAN means LESS timing - not more. Running a lot of timing when running lean is a recipe for disaster and big detonation. More timing makes it MORE lean. Bad idea. Ask me how I know.

Tim

 

so it could be "dangerous" to have the engine running in 14:7 at the higher kpa and rpm value for a short time? During tuning?

 

How much is a significant change when using the PE vs RPM tables? I have altered the numbers up and down by as much a .4 and saw no results at all, every pass was a 13.2x@104.7x. Should I alter the VE tables instead? I have no access to a WB, all I can say is my o2 is at .880 which means about nothing.

 

Why did you suggest it to begin with, then?.

The proper answer is setting the calibration up on an ECM and having the WOT DC at 90% or what ever safe duty cycle you want to run, and then tip-into WOT. Then with a WB watch what happens.

 

I suggested it to shoot for what the VE tables were designed to do. Furthermore - I said close and I didn't say that you should run the car at 100kPa. I do it by extrapolation. I determine the VE trend by getting as much data as possible in the upper VE curves. I then compare that to generated VE curves using engine simulation software. Using both of these allows one to get the upper VE curve close.

Wide Band is great ... I always suggest it. But, it isn't all it's cracked up to be. Cam Overlap. Ya. Lots and lots of unburned oxygen indicating a leaner condition than what really exists. You're running a turbo so overlap is at a minimum on the cams you deal with. What about those guys who are running a lot of overlap? Overlap helps create a lot of power. Ever read Vizard or run a cam with less than 110 on a fuel injected motor?

Tim

 

Yep, and its almost impossible to run the car in closed loop because what the 02 thinks is 14.7 is nowhere near stoich.
So I agree with the WB not being ***. Still plug reading.

I also just switched to the big TPIS solid 242/242 @112 from my 230/230 @110 and went slower.grrrrrr
But then again DA was 3300ft. so maybe this week will be beter.

 

You extrapolate the VE tables?.
Whatever.

Care to again define what your talking about in the comment not all it's cracked up to be?. You got a better more cost effective answer?.
Care to actually qualify the unburnt oxygen?.
Hmm, when'd you read my cam specs?.

And feel free to read up on what gains there are by running alot of overlap in turbo applications before trying to guess at what I'm doing or planning to do. Hint: it's nothing like you might expect, and we're not talking Miller Cycle stuff.

Do you really want to get into time spent reading?.
Vizard isn't the only author of note about engine theory.

 

Anybody who doesn't do any extrapolation / interpolation should re-evaluate what they are doing IF they need to do VE tuning. It's impossible to get data for EVERY point. Most people are extrapolating / interpolating and either not admitting to it or they just don't know that they are doing it. Grab many points and look at the trend. It'll bite you on the nose. Data is data. Mathematics applies. Extrapolation / interpolation is valid. Maybe my college education and my 3 years of calculus is wrong. Maybe.

It's not all it's cracked up to be = it's not the be all end all. Don't take it's reported values as absolute truth regarding what AFR the engine is producing. Some people don't understand that and nobody is telling them ... well, I guess I just did. I never said anything about a better or more cost effective answer - you brought that up.

No. It's an oxygen sensor.

I didn't.

Cool. Lots of overlap on a forced induction motor so that you can blow all that prescious PSI right out the exhaust. Sweet. One of the cool things about overlap is that it uses the exhaust velocity to help pull in the new intake charge ... on an NA application.

No - I don't really want to get into time spent reading. What's the point in you and I tooting our horns about what we've read? There is no point. Furthermore, I never said anything about Vizard being the only author of note ... you did. Stop twisting my words.

Tim

 

Due to certain obligations (see avatar), I haven't had the time to frequent the DIY PROM forum for a while and thus have been doing a lot of reading of the past posts these last few days.... and I have an opinion on where all of this has gone as of late and maybe some of you would like to read it. If not - Mind your business!

I've been around these parts somewhat of a long time.... Longer than some of the folks yapping in here lately. I also went through ASEP and have enough training on EFI to be fairly dangerous. I have a decent amount of knowledge on EFI, burn a lot of PROMs (many for others for free as I have time), am requested to help out at dyno tune sessions by others, and am constantly tinkering with my own..... Don't mistake that for bragging - it is merely setting the scene.

I have to say that I doubt I will ever post/answer a question in here again - assuming things stay the course or continue to degrade. It just isn't worth it. The environment is hostile to say the least and often the ones that know the answers have serious problems with just simply giving that answer out. Some of you need to get over yourselves... others need to think for yourselves.... The bottom line is that this is not the 'family' of tuners it once was. And that sucks.

I know who knows their stuff. I also know who is a jacka$$. I refuse to take advice from the jacka$$es that know their stuff. I am about to embark on tuning a fairly radical combo (see sig) that is going to be a challenge for me to tune.... I'll stick to Emails and PMs for my questions from here on out. Consider yourself a non-jacka$$ if you get an Email from me.

-Out

 

In this day of politically correctness, and english majors looking for warm fuzzies, it's really easy to assume, and prejudge people. What some folks take as having an attitude, is what's just in fact a passion for the other. So rather then ask a guestion, and find out what'd going on, it's just easier to go off on a little rant, and start name calling. Now that's being mature about it.

As far as anyone thinking they know someone, from a few posts on the net, that's just assuming alot.

But, getting back to 1st posting:

If you want to make universal PE AFR changes, then the easy way is just using the PE AFR vs Temp Correction. If you want to tune the fuel in specific areas of the rpm band, then you add or remove fuel as a % vs rpm.

Now, as you progress into higher levels of HP and tune, then you need to really run open loop and resort to a WB. And the reason for that is while 14.7 is universally safe for mild engines, it's not universally SAFEST, or BEST for all engines.

 

Hi.. Grumpy!

Ok, thanks I'll keep that in mind next year........

Engine broke a few days ago so dyno tuning wont be this year, rebuild time.................

Have a post on TPI board about upgrades!

/N.

 

That makes perfectly zero sense..... and you are a problem here - regardless of how much you know.

 

MAT87GTA: I hope you keep posting on an open forum. It does not help people who use these boards for reference and knowledge if everyone "takes their ball home" and just communicates through emails and PMs.

 

Time to start over, let it go! lets get "OUR" board back in shape.



True

 

WE ARE ALL HERE FOR THE SAMETHING!!!! AND THAT IS "PERFECTION MY FRIENDS".

 

Grumpy/Trax,


The comments you guys were making regarding overlap are very interesting. I recently read an article by Vizard regarding the subject of valve timing events. You can find it in the Sept. issue of GMHTP. As part of that, he discussed Motors and Machine Services and their cam selection program. Vizards point regarding overlap is that it represents probably the most critical component in properly speccing a cam for a given motor/cylinder head combination and a specified rpm power band. I am currently running a Xfire with TFS heads and a CompCams HYD Roller. When I first started looking for a "good" cam, I was told not to go below 112d LCA due to the constraints of ECM control and good vacuum signal. MMS and Vizard maintain that the increase in LCA is indicative of a duration that is too long. Cam grinders inflate the LCA to "protect" users from putting in a cam with too much duration. For $40, I asked MMS to spec out a cam given a number of criteria that MMS requires. The cam they came up with uses a 108LCA with 50d overlap. My current cam is a 112LCA and 43d overlap. The duration for the spec cam is slightly more on the intake side than what I currently have and also suggests that I could use a single pattern cam due to the exhaust port efficiency of the TFS 23d heads. Vizard and MMS both point to the importance of the LOW LIFT numbers for a cylinder head and how that helps to determine OVERLAP. Given that I am contemplating switching to this spec cam, I'd be interested in your comments regarding the use of a 108LCA cam with ECM control. It seems that 87 TA may have had some unpleasant experience with the O2 sensor not operating properly.

:hail:

 

It was impossible to run the car closed loop without glowing the headers because of unburnt fuel.
I spent about an hour with a hand held pryo, played with timing anywhere from 6 degrees at idle to 35 making no more than a 50 degree varience in temp.
The only way to get egt down was to run car closed loop and use pyro and plug readings.
Oh yeah I also changed o2 twice during that time to be sure that was not the problem. I just swithed to a larger duration cam with less overlap, just pulled best ET and car drives wonderful - I am more than happy how well it drives and runs now.

 

87 TA,

So you're saying that the tighter LCA exaggerated the EGR effect? Or were you running too much overlap? What were the specs of the cam you had a problem with?
Duration?
Sorry didn't respond to you sooner but TG was down most of the day. According to MMS and Vizard, optimum cam specs for my motor would produce 17" Hg vacuum

 

Generally a tight LSA and overlap go hand in hand.
A tighter LSA increases exhaust scavaging, pushing out exhaust while using that to pull in intake charge in. I actually think If we could control inj. timing I could have reduced the effects of raw fuel in the header. Well maybe not.

230/230 @ .05
560/560
110 lsa
OPEN/CLOSE
IN 37 BTDC 69 ABDC
EX 77 BBDC 29 ATDC

 

87 TA,

What was the advertised duration? 280-290?

Duh. Never mind.

 

286/286

 

87 TA,

66d in overlap is pretty healthy. If you haven't read the Vizard article in GMHTP, I would highly recommend it to you. Here'e just a quote which would be relevant to your motor.

David Vizard

" Remember low lift is where the valves are during the overlap period. Obviously the more rpm the engine is expected to turn, the more overlap required-but only to a point. If cubic inches get bigger more overlap is required for a given rpm band.
On the other side of the coin, the greater the low lift flow of the valves, or the faster the valve opening acceleration, especially the inlet, the less overlap required for optimum results."

His point is that overlap needs to be determined first as a function of the low lift flow of the heads. Once that is done then LCA can be calculated. And LCA he says,

" Once the amount of overlap has been decided, the next step is to determine what the LCA will be. For a given cylinder head, the bigger the motor, the tighter the LCA required and vice versa. If the high lift airflow of the heads is increased it has almost zero effect on the LCA. If the low lift flow is increased, the LCA gets wider and vice-versa. As the compression ratio goes up, the LCA needs to get wider...."
With overlap and LCA determined, duration is plug and play using
(overlap/2 + LCA)2=Duration

The AFR heads are well known for their low lift numbers. Perhaps you did have too much overlap.

The calc for my cam is between 50-53d overlap and a 108LCA. Probably won't run into the same issues you did. This represents about a 10d increase in overlap from the cam I currently have in the motor.

 

Excellent info Dominic Sorresso!
Thank you very much.
Wish I would have read that prior to my last cam install.
But it seems to be working pretty well.

 

87 TA,

I would suggest doing what I did. For $40,
I asked MMS to calc a cam for my heads and desired rpm range. I did this just to see how far off my "guess" was compared to what the calculated optimum is. My current cam is a 264/270 advertised with a
43d overlap and 112LCA. The calc'd cam came back with a 266/265 advertised, 50d overlap and 108LCA, This will put me in the 5200rpm range for power peak. Remember I have a Xfire so I am optimizing for the longer runners in induction system. The cam I am thinking about is a 269/269 with a 53d overlap and a 108LCA. That should give me a power peak of about 5400rpm.

 

Hmmm...

I only have 6 deg of overlap on my ZZ9 cam........Time for a cam swap? or maybe this would fit my blower application?

 

Just a few other notes about overlap.

As you increase overlap, you increase the amount of self EGR-ing the engine does at low rpm. So that's going to mean a bit mroe fuel and timing at idle, all other items remaining the same.

If your going to try and run closed loop, you have to remember the ecm is just looking for peaks and valleys on the O2 voltage for feedback on mixture. It doesn't look for how long of duration the O2 exceeds or runs under the max and mins.. So your going to have to look at the threshold voltages, and commanded AFRs for what the ecm thinks is Stoich vs what is coming out of the pipe.

As you increase the overlap, the exhaust back pressure is more and more of a concern. Just looking at both ends of the scale should make that apparent, ie a turbo motor wants little to no overlap, and a Nitro Motor, absolutely no backpressure.

Then with the larger overlap cams you can get into where the self EGR-ing of the motor is trying to confuse whatever gas analyzer you maybe using, not alot, but maybe enough to be a little misleading since some intake charge is being sucked out with the exhaust, that will slew things to the lean side of what's indicated.
AND,
this will drop EGTs slightly. So while at one time the engine may have made best HP at a given EGT, with a cam change it might change what was optimum best.

And there are at least 3 clearances that have been used for determing overlap timing.

YMMV.

 

Bruce,

To your point, Vizard discusses the effects supercharging and Nitrous has on cam selection. In some turbo motors you would have no or negative overlap. Also, the choice of cylinder heads in these applications is important. The supercharged heads do not need to have the intake/exhaust efficiency ratio (65-80%) used for NA type motors.
Ths is really an excellent article and I would urge everyone to read it if you are interested in learning more about the valve timing events and the consequences on cam selection. Vizard also discusses valve lift and the "optimum" lift needed. For example, port flow efficiency actually increases once the valve lift meets or exceeds 25% of the valve diameter. So with 2.02 valves, you'll want a valve lift of at least .506"
assuming the head ports support that amount of flow. And Denny Wycoff and his group at MMS are very helpful. The nice thing is they "have no cam to grind" (pun intended), so their cam recommendations are based on what your motor needs. Luckily we can obtain low lift for many heads from the Chevy High Performance cylinder head flow library (if your heads are unaltered).