Tuning larger LT-5 cams

[XfireZ51]

Originally Posted by tomtom72

Dom, I would like to add my Thank You also. No, I don't understand much of this. I haven't yet to plow thru the corvette FI book by Mr. Probst. I got side tracked with night courses for my job.

I am going to ask what could be a really novice Q. This fine tuning that you are doing would only benefit an LT5 that has it's cams timed correctly, right?

TIA

Tom

Tom,

Probst's FI book is a good place to start, but frankly it was too general for me. To really learn about tuning, I would visit thirdgen.org and their
DIY Prom forum. Many valuable articles and stickies available like
Tuning 101. Also, many knowledgeable posters and moderators on there sharing lots of good information.
As to you question, there's no doubt that you want to base a tune on mechanicals that are correct. The objective of a tune is actually to have the ECM intervene as little as possible. IOW, VE and SA tables that are close to optimal as possible w the ECM making "minor" changes or adjustments as dictated by operating conditions, ie driving through the mountains or varying elevations. However, every motor is different even tho they are the same. The right tune for one stock LT-5 is not necessarily optimal for another. Close but not necessarily optimal. I retuned my motor after adding just the Fidanza as an example.
When we pulled the motor out of #474, Pete checked the cam timing. I don't recall the exact #s but the intakes were something like 109/120.
However, I had tuned that motor just a few weeks before to produce ~400rwhp on a ported top end w headers/MF exhaust. So you can attempt to optimize the motor performance with the conditions you have.
But the performance you achieve will be limited by how optimal the mechanical condition of the motor is.

[XfireZ51]

This past weekend gave me the opportunity to migrate the tune for my motor over to the Blue Turtle. Essentially, Dave's motor is a copy of mine with the ported heads, top end, intake cams, and headers. Some differences are in the details. My heads were done by GVD, and I did my own top end porting 2 years ago. The headers are the Watson 1 7/8" with a MagnaFlow system behind them. With Pete chasing down the mechanical issues, we used my VE and SA tables for Dave's car so Pete could start with a tune that was pretty close to what was needed and save time. One main difference between the tune on Dave's motor and mine is that I am running Closed Loop while Dave's is Open Loop. However, the base VE tables are very similar although I haven't spoken with Pete on the tweaks he did afterwards. Not sure if Pete made any changes to the SA tables I had. However, Pete burned a chip with my VE and SA tables onto the Haibeck calibration, installed it, and the car idled pretty well right off the bat, albeit without the IAC issue resolved (which Pete fixed later). AFR was at about 14.3, the Stoich ratio I have targeted for a 10% ethanol fuel. I'll be interested in seeing where and how much my base and Dave's final calibrations differ.

P.S. Just spoke with Pete. As a point of clarification, Pete tuned the motor in Open Loop but then finalized the calibration by re-enabling Closed Loop. I originally tuned the motor using the BLMs in Closed Loop

[rkreigh]

I'm facing VA emissions with the big 234 cams (not sure what LPE timed them at). I called Graham for some advice and help. for an emissions profile, he recommended going back to an open loop chip and pulling fuel out to clean up the idle. I have an old LPE closed loop chip, but it was before I had Marc pull the secondaries out which does nothing to help the emissions either I can get the car down to 130 or so HC, but the new standard is 48

soooo........ I'm going to try fresh oil, plugs, cats, and getting an emission chip burned.

I'll need someone in VA that has an exhaust gas analyzer who is willing to work with Marc to do a mail order tune.

any suggestions?? I need to get this done NLT end of July so I need to move out.

HELP!!!!

sorry for the hijack, but it's relavent, and I'll start another thread too.

[HAWAIIZR-1]

Originally Posted by rkreigh

I'm facing VA emissions with the big 234 cams (not sure what LPE timed them at). I called Graham for some advice and help. for an emissions profile, he recommended going back to an open loop chip and pulling fuel out to clean up the idle. I have an old LPE closed loop chip, but it was before I had Marc pull the secondaries out which does nothing to help the emissions either I can get the car down to 130 or so HC, but the new standard is 48

soooo........ I'm going to try fresh oil, plugs, cats, and getting an emission chip burned.

I'll need someone in VA that has an exhaust gas analyzer who is willing to work with Marc to do a mail order tune.

any suggestions?? I need to get this done NLT end of July so I need to move out.

HELP!!!!

sorry for the hijack, but it's relavent, and I'll start another thread too.

Ron,

Thanks for posting the question. I only have a 350 with SGC Stage I int/exh cams and not sure how strict the standards are here in Japan. I am getting ready for my first test so I'm all ears to know what helps to pass. I have my still have my stock secondaries and based on Marc's advice about emissions he also burned a chip for me. Thanks for the idea and I'll change my oil and get some new plugs too.

[XfireZ51]

Ron,
Is there any chance you could do a run thru the emissions test while datalogging the run with a scantool? Just making some "uneducated" guesses based on my experience with my modded Xfire, I would try:

1. Hotter spark plug
2. Activate Decel Fuel Cut-Off
3. Raise the TPS% for secondaries so you are running only
primary injectors for the emissions cycle.
4. Bump timing
5. Lean out Acceleration Enrichment pump shot
6. Increase the AE Coefficient slowing down pump shot
response to throttle changes.

You'll need to make certain you don't
go into Lean Misfire. My initial thought is that the HC spikes during acceleration/decel which makes up a significant portion if the test. Not to mention the "tech" driving the car.

[Paul Workman]

Couple thoughts...

1. Something we discussed at one of our FBI bull sessions** was pulling the plenum and blocking off the secondary ports and shutting off the "Full Power" switch. This essentially reverts the mods to stock and keeps the secondaries from being activated, depending on the chip calibration. (Depending on the circumstances of the mods and calibration, a special calibration (primaries only) might be one way to assure the car is compliant.)
   
2. Also, mixing fuel for a 15% alcohol ratio has helped some of the cammed motors; one LT5 and a few pushrod motors too that I've read about recently.

**(Next BS session is tonight 6/24 at Home Run Pizza, if anyone is interested (see East Central Region page - look for Bloomington Gold threads)



P.

[rkreigh]

anyone do any open loop tuning to fiddle around with the calibrations? with the big cams I've heard the 02 sensors can "detect a false lean condition" and add fuel when in fact the car is already running rich

the lack of vacuum signal and high overlap of the cams contribute somehow to this.

I bit the bullet and ordereded some big manaflow universal 3" cats and although it pains me, they were only 75 each and getting them installed although it will violate my nice b&b exhaust, the fresh cats, alchy, fresh oil, and running a tank with seafoam throught the car is the route I will take.

I'm not overly optimistic but I gotta try something and before the end of july!!

[XfireZ51]

Ron,

Running O/L forces the fueling to be based strictly on the VE tables. O2 sensors feedback to the ECM for pulsewidth mod for the Integrator and BLM calcs. There are some threads on ThirdGen.org that discuss Closed Loop tuning for larger cams. The greater overlap does cause fresh air to be detected in the exhaust by the O2. Consequently the ECM interprets that as a lean condition and adds fuel. That's why you see the BLMs drop to minimum 115 that is in the calibration. In fact, the INT goes lower than that. What most people don't realize is that a 128 BLM DOES NOT necessarily correspond to 14.7:1 AFR. When running C/L, you'll see the AFR toggling rich/lean in order to not oversaturate the cats. Probably a reason why yours may very well be shot.
The magic 128 BLM for C/L indicates where the O2 swing points are. The voltages can be manipulated based on airflow. It means you can modify the calibration to tell the ECM that what appears to be lean actually is not. And it can be done
in such a way to affect principally only the idle. Being able to use C/L with the larger cams also allows use of additional parameters such as proportional gains which make a difference in managing surging for example.
At Bowling Green, Graham said something very interesting, if I recall correctly, in that the LT-5 wants to stall. Increasing the overlap exacerbates the oscillation bringing the LT-5 into areas where it will stall. One reason why people raise the idle when going to larger cams. So being able to control idle more tightly becomes even more important when using larger cams. C/L presents finer control of the motor which is why I believe Graham suggested C/L for your emissions calibration.

[C4Fanatic]

Suddenly wishing I had taken Dom for a ride in the Skunk while I was at BG this weekend!

[-=Jeff=-]

Originally Posted by C4Fanatic

Suddenly wishing I had taken Dom for a ride in the Skunk while I was at BG this weekend!

now another reason to come back

you can stop at Portillo's at that time too