What say you, Graham?

[XfireZ51]

Now that Graham has graciously joined our little group, I thought he deserved his own "stickie" thread. It would be great to immortalize some of the great insights Graham can bring to the understanding and background of the ZR-1 and LT-5 in particular.


I'll start off by asking this question.

Graham,
What did you guys do, if anything, to mitigate the "split blm" issue we run into when tuning. Seems that the tune is a compromise between left and right banks. It would be nice if they both ran more evenly. And it appears to be exacerbated, particularly at lower rpms, when using larger cams and/or having ported top end, heads etc.

So

WHAT SAY YOU, GRAHAM? :saluting:

[Tyler Townsley]

First off we need a picture!!

http://thepandatrap.com/gallery/ZR-1s/20110422133223

Tyler

[Blue Flame Restorations]

Love that pic and my EX5023.....:)

[grahambehan]

First off we need a picture!!

http://thepandatrap.com/gallery/ZR-1s/20110422133223

Tyler

Tell you what Tyler gb is not in the picture!

[Blue Flame Restorations]

Geoff and who is the mystery man???

[grahambehan]

Now that Graham has graciously joined our little group, I thought he deserved his own "stickie" thread. It would be great to immortalize some of the great insights Graham can bring to the understanding and background of the ZR-1 and LT-5 in particular.


I'll start off by asking this question.

Graham,
What did you guys do, if anything, to mitigate the "split blm" issue we run into when tuning. Seems that the tune is a compromise between left and right banks. It would be nice if they both ran more evenly. And it appears to be exacerbated, particularly at lower rpms, when using larger cams and/or having ported top end, heads etc.

So

WHAT SAY YOU, GRAHAM? :saluting:

Really intersting, nice flag tho!

[XfireZ51]

Really intersting, nice flag tho!

Is this something you did not encounter?

[grahambehan]

Is this something you did not encounter?

No we did not encouter a major difference bank to bank at design release.

Graham

[XfireZ51]

What complicates the issue is installing different injectors ie Accels, RCs, FICs. I don't suppose use of ethanol was a consideration at the time.

[LancePearson]

What complicates the issue is installing different injectors ie Accels, RCs, FICs. I don't suppose use of ethanol was a consideration at the time.


I nominate Ethanol as one of the bad ideas of all time in automotive terms and when used or let sit for more than a few days in any engine with a carb. especially, boats, et al. as well.

[XfireZ51]

Lance,

My point was that Graham did not experience significant divergence of BLMs bank to bank perhaps because the OEM injectors were better matched. Or since it was in the design phase, they may not have had the normal variance found on production pieces. More than 20 years later, various injectors are being used, w a difference in electrical and mechanical properties, and this could be aggravating the differential side to side. Throw mods into the mix and voila!
I'm no code writer, but it's my understanding that due to SPFI, it would not be hard to program individual L/R fuel trims to help even things out.
What's interesting is that it is almost always the left bank which runs leaner than the right. So it may not be injectors. This "split BLM" is not as pronounced in stock motors as it is in modded ones. And idle or low rpm operation has a greater degree of it than high speed cruising from my observation of it.

[Hib Halverson]

My experience has been that, given injectors that are well-matched–and not all OE injectors were well-matched--the bank/bank difference in long-term fuel trim (BLM) was not greatly different unless there was a problem somewhere.

To me, from the perspective of the LT5 being a very high-performance engine, well-matched means a flow difference of no more than 1.5% across 16 injectors.

As for Graham B....now that he's finally arrived here at the ZR1 Net forum, we need to start a thread about country western singing when consuming large quantities of beer.

[scottfab]

This is good food for thought but how many engines have you looked at for left vs right running more lean?
Seems counter intuitive. I wonder what would possibly contribute to this? Injector variances left to right would normalize out over many engines. Placement of the IAC on the right side? ???? nahhh


Lance,

My point was that Graham did not experience significant divergence of BLMs bank to bank perhaps because the OEM injectors were better matched. Or since it was in the design phase, they may not have had the normal variance found on production pieces. More than 20 years later, various injectors are being used, w a difference in electrical and mechanical properties, and this could be aggravating the differential side to side. Throw mods into the mix and voila!
I'm no code writer, but it's my understanding that due to SPFI, it would not be hard to program individual L/R fuel trims to help even things out.
What's interesting is that it is almost always the left bank which runs leaner than the right. So it may not be injectors. This "split BLM" is not as pronounced in stock motors as it is in modded ones. And idle or low rpm operation has a greater degree of it than high speed cruising from my observation of it.

[Paul Workman]

Dom, have you tried left-right swapping of the O2s to see if the BLM characteristics follow the sensors? I'd be curious to see what effect that might have on BOTH BLMs and injector dwell time; before and after the swap.

P.

[XfireZ51]

The "split BLM" issue is not unique to the LT-5. The LT-1/4s exhibit similar bank to bank differential. My suspicion, and that's all it is, is based on my experience w the Xfire motor. There you have a much simpler example of individual bank fueling. The fueling for that motor used twin TBIs in series. The "rear" TBI (left bank) had the regulator built in. I measured fuel pressure differential between the two TBI was .5psi. This was enough for GM to use staggered injectors of
63/65 # F/R to equalize fuel delivery. No other TBI injectors were available that would retain the stagger and deliver more fuel needed for higher hp. It became necessary to run individual fuel lines to each TBI so that equal size injectors could be used. So I am speculating that there may be a slight pressure drop at the left hand fuel rail due to the added distance fuel travels to reach it. Perhaps the use of injectors with different mechanical and electrical properties could also magnify the differential.

[scottfab]

The "split BLM" issue is not unique to the LT-5. The LT-1/4s exhibit similar bank to bank differential. My suspicion, and that's all it is, is based on my experience w the Xfire motor. There you have a much simpler example of individual bank fueling. The fueling for that motor used twin TBIs in series. The "rear" TBI (left bank) had the regulator built in. I measured fuel pressure differential between the two TBI was .5psi. This was enough for GM to use staggered injectors of
63/65 # F/R to equalize fuel delivery. No other TBI injectors were available that would retain the stagger and deliver more fuel needed for higher hp. It became necessary to run individual fuel lines to each TBI so that equal size injectors could be used. So I am speculating that there may be a slight pressure drop at the left hand fuel rail due to the added distance fuel travels to reach it. Perhaps the use of injectors with different mechanical and electrical properties could also magnify the differential.

A way to isolate on this theory would be to re-route the fuel to the left side first. Painful to do but would be conclusive.

[mike100]

It could be cylinder to cylinder airflow difference, especially at idle speeds. Perhaps the rear cylinders are a little hotter as well.

I don't see it as being a very big deal so long as your blm map is close enough to center to be able to allow adjustment. As I recall, the LT1 engine has calibrated vac leak holes to each intake port to allow fine tuning of individual cylinders rich/lean from some mechanical design issues that can't be overcome.

[Hog]

LT1's also experience a cylinder to cylinder to cylinder variance, hence the individual cylinder fuel trimming tables in the calibration.

peace
Hog

[rkreigh]

be cool to put a wideband or egt sensor on each header tube to see the AFT variance

maybe a really nicely flow balanced set of injectors would help.

the chevy motors (especially BB chevy) have "good ports and bad ports" that flow pretty differently. I don't suspect that's an issue but I'd be willing to bet that there is a difference in flow from front to back on each side due to the manifold (air doesn't like to make sharp turns)

the LT5 probably isn't nearly as bad as the older stuff in that respect.

when was data logging with EASE to have marc burn me some chips I noticed the difference in the bank to bank BLM too and thought something was wrong.

[XfireZ51]

Ron,

I use Ease as well. Look at your scans and tell me if the left bank wasn't running leaner than the right.
BTW, I used a laser thermo to measure heat from exhaust gases of each cylinder.

[XfireZ51]

Here's a thread on the SPLIT BLM issue found in the LT1 if you are interested.
Note this solution works mainly for idle.

http://www.thirdgen.org/techboard/diy-prom/410002-i-slayed-miniram-split.html?highlight=ULTM8Z

[XfireZ51]

Well we have determined its NOT a case of leaking injectors. Plenum was off so Pete and I took advantage of that fact to verify injectors are good to go. These are Accels with probably 20k+ on them. Cool. More coming later. We'll be swapping out plugs and O2 sensors as part of the upgrade.

[Hib Halverson]

(snip)

the chevy motors (especially BB chevy) have "good ports and bad ports" that flow pretty differently. (snip)

The Big-Block is the only Chevy engine like that, ie: "good" ports and "bad" ports with a significant difference between the two types.

[XfireZ51]

In the process of doing a bit of upgrading, I think we may have discovered the source of the wide BLM variance. Exhaust leak at the left side collector.
Some times it's a matter of Occam's Razor.

[tpepmeie]

Old thread. Dom, was your bank 2 leaner (ie, cyls 2, 4, 6, 8). I've got lab-grade O2s, and a custom fuel rail and regulator. Aftermarket ECU. Have a bank-to-bank lambda offset of .05-.1 Lambda.

[XfireZ51]

Hi Todd. Good to hear from you. Actually its the left bank(Driver) that is on the lean side. The discrepancy is greater between the two banks at slower engine speeds. At higher rpms, tends to straddle 128 BLM +-2-3 with copious tuning.

Earlier I had a real issue which turned out to be defective secondary injectors.
FIC quickly replaced them gratis. Switched those out along w a new set of coils.

[tpepmeie]

Ok. I agree at lower loads and engine speed the variance is greater. I?m running alpha-n right now. There?s something mechanically causing the variation. Have swapped sensors and same phenomenon. I?ve got the iac passage plugged and idling off the primary blade at the moment.


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[rkreigh]

Hi Todd,


if the injectors are all balanced and ignition / compression good it has to be in the intake not providing good balanced flow. Like you said, something mechanical here. I'd love to tune the car with a haltech or MS pro and see what's going on in each cyl and like Duttweiler says,



"give the engine what it wants and needs"


he does alot of tuning by individual cyl and picks up both efficiency and power

[Paul Workman]

Hi Todd,


if the injectors are all balanced and ignition / compression good it has to be in the intake not providing good balanced flow. Like you said, something mechanical here. I'd love to tune the car with a haltech or MS pro and see what's going on in each cyl and like Duttweiler says,



"give the engine what it wants and needs"


he does alot of tuning by individual cyl and picks up both efficiency and power

Showing my ignorance here, but I'm intrigued: to tune individual cylinders (I assume) dwell and timing would have to be individually controlled. That would call for some pretty fancy mods to the ECM/DIS, wouldn't it? Please DO TELL. (Always looking for a good article for the HOTB!:))

[rkreigh]

hi Paul,


Haltech, Motec, Holley and many others can control spark timing and fuel for each cyl



for my haltech I have EGT 8 channel so you can tune trying to get the egts relatively even regardless of AF which does ok.


more advanced systems now have a WB on each cyl to tune AF ratios to target for each


for the LS engines the #7 runs lean so we feed it more fuel