GREGGPENN

I went to check my AFR before finishing up my interior redo. At the dyno, I found my tune was pretty close.

AFR was oscillating above/below 14.7 when not in WOT -- as it should be. During WOT runs, it's peak richness dipped just into the upper 11's at 4k rpms.

The graph looked very good otherwise. AFR started in the 13:1 range for each run. Then, it gradually gained richness until peaking just under 12:1 at 4k rpms. After that, it gradually leaned back out by 5k rpms.

Basically, it stayed at or richer than 13:1 AFR through out the pulls.

My question is what's too rich? When I pull some fuel from the enrichment by RPM tables, I ended up getting a dip in power where I pulled fuel. First, I pull 3%, then 6% (after seeing very little affect on AFR. I got it up above 12:1 by pulling 3% @ 3600, 6% @ 4000, and 3% at 4400 rpms BUT, I lost 30ft/lbs of TQ in the peak rpm.

Oddly enough, the dip was VERY pronounced -- which makes me believe fueling changes should not be "abrupt". It was set like this....

4800 - 8%
4400 - 7%
4000 - 6%
3600 - 6%
3200 - 4%
2800 - 2%

After dyno tuning, I had it set like this....

4800 - 8%
4400 - 3%
4000 - 0%
3600 - 3%
3200 - 4%
2800 - 2%

As mentioned, this SEEMED to cause a 500rpm dip of 30ft/lbs at 3600 rpms. Now I'm wondering if I should have left it alone...OR if I should have done something more like this....

4800 - 8%
4400 - 6%
4000 - 5%
3600 - 4%
3200 - 3%
2800 - 2%

With gradual increases, does the ECM respond more favorably? IOW, when the ECM "saw" the drops in fueling, is it possible that it overcompensated at took a few rpms to correct?

If not, then I wonder if the DYNOJET started to error and introduced a false dip at 3600rpms. We could not hear/feel the dip. And, after several pulls, I decided to wrap it up until I could figure out what happened.

Thoughts?

Should I put fueling back where it was before my dyno run? At least I did gain power with a small reduction in timing. So, the runs weren't a total loss. (FYI, I made timing changes first until hitting max power,,,then tried to lean out the AFR a bit.)

BTW,,,In case you're curious, it looks like I gain about 100rwhp and 50rwtq vs stock setups. My setup is in my sig below.

tequilaboy

First thought is if the car wants more fuel, give it more fuel.

Maybe something like this (assuming you are adding fuel and the - is just a dash):

4800 + 10%
4400 + 8%
4000 + 6%
3600 + 6%
3200 + 6%
2800 + 6%

I have to wonder if leaning it out was accompanied by knock and knock retard to result in the loss of 30 lb-ft.

Might want to get the fueling where you want first, then adjust spark advance for best power.

GREGGPENN

Yes, the dash was just a separator. I am not removing fuel with a negative value (like the stock BIN does).

The values you showed above (as an example) would have made mine run richer. (The first of my 3 tables in the OP was where I THOUGHT I might need to lean it from.) Maybe it was OK as is --IF-- as you posted in C4Tech that upper 11's are acceptable for ARAP bins. Mine BARELY dipped in the upper 11's and was in the 12's otherwise. In fact, I really liked the curve since it was the richest at torque peak, then leaned out as revs got higher. (By that I mean it leaned back up to 13:1 as the leanest WOT mixture.)

Since I never went leaner than the 12's, I'd wonder how knock counts could have occurred. Do you really think that's possible? FWIW, it liked timing to stay under 31-32 degrees advance. Going into the dyno, I had it set to 33 above 3k rpms. I tried 34.5 and the power went down (AFR went way up). When I tried 31, power went up 5% (everywhere) and the AFR returned to the original run.

I tried 30 advance w/o any gain. Then, I tried getting AFR out of the 11's, that's when I started noticing the dip at peak.

I left, thought about it, and put fueling back where it was before the run. I liked the fueling curve. As long as lower-mid 12's are good (with a minor dip into the 11's), then I'm fine where it is. My goal was to see if I could get more HP (vs TQ). That didn't seem to happen.

Had I done one more run with my original fueling and the final spark curve, I might have gotten another 5hp/5tq (vs the dip I was seeing).

Temps were going up in the dyno room. So that wasn't helping my readings.

Yesterday, I put the ECM back into the dash. Before doing so, I put fueling back to where I'd started. Based on the dyno, I bet I ended up with 410rwtq and 320rwhp. That was lower than I hoped but I alse knew the Lawrence Keech sidepipe system is somewhat restrictive. (It has a short 3" center section and single inlet.)

With true duals, I wouldn't be surprised if I picked up another 30rwtq/30rwhp. And, that's about what I hoped for. Not really unhappy though. I'm still 100rwhp over stock with 60ft/lbs more torque. The way it drives (without consideration of the numbers) is even more satisfying.

BTW,,,It's responsiveness in the lower rpms is over-the-top better than the stock 350. :-) Peak hp was at 4700rpms. Peak torque was at 3600. Wish both of those numbers were 500rpms higher. THAT would also be good!

bjankuski

Greg,
Typically most NA cars on the dyno make most power and torque with an AFR ratio of 12.5 to 12.8. It makes me wonder why you had a 30 ft/lb drop in torque when you leaned the AFR into the 12's. I would suspect something else was going on like knock due to excessive water temperature or over advanced timing.

The bottom line is set the AFR where the car likes it, not all engines respond the same.

GREGGPENN

I suppose water temp could have been the issue. As stated, the shop was getting warmer. The owner insisted on doing the runs (and operating the car). So, I was not monitoring temp. OTOH, I mentioned wanting to keep it around 190-210.

In hindsight, if I was smart, I would have run my own datalogs while he ran the dynos. By the time I was down to 31-deg advance, I didn't consider knock a possibility.

The first run laid down a perfect curve (w/o any dips). That was at 33-deg. After 7 runs, I didn't think/know that water temp had gotten high enough to cause knock. Plus, I had already pulled 2-deg up top (and was running 31-deg).

Seems like the best likely explanation though.

Can a richer WOT mixture prevent (help prevent) knock? Like, in my case, could staying in the very low 12's helped prevent knock (vs 12.5:1 or 13:1)?

GREGGPENN

Since I'm running a small cam (with high cylinder pressures), could I go from no knock (at 205-degrees) to some knock (at 215-deg) even if a couple of degrees advance had been pulled? (I'm guessing at what water temps MIGHT have been.)

Obviously, the fueling being pulled (as described above) would factor into this question as well.

bjankuski

The answer to your question is yes. I do not know what happened on your runs but a 10 degree change in temperature could have caused deto.

simple green

I agree, sounds like detonation. My understanding is that you set AFR first and then increase timing accordingly

GREGGPENN

Unfortunately, my first thought was about the recent MAF limitation thread you contributed to.

Since my dip was RIGHT at the torque peak (vs the HP peak), I started thinking about that thread. Though I couldn't remember the specifics, I remembered thinking that a car going above 400rwhp below 4k rpms might have some issues.

That thread made me wonder if my dip was due to limitations in PW calculations and if the AFR lowered accordingly. I never completely understood the logic but thought I remembered MAF limitations could cause too rich vs too lean. And, I didn't see another explanation for the motor going rich around the torque peak. After all, with the stock bin, GM added another 6% enrichment to the torque peak of a TPI.

Since I'm running a TPI, I expected peak VE at peak TQ. And, that some add'l enrichment would be required. Assuming the AFR measurement was correct in my dyno, it appears I could have got by with a flat 15% enrichment from idle to 5500 rpms.

So, heat must have really been the problem. The 383 is generating more BTUs than the OEM motor. I'm still running the stock radiator and I've yet to pull the shroud for more thorough cleaning. (Most of the time, I don't have an issue anyway since I normally don't pull several WOT runs back-to-back. And, I don't do them with a fan as a substitute cooling source! )

GREGGPENN

The thing you might be most interested in knowing is the timing curve from your 355 superram is what I switched to at the dyno. When I saw it DIDN'T LIKE more timing than 33-deg, I dropped in your SR top row to see what happened. I gained power from idle to redline.

So, I'm running 31-deg advance using AFR 195's with an inverted dome setup. 40cc quench and a 20cc dish IIRC. 56cc chambers on the heads.

tequilaboy

The bpw limitation would result in a leaner mixture than intended, so I don't think this is an issue here.

However, you do seem to have an offset between the target AFR and actual AFR.

With normal coolant compensation, 0% in the rpm table should result in a 12:1 target AFR. From your info, it would suggest that you had to add ~6% to the rpm table achieve 12:1 as measured by the wideband. This would suggest ~6% error in the MAF calibration or use of a fuel that requires a richer target AFR (like E10), or error in the WB measurement.

E10 needs approx. 5% richer targets, so the numbers are close enough to suggest a possible relationship.

Factory cals are tuned to be extra rich at the torque peak primarily to provide some internal cooling due to the extra fuel. This is desireable.

Unfortunately without scan data, you don't have a complete picture, hard to say if you can really trust the WB data in this case.

15% rpm enrichment should put your target AFR into the 10.70-11.30 range (depending upon how your xdf is scaled). This should've resulted in a measured AFR in the vicinity of 11.5 or so. Probably richer than necessary if its real, but I suspect the WB is reading a bit lower than actual.

Hard to say which info can be trusted. Fuel is an unknown, Target AFR is an unknown, knock retard is an unknown, MAF cal is suspect, WB cal is suspect. Dynojet should be considered reliable/repeatable.

Unless you're planning on towing while racing or racing while towing with the vette, the cooling system is likely to be adequate with aggressive fan control.

I forsee another trip to the dyno.

GREGGPENN

My stoich is set at 14.7. My base enrichment is 13%. With an extra 6% added for enrichment by RPM, I'm up to 19% for my torque peak. With E10, which I'm pretty sure is sold at all my local stations (including BP with 93 octane), it sounds like you're saying that won't "hurt".

OTOH, I wonder if the 14.7 setting will hurt. Scans run by me show the NB thinking the car is tuned correctly. WB also showed correct oscillation around 14.7 -- when not in WOT mode. OTOH, reading the plugs shows a motor on the lean side.

If I understand you correctly, it would require a 14.2-14.3 AFR setting (for stoich) in the tune -- to obtain correct operation. In past C4Tech discussions, I'd thought the O2 would "read" E10 as being too lean and automatically add more fuel (in closed loop operation). Which is correct?

Knowing the answer to this would help me understand your confusion about my WOT AFR. I understand what your saying....With 13% (base) + 6% add'l enrichment (by rpm), my AFR should have dipped well into the 10's. But the dyno said otherwise.

According to a website and the station attendants (where I buy 93% BP fuel), they say it's E10. If it's pure petrol, it might make more sense. But, I don't see how a scan would have helped that. A scan would have confirmed if the KS had activated though.

tequilaboy

For E10, I like to use 14.12 for stoich. This should be on the safe side. Some choose to split the difference between pure gas and E10 and target something like 14.4 to work reasonably well if the actual fuel composition is unknown.

I would suggest going back to stock coolant compensation for PE, so that the rpm settings can be more easily compared with others. 14.73 and 22.67% coolant gives 12.0 with 0% rpm enrichment.

Using your numbers, 14.7 for stoich, +13% coolant and +6% rpm, I come up with a PE target of 12.35 which is close to your actual WB result. YMMV if your xdf is scaled differently.

A scan would confirm your AFR target and if any knock was present. Also would indicate if the MAF flow changed for any reason from run to run. The more info, the better.

GREGGPENN

I'd still like to know if E10 and a 14.7 setting causes a motor to run lean (in closed loop). Any explanation would be awesome! (I bet I misunderstand this topic).

I think that explains the rest. And, I suspect the WB was accurate.

FWIW, I configured my XDF so it would gradually get [somewhat] richer as metered air increases (especially for values over 100). I thought that would smooth the transition into WOT. Plus, Any time I'm running that high up in the MAF tables, there's a good chance I want more power/richer mixture. (I'd kindof forgotten about this since I tuned for driveability last fall.)

Based on my NB scans, I believe I (we) did a decent job of this. You (and IRocZ89) helped me to understand NB readings last fall. Lowering my temp enrichment was a result of that. (It was also a result of my MAF table strategy mentioned above.) I bet that's why I was richer in the area I'm questioning.

At this point, understanding E10 and how the O2/ECM interprets it would help. Knowing whether I'm actually lean when closed loop derives 14.7 AFR for E10 is important. Also knowing if/how much TQ/HP I might be losing with upper 11's vs 12.5AFR might also help. Either of these topics COULD lead me to pulling the ECM back out. As it stands now, I'm leaning toward leaving things alone. That's because, I'm probably "misering" fuel as best as possible. Plus, I'm rich enough in my peak torque region to ensure adequate power/cooling even when E15 arrives.

The question is whether E15 would cause problems in closed loop -- with a 14.7 target.

tequilaboy

With a 14.73 target, you will get a pulse width intended to achieve 14.73. If the fuel's stoich is really 14.12, then the the bpw which is based on the 14.73 target will be too small and result in a lean mixute (without correction).

Once in closed loop, the ecm will adjust the blm to compensate the mixture back to the fuel's 14.12 stoich ratio.

Since you've been tuning, you may have already compensated for this effect in the MAF tables (by raising them) to keep the blms under control.

I think it makes sense to target the fuel's correct stoich ratio and correct the MAF tables and injector offsets as necessary to achieve the desired target AFR without much correction.

Same goes for E15. Correct the stoich target to 13.8 or so.

GREGGPENN

O.K....So the key question (to me) is whether the O2 corrects to the mixture --OR-- to the stoich value? Does Ethanol burn leaner/cleaner than gasoline AND require more fuel to create the same "residuals" in the exhaust?

It sounds like your saying (as I had previous thought) that closed loop operation will correct/trim for the fuel being used. So, it's not that you'll get a 14.7 ratio with any fuel blend BUT that you'll get a mixture that emits the same level of by-products (air/fuel?) as measured by the O2 sensor. If so, I assume that creates the correct "stoich" (as required for the catalytic converters).

But, in open loop (during warm-up and WOT), setting stoich to 14.7 when 14.2 (or less) is really the desired mixture for ethanol, will result in a leaner-than-desired condition during warm-up and WOT. (Assuming warm-up and WOT were correct for 100% gasoline).

In my case, I set the MAF tables until I hit 128ish BLMs for the RPM of daily driving. As mentioned, I added a slope of extra fuel in the upper entries of the MAF tables. (This ended up with a gradual drop in BLMs to a low of 120ish. After completing driveability tables, I set warm-up percentages by observing field results during an entire winter. I finished by setting WOT based on calculations, then NB and street performance, then by confirming with WB during a dyno session.

Since this was done using current E10 fuels, the error when converting to E15 should be minumal. Do you agree?

Conclusion: Based on my dyno runs, it appears that my add'l enrichment in the upper cells of the MAF table may have created the dip in AFR I observed during my dyno. In essesence, I replaced the need for add'l RPM enrichment. I suspect if I zeroed my RPM enrichment, I would stay pretty close to the 12-12.5:1 AFR ratio during WOT. By adding/leaving the add'l 6% I have the "buffer" necessary to handle E15 at WOT. And, I have a bit of extra cylinder cooling. Since I also err'd on the side of slightly rich for cold, start-up conditions, I should be happy with cold-weather start-up with E15 as well.

OTOH, I might have "cheated" myself out of another 5-10rwtq/rwhp on a dyno printout. Not sure I feel the need to pay for a slightly higher graph! LOL

dan_t

I haven't read all of this - but the AFR specified IS USED in the $8D map setup. Its only used to help the ECM "guess" the change needed to correct the O2 signal so it will work around it, but it will take a little longer.

GREGGPENN

Correction of prior post to make more sense....

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After sending my dyno to a builder (via email), he believes I REALLY cheated myself out of a better dyno. Because my runs were around 210-220 degrees vs 180-190 (with my compression), that could have cost me 5%. Because my KS kicked at/near torque peak, that number could be higher. (As pointed out by Tequilaboy, I should have run scans while tuning.) And, because I used NET values at 5% smoothing, I was "handicapped" to the lowest average value. IOW, he thinks I could be 20-30rwtq lower than potential.

Maybe I will have to go back again someday!