AFR suggestions for max mpg at cruise

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Max Welton
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Re: AFR suggestions for max mpg at cruise

Post by Max Welton » Tue Mar 19, 2013 6:49 pm

volkaholic1 wrote:cylinder heads never get over 275F even when it is 95F outside.
It hasn't been mentioned yet ... make sure your CHT measurements are accurate. If you are using the cheap VDO setup and the "cold" end of the thermocouple is inside the engine room, be very very afraid. :cry:

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Re: AFR suggestions for max mpg at cruise

Post by Piledriver » Wed Mar 20, 2013 2:37 am

Any datapoints I have provided are correlated to a temp compensated TC setup in my DVM, that I personally compared to traceable stds as being +/-1C in the range in question.

Unfortunately I cannot log that, as I don't have a TC on my MS3 setup yet, and the DVM has no logging capability..

My CLT does not stop at 200F, it can go well over 300F as I turned on the extended CLT range option MS2/3 has, it is shielded from external airflow and tracks to CHT @ cruise RPM very fast/closely, admittedly with an offset of ~-75 degrees C @3300 RPM as it is an open element GM sensor in the hot cooling air exhaust off the T4 head right next to the ex stub pipe. At idle offset gets down to <20C. (cooling airflow speed dependant)

The setup I had in my MS2 had 1 temp compensated TC channel on an *error board , but it was single ended and only worked with electrically isolated TCs as are used for EGT probes.
I did hang one on the lower ex stud against the head for comparison, it did seem to track pretty well to the TC under the plug, but that's still not the "standard" setup.


Sooner or later I'll pull the trigger on a 8 channel CAN+EGT or full IOX setup from JBPerformance, but I don't have the spare change ATM, esp as I know for ~certain I don't actually have an issue ATM.
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Re: AFR suggestions for max mpg at cruise

Post by Steve Arndt » Wed Mar 20, 2013 10:15 am

The point of my asking the question is I'm trying to get my engine to run cooler. Since switching to a milder cam my squishy engine's dynamic compression is sky high. Over 9.5 to 1 on the KB calculator. It runs much hotter head temps compared to the wilder cam before. The only other change besides the cam was going from .044 to .054 deck clearance.

I'm running quite a bit of advance and low 16 to 1 ratios on level cruise and the heads are staying cool. I'm trying to figure out when I need to taper from advanced and lean, to richer and retarded when starting a hill climb. At what load level of MAP. With four oversize 45mm ITBs the transition happens very quickly.

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Re: AFR suggestions for max mpg at cruise

Post by Piledriver » Fri Mar 22, 2013 2:25 am

I doubt my setup would make a wonderful "model" for your engines AFR transitions, as I can't make mine knock even adding timing to the point where it really shouldn't even run.

I tried for a hard transition at 83-87KPA, 22:1 below that and over 2200 RPM, ~13.1 everywhere else.
(set to 19:1 now, `cause my current WB only reads to 20:1, the better ones will read to free air)

But.. I will say the leaner you go, the cooler it will be, and the more timing you will need.

You will know when you start getting lean miss, and if your WB is fast enough, it will confirm it.

To find the "right" timing I simply cheated by limiting my EGT to (EDIT---1250F) and tweaked to get that.
(obviously not perfect, but lacking a in cylinder pressure monitor for PPP you use what you have)

Your target should actually be much lower due to the squishy pistons and much higher CR, probably ~900F range.

The only oddball thing in my setup is the Pulstar iridiums driven by std LS2 coils.

I don't know how much of an ignition efficiency difference they make vs. std $7 fine-tip NGK iridium plugs, but they show ~zero wear after ~40K miles, and I have been too lazy/cheap to swap them out just because.

Another thing I'd like to play with is cooled EGR...
Last edited by Piledriver on Sat Mar 23, 2013 1:47 pm, edited 1 time in total.
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Re: AFR suggestions for max mpg at cruise

Post by MarioVelotta » Sat Mar 23, 2013 1:31 pm

Piledriver wrote: To find the "right" timing I simply cheated by limiting my EGT to 1250C and tweaked to get that.
(obviously not perfect, but lacking a in cylinder pressure monitor for PPP you use what you have)

Your target should actually be much lower due to the squishy pistons and much higher CR, probably ~900C range
Are these suppose to be in Fahrenheit? 1250C is about 2200F correct?
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Re: AFR suggestions for max mpg at cruise

Post by Piledriver » Sat Mar 23, 2013 1:46 pm

My bad, 1250F, gotta quit posting in a hurry.
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Re: AFR suggestions for max mpg at cruise

Post by MarioVelotta » Sat Mar 23, 2013 1:57 pm

Piledriver wrote:My bad, 1250F, gotta quit posting in a hurry.
:mrgreen:
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Re: AFR suggestions for max mpg at cruise

Post by MarioVelotta » Sat Mar 23, 2013 9:50 pm

Steve Arndt wrote:The point of my asking the question is I'm trying to get my engine to run cooler. Since switching to a milder cam my squishy engine's dynamic compression is sky high. Over 9.5 to 1 on the KB calculator. It runs much hotter head temps compared to the wilder cam before. The only other change besides the cam was going from .044 to .054 deck clearance.

I'm running quite a bit of advance and low 16 to 1 ratios on level cruise and the heads are staying cool. I'm trying to figure out when I need to taper from advanced and lean, to richer and retarded when starting a hill climb. At what load level of MAP. With four oversize 45mm ITBs the transition happens very quickly.
Today I did some testing. On my little motor I found that cruising a back road in 3rd gear at sustained 3-3300 I could get a happy medium around 270 CHT to 1250 EGT this was at 42-43 degrees and 15.5-16:1.

When I brought timing down to 34, the CHT would drop down to 240-250 but EGT would be at 1350 and a higher PW.

I would say take some timing back out and see what you end up with.
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Re: AFR suggestions for max mpg at cruise

Post by Piledriver » Sun Apr 28, 2013 1:47 am

I finally got a knock signal and heard some knock on my engine. :lol:

Just have to let it idle in traffic on the freeway for an hour and get the CHT to >350F and have 30 degrees of timing at 1700 RPM and 90 MAP :twisted:

I got some good data now that TS betas finally has real time fuel consumtion etc gauges.

Based on some recent testing I'll be staying at 19:1 or leaner at cruise, 22:1 if I go back to my old wideband that can see 22:1.

Related thread:
http://www.msextra.com/forums/viewtopic ... 5&start=20
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Re: AFR suggestions for max mpg at cruise

Post by luftvagon » Wed May 01, 2013 9:56 pm

Does your exhaust pop when you go that lean?

http://i.imgur.com/l6CGpxG.png

This is my latest AFR target. I get slight popping on deaccel and shifts.
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Re: AFR suggestions for max mpg at cruise

Post by Piledriver » Wed May 01, 2013 10:17 pm

No, but I have aggressive fuel cut settings and no exhaust leaks AFAICT.
(any exhaust leaks can jack severely with your AFR readings)
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Re: AFR suggestions for max mpg at cruise

Post by Piledriver » Sun Nov 06, 2016 6:38 pm

Just a long term follow up...
Finally sourced another set of the iridium Pulstars, these aren't exactly like the first set, they are part#"BE1-iT" no idea what the difference is.

I wasn't able to pull the super lean cruise AFRs with either the "new" BE1-H (inconel/copper core electrode) Pulstars, or NGK iridiums, but I'm back at 20:1 with no evidence of lean misfire with the BE1-iTs, only swapping plugs and changing the AFR targets/adding the timing back in.
It even accelerates smoothly @20:1.

With the "normal" plugs, even 17:1 was having significant lean misfire, std LS2 coils, I need to make some mounts for the truck coils one of these days.

Its air cooled, and had a hard time staying >200F CLT when the outside temps are <80F when running that lean, so having proven it really WAS the plugs, I'll probably yank them back out and save them for next summer, as I switch to ~stoich AFR targets in winter to run at normal head temps. When its 100++F outside the head temp safety margin helps, also helps economy 3-4 MPG at cruise.

I actually need to hook the JAW WB serial setup back up so I can verify calibration when running that lean, seems to hit a wall at ~22:1 (the wideband, not the engine, it will still do 23:1 (indicated) with slight lean misfire) but 20:1 is smooth as 13:1.
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Re: AFR suggestions for max mpg at cruise

Post by MarioVelotta » Tue Nov 08, 2016 12:09 am

Pretty crazy stuff Pile. I've never used these plugs. I wonder how they would do in a dual plug configuration.
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Re: AFR suggestions for max mpg at cruise

Post by Piledriver » Tue Nov 08, 2016 3:18 am

I imagine dual plug setup would work pretty well enough by itself, but it might let you run even leaner..
I was just wondering if I was imagining it--- I wasn't, this was a true A/B/A test.
They don't seem to be worth an extra iota of power at normal AFRs but they DO make a huge difference if you are going for lean burn.
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Re: AFR suggestions for max mpg at cruise

Post by RHough » Wed Nov 08, 2017 11:57 am

Great old thread!

I always used 16.4:1 as best economy mixture based on information in a Weber tuning manual. I never considered going leaner with a larger throttle opening to reduce pumping losses. Hmmmm...

My 1967cc 92x74 has 9.0:1 CR, W-120 cam, L5 heads, CB IDF ITBs and LS2 coils running on Microsquirt. (Thanks Mario)

I have seen 35mpg (US Gal) with 16.4:1 and 45-50° lead at 2900-3100 RPM cruise. Long term average is 25+ for normal daily driver type cycles. Not enough time to get temps up and lots of start/stop/idle really kills the mileage.

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