GreenSwede

Weber 38 Wb Readings - Lean On Anything Else Than Wot?

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(edited)

So I installed the wideband sensor and the gauge to see what the 38 is doing. After a test run (thought I´m not entirely satisfied with the idle and will check timing to be sure I´m right on) I got the numbers below.

 

Problem is I don´t know what to aim for. I´m guessing 14.7 through the whole register is not going to happen..=)

 

Stock engine with TEP headers and and a Weber 38/38 DGMS.

 

On idle I´m around 12.5 - is that reasonable?

On WOT it´s rather steady on 14.5 - 14.7, regardless of RPM. - Seems good, right?

But on light, medium or any other throttle opening except for WOT I´m between 15.5 and 17 - Why?

 

Any thoughts or hints are more than welcome!

Edited by GreenSwede

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Idle seems rich, WOT is lean, cruise would be about right.

 

Idle may have been adjusted for emissions so if that is what this engine wants then that is what it needs.

At WOT in order to make max power it will need a little extra enrichment –around 12.1 to 13.1 mark.

At cruise with additional ignition advance the engine can be leaned out and less fuel is where you'll gain fuel efficiency.

 

This will probably start some debate but when I set up Target maps for fuel injection I try to avoid burning at or near stoich as much as possible, the reason being a complete burn produces the hottest flame temperature.

 

Which wideband setup are you using?

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(edited)

I´m using an AEM analog gauge with the provided Bosch (I´m fairly certain it is) sensor. Sensor installed just after the reducer (2 1/2" > 2") after the collector on the 4-1 header.

 

The WOT is lean? I thought that was about right, going stoich. Ok, I´ll have a more careful look and see if it´s steady or if it differs a bit on high RPM´s - bigger mains should richen the lower range and bigger air corrections the higher RPM´s - right?

 

And where should I be on idle? Stoich?

 

My concern was mostly the 17´s on throttle, accelerating quite fast but not pedal to the floor. I was thinking that there´s still load, and I don't want to be lean under load, right? It only goes down to below 15 if I WOT.

 

I´ve been searching but would like to know more or less achievable goal numbers running a 38? Or the magic numbers to aim for.

 

I know too little about what numbers I want, for example when is lean badleansothingswillnotgowellinsidethemotor-lean?

 

And before I do anything, I´ll check timing.

Edited by GreenSwede

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I´ve now done some more searching and 13 seems to be the number to chase. Will check idle setting from scratch, I think I had to screw the idle mixture screws out way too much. And the idle speed screw as well. Then I guess I´ll order some jets.

 

By the way, this is what´s in it now:

 

50 IDLE
135 MAINS
185 AIRS 
PUMP JET 55
E-TUBES F50
 

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Yeah, 13 is good for WOT and 1/3+ throttle.  If you let it go leaner below about 1/3, you get better economy, and it's pretty safe.

 

If it was me, I'd fatten the mains 5 and see what happened.  You may end up going 10 fatter, and then opening up the airs quite

a bit to get the WOT in range...

 

I was never 100% happy with the 38/38 I had- it didn't respond nearly as predictably as the 40's do.

 

t

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(edited)

I believe I got the number 13 from one of your old posts, Toby. The choice of the 38 was partially a money issue and the rest that, from reading posts here, that duals was not a good idea without going with a rougher cam. And maybe pistons. Also the engine is recently rebuilt with new cam and so on, and I have already put way to much money in the taiga-colored black hole..

 

And as always, I seemed to just find all the positive post on 38´s before buying one.

 

Anyhow, thanks! I'll get on it during the week, just resetting everything and then order some jets. WOT is the most interesting thing, I guess, since most of the use of it will be on track. My R-Kumhos is landing any day now.. In the sporty dimension of 185/70-13=)

 

Oh, another thing! Which steps are appropriate when trying out the airs? 5 at the time? I´m thinking I´ll buy a variation so I won't have to wait for an order between each trial. At least this time I´ll se if anything happens with the AFR, with the 32/36 I was just guessing. And cursing.

 

And, by responding predictably you mean respond to jetting?

Edited by GreenSwede

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(edited)

Mains by 5's and airs by 10.  I often want 2.5's on mains....

 

Also, the 'idle' had a big effect on the 1/6 to 1/3 throttle cruise, I recall- and those by 5's.

 

Alfa1750 on ebay used to sell jets out of Italy for half of what I could find them anywhere else. http://www.ebay.com/usr/alfa1750

 

hth

t

Edited by TobyB

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Yeah, what they said ;-)

 

I'd feel really concerned about seeing anything leaner than 13.3 at WOT. 14.7 at WOT scares the poop out of me. I think that is buring piston territory.

 

ar_kid I think most automakers do shoot for 14.7 at cruise. Seems to work for them ;)

 

S14 suggested targets attached...

post-9251-0-58401100-1396882694_thumb.jp

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(edited)

Maybe this will help you with the correlation of AFR and output.  The big lean spike here for my setup is from the accelerator pump hitting late.  but study the afr and output, its interesting.  Also, the AFR graph is slightly behind the output graphing because the dyno uses a meter at the tail pipe.  You can see the line he drew when explaining this.  Looks like peak torque hit somewhere around 12.8-13.0 AFR.  And HP plateaued when it enriched beyond that point. Makes me wonder if +/-13.0 AFR is the best for our motors..

 

I also idle at about 12.5  AFRat 900 rpm.

 

 

 

5AFED6A6-0FE0-4AF7-A343-E2BD3BCA2AF4.jpg

Edited by eurotrash

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ar_kid I think most automakers do shoot for 14.7 at cruise. Seems to work for them ;)

 

Ray that is an Alpha-N target map which is more suited to a race engine where gas mileage is not a concern. A load based map with additional ignition advance at cruise will make use of lean-burn.

My experience of running at or near stoich is an engine that produces more heat -albeit on a air-cooled engine.

Rgrds

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Makes me wonder if +/-13.0 AFR is the best for our motors..

I kept finding powah on my particular engine (11.5:1, aggressive cam, sidedrafts header etc) as I went into 13.2- 13.5 territory.

Too chicken to go any leaner 'cause, well, B'GAWK!!!!

 

t

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I use a k-type thermocouple under the spark plug, the rise in temp is almost instant with load but I find carving the ignition map the scary part

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(edited)

Well, my engine seems to run quite fine at 14.7. But I don´t want to walk the edge.. Here´s a crappy video, I taped the phone to the steering wheel so at least I got "logs" from running straight forward. First I´m easy on throttle, then you´ll see the AFR fall to 14.4ish as the acc pump kicks in when I hit WOT. 

 

I´d like to just richen the WOT to around 13-13.5, cause staying there keeps the needle steady throughout the gears and at least to 5-5000 rpm. Then it seemed to lean out just before I let go of the accelerator.

 

And, last edit. I went youtubing. Ta-daa! 

 

Edited by GreenSwede

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