Well I have been running my 434 pig rich with 40 degrees of timing and been running 11 - teens at around 125-128 depending on tracks. I just bought a Wide band (Tech Edge) and my WOT runs are 10-11:1 thru the RPM's

Now I got my drivablility much smoother while using the Wide band and with the BLM's and Integrater locked, I can cruiz around between 13.0-14.5:1, car is nice and smooth.

So I go to the track yesterday and make a few passes. I run out of fuel, lean right out at the end of 3rd and 4th gear about 5K RPM.
So I stuff more fuel in under my PE tables. Mind you, I am running 13.0 then it just falls apart. (38 degees timing)
So the next pass I get through 3rd gear to 7000 rpm and 13.0 on the Wide band. But now about 100 ft from the end of track about 6000 RPM the Wide band goes from 13.0 to 20 and the car falls and I get out of it. No warning just instantly runs out.

I gues my question is, what does a typcalle PE table look like. My goal is to have max fuel at about 5200 (max torque) then lean out from there, but this thing is needing more on the big end. It doesnt follow the rule-of-thumb.

I left last night with a 11.5 @ 116 and a 1.50 60ft with a 6 speed. which is very depressing since the car has done 128.

Any of you tunning with a WB are you tuning for 12.5 or 13.0 and what have you found the sweet spot for timing? I know when its fat it likes the timing to make power, but now when its inline with 12.5 13.0, I think it could be less.

Any thoughts?
John

 

Are you making your timed runs with the BLMs locked? Just curious. And you pose some interesting Qs. Seems odd that adjusting your fuel curve (VE table) at normal rpms should hurt the top end so much - what did you change there besides PE fuel? I don't shift above 6,000 in mine - so I have no comparable data, just a couple of ideas you might consider:

1. Re the wide band as instrumentation - You know it records spark misfire as a lean condition, right? So showing lean @ high rpm on the WB could be fuel, but it could also be a spark problem. You need to datalog InjPW to figure out which you running into, I don't think you can just assume the WB is giving correct info. Or datalog WB vs. rpm.

2. Not to restate the obvious, but you raised the fuel cut-off points in the ECM constants table to some high values, right?

3. I believe the 8D mask has only 8-bit math for the intake air calc (if I remember that part of the code correctly). As such, it wouldn't calculate proportional fuel flow for intake air much above ~500 cfm. If you are using your real cyl vol and inj size in the ECM constant table, I think the 8D prog is running out of calculation space, and has no way to know how much fuel to add at the upper end for a 434 cu in engine. That flow is beyond its normal control range.

4. On the TGO PROM board I think I saw a software patch from RBob that extends the 8D VE tables up to ~6400 rpm - that might be worth trying, although it won't solve the air flow limitation (it's meant for a 350). You need to change the base code per Bob's instructions & then recompile the prog to make the patch. I don't know of anybody who has tested it yet on a real engine though...

5. Re spark timing at high rpm, you may not be getting as much timing as you think from the main spark table. Some of the ECMs have a 'spark latency' variable in the code - I think that includes the 8D mask. There was quite a bit of discussion of that variable a while back on the GN boards - there, it seemed to retard the timing more than expected @ high rpms. I have not seen anyone do similar tests on the 8D program, so the real spark advance the engine sees may be less than you programmed.

6. Lastly, don't forget there is one more spark table to look at - the stock 'base coolant advance correction' table changes timing at very high temp/rpm.

BTW, here is a log I saved of WB O2 voltage (blue line) vs. rpm (gray line) showing what a misfire looked like - from a burned plug wire: http://temp.corvetteforum.net/c4/doc.../misfire_s.jpg

Use at your own risk, YMMV, hope this helps, etc... good luck. :)

 

What fuel pump do you have?

 

thanks for the reply Doctor J

I do have the BLM locked and the Intergrater Narrowed.

On the PE table its upper limit is 6400. What ever Fuel I put in here, rides up to 7000. When I was running 11:1 before the wide band, there was no problem. It would lean out on the big end from 11:1 and would pull 4th to 7000.
I really would like however is to know who is tuneing speed density with a WB and if there settup for 12.5, or 13.0 or what? And also where they have found the best Full timeing numbers to be.

Thanks

And I am running a Walbro pump at 60PSI

JW

 

FWIW:
I've been tuning SD with my WB for two years now, and over that time couldn't find any statistically significant power difference between 12.5 and 13 AFR. Over 12 was definitely too rich for my combo, on the basis of several hundred measured power tests and datalogs that I've run.

Caveats: My interest is road racing, so there are no quarter time slips to use for the kind of evaluation you want. I have a 350 with 113 heads, so the scale-up factor to your heads/cam/displacement is not obvious to me. Also, my testing only covered one cam with a couple of different intakes & exhaust systems - my newest cam hasn't been fully wrung out yet for AFR vs. power.


I set timing by rpm band using the datalogger I built, to measure the WOT rpm vs. time curve @ 120 data pts / sec (logger was described here- http://forums.corvetteforum.com/zero...postid=3960101 ).
The best tool I found for predicting max values was the DCR calculation here: http://members.uia.net/pkelley2/DynamicCR.html


The best change I found in getting consistent power measurements was when I switched to a crank trigger system earlier this year - getting the 'scatter' out of the HEI spark plot made the power curve smoother. That was a more significant change than tweaking the AFR or spark advance a couple degrees.

IMHO I'd think your power loss is more apt to be an spark problem rather than fuel or timing related - you do still have your knock sensor hooked up, right? Or, since it showed up at the end of the season, are the valve springs loosing their rate?


The other unknown in your set-up is the fuel delivery system - @ 60 psig, I wonder what the Cv of the fuel regulator looks like? I don't know of anybody who is running a stock unit that high. The GN guys have done some testing on aftermarket regulators: http://www.gnttype.org/techarea/fuel...inearticle.htm


The other thought I had was about changing the 8D code to accomodate a large displacement engine. The guy here - SuperSport - tunes BBCs with SD - he's also written his own code for SBs with blowers. He's a certified genius with Assembly language, and might be a resource to change the air flow calc in 8D so it could read airflow to the same scale a big block reads: http://www.efi-tuning.org/forum/inde...4602b340750b0b

HTH
DrJ
Edit for spell check :(


[Modified by DOCTOR J, 12:53 AM 10/1/2003]

 

I agree with the spark accuracy.
I was considering a crank trigger settup for this motor. But I havent done the research to see if the MSD would work with the 7727. Then I saw the Cadillac Northstar coil packs as an option, but I just havent had the time to dig into the change yet.

Do you think that the ripple in the distributer timing that we see on our data logs, is hurting WOT power? Or just emissions issue.

So far, the distibuter has been OK to 7K.

John

 

My crank trigger went in at the same time as a new cam, so I never made back-to-back runs on the trigger alone. The rpm vs. time trace is definitely smoother throughout the whole rpm range with the trigger. That can't hurt power. IMHO it's worth a small % gain between 4500-5500 on mine.

I'm looking at the Northstar coil pack for a winter project - it seems like a fairly easy HEI conversion. Wonder why nobody is using it?

DrJ

Edit for spell check :(


[Modified by DOCTOR J, 7:40 PM 9/22/2003]

 

I found that my 383 with SD setup likes 22-25* timing up top. Now we have different engines, but remember this about a engine. They are all different, and even two of the same specs, may like two different things. The key is to give the engine what it likes. Not what everyone else is running.

Try one thing at a time. You have tried fuel. If adding fuel or taking fuel out doesn't seem to fix the problem, then try lowering the timing 2* @ a time.

Also are you running a solid roller, or solid cam? Because if I'm not mistaken you're most likely getting into valve float at those RPMS?

What size injectors?

O you need to unlock your INT and BLMS. you lock the BLMS when you are fine tuning for crouise range . Not WOT. It doesn't look at the o2 sensor in WOT.

One other note have you set your WOT to 100% so that it doesn't kick in? Then tuned for 128 BLM in the 60-100 KPA range? You must have these upper KPA/RPM ranges programed right first. Once they are right you can reset your WOT throttle %. Then you are to program your WOT tables. The WOT tables assume that the VE table is set to give 128 BLM or 14.5-7:1 AFR because it uses the VE table when you go into WOT. You may have your WOT mult. set to give you 12.5 in WOT but if your already running super rich at say 5000RPM @ 80KPA then you will be way richer than the 12.5 you were looking for, and same goes for being lean in the VE table @ a gieven range. I throw this out because I don't know what or how much you know?


[Modified by 88_vette, 10:35 PM 9/30/2003]