EEHack Cylinder Balance Test

I recently downloaded eehack and was playing around with the cylinder disable feature and cylinder strength test. When I manually disable cylinders 1-4, the result is very noticeable. 5-6 not do much so and 7-8 almost undetectable. When I run the cylinder strength test, it shows 1-4 in the mid to low 40s for cylinder strength and 5-8 in the upper 50s, low 60s. I have two questions based on this.

Should I be looking for a mechanical problem with these results?

My logic tells me that the cylinders that yield the least change in engine operation would be the weakest cylinders, why is the result opposite of that?

The car is a 383 lt4 with Afr heads long tube headers and a cam with about 232 duration at 0.050 lift. I'm only seeing 65-70 kpa at idle, so are my results normal? The car does not feel like its weak or has a mechanical issue.

Thanks in advance for any help.

What is the LSA of that cam, and what is your idle spark timing? 65kpa @ idle seems low. Have you checked for a vacuum leak?

Attachment 11804

Cam card.

I have no vacuum leaks that I can find. Everything is fresh with only break in miles on it so far.

What's the static compression ratio, and have to done any tuning?

About 10.8:1. I have been trying to tune for several weeks. These results are with added timing at idle and stock MAF tables.

For tuning idle, did you use the control section in eehack to find the timing (and target rpm) that gives best map reading with lowest advance?

Your cylinder balance test is more or less consistent with what I've been seeing only mine idles around 45kpa and is a 355. My cam is similar lift and duration but 113 lsa so possibly less choppy than yours.

The test looks at MAP and RPM variance to calculate a relative cylinder strength, so my numbers are skewed towards the lower idle vacuum.

Code:

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CYLDROP Memo ::
(Higher is better...)
CYL1=29.3 CYL2=30.0
CYL3=33.1 CYL4=33.0
CYL5=34.8 CYL6=34.6
CYL7=35.7 CYL8=36.3

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I wouldn't fixate on the balance test too much, but I would check again with some starting fluid to see if you don't have a vacuum leak somewhere. That idle vacuum seems pretty weak to me. How does it drive?

Yes, that is how I got to 65 from about 70. I am going to check my map sensor vs a mechanical gage tonight. I will look again for vacuum leaks as well. I don't have any starter fluid, but I will check carefully again.

Well, the map reading has been confirmed with the mechanical gage. I datalogged a bit tonight in speed density mode and will load revisions tomorrow night and see where everything is.

i'd think there's bad idle mixture or insufficient timing advance, to be getting that little idle vacuum with that cam, but every cam is different and i don't know that specific one. if you have weak cylinders at idle, your vacuum overall will be crap, but you'd also see it easily on a mechanical vacuum gauge.

if the cylinder drop test and your own manual tests can narrow down what cylinders are weak, add a bit o' fuel to them and try again.

do try eehack's timing skew feature and see where that gets you. you can control timing, fuel, try open loop or closed loop only, try different air fuel ratios, and control idle speed target all while observing the map value and feeling it, eventually you'll find ideal values. maybe your cam wants more or less timing, or maybe you have a couple of dead cylinders that'll wake up when you add fuel.

I noticed last night that under stay cruise, it basically has about 11" of vacuum until it reaches about 2000 rpm, then it jumps up to about 15". The only way it gets over that is under closed throttle decel. I will pick up some starter fluid tonight and recheck.

With the cylinder balance test on EEhack is it more important the numbers are high or that they are all close to each other? Mine are not as high as some I see reported here but are all close.

yeah close is the ideal