QUESTION ON CYL BALANCE TEST

[tuff]

I have a buddys car that we just put in a 408 solid rooler motor with big compression.We have been having problems with the car trying to make horsepower.With his setup we should be around 600rwhp and were 80rwhp down from that.The car runs like shit and its been dyno tuned.The tuner even said there is somthing wrong with the car after two pulls.I hooked up my laptop to his car to do a balance test and when i did the cyl were all weak some so bad the bar bearly moved.I know when i do mine its alot longer and the rpms even view.What doe's the balance test really do?Im starting to think his timing chain is one tooth off.We have been threw all the basic and were starting to think the chain.A motor that should pull to 7500rpms only pulls to 6400.Is there any other test that we can do with efi before we pull the front end of the motor apart.Thanks for any input.

[Blacky]

The cylinder balance test does not tell you if there is a problem with the overall operation of the engine. All it can tell you is the relative performance of each cylinder when compared to the other seven.
The magnitude of the bar graphs in the test are not important, what is important, is the differences between each cylinder.
The test provides a hint to you of which cylinder may have a problem. The problem could be spark plugs, fuel injectors, compression - anything that is particular to a single cylinder.

The way the test works is this:
The RPM is manually set (by you) to a level where when the test is run the engine will not stall. If the engine does stall during the test, increase the rpm prior to starting the test.

EFILive measures the average rpm over a 3 second period. This rpm becomes the reference rpm.
2. EFILive cuts fuel to cyliner 1, and measures the drop in rpm from the reference rpm over a period of 3 seconds.
3. EFILive repeats step 2 for each cylinder.

The cylinder which had the highest rpm drop is the strongest cylinder (it was doing the most work before its injector was cut). The cylinder that had the smallest rpm drop is the weakest cylinder (it was doing the least work before its injector was cut).

Regards
Paul

[joecar]

Several reasons why power may be down (your tuner said "there is something wrong")...
a. Compression leak (head gasket, piston rings, or valve seats).
b. Cam timing angle is off (like you said "chain off one tooth").
c. Weak/broken valve spings, bent pushrods.
d. AFR/EQ is off (tuning calibration (maf, ifr, ve, ...), intake leak, exhaust leak, bad HO2S).
e. Other reasons.

[tuff]

[quote="joecar"]Several reasons why power may be down (your tuner said "there is something wrong")...
a. Compression leak (head gasket, piston rings, or valve seats).
b. Cam timing angle is off (like you said "chain off one tooth").
c. Weak/broken valve spings, bent pushrods.
d. AFR/EQ is off (tuning calibration (maf, ifr, ve, ...), intake leak, exhaust leak, bad HO2S).
e. O

I think we are on to something i looked at the maf scale and it looked stock and he has a slp85.I took the values and started monkeying around with them and the car runs much better.Before he couldn't even get it out of his driveway giving it almost half throttle.Now it will respone when you step on the gas.Im having my doughts about the tuner.I here people say with a cam the size he has probley should tune SD.Even if i disconnect the maf it has better throttle responce.Just some info on the motor it is a 408 with 13.5 compression and the cam is over 700 lift with big duration that i don't know the spec on.Do you think we should just sd tune the motor or rescale the maf. Is it possible to run out of maf?Is it possible that a poorly scaled maf will not let the car rev to max rpm even with the afr tuned correctly?

[tuff]

BTW car was tuned openloop no o2s leaded fuel.

[joecar]

I am still learning, and I am no expert, but here's my comments:
a. with over .700" cam lift and 408 ci, the maf can't match the actual air flow (restrictive);
would a bigger descreened maf and bigger throttle body help...?
Maybe or maybe not.
May need to try this (need to dial in MAF table).
b. if cam has very long duration, the vacuum will be very low, and SD relies on vacuum; but on the other hand the compression ratio is 13.5:1 so there may be sufficient vacuum (need to dial in VE table and cylinder volume).
c. bigger injectors may be required so the AFR can keep up with increased air flow (need to dial in IFR table).

[tuff]

The injectors are 42psi tuner said theres more than enough injector.But on the other hand i think the car is not tuned right and there is more left in it.If we can't get any type of local help ill have to try to the best that i can.I never scaled a maf before so that is like greek to me.But im willing to learn just need somone to point me in the right direction.

[joecar]

Injectors are big enough if injector duty cycle never exceeds 70%.

Scaling a maf is difficult and tedious...

One possible way to scale maf is if the dyno shop can measure the air flow drawn by engine; if so, then you can look at the difference between actual maf and PCM maf, and iteratively adjust maf table (...adjust, log, compare...).

Also, adjusting maf table will cause LTFT's to move; when LTFT's are just barely negative (...may need second opinion here...) then either the maf table and/or ifr table is correct; but you're in open loop so O2's don't influence LTFT's and don't influence AFR.

When maf is scaled right, engine is very responsive;
there are various threads in various forums regarding maf table calibration.

[tuff]

Im thinking just do a SD tune.I just don't know if it will mess up his WOT afr if so then its time to find a diffrent tuner.

[HioSSilver]

Do a ckp learn then redo your cylinder test. With a new engine the pcm don't know where to start a cylinder test to get accurate readings.