Seeing some really high VE table values idle tuning big cam. Why?
12-06-2007, 04:25 AM
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Seeing some really high VE table values idle tuning big cam. Why? Did the initial startup on my friends 2000 Camaro w/ a Procharger, LQ9 heads, and a not so tune friendly 232/240 598/608 115LSA cam. I pulled initial "idle tune" data for a similiar cam from the HP tuners "tune repository". The car was running very lean and didn't want idle above 400RPM as such. I modified the VE table values in the idle range to approx 10% higher than a stock cam and it's idling nice at 14.6 AFR on the AEM wideband.
Everything I know about big cams is that the VE table values in the 400-1200 range should be WAY smaller than stock, not BIGGER. What could cause this?
I'm thinking something is off in the idle airflow table values that is skewing these numbers so much. I've compared them to a couple other big cam tunes + my 02 STS idle #'s (I have a 228/228 cam) and not much is different.......
Much confused. The end result is a good idle....but the method is obviously wrong. Trying to do my friends car right
I didn't get much log data (about 3 minutes). LTFTs and STFTs were 0 even w/ the O2's running. I just set up to log LTIT's and STIT's now. Hoping that will shed some light on this....?
Any input, please chime in. Thanks in advance.
Everything I know about big cams is that the VE table values in the 400-1200 range should be WAY smaller than stock, not BIGGER. What could cause this?
I'm thinking something is off in the idle airflow table values that is skewing these numbers so much. I've compared them to a couple other big cam tunes + my 02 STS idle #'s (I have a 228/228 cam) and not much is different.......Much confused. The end result is a good idle....but the method is obviously wrong. Trying to do my friends car right
I didn't get much log data (about 3 minutes). LTFTs and STFTs were 0 even w/ the O2's running. I just set up to log LTIT's and STIT's now. Hoping that will shed some light on this....?Any input, please chime in. Thanks in advance.
12-06-2007, 08:39 AM
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You need to be careful about how you determine
rich / lean. Big cams let a lot of air through to the
exhaust and / or exhaust back into the intake. This
can fool both narrowband and wideband O2 sensors
(the fresh air into exhaust). In any case there is no
cam (worth having) that will give you a higher idle-
range VE than stock. It should be well lower, how
much so depends on the overlap and lobe - for how
long is the cylinder just a hole between intake and
exhaust.
Changing too many things at once makes it more
difficult to assign the error(s) to their source(s) in
the tuning process. You might find it easier in the
end to put a set of stock injectors, stock tables
(with whatever windage for fuel pressure vs stock,
air vs manifold referenced, whatever kind of fuel
system details you can see to apply to the model).
Just for the idle - cruise, however far you can go
without running out of delivery. Then with the
bottom end of it clean (figure no fuel errors, get
to the airflow without that question in the mix)
you can go back to the new injectors, fix the IFR
and assign any very-low-end "drift" to the offset
table and deal with that dimension against a pretty
good airflow basis.
But anyway, cam in reality punks out the low end
breathing, any tune that says otherwise is probably
well into "two wrongs make a right" territory and not
a good basis for adding Wrong #3.
rich / lean. Big cams let a lot of air through to the
exhaust and / or exhaust back into the intake. This
can fool both narrowband and wideband O2 sensors
(the fresh air into exhaust). In any case there is no
cam (worth having) that will give you a higher idle-
range VE than stock. It should be well lower, how
much so depends on the overlap and lobe - for how
long is the cylinder just a hole between intake and
exhaust.
Changing too many things at once makes it more
difficult to assign the error(s) to their source(s) in
the tuning process. You might find it easier in the
end to put a set of stock injectors, stock tables
(with whatever windage for fuel pressure vs stock,
air vs manifold referenced, whatever kind of fuel
system details you can see to apply to the model).
Just for the idle - cruise, however far you can go
without running out of delivery. Then with the
bottom end of it clean (figure no fuel errors, get
to the airflow without that question in the mix)
you can go back to the new injectors, fix the IFR
and assign any very-low-end "drift" to the offset
table and deal with that dimension against a pretty
good airflow basis.
But anyway, cam in reality punks out the low end
breathing, any tune that says otherwise is probably
well into "two wrongs make a right" territory and not
a good basis for adding Wrong #3.
12-07-2007, 01:04 AM
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Injector Flow is at 70-75 across the RPM range (low to high) and the IPW is 1.277 for default and minimum. Short pulse modifier is stock. Converted to a 2002 "tune" for the PCM so that I could use the primary VE table in SD mode. Car had the same prob w/ the stock 2000 program using the secondary VE table. The VE values are in the 60-70 range....which is way too high. Step on the throttle and the car goes lean fast.
Fuel pressure is good. Plugged a tester right to the rail. 64PSI solid.
Timing is 28 degrees advanced at idle.
I could send the graphs and log, but it won't give you any more info than I provided. The other values in the tune are for a stock 2002 Camaro A4, save the RAF values which are increased 10% from stock for starters.
Thinking something mechanical is causing the prob. Just not sure what.
Again, any input would be great. Thanks.
12-07-2007, 11:26 AM
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If you guys swapped out the Map sensor for a 2 bar make sure you scale it. Check it with Key on Engine Off should read between 94-99 Kpa depending on conditions.
Brent
Brent
12-07-2007, 11:43 AM
#7
That cam (assuming that IS EPP's "FI" cam) was easy as pie to tune Seriously.
I have a 2-bar tune at home that uses some ported truck heads, that cam, ls6intake, 60lbers, progressive meth, and TTi X-twin turb kit. I will post the file when I get home tonight.
Seriously.I have a 2-bar tune at home that uses some ported truck heads, that cam, ls6intake, 60lbers, progressive meth, and TTi X-twin turb kit. I will post the file when I get home tonight.
