anyone have cam lope and been able to tune it

[oldred95]

For ages everyone said no lope on a TBI. Well things have changed and I'm interested in hearing some cam lope on a TBI engine and how refined the tune is on it. I'm very seriously considering a summit 1105 cam and another user has the same cam in a small block hot rod carbed engine and he said it has a nice lope to it.

[95nProgress]

My cam is not too big at 212/218 but if one is doing their own tuning I definitely believe that a larger cam is doable. The LT4 Hot cam is most likely in my future. For idle what you would want to do is set it to be in open loop. I currently am doing this with mine and have a target idle AFR of around 13.0 ~ 13.2 and it has really smoothed out my idle. Basically all speeds under 3mph trigger the ECM to go into open loop.
To put some theory behind this think about what is happening with a lopey cam at idle. There is a lot of unburned intake air/fuel that is getting past and out the exhaust because of overlap. If running in closed loop the o2 will see this as being rich and pull fuel. By forcing closed loop idle you can set whatever idle AFR you want.
However, there is one item that I am not sure how to handle and that is the map sensor readings. With a "large" cam with some overlap your spark and fuel tables will loose some resolution. Maybe someone with some experience in this area will chime in.


Brian

[HaulnA$$]

.....However, there is one item that I am not sure how to handle and that is the map sensor readings. With a "large" cam with some overlap your spark and fuel tables will loose some resolution. Maybe someone with some experience in this area will chime in.


BrianThere is no way around the loss of resolution when you are idling at 60 or 65 kPa MAP or more. The tune has to be dead nuts on to bring out the lope. Although it is easier to do in open loop, it can be done in closed loop but you have to do a lot more tuning starting with the O2 thresholds. HTH

[Fast305]

There is no way around the loss of resolution when you are idling at 60 or 65 kPa MAP or more. The tune has to be dead nuts on to bring out the lope. Although it is easier to do in open loop, it can be done in closed loop but you have to do a lot more tuning starting with the O2 thresholds. HTH

You don't really lose resolution, your MAP and idle RPM will change, it simply puts you on a different portion of your VE table. I have had multiple TBI engines now with over 225* @ .050" duration camshafts in them. 10-15 in/hg in Park/Neutral without the A/C. My old 312 in the van idled at 750 RPM with only 8 in/hg showing on the vacuum gauge.

[HaulnA$$]

You don't really lose resolution, your MAP and idle RPM will change, it simply puts you on a different portion of your VE table.....When you cut down the number of VE cells between where you idle and atmospheric pressure, then you have effectively lost resolution in the VE table. Technically, the VE table remains the same size but the effect shrinks the number of usable data points in the data set. JMHO

[Fast305]

When you cut down the number of VE cells between where you idle and atmospheric pressure, then you have effectively lost resolution in the VE table. Technically, the VE table remains the same size but the effect shrinks the number of usable data points in the data set. JMHO

True, I was just looking at it as though the engine was only going to be using a certain range of cells anyway.

[91chevZ71]

If you had your injector settings perfect it would work in closed loop. Open loop idle set to about 7 MPH works