Hey guys,

So I had my car to my tuner twice - the first time the idle RPM was about 850 and the second time the idle RPM was 750. The difference between idles is night and day - it went from having barely any lope at all to having tons of lope.

So the question - what really gives an idle the lope? Is it 100% just RPM? Is it spark advance? IAC? Vacuum? BLMs? What?

I'm in an open loop tune so DataMaster always says 128 for STerm and LTerms. My IAC at idle is 75-85, spark advance averages about 19-22 degrees, and idle RPM is 750. BAR is 100.4 KPa while MAP KPa is between 60-65. MAF AFGS reads 10-11.

 

its the duration in the valve events due to the cam

 

Basically, your cam has some valve overlap, it means that the intake and exhaust valves are open at the same time for some amount of time. When the engine is running slowly, this doesn't work so well and some intake charge gets get pushed back by exhaust, making it innefficient and you hear the roughness as a lope. At higher rpms when the cam is working, the exhaust scavenging actually helps draw the intake charge into the cylinder and a little intake charge might actually get drawn out the exhaust, but the engine is more efficient and making more torque.

 

If all he did was change RPM and you didnt have a different cam or anything put in then probably the timing at the two RPM's are quite a bit different. I think more timing (to a point) smooths out a lopey cam at idle since it makes the engine run overall easier while reduced timing at idle on a lopey cam kinda increases the rough idle.

 

Cool - that's the info I was looking for. I understand the cam specs that make it lope but it's the same cam before and after so I was curious what settings in the tune he did to get it to lope more. Didn't think 100rpms would make that much of a difference. Just a curiosity type of thing - want to understand the tuning/programming aspect of what's going on with the car.

 

As said in post #4 can you check out " Closed TPS Spark Advance Vs RPM " table. The low end settings are for 0-400, 400-800, 800-1200 RPM . Since you dropped idle from the 800-1200 box to the 400-800 box you may have changed idle timing, 20* is the stock setting. You should compare it to the 800-1200 setting from your tuner. I'm running 32* at 750 RPM/Drive with my hot cam 210/228 112 lsa.

 

Thanks for the info!