I was wondering why do aftermarket cams such as 272 and 280 cams make the Evo more prone to stalling at idle? I know the cams change the intake and exhaust valve so I assume this has something to do with it. Does it keep them open for to long or for not enough? I know if u get a AEM u won't have any problems but I'm just wondering.

 

The longer duration and greater overlaps create less of an engine vaccum at idle, so the Maff thinks the motor has less air flowing through it. Now since the factory ecu is not programmed for the less vaccum/airflow at idle it stalls. Now you can reflash the stock ecu and get it to idle pretty good, or run a full standalone and have it idle better than stock.

 

the other guy is right.. but in an old v8, with no computer, the overlap also causes low vacuum, thus created buy a motor that isnt running efficently.. the bigger cams are made to run eff. at higher rpms.. the aem can correct bad idle, but you will sacrifice some power... you want big cams you get big power, but you will give up bottom end.. you cant have the best of both worlds.. but with technology, its made the low vs. high end power battle easier to regulate..

 

There really is no overlap on HKS 264 or 272 cams.
The exhaust is closed (@ 1mm) before the intake valve opens.

The 280 specs are a little unclear but they also appear to have no appreciable overlap either.

 

That's exactly right as per the traditional guidelines Tim, but it seems apparent that low lift overlap is significant enough to make itself apparent in this case.

For example, the mapped valve events for the HKS 272 set installed at 0/0 show a total of about 70 deg overlap at <1mm. At low engine speeds, that long but low lift overlap is enough to upset the fuel mixture, dirty the emissions, and give a bumpy idle.

 

I don't have 0mm specs but if it's really 70 degrees that is just amazing that there is that much overlap outside of 1mm of lift.

 

Yep, but if you think about it, those long, slow ramps in the HKS cams are what allows them to be used with the factory springs.

 

are you also using cam gears as well, or just cams??

 

No, I have the factory cam gears. I was told from 2 reputable tuners that I would not need them.