View Full Version : Big turbo... Diffrent cam?

09-15-2007, 05:18 PM
Just outta cutriousity, how many people accualy change out the camshaft if they chip thier car or throw a bigger turbo on it?

09-15-2007, 05:25 PM
Not too many...

09-15-2007, 05:59 PM
i figured that much, i was jsut curious is people knew how much valve overlap time, there is and if you jack that boost up if theres much blow by. I know the vavle overlap time is smaller because its not natural asiperated, but i figured if your throwing in alot more before the exhaust valve closes up if youd have some blow by. If someone has a graph of the valve over lap time id be appreative if i could veiw it.

09-15-2007, 06:02 PM
not worth it till you are running a large enough turbo to put your peak hp up in the very high rpms. It would be worthless with the stock turbo since it cant make any real power after 5500 rpms.

09-15-2007, 06:17 PM
yea i knew if would be more trouble then its worth, i was more or less jsut wondering how much blow by coould occur if your pushing a ton of air in there at once, when the cams keeping that valve open to be more efficent with less air getting thrown in the cylinder.

09-16-2007, 10:08 AM
That depends on the cam, the intake pressure, and the exhaust back pressure. It would also vary depending on rpm.

09-16-2007, 04:21 PM
hahaha well yea thats a given, and thats what im trying to figure out. does anyone know the lift on the stock cam? ill jsut graph it out and figuer out how much valve overlap time there is. and then take into consideration how much intake pressure there is. then ill graph out anouther cam and figure out if theres any real advantage

Don Supreme
09-17-2007, 11:01 AM
I really don't have the specs, but I believe the stock intake CAM only has 190 duration and exhaust is something like 216.

I don't remember extactly or any information on the lift.

09-22-2007, 01:07 PM
I doubt it has much of any overlap considering the exhaust pressure will probably be higher than the intake pressure at all times on a stock turbo. Turbo cars like mild cams anyway. As an example, an excellent cam upgrade for an S4 is from the naturally aspirated 30v V6 since it has a nearly identical cam (intake I think) to the RS4.

Bob at QEDpower can help you pick cams for power levels over 350 or 400 hp.

09-22-2007, 02:15 PM
Still running mild cams on my car, schrick cams which are around a 252/264 IIRC.