I currently have a standard 993tt with k16s. If I was to install factory K24s, 100 cell cats and remap the ECU to match, would there be the same amount (or lack of) lag? If so, would I then have more torque lower down the rpm range since the K24s would be able to spin up at close to the same speed as the K16s but allow more boost?

Basically, I know that the K24s would normally introduce more lag if I did a direct swap but withe the free flowing 100 cells and the ECU remap would that negate the lag and give me the same pick-up as the k16s?

 

If you install K24's (stock K24's) and ECU and 100 cell cats you will have 450 RPM of lag.. You have to start to increase the compressor wheel size and increase boost at lower RPM's to get you back to K16 levels.. The K24's won't reach the RPM of the K16's.. Never.. A/R of the turbine housings and larger turbine wheel will prevent that from happening.. It won't happen with stock K24 to give you the same early pickup as K16's..

 

When turbo lag is discussed, are we talking about at what point on the rev range they build useful boost (which I guess can be seen from the torque curve and so we can see that x turbo builds useful boost x00 rpm lower than y turbo), or are we discussing their transient response (how quickly they build boost after opening the throttle at any rev range)? If its transient performance that we're interested in, how do we measure that?
I swapped to Kevin's stage 2 K16s and didn't notice any change in power delivery (apart from there being lots more of it), but have never driven a K24 equipped car to see what the difference is.

 

I have to concur, My stage 2's didnt feel "torquey" like my K-16's feel in my
996TT. But I will say that through the mid-range and up top, my stage 2's (Kevin)
pulled very very hard all the way to redline. More similar to K-24's in their "feel" to
me!
My opinion may be challenged but that would make you wrong
Marty

 

Lag basically is the pause of/or application of torque in the RPM band.. Drive a friends 930 or 965 and you will get a first hand encounter with lag.. When building K24's you have to address the headers and camshafts more importantly cam timing and ECU tuning to minimise lag.. It can be done but requires some dollars spent.. I have posted a dyno sheet with the new generation of compressor wheel and camshafts that go hand in hand with K24's..

 

You have to really understand some things to determin which turbo is best for you. As with all things in life there is no free lunch. Both K24's & K16's in stock form are weak. Both require compressor upgrades.

Use this info to determin which "frame" to use as a starting point. Compressor wheels are another subject altogether. Both turbos accept the same compressor wheels.

K24's will have better top end power but boost onset will increase by 400 RPM's. The reduced backpressure from the K24's will have lower EGT's than K16's.

K16's on the other hand will respond better but have more backpressure than K24's. EGT's will be higher for the same level of boost verses the K16's.

All in all I suggest the K24 based turbo (hence my avatar). You can improve boost response by a large margin by installing a very good flowing exhaust. I have no problem driving around the extra lag.