I'm no expert when it comes to turbos but just reporting my experience as an end user with running both K24 and K16 based turbos. My K16s ramp up a lot more gradually (evenly) than my K24s did which had a much more noticeable punch around the 3500 rpm. My K24s were at 1.3 bar at 3500. The K16s just pull evenly from down low to up high in a more NA fashion which makes throttle modulation easier than with the K24 turbos especially as you are exiting corners with the turbos spooling. I find this gradual ramp up mainly beneficial in slow tight medium speed corners where I'm exiting in 3rd with RPMs below 3000 rpm for example, where in the same situation the K24 would be bogging to a certain extent only to reach it's sweet spot and sudden "rush" of power mid turn. This sudden rush of power is not what you want to break the tires loose when pulling though a corner at high Gs. Yes, I could take the corner in 2nd but in many cases that would require an upshift while highly loaded mid turn which certainly is not ideal. I was told my programming was written to limit boost down low and ramp it up gradually to make it easier on my engine as it sees basically continuous track duty. Data wise, my car is faster with the 16s. Faster in the sense of lap times, not a straight line measurement. I feel the K16s are faster as they provide more usable power through out the power band with out having to row the gears to keep the car above the spool point of the K24s. I will say that pure butt dyno wise, the K24s provided a bit more "excitement"as you could really feel the shove in the back when they hit their 3500rpm sweet spot while the K16s are a little more boring as the power delivery is much more linear. That's all I know...which isn't much...

 

Just as the name implies, zero clearance is a coating (the black stuff you see on the inside of the compressor housing) that provides a "zero clearance" between the wall of the housing and the compressor wheel. The compressor wheel basically wears it's own pattern into the wall of the housing increasing the efficiency of the turbo. There was a fairly extensive break in procedure in the instructions to do this "wear in" gradually. Not sure how much benefit it gives you but that's the theory anyway.

 

thx as always john. i'm not clear still, but thru no fault of yours! so thx again, i will ask again and dig much deeper, if/when i ever need to upgrade my own snails as hybrid 16/24's perfectly suit my driving style and conditions though i'm sure 28's would do in a pinch lol

add: and to your points about the perceived advantages of a 16 vs a 24 based turbo? i fully agree, and appreciate a more linear power curve, it makes the power much more quickly usable, and even predictable in its delivery. i have found.

 

Kevin at UMW

 

You are welcome. Basically, the tighter the seal you can get between the wall of the compressor housing and the wheel, the less "blow by" you will have resulting in greater compressor efficiency. The zero clearance coating fills this gap hence the reason for the extended break in that allows the compressor to gradually create it's own pathway in the coating. That's the theory.

Yes, the more linear a power delivery of a turbo is across it's RPM range, the easier it its going to be able the modulate the throttle. That is why I like the K16 based turbo better for track work. You will never have the part throttle modulation of a GT3 engine but it can be close. But there will always be the instance where you accidentally light up the rears going uphill at 90mph with a bit too much right foot....

[url=https://flic.kr/p/pnjKRX]

 

One factor here, unless requested otherwise, is that Kevin uses a wg spring that cracks at around 0.7 bar (on his stage 2ZCs) and is very well suited to N75 based boost control. This gives the DME some better boost control authority, particularly if you're after a more linear response from K16 based turbos.

 

are those the 1.0 wg actuators? thinking most all recommend using those.they work for me.

 

nice! good to know that wasn't braking

 

I have no idea what waste gate springs Kevin uses. The waste gates have his springs in them and they are set up to work with the turbos. My RUF K24/26 turbos had matched RUF waste gates on them. I just looked through my maintenance records and the RUF waste gates were set to start cracking at 8psi and they were open at 11psi. Those turbos actually spooled rather quickly for K24s being fully on boost at 1.3bar at 3500rpm.

 

pretty sure he like most tuners use the 1.0 actuators to handle the higher boost evoms and others make them too, as do others I'm sure. but the cracking open at .7bar are oem levels if i'm not mistaken.

 

I run the UMW stage 2 ZC as well, the gates crack at 0.7 bar but use a nonlinear spring that Kevin spent many hours testing and revising for the 996tt. Not your typical 1 bar wastegates. I've had good luck running anywhere from 0.8 to 1.4 bar with them in conjunction with an EBC, haven't tried more but have some gain left on my EBC.

Pertaining to the OP, you can definitely dial back the massive k16 midrange pop either through tuning or an EBC, IF you have proper wastegates.

 

interesting. all i've learned is the wg's not dialed right ( i think you just said this too..) with the n75 and other check valves can deliver some crazy gauge numbers and behavior to match. took me the better part of a year to sort it all out and get back to 1.2 where i belong.

 

Kevin's stuff is pretty conservative as well. For my application he did not want to use a 5 bar fpr but instead had me install his injectors running on the stock 3.8 fpr. Even in my relatively detuned application running just 1.3 bar he wanted more fueling margin than the stock injectors/5.0fpr would afford. It all seems to work well. I'm happy with it.

 

I am by no means a turbo expert either, but based on what I've read both in US and German forums and based on my experiences behind the wheel of several different turbos, I have been looking at exactly what you specified in the thread title: billet K16s. I have not yet settled on a source, but pwdrhound makes a strong case for UMW (as a matter of fact, after searching various forums on various tech topics from brakes to suspension, etc., it is starting to look to me like all I have to do is follow pwdrhound's lead and copy his car. LOL) though a source more local to me has a lot of appeal too.

This is what I was talking about earlier in the thread. Especially for an amateur driver, going fast means being at ease in the car. Yes you can go fast with lots of lag, but it is not easy. This is what makes a GT3 appealing. At least for the first iteration, my goal is performance as close as possible to NA. My 996 is getting all OEM 7GT2RS bodywork (long story, maybe I will do a thread on the conversion) and my goal is performance as close as possible to the real thing. One thing an acquaintance (who owns a modified 6tt and has driven numerous other modified 6 and 7 turbos) who drove a real GT2RS told me is that the power delivery in the RS was much more linear than in any modified tt he'd ever driven. This is the direction I'd like to go with my build too. Hybrid K16s or possibly A28s seem the way to go for this.

But crffl, based on your original question, you are already more than familiar with all this so I am not really of any help to you.

 

years ago, when I bought my 2001, I started off with k24s with oem wgs and fvd tune. Soon after that I wanted more power and went with ZC k24 based UWMs and Wgs/giac tune... I do not road race but did go 1/4 mile track often. Needless to say, I went 2 mph faster in the quarter over the stock 24s... I also was testing back in 2004 the UWM Wgs...
With all that said, do your homework and research and make the right choice. Just sharing my real work experience like others...
markski