alot of it is about the feel too rather then actual power level at certain rpms. larger turbos peak level out further in the powerband which is where the car feels the fastest. my alpha30s did not lose in spool to my K24s on the dyno

 

Yep..never notice the difference and WAY more power...

 

What else do you have in mind?

There are some interesting K16 based Turbo options (billet, 16g) that make similar power and spool way faster. You concern is the same reasons I haven't gone with 18g's.

What kind of driving are you doing though. Once you are rowing through the gears, there really is no difference as you shouldn't be dropping below 4500-5400 rpm depending on your shift speed. But you will feel it from the jump or exiting slow corners and punching it.

 

I occasionally autocross the car and am considering k16 billets.

 

^^Agreed.

And as Prodigy said, if you're getting lag, it's because you're in the wrong gear.

 

I went with the 18g over the K16 billets when I did my build because I didn't want that low end hit of quick boost all that fast..
I am a old Chevy small block guy instead of a big block guy..I like to wind out the gears into the higher RPMs to get the power..
I didn't want to worrry about traction/chassis with that quick hit off the line.
To each his own...
Plus there are more options for increasing power with 18s in my opinion

 

IMO K16 billets will be significantly better for that, but don't get them tuned with the huge torque and non linear powerband. Will be hard to put power down that way.

If you are going to make the choice, make one you are comfortable with. If lag is an issue that's important to you, there are better options. You will find yourself in the wrong gear on the auto-x, as some courses will not be great for your gearing. You will have more ability to stay in say 3rd instead of going down to 2nd since boost comes on about 700 rpm quicker = faster times.

On the street, if you are doing spirited driving, but shifting lazily or staying in a gear for a section of road, that is when you will feel it too. I'm very lag sensitive myself so I know where you are coming from. Lag on the TT is still not huge, but can be felt. Decisions, decisions.

You will be happy with 18g's, but maybe happier with 16 billets.

 

18gs will probably be a bit easier on the motor long term since the power comes on a bit higher in the power band.

 

Not looking to add to the mess, but I'll add my two cents... 18g's are the best all around turbo up to 600whp...I have been in almost every type of turbo in a 996. K16, 18g, GT28, alpha 28, etc...(no billet turbos though) The lag between K16's and 18g's is hardly noticable, and the delta in power is great. The only reason lag IS noticable is that you can barely feel the K16's spool. A long time ago, I actually had an opportunity to race a gt28 car, which was supposedly the fastest spooling turbo, and we were neck and neck at first, then I pulled away very easily. We were both at 1.2bar. I also raced one of the fastest modded cars (with stock K16's) I have seen (we posted video of it when it happened a few years ago). Starting at about 40 in second, he had a 1/2 car jump for about 2-3 seconds then it was all over...You would MORE than make up that 2-3 seconds on the top (straight away)...

You really need a ride in each car to realize the difference is very subtle...but the pull of an 18g car....= fun...

As was said, especially at the race track, you need to be in the right gear. If you have to wait for your turbos to spool, you should have been in a lower gear to be ready to exit the corner...

 

It's impossible to always be in the right gear at the track. Some turns are not suited for your gear ratio. And if you can avoid an extra shift, many times that is better than being in the right gear, so spool/throttle response time is vital. The closer to NA you can get, the faster you shall be. And the Auto-x is even worse because there are new courses all the time and it will be hard to have enough time to figure out which gear is better. 2nd gear on the TT is horrible for track, auto-x use if you expect to carry any momentum.

If a stock K16 car got the jump on you with 18g's that says a LOT about the spool time because the delta in hp had to be about 100 whp or more. For short burst, quicker spooling turbo's will win.

 

I am seriously thinking about going to Markski's tweeked K24/20s over my 18s..I am not a track road racer.
More lag but a lot more top end fun.

 

We did the first 18gs 8 year ago when no one even knew they could be fitted in the k24...
ever since then they became the most popular k24 option on the market...
we tried 16gs prior to that....
if you dont want lag get a 100hp go cart... but dont expect any after market turbo to have NP lag because a k16 in 3rd gear hits full boost at 3300...

 

 

Screw it, im putting the 18s on this winter.

 

First off, I would like to say I am new to the 996 world so please forgive my silly questions that will follow. I have had my share of turbo cars, so I'd like to think I know a little : )
I also am considering either the 18G or the 20G upgrade. The price seems so much better than the other option out there. I have a GT2 that came with Evoms intake, diverter valves, 100 cell cats, exhaust, headers, and a tune. Person I bought the car from claimed the tune was by Evoms but after a few calls to Evoms they couldn't find the car on their system so they told me to take it to their local dealer Stuttgart in OC where they read the ECU to find out the tune was not an Evoms tune. I guess it has a turbo tune not a GT2; I don't quite understand why it would have a turbo tune not a GT2 tune. Any suggestions on that? Why would they do that? Are there any advantages?
They said they would gladly send a tune for it for $3.5K. I figured the car was running fine and wanted to wait until I do the other mods I wanted to do before forking out the $. One issue it had was that the boost was not consistent; used to run 0.6-0.7 bar most of the time and run 1-1.2 once in a while. It felt good at around 1bar. I also saw a few 1.3-1.4bar which put a smile on my face from ear to ear. I bought and installed the 1bar gates from Evoms in hopes to stabilize the boost at around 1 bar. I also installed silicone intercooler hoses when I did the gates because I read somewhere the stock ones could leak. My car started running a lot better now that it was making 1-1.3 bar.
Soon after that I had a 12lb flywheel and Spec 3+ clutch installed because the clutch was slipping at 1bar. I took it easy for 500 miles to break in the clutch before really getting on it. After the break in though, I wouldn't get the boost levels I was getting before. The boost stayed around 0.9-1bar. Having had the pleasure of experiencing 1.2-1.4bar, I got really disappointed with the now 1bar power levels.
I also have a pair of damn near, brand new 997 Turbo intercoolers that came off a new car with 200 miles, which I read are more efficient than the 996 GT2 ones. Is that true?
I am also planning on doing the 5bar fpr(not sure if the car has it or not, maybe they did that with the other mods), inline fuel pump, Water\meth injection(50\50, or 100% meth?), intercooler Y-pipe, and possibly a different exhaust system.
Exhaust idea: Start with 3"-3.5" piping out of turbos and step up to 200 cell cats with 4"-4.5", make a 90deg to the center to meet both banks with a Xpipe, and out the sides. No mufflers or maybe a pair of tiny, Burns light weight ones… By stepping up an inch into a 200cell cats would there be less restriction\back pressure to adequately help the 18G, 20G turbos spool up fast?
I don't want to switch to one of the IPD plenums or change the injectors which are both a pain in the rear to install. I think I should have enough fuel with the 5bar fpr, the inline pump and the meth injection to make around 600whp. Right? I can always run multiple meth jets to add more fuel\methanol.
Here is a good question… These are mass airflow cars which measure the air fed to the motor and adjust fueling accordingly which means if I go with bigger turbos, it would not make a difference as opposed to a speed density system? Provided there is enough fuel...Is there a limit in the map, a MAF limit, which might create a restriction?
How much air, boost can the MAF take? At what power or boost level would it fail?
I have read about the Hitachi MAF sensors being used. Are they necessary for the high power, high boost cars or there are other options? What blow through MAF sensors are preferred among Porsche tuners?
I also read in a few posts that the stock motors are good for around 750whp with proper AFR and timing. Is this true? What is the boost limit before blowing head gaskets?
I would hate to have to rebuild the motor. Too much time and $ involved!
Almost forgot… Is the GT2 fuel pump better than the regular Turbo pump? If it is better, will I still need a second pump to make around 600whp?
What boost would you have to run to make above power on 18G and 20G?
Is the lag between the two noticeable? I am guessing not.
Thank you all for your time. Sorry about the novel. lol