You sure they were unmodified K16's? What were the supporting mods and what fuel? AWD or RWD? Seems like very high power for K16s but the 60-130 time supports the dyno numbers.

My K24 wont make any more boost and the N75 is maxed out and Ive tightened the wastegates even. The fuel pressure doesnt affect the power as the AFR is fine. The exhaust might be a small restriction in my case with 200 cell cats and 2.25" piping for stock exhaust outlets. I measured the exhaust system back pressure which was around 0.3bar.

The exhaust system is the only thing I can think of that limits my power, othwerise I have all of the necessary supporting mods I think.

Yeah, completely unmodified other than the wastegates changed to 1 bar. I was kind of curious about it myself since my goal was 500 whp on K16s and got well over that- it was confirmed when I sold them to a local guy who sent them out to be rebuilt into hybrids and the tuner confirmed it when he got them- they were on their last leg, but unmodified. I've seen another K16 E85 car in the 550 ballpark since, but not many guys push them like that.

E85, RWD, ID1300 injectors, Walbro 525 pump with -8 lines, Syvecs S7+ engine management- the rest typical bolt ons (catless 3" X exhaust, intercoolers, etc) and things that in the end made little to no difference to power output (997TT intake manifolds probably didn't add much, headers and plenum/TB/Y-pipe don't add much).

The ECU probably did most of the work- modifiying the variocam tables picked up 40ish whp on pump gas compared to OEM settings. I left the variocam settings the same from pump gas to E85 but corrected the fueling and added timing on E85 which picked up another 50 whp peak and 100ish from 4500-5500 where I was knock limited on pump gas. Couldn't run any more boost compared to pump gas (1.25ish bar peak around 4500 rpm, tapering to 0.9 bar by redline), with wastegate duty cycle at 100%. The EMAP was forcing the wastegates open no matter we tried and the turbos were way outside of their efficiency range anyway so didn't go to crazy lengths to try and keep the wastegates shut (I wasn't going to safety wire them shut just for a glory run), so power fell off quick once the boost couldn't be maintained. Peak was 5900 rpm and it was below 500 whp by 6600 rpm.

Nice one with the Syvecs and Variocam tuning. Seems you had all the right mods to get the maximum power out of them and the 997 intake manifold was a nice upgrade as well. I think the exhaust is my achilles heel. Will get it sorted next.

Yeah, I figured I'd see what every last ounce of power from a K16 is, so lot of stuff on my car won't be on the typical K16 setup. The other car that made 550ish I think had a more normal setup- stock ECU, stock manifolds, etc.

I dont think the 997 intake manifolds made much of a difference after seeing some flow testing results. Cyl to cyl balance is improved but overall flow is very similar. Big difference is the 2 rear cyls on the 996 manifolds seemed to get ~10% less airflow than the rear cyls on the 997 manifolds. Might've picked up 10-15hp from getting 2 cyls to equal airlflow as the other 4. I'd skip it and go straight to GT3 manifolds if I could do it over.

You guys with K24's have some major balls only running a 5bar for fuel modifications

Yup. Before I did injectors, I calculated the injector duty cycle with ~1bar of boost and it was 95% with the 3.8 bar FPR. A 5bar FPR helps a little but not much

Modifying the variocam on these engines brings huge results, upwards of 100+ whp with larger turbos. The stock variocam is all wrong from a performance standpoint, probably more targeted for fuel economy and emissions.

would going for a set of k24s and a tune be easier on the engine from a torque point of view versus a tuned billet k16 turbo?

Yes

And easier on the rods too.

except k24 cores seem impossible to find.

I looked 4.5 years for a set before I found them

With the unavailability of K24s, is there a modern turbo equivalent that would suffice that won't put the rods at (more) risk or is that a unicorn?

Depending on the power goals there is no need to search for K24's, K16s has a bigger exhaust wheel than the fast spoolong Alpha28's. If you are afraid of the rods breaking the tuner can map the boost control so that torque isnt ramped in so early and reduce the torque to preserve the rods.

SRM offers K24 upgrades without the core charge but I'm 99% sure those are non-original K24's and made in the far east. Weather that makes a difference or not is to the buyer to decide.
https://sillyrabbitmotorsport.com/bi...k24-turbo.html

Not many aftermarket bolt on upgrades other than I know of:
Alpha 28 ~750hp with better spool than K16's but care needs to be done to map the boost in with stock engine.
Alpha 30 ~1000hp
SRM EFR 7163 ~1100hp

I'd like to get a kit with EFR 6758 turbos, they should be capable to 950-1000hp with better / equal spool than the K24's but no-one makes those for the 996 or 997 platform. I've been toying of the idea of a custom setup with manifolds, exhaust etc.

please do as much research as you possibly can on sillyrabbit before purchasing. I was in the Audi world and they have a very poor reputation for the Audi sedans.